32. Giáo Trình Sử Dụng Thuốc Bảo Vệ Thực Vật - Nguyễn Trần Oánh, 171 Trang

B GIO DC V O TO TRNG I HC NNG NGHIP H NI

PGS.TS. Nguyn Trn Onh (Ch bin) TS. Nguyn Vn Vin , KS.Bi Trng Thy

GIO TRNH

S DNG THUC BO V THC VT

H ni 2007

Trng i hc Nng nghip H Ni Gio trnh S dng thuc Bo v thc vt 2

LI NI U

T thp nin 70 ca th k 20, cng vi s pht trin v bo ca cc ngnh khoa hc khc, lnh vc ho hc v k thut s dng thuc bo v thc vt (BVTV) c s i thay rt mnh m: S hiu bit su sc hn v phng thc tc ng ca thuc BVTV cho php pht hin ra nhiu hot cht mi c phng thc tc ng khc trc, c hiu lc cao vi dch hi, dng liu thp, nhng li an ton vi ng vt mu nng v cc sinh vt khc khng phi i tng phng tr. S tin b trong cng ngh gia cng, ng gi, cng ngh sn xut cht n v ph gia cho php gia cng c nhiu dng ch phm mi, p ng c yu cu qun l thuc BVTV ngy cng cht ch ca cc quc gia v cc t chc quc t. Do khun kh cun sch v s tit hc hn ch, nn chng ti ch mong trnh by c nhng kin thc c bn v thuc BVTV mt cch h thng ngi sinh vin ngnh BVTV khi ra trng c th p dng. ng thi cun sch ny cng c th l ti liu tham kho cho cn b k thut trong v ngoi ngnh. Ni dung cun sch gm hai phn: Phn A: Nhng hiu bit chung v thuc BVTV, qun l v s dng nhm cung cp cho sinh vin nhng kin thc c bn trong lnh vc thuc BVTV v c bit cc c s khoa hc nhng qui nh ca Nh nc ta v vic s dng an ton v hiu qu thuc. Phn B: Cc thuc bo v thc vt, cung cp cho sinh vin ngnh nng nghip nhng c tnh sinh hc c bn ca cc nhm thuc BVTV.

gii quyt mu thun gia s lng v chng loi thuc BVTV Vit nam, tng nhanh vi khun kh cun sch hn hp, nn chng ti ch gii thiu c im chung ca tng nhm thuc (phn loi theo thnh phn ho hc) v tn chung ca mt s loi thuc thng dng nht trong nhm ( c lu n cc thuc nm trong danh mc ng k Vit nam).

Gio trnh S dng thuc Bo v thc vt c bin son trong khun kh ca chng trnh mn hc do tp th cn b B mn Bnh cy-Nng dc- Khoa Nng Hc- Trng i hc Nng Nghip H Ni chu trch nhim nh sau:

- Ch bin: PTS.TS. Nguyn Trn Onh - Bi m u v phn A: Nhng hiu bit chung v thuc Bo V Thc vt, qun l v

s dng thuc do PGS.TS. Nguyn Trn Onh bin son. - Phn B: Cc loi thuc bo v thc vt: + Chng VII: Thuc tr su v cc ng vt gy hi khc ; chng IX; Thuc xng hi; Chng X; Thuc tr c; Chng XI: Cht iu khin sinh trng cy trng do TS. Nguyn Vn Vin bin son. + Chng VIII: Thuc tr bnh do KS.Bi Trng Thy bin son. Tuy c nhiu c gng, nhng do thu thp thng tin cn cha y , cng vi trnh

ca ngi bin son c hn, nn cun sch ny khng th trnh c thiu st. Nhm tc gi rt mong nhn c nhiu kin ng gp ca bn c trong v ngoi ngnh vic bin son gio trnh ny trong nhng ln sau c tt hn.


Trc khi hc mn S dng thuc bo v thc vt, cn phi hc mn Cng trng chuyn khoa, Bnh cy chuyn khoa hoc Cn trng nng nghip, Bnh cy nng nghip.

CC TC GI


M U

VAI TR CA BIN PHP HO HC BVTV TRONG SN XUT NNG NGHIP; LCH S PHT TRIN, XU HNG V TNH HNH S DNG

THUC BVTV TRN TH GII V VIT NAM Gip hc vin thy r c vai tr quan trng ca bin php ho hc trong sn xut nng nghip. Gii thiu cho hc vin lch s pht trin ca bin php ny cng nh tnh hnh s dng thuc BVTV v xu hng nghin cu thuc BVTV th gii v Vit nam, hc vin thm yu ngh v hng th vi mn hc. 1.VAI TR V NGHA CA BIN PHP HA HC BVTV TRONG SN XUT NNG NGHIP:

p ng c nhu cu ngy cng tng do vic bng n dn s, cng vi xu hng th ho v cng nghip ho ngy cng mnh, con ngi ch cn mt cch duy nht: thm canh tng sn lng cy trng.

Khi thm canh cy trng, mt hu qu tt yu khng th trnh c l gy mt cn bng sinh thi, ko theo s ph hoi ca dch hi ngy cng tng. gim thit hi do dch hi gy ra, con ngi ta phi u t thm kinh ph tin hnh cc bin php phng tr, trong bin php ho hc c coi l quan trng.

1.1. Bin php ho hc BVTV ng mt vai tr quan trng trong sn xut nng nghip vi nhiu u im ni tri:

-Thuc ho hc c th dit dch hi nhanh, trit , ng lot trn din rng v chn ng nhng trn dch trong thi gian ngn m cc bin php khc khng th thc hin c.

-Bin php ho hc em li hiu qu phng tr r rt, kinh t, bo v c nng sut cy trng, ci thin cht lng nng sn v mang li hiu qu kinh t, ng thi cng gip gim c din tch canh tc.

-Bin php ho hc d dng, c th p dng nhiu vng khc nhau, em li hiu qu n nh v nhiu khi l bin php phng tr duy nht.

n nay, thuc BVTV li nhng du n quan trng trong hu ht cc lnh vc ca nn nng nghip hin i. Nhng loi ngi vn tip tc tm kim cc dng sn phm mi d s dng hn, c hiu lc tr dch hi cao hn, thn thin hn vi mi sinh v mi trng.

1.2. Thuc BVTV cng l mt trong nhng nhn t gy mt n nh mi trng. Do b lm dng, thiu kim sot, dng sai, nn nhiu mt tiu cc ca thuc BVTV bc l nh: gy nhim ngun nc v t; li d lng trn nng sn, gy c cho ngi v nhiu loi ng vt mu nng; gy mt s cn bng trong t nhin, lm suy gim tnh a dng ca sinh qun, xut hin cc loi dich hi mi, to tnh chng thuc ca dch h v lm o ln cc mi quan h phong ph gia cc loi sinh vt trong h sinh thi, gy bng pht v ti pht dch hi, dn n hiu lc phng tr ca thuc b gim st hoc mt hn.

s dng thuc BVTV c hiu qu v an ton, chng ta phi hiu ng v thc hin ng nguyn tc bn ng: ng thuc; ng lc; ng nng liu lng v ng cch.

Mun thc hin tt c cc nguyn tc trn, chng ta phi hiu thu o mi quan h qua li gia cht c, dch hi v iu kin ngoi cnh.; phi kt hp hi ho gia bin php ho hc vi cc bin php BVTV khc trong h thng phng tr tng hp.


2. LCH S PHT TRIN CA BIN PHP HO HC, TNH HNH SN XUT V S DNG THUC BVTV TRN TH GII V VIT NAM: 2.1. Lch s pht trin ca bin php ho hc trn th gii: Qu trnh pht trin ca bin php ho hc BVTV trn th gii c th chia thnh mt s giai on:

Giai on 1 (Trc th k 20) : Vi trnh canh tc lc hu, cc ging cy trng c nng sut thp, tc hi ca dch hi cn cha ln. bo v cy, ngi ta da vo cc bin php canh tc, ging sn c. S pht trin nng nghip trng ch vo s may ri.

Tuy nhin, t lu, con ngi cng bit s dng cc loi cy c v lu hunh trong tro ni la tr su bnh. T th k 19, hng lot s kin ng ghi nh, to iu kin cho bin php ho hc ra i. Benediet Prevest (1807) chng minh nc un si trong ni ng c th dit bo t nm than en Ustilaginales. 1848 lu hunh c dng tr bnh phn trng Erysiphacea hi nho; dung dch booc ra i nm 1879; lu hunh vi dng tr rp sp Aspidiotus perniciosus hi cam (1881). M u cho vic dng cc cht xng hi trong BVTV l s kin dng HCN tr rp vy Aonidiella aurantii hi cam (1887). Nm 1889, aseto asenat ng c dng tr su Leptinotarsa decemeatas hi khoai ty; 1892 gipxin (asenat ch) tr su n qu, su rng Porthetria dispr. Na cui th k 19 cacbon disulfua (CS2) c dng chng chut ng v cc rp Pluylloxera hi nho. Nhng bin php ho hc lc ny vn cha c mt vai tr ng k trong sn xut nng nghip.

Giai on 2 ( T u th k 20 n nm 1960): Cc thuc tr dch hi hu c ra i, lm thay i vai tr ca bin php ho hc trong sn xut nng nghip. Ceresan - thuc tr nm thu ngn hu c u tin (1913); cc thuc tr nm lu hunh (1940); ri n cc nhm khc. Thuc tr c cn xut hin mun hn (nhng nm 40 ca th k th k 20). Vic pht hin kh nng dit cn trng ca DDT (nm 1939) m ra cuc cch mng ca bin php ho hc BVTV. Hng lot cc thuc tr su ra i sau : clo hu c (nhng nm 1940-1950); cc thuc ln hu c, cc thuc cacbamat (1945-1950). Lc ny ngi ta cho rng: Mi vn BVTV u c th gii quyt bng thuc ho hc. Bin php ho hc b khai thc mc ti a, thm ch ngi ta cn hy vng, nh thuc ho hc loi tr hn mt loi dch hi trong mt vng rng ln.

T cui nhng nm 1950, nhng hu qu xu ca thuc BVTV gy ra cho con ngi, mi sinh v mi trng c pht hin. Khi nim phng tr tng hp su bnh ra i.

Giai on 3 (nhng nm 1960- 1980): Vic lm dng thuc BVTV li nhng hu qu rt xu cho mi sinh mi trng dn n tnh trng, nhiu chng trnh phng chng dch hi ca nhiu quc gia v cc t chc quc t da vo thuc ho hc b sp ; t tng s hi, khng dm dng thuc BVTV xut hin; thm ch c ngi cho rng, cn loi b khng dng thuc BVTV trong sn xut nng nghip.

Tuy vy, cc loi thuc BVTV mi c nhiu u im, an ton hn i vi mi sinh mi trng, nh thuc tr c mi, cc thuc tr su nhm perethroid tng hp (1970), cc thuc tr su bnh c ngun gc sinh hc hay tc ng sinh hc, cc cht iu tit sinh trng cn trng v cy trng vn lin tc ra i. Lng thuc BVTV c dng trn th gii khng nhng khng gim m cn tng ln khng ngng.

Giai on 4 (t nhng nm 1980 n nay): Vn bo v mi trng c quan tm hn bao gi ht. Nhiu loi thuc BVTV mi, trong c nhiu thuc tr su bnh sinh hc, c hiu qu cao vi dch hi, nhng an ton vi mi trng ra i. Vai tr ca bin php ho hc


c tha nhn. T tng s thuc BVTV cng bt dn. Quan im phng tr tng hp c ph bin rng ri. 2.2. Tnh hnh sn xut v s dng thuc BVTV trn th gii:

Mc d s pht trin ca bin php ho hc c nhiu lc thng trm, song tng gi tr tiu th thuc BVTV trn th gii v s hot cht tng ln khng ngng, s chng loi ngy cng phong ph. Nhiu thuc mi v dng thuc mi an ton hn vi mi sinh mi trng lin tc xut hin bt chp cc qui nh qun l ngy cng cht ch ca cc quc gia i vi thuc BVTV v kinh ph u t cho nghin cu mt loi thuc mi ra i ngy cng ln.

Trong 10 nm gn y tng lng thuc BVTV tiu th c xu hng gim, nhng gi tr ca thuc tng khng ngng. Nguyn nhn l c cu thuc thay i: Nhiu loi thuc c, gi r, dng vi lng ln, c vi mi sinh mi trng c thay th dn bng cc loi thuc mi hiu qu, an ton v dng vi lng t hn, nhng li c gi thnh cao.

Tuy vy, mc u t v thuc BVTV v c cu tiu th cc nhm thuc tu thuc trnh pht trin v c im canh tc ca tng nc.

Ngy nay, bin php ho hc BVTV c pht trin theo cc cc hng chnh sau: -Nghin cu tm ra cc hot cht mi c c ch tc ng mi, c tnh chn lc v hiu lc

tr dch hi cao hn, lng dng nh hn, tn lu ngn, t c v d dng hn. Thuc tr su tc dng chm (iu khin sinh trng cn trng, pheromon, cc cht phn di truyn, cht trit sn) l nhng v d in hnh. Thuc sinh hc c ch dng nhiu hn.

-Tm hiu cc phng php v nguyn liu gia cng thnh cc dng thuc mi t nhim, hiu lc di, d dng, loi dn dng thuc gy nhim mi trng.

-Nghin cu cng c phun ri tin tin v ci tin cc loi cng c hin c tng kh nng trang tri, tng bm dnh, gim n mc ti thiu s ra tri ca thuc. Ch dng cc phng php s dng thuc khc bn cnh phun thuc cn ang ph bin. Thay phun thuc sm, i tr v nh k bng phun thuc khi dch hi t n ngng. 2.3. Lch s pht trin ca bin php ho hc, tnh hnh sn xut v s dng thuc BVTV Vit nam: C th chia thnh ba giai on: Trc nm 1957: Bin php ho hc hu nh khng c v tr trong sn xut nng nghip. Mt lng rt nh sunfat ng c dng mt s n in do Php qun l tr bnh g st c ph v Phytophthora cao su v mt t DDT c dng tr su hi rau. Vic thnh lp T Ho BVTV (1/1956) ca Vin Kho cu trng trt nh du s ra i ca ngnh Ho BVTV Vit nam. Thuc BVTV c dng ln u trong sn xut nng nghip min Bc l tr su gai, su cun l ln bng pht Hng yn (v ng xun 1956-1957). min Nam, thuc BVTV c s dng t 1962. Giai on t 1957-1990: Thi k bao cp. Vic nhp khu, qun l v phn phi thuc do nh nc c quyn thc hin. Nh nc nhp ri trc tip phn phi thuc cho cc tnh theo gi bao cp. Bng mng li vt t nng nghip a phng, thuc BVTV c phn phi thng xung HTX nng nghip. Ban Qun tr HTX qun l v giao cho t BVTV hng dn x vin phng tr dch hi trn ng rung. Lng thuc BVTV dng khng nhiu, khong 15000 tn thnh phm/ nm vi khong 20 chng loi thuc tr su (ch yu) v thuc tr bnh. a phn l cc thuc c tn lu lu trong mi trng hay c c cao. Vic qun l thuc lc ny kh d dng, thuc


gi thuc km cht lng khng c iu kin pht trin. Song tnh trng phn phi thuc khng kp thi; p ng khng ng chng loi, ni tha, ni thiu, gy tnh trng khan him gi to, dn n hiu qu s dng thuc thp. Mt khc, ngi nng dn khng c iu kin la chn thuc, thiu tnh ch ng v li nh nc. Tuy lng thuc dng t, nhng tnh trng lm dng thuc BVTV vn ny sinh. phng tr su bnh, ngi ta ch bit da vo thuc BVTV. Thuc dng trn lan, phun phng l ph bin, khuynh hng phun sm, phun nh k ra i, thm ch dng thuc c vo nhng thi im khng cn thit; tnh trng dng thuc sai k thut ny sinh khp ni; thm ch ngi ta cn hy vng dng thuc BVTV loi tr hn mt loi dch hi ra khi mt vng rng ln. Thuc li nhng hu qu rt xu i vi mi trng v sc kho con ngi. Khi nhn ra nhng hu qu ca thuc BVTV, cng vi tuyn truyn qu mc v tc hi ca chng gy nn tm l s thuc. T cui nhng nm 80 ca th k 20, c nhiu kin xut nn hn ch, thm ch loi b hn thuc BVTV; dng bin php sinh hc thay th bin php ho hc trong phng tr dch hi nng nghip. Giai on t 1990 n nay: Th trng thuc BVTV thay i c bn: nn kinh t t tp trung bao cp chuyn sang kinh t th trng. Nm thnh phn kinh t, u c php kinh doanh thuc BVTV. Ngun hng phong ph, nhiu chng loi c cung ng kp thi, nng dn c iu kin la chn thuc, gi c kh n nh c li cho nng dn. Lng thuc BVTV tiu th qua cc nm u tng. Nhiu loi thuc mi v cc dng thuc mi, hiu qu hn, an ton hn vi mi trng c nhp. Mt mng li phn phi thuc BVTV rng khp c nc hnh thnh, vic cung ng thuc n nng dn rt thun li. Cng tc qun l thuc BVTV c ch c bit v t c hiu qu khch l. Nhng do nhiu ngun hng, mng li lu thng qu rng gy kh cho cng tc qun l; qu nhiu tn thuc y ngi s dng kh la chn c thuc tt v vic hng dn k thut dng thuc cng gp khng t kh khn. Tnh trng lm dng thuc, t tng li bin php ho hc li nhng hu qu xu cho sn xut v sc kho con ngi. Ngc li, c nhiu ngi bi xch thuc BVTV, tm cch hn ch, thm ch i loi b thuc BVTV trong sn xut nng nghip v tm cch thay th bng cc bin php phng tr khc. Tuy vy, vai tr ca bin php ho hc trong sn xut nng nghip vn c tha nhn. pht huy hiu qu ca thuc BVTV v s dng chng an ton, phng tr tng hp l con ng tt yu phi n. Phi phi hp hi ho cc bin php trong h thng phng tr tng hp; s dng thuc BVTV l bin php cui cng, khi cc bin php phng tr khc s dng khng hiu qu. Trong thi gian ny, mi quan h quc t gia nc ta vi cc nc, vi cc t chc quc t( FAO, WHO, CIRAP)... v cc t chc trong khu vc vn c nay cng c y mnh v pht huy tc dng, gip chng ta nhanh chng hi nhp c vi tro lu chung ca th gii.

CU HI N TP 1/ Vai tr ca bin php ho hc BVTV trong sn xut nng nghip? 2/ Nhng xu hng chnh trong vic pht trin thuc BVTV hin nay?


PHN A NHNG HIU BIT CHUNG V THUC BO V THC VT

QUN L V S DNG

CHNG I C S C CHT HC NNG NGHIP

Thuc BVTV cng l mt cht c, nn trong chng ny cung cp cho hc vin nhng khi nim c bn nht v cht c, yu cu ca cc cht c dng trong nng nghip v phn loi cc thuc BVTV. 1. KHI NIM CHUNG V CHT C 1.1.Cht c: L nhng cht khi xm nhp vo c th sinh vt mt lng nh cng c th gy bin i su sc v cu trc hay chc nng trong c th sinh vt, ph hu nghim trng nhng chc nng ca c th, lm cho sinh vt b ng c hoc b cht. y l mt khi nim mang tnh qui c.

Rt kh c th nh ngha th no l lng nh. Cng mt lng cht c nh nhau, c th gy c vi loi sinh vt ny, nhng li khng gy c vi loi sinh vt khc; hoc c th gy c hay khng gy c tu theo phng php s dng chng. Cng rt kh nh ngha th no l gy bin i su sc, ph hu nghim trng nhng chc nng ca sinh vt . mt lng thuc nht nh, cht c c th kch thch sinh vt pht trin, nhng lng cht c cao hn, c th gy ng c hay gy c ch sinh vt. C hai trng hp, cht c u gy bin i su sc v ph hu nghim trng nhng chc nng ca sinh vt.

1.2.Tnh c (c tnh): l kh nng gy c ca mt cht i vi c th sinh vt mt lng nht nh ca cht c . 1.3. c: biu th mc ca tnh c, l liu lng nht nh ca cht c cn c gy c mt tc ng no trn c th sinh vt khi chng xm nhp vo c th sinh vt. 1.4. Liu lng: l lng cht c cn thit c (tnh bng mg hay g) gy c mt tc ng nht nh trn c th sinh vt. Trng lng c th ln hay nh c lin quan cht ch n kh nng gy c ca mt cht c. din t chnh xc hn, ngi ta th hin c bng lng cht c cn thit gy c cho mt n v trng lng c th ca sinh vt ( tnh bng g/g hay mg/kg). Trng hp gp nhng c th sinh vt nh, c kch thc kh ng u nhau, ngi ta c th biu hin bng g/ c th ( v d: g /ong). Trong nghin cu c l, ngi ta quan tm n cc liu lng sau: Liu lng ngng: l liu lng rt nh cht c tuy gy bin i c hi cho c th sinh vt, nhng cha c biu hin cc triu chng b hi. Liu lng c: l liu lng nh cht c gy nh hng n sc kho ca sinh vt v cc triu chng ng c bt u biu hin. Liu gy cht : l liu lng cht c gy cho c th sinh vt nhng bin i su sc n mc khng th hi phc, lm cht sinh vt.


nh gi tc ng ca cht c n c th sinh vt, hay so snh c ca cc loi thuc vi nhau, ngi ta cn chia ra: Liu di liu gy cht: l liu lng cht c ph hu nhng chc nng ca c th sinh vt, nhng cha lm cht sinh vt.

Bng 1. PHN LOI C CA THUC TR DCH HI ( theo qui nh ca WHO) Tr s LD50 ca thuc ( mg/kg) Dng lng Dng rn Qua ming Qua da Qua ming Qua da Rt c 20 40 5 10 c 20 200 40 400 5 50 10 - 100 c trung bnh 200 2000 400 4000 50 500 100 - 1000 t c >2000 > 4000 > 500 >1000

Liu gy cht tuyt i: l liu lng cht c thp nht trong nhng iu kin nht nh lm cht 100% s c th dng trong nghin cu. Liu gy cht trung bnh (medium lethal dose, MLD = LD50): l liu lng cht c gy cht cho 50% s c th em th nghim. Gi tr LD50 ( qua ming v qua da ng vt th nghim) c dng so snh c ca cc cht c vi nhau. Gi tr LD50 cng nh, chng t cht c cng mnh. Gi tr LD50 thay i theo loi ng vt th nghim v iu kin th nghim.

Bng 2. PHN LOI NHM C CA THUC TR DCH HI ( theo AAPCO- M, dn theo Farm Chemicals Handbook)

Nhm c Nguy him

( I) Bo ng

(II) Cnh bo

(III) Cnh

bo (IV) LD50 qua

ming(mg/kg ) < 50 50 - 500 500 5 000 >5 000

LD50 qua da ( mg/kg )

< 200 200 - 2 000 2 000 2 0000

>2 0000

LC50 qua h hp (mg/l)

< 2 0.2 - 2 2 - 20 > 20

Phn ng nim mc mt

Gy hi nim mc, c mng,

sng mt ko di >7ngy

c mng sng mt v gy nga nim mc 7 ngy

Gy nga nim mc

Khng gy nga nim mc

Phn ng da Mn nga da ko di

Mn nga 72 gi

Mn nga nh

Nh 72 gi

Phn ng nh 72

gi Nhng tr s ghi trong cc bng 1-2-3 c tnh theo liu lng hot cht. Nhng vi thuc BVTV, ngi ta li s dng cc thnh phm khc nhau. V vy, c ca cc dng thuc thnh phm rt quan trng v thng thp hn c ca hot cht.

xc nh gi tr LD50 ca thuc thnh phm thng phi lm th nghim nh xc nh tr s LD50 ca hot cht. Nhng trong trng hp khng th tin hnh lm th nghim, FAO


a ra mt cng thc tnh tm chp nhn c trung bnh ca mt thnh phm n cng nh hn hp nh sau:

LD50 hot cht LD50 ca thnh phm = x 100 % hot cht c trong sn phm LD50 ca thnh phm ca hn hp:

CA CB C.... CZ 100 + + + = TA TB T.... TZ Tm

Trong : T= LD50 qua da /ming ca hot cht C= T l a.i. c trong sn phm Tm= LD50 qua da /ming ca thuc hn hp A,B,Z = Tn hot cht

Lu : Hai cng thc ny u mang tnh tng i v khng cho bit c theo dng v c bit vi thuc hn hp, c trng hp c ca thuc khng gim m cn tng hn.

Bng 3- BNG PHN LOI C THUC BVTV VIT NAM V CC BIU TNG V C CN GHI TRN NHN

LD50 i vi chut (mg/kg) Qua ming Qua da Nhm c

Ch en

Hnh tng (en)

Vch Mu

Th rn Th lng Th rn Th lng

Nhm c I Rt c

u lu xng cho trong hnh thoi vung

trng

50 200 100 400

Nhm c II c cao

Ch thp cho trong hnh thoi

vung trng

Vng > 50 - 500 > 200 2 000 >100 1

000 > 400 4

000

Nguy him

ng cho khng lin nt trong hnh thoi

vung trng

Xanh nc bin

500 2 000

> 2 000 3 000 >1000 >4 000 Nhm

c III

Cn thn Khng biu tng Xanh l cy > 2 000 > 3 000 > 1 000 > 4 000

so snh c ca cc loi thuc, ngi ta cn dng cc ch tiu khc nh: Nng gy cht trung bnh (medium lethal concentrate - LC50) : l nng gy cht

cho mt na (50%) s c th dng trong th nghim, trong mt thi gian xc nh. LC50 c


tnh bng mg/l, g/m3 hay ppm. i lng ny thng dng khi khng th xc nh c liu lng chnh xc v thng c th vi cc ng vt sng trong nc.

Thi gian gy cht trung bnh ( medium lethal time- LT50): l thi gian gy cht cho mt na (50%) s c th dng trong th nghim, ti nng hay liu lng nht nh. LT50 c tnh bng gy, pht, gi. Tr s ny thng c dng th nghim vi ng vt thu sinh hay kh trng.

Thi gian qut ng trung bnh ( medium knock -out time- KT50): l thi gian qut ng cho mt na (50%) s c th dng trong th nghim, ti nng hay liu lng nht nh. LT50 c tnh bng gy, pht, gi.

Liu qut ng trung bnh (medium knock-out dose- KD50) : l liu lng cht c qut ng mt na (50%) s c th dng trong th nghim. c tnh bng g/g hay mg/kg.

Cm t qut ng y c hiu l s c th b ngt hay b cht. Liu hiu qu trung bnh (effective dose - ED50): Dng nh gi cc thuc khng trc tip git sinh vt ( i ho sinh trng hay trit sn), nhng tc ng n giai on pht trin k tip, s mn , t l (%) trng n. 2. YU CU CHT C DNG TRONG NNG NGHIP 2.1. Mt s nh ngha: Dch hi (pest): dng ch mi loi sinh vt gy hi cho ngi, cho ma mng, nng lm sn; cng trnh kin trc; cho cy rng, cho mi trng sng. Bao gm cc loi cn trng, tuyn trng, vi sinh vt gy bnh cy, c di, cc loi gm nhm, chim v ng vt ph hoi cy trng. Danh t ny khng bao gm cc vi sinh vt gy bnh cho ngi, cho gia sc. Thuc tr dch hi (pesticide ): L nhng cht hay hn hp cc cht dng ngn nga, tiu dit hay phng tr cc loi dch hi gy hi cho cy trng, nng lm sn, thc n gia sc, hoc nhng loi dch hi gy hi cn tr qu trnh ch bin, bo qun, vn chuyn nng lm sn; nhng loi cn trng, ve bt gy hi cho ngi v gia sc. Thut ng ny cn bao gm c cc cht iu ho sinh trng cy trng, cht lm rng hay kh l hoc cc cht lm cho qu sng p hay ngn nga rng qu sm v cc cht dng trc hay sau thu hoch bo v sn phm khng b h thi trong bo qun v chuyn ch. Th gii cng quy nh thuc tr dch hi cn bao gm thuc tr rui mui trong y t v th y.

Thuc bo v thc vt (sn phm nng dc) : l nhng ch phm c ngun gc ho cht, thc vt, ng vt, vi sinh vt v cc ch phm khc dng phng tr sinh vt gy hi ti nguyn thc vt. Gm: cc ch phm dng phng tr sinh vt gy hi ti nguyn thc vt; cc ch phm iu ho sinh trng thc vt, cht lm rng hay kh l; cc ch phm c tc dng xua ui hoc thu ht cc loi sinh vt gy hi ti nguyn thc vt n tiu dit (Php lnh Bo v v Kim dch thc vt nc CHXHCNVN v iu l Qun l thuc BVTV).

Ti nguyn thc vt gm cy, sn phm ca cy, nng sn, thc n gia sc, lm sn khi bo qun.

Sinh vt gy hi ti nguyn thc vt bao gm: cn trng, nm, vi khun , c di, chut v cc tc nhn sinh vt gy hi khc.

Nh vy, gia thuc tr dch hi v thuc BVTV c s ging nhau: chng u l cc loi cht c, c hot tnh tr dch hi. Nhng thuc tr dch hi rng hn, tr c tt c cc loi dch hi ; cn


thuc BVTV ch tiu dit cc loi dch hi gy hi cho ti nguyn thc vt. Ni cch khc, thuc BVTV l mt b phn ca thuc tr dch hi. 2.2.Yu cu ca thuc BVTV:

Thuc BVTV l nhng cht c; nhng mun l thuc BVTV phi t mt s yu cu sau: -C tnh c vi sinh vt gy hi. -C kh nng tiu dit nhiu loi dch hi ( tnh c vn nng), nhng ch tiu dit cc loi sinh

vt gy hi m khng gy hi cho i tng khng phng tr ( tnh chn lc). -An ton i vi ngi, mi sinh v mi trng. -D bo qun , chuyn ch v s dng. -Gi thnh h.

Khng c mt loi cht c no c th tho mn hon ton cc yu cu ni trn. Cc yu cu ny, thm ch ngay trong mt yu cu cng c mu thun khng th gii quyt c. Tu theo giai on pht trin ca bin php ho hc, m cc yu cu c nh gi cao thp khc nhau. Hin nay, yu cu an ton vi ngi, mi sinh v mi trng c ton th gii quan tm nhiu nht.

3. PHN LOI THUC BVTV: Theo yu cu nghin cu v s dng. 3.1. Da vo i tng phng chng:

Thuc tr su (Insecticide): Gm cc cht hay hn hp cc cht c tc dng tiu dit, xua ui hay di chuyn bt k loi cn trng no c mt trong mi trng (AAPCO). Chng c dng dit tr hoc ngn nga tc hi ca cn trng n cy trng, cy rng, nng lm sn, gia sc v con ngi.

Trong thuc tr su, da vo kh nng gy c cho tng giai on sinh trng, ngi ta cn chia ra: thuc tr trng (Ovicide ), thuc tr su non ( Larvicide).

Thuc tr bnh (Fungicide): Thuc tr bnh bao gm cc hp cht c ngun gc ho hc (v c v hu c), sinh hc (vi sinh vt v cc sn phm ca chng, ngun gc thc vt ), c tc dng ngn nga hay dit tr cc loi vi sinh vt gy hi cho cy trng v nng sn (nm k sinh, vi khun, x khun) bng cch phun ln b mt cy, x l ging v x l t... Thuc tr bnh dng bo v cy trng trc khi b cc loi vi sinh vt gy hi tn cng tt hn l dit ngun bnh v khng c tc dng cha tr nhng bnh do nhng yu t phi sinh vt gy ra (thi tit, t ng; hn...). Thuc tr bnh bao gm c thuc tr nm (Fungicides) v tr vi khun (Bactericides). Thng thuc tr vi khun c kh nng tr c c nm; cn thuc tr nm thng t c kh nng tr vi khun. Hin nay Trung quc, mi xut hin mt s thuc tr bnh c th hn ch mnh s pht trin ca virus ( Ningnanmycin ...).

Nhiu khi ngi ta gi thuc tr bnh l thuc tr nm (Fungicides). Trong trng hp ny, thuc tr nm bao gm c thuc tr vi khun.

Thuc tr chut (Rodenticde hay Raticide): l nhng hp cht v c, hu c; hoc c ngun gc sinh hc c hot tnh sinh hc v phng thc tc ng rt khc nhau, c dng dit chut gy hi trn rung, trong nh v kho tng v cc loi gm nhm. Chng tc ng n chut ch yu bng con ng v c v xng hi ( ni kn o).

Thuc tr nhn (Acricide hay Miticide): nhng cht c dng ch yu tr nhn hi cy trng v cc loi thc vt khc, c bit l nhn . Hu ht thuc tr nhn thng dng hin nay u c tc dng tip xc. i a s thuc trong nhm l nhng thuc c hiu c tc dng dit nhn, c kh nng chn lc cao, t gy hi cho cn trng c ch v thin ch. Nhiu loi


trong chng cn c tc dng tr trng v nhn mi n; mt s khc cn dit nhn trng thnh. Nhiu loi thuc tr nhn c thi gian hu hiu di, t c vi ng vt mu nng. Mt s thuc tr nhn nhng cng c tc dng dit su. Mt s thuc tr su, tr nm cng c tc dng tr nhn.

Thuc tr tuyn trng (Nematocide): cc cht xng hi v ni hp c dng x l t trc tin tr tuyn trng r cy trng, trong t, ht ging v c trong cy.

Thuc tr c (Herbicide): cc cht c dng tr cc loi thc vt cn tr s sinh trng cy trng, cc loi thc vt mc hoang di, trn ng rung, quanh cc cng trnh kin trc, sn bay, ng st... v gm c cc thuc tr rong ru trn rung, knh mng. y l nhm thuc d gy hi cho cy trng nht. V vy khi dng cc thuc trong nhm ny cn c bit thn trng. 3.2. Da vo con ng xm nhp (hay cch tc ng ca thuc) n dch hi: tip xc, v c, xng hi, thm su v ni hp. 3.3. Da vo ngun gc ho hc: Thuc c ngun gc tho mc : bao gm cc thuc BVTV lm t cy c hay cc sn phm chit xut t cy c c kh nng tiu dit dch hi.

Thuc c ngun gc sinh hc: gm cc loi sinh vt (cc loi k sinh thin ch), cc sn phm c ngun gc sinh vt ( nh cc loi khng sinh...) c kh nng tiu dit dch hi.

Thuc c ngun gc v c : bao gm cc hp cht v c ( nh dung dch booc, lu hunh v lu hunh vi....) c kh nng tiu dit dch hi.

Thuc c ngun gc hu c: Gm cc hp cht hu c tng hp c kh nng tiu dit dch hi ( nh cc hp cht clo hu c, ln hu c, cacbamat...).

Gn y, do nhiu dch hi hnh thnh tnh chng nhiu loi thuc c cng mt c ch, nn ngi ta phn loi theo c ch tc ng ca cc loi thuc ( nh thuc km hm men cholinesterase, GABA, km hm h hp...) hay theo phng thc tc ng (thuc iu khin sinh trng cn trng, thuc trit sn, cht dn d, cht xua ui hay cht gy ngn).

Phn chia theo cc dng thuc ( thuc bt, thuc nc...) hay phng php s dng ( thuc dng phun ln cy, thuc x l ging...). Ngoi cch phn loi ch yu trn, tu mc ch nghin cu v s dng, ngi ta cn phn loi thuc BVTV theo nhiu cch khc na. Khng c s phn loi thuc BVTV no mang tnh tuyt i, v mt loi thuc c th tr c nhiu loi dch hi khc nhau, c kh nng xm nhp vo c th dch hi theo nhiu con ng khc nhau, c cng lc nhiu c ch tc ng khc nhau; trong thnh phn ca thuc c cc nhm hay nguyn t gy c khc nhau... nn cc thuc c th cng lc xp vo nhiu nhm khc nhau. CU HI N TP 1/ Nhng hiu bit chung v cht c? 2/Nhng nh ngha cn bit v yu cu c bn ca mt cht c dng trong nng nghip? 3/ Cc cch phn loi thuc BVTV?


CHNG II

C S SINH L, SINH THI HC CA THUC BO V THC VT TRONG PHNG TR DCH HI

S dng thuc BVTV an ton v hiu qu l yu cu c bn ca bin php ho hc. Mun vy , hc vin phi hiu r c s sinh l sinh thi ca thuc BVTV trong phng tr dch hi. l mi quan h qua li gia 3 nhm yu t: Thuc BVTV, Dch hi v iu kin ngoi cnh. 1. IU KIN CA MT LOI THUC C TH GY C CHO SINH VT: 1.1. Thuc phi tip xc c vi sinh vt

L iu kin tin quyt thuc pht huy tc dng. Mun thuc tip xc c vi dch hi nhiu nht, phi nm chc c tnh sinh vt hc, sinh thi hc ca dch hi v c tnh ca tng loi thuc, tm bin php x l thch hp thuc tip xc nhiu nht vi dch hi v hn ch thuc tc ng n cc sinh vt khng l i tng phng tr, gim nguy c gy hi ca thuc n mi sinh, mi trng. Mi loi sinh vt c nhng c tnh sinh hc khc nhau:

- Cn trng: cn hiu r kh nng di chuyn ca cn trng ( rp t di chuyn, nhng cc su hi khc li di chuyn mnh); ni chng sng, ni gy hi v cch gy hi, thi im hot ng chn thuc v phng php x l thch hp.

- Nm bnh v nhn : l nhng loi sinh vt t hay khng t di chuyn. Phi phun thuc ng vo ni chng sng, ht thuc phi mn, trang tri tht u trn b mt vt phun, lng nc phun phi ln mi pht huy c tc dng.

- Chut: Chut di chuyn rt rng, nn phi to iu kin cho chut tip xc vi b, bng cch ri b trn nhng li i ca chut, chn b khng hoc t mi, hay ch c mi hp dn, trnh dng nhng b gy tc ng mnh chut khng s v phi thay mi b lin tc la chut.

- C di : phi phun, ri v trn thuc vo t, to iu kin cho c di nhn c nhiu thuc nht. Dng cc thuc tr c ni hp phun nhiu ln lin tip nhau di liu gy cht s tng c hiu qu ca thuc. Khi phun thuc tr c khng chn lc rung c cy trng, phi phun nh hng, trnh cy trng tip xc vi thuc, b thuc gy hi v lm tng tnh chn lc ca thuc tr c. 1.2. Thuc phi xm nhp c vo c th sinh vt v sau phi dich chuyn c n trung tm sng ca chng :

Con ng xm nhp ca thuc BVTV vo c th sinh vt: -Thuc xm nhp vo c th dch hi bng con ng tip xc (cn gi l nhng thuc

Ngoi tc ng): l nhng thuc gy c cho sinh vt khi thuc xm nhp qua biu b chng. -Thuc xm nhp vo c th dch hi bng con ng v c (cn gi l nhng thuc c

tc ng ng rut hay Ni tc ng): l nhng loi thuc gy c cho ng vt khi thuc xm nhp qua ng tiu ho ca chng. pH dch rut v thi gian tn ti ca thuc trong d dy v rut non nh hng rt mnh n hiu lc ca thuc.

- Thuc c tc ng xng hi: l nhng thuc c kh nng bay hi/ bi, u c bu khng kh bao quanh dch hi v gy c cho sinh vt khi thuc xm nhp qua ng h hp.


-Thuc c tc ng thm su: l nhng thuc c kh nng xm nhp qua biu b thc vt, thm vo cc t bo pha trong, dit dch hi sng trong cy v cc b phn ca cy. Cc thuc ny ch c tc ng theo chiu ngang, m khng c kh nng di chuyn trong cy.

-Thuc c tc ng ni hp: l nhng loi thuc c kh nng xm nhp qua thn, l, r v cc b phn khc ca cy; thuc dch chuyn c trong cy, dit c dch hi nhng ni xa vng tip xc vi thuc. Nhng thuc xm nhp qua r ri dch chuyn ln cc b phn pha trn ca cy cng dng nha nguyn, gi l vn chuyn hng ngn. Do mch g l nhng t bo, nn cht c t b tc ng. Ngc li, c nhng thuc xm nhp qua l, vn chuyn xung cc b phn pha di ca cy, theo mch libe, cng dng nha luyn, gi l vn chuyn hng gc hay cc thuc mang tnh lu dn. Mch libe l cc t bo sng, nn thuc b cc cht trong t bo sng, men tc ng v cc yu t sinh hc tc ng. C thuc li xm nhp c qua l v r, vn chuyn c hng ngn v hng gc.

S xm nhp v di chuyn ca cht c vo trong c th sinh vt S xm nhp v di chuyn ca cht c vo trong nm bnh: B mt cht nguyn

sinh c tnh khuych tn mnh, cn tr cc cht trong t bo khuych tn ra ngoi. Ngc li, c khi nguyn sinh li c tnh hp ph v to h s cn bng. Trong iu kin bnh thng h s hp ph ny thp. Khi b cht c tc ng, h s cn bng ny s tng ln, cht c theo vo t bo mnh hn. Mt khc, mng nguyn sinh cht c tnh thm chn lc, cho nhng cht ho tan i qua vi tc khc nhau. Nhng tnh thm ny s b thay i theo iu kin ngoi cnh. B cht c kch thch, tnh thm ca mng t bo cng tng nhanh, cht c xm nhp nhanh chng vo t bo cho n khi trng thi cn bng v p sut c thit lp. Mng t bo cng c kh nng hp ph mnh, c bit l cc ion kim loi nng nh ng, thu ngn... Trn mng t bo, cc ion ny tp trung li vi nng cao cng xm nhp trc tip vo t bo nm bnh mnh .

S xm nhp v di chuyn ca cht c vo trong c th cn trng: Nhng thuc cng d ho tan trong lipit v lipoproteit cht bo, s cng d xm nhp vo c th sinh vt qua con ng tip xc. Biu b cn trng khng c t bo sng, c cu to bng lipit v lipoproteit bin tnh, c tc dng gi khung c th, ngn khng cho nc trong c th cn trng thot ra ngoi v cc cht khc bn ngoi xm nhp vo c th. Nhng lp biu b bao ph khng u trn ton c th, c nhng ch mng, mm nh cc khp u, ngc bn chn, chn lng v.v... thuc xm nhp qua d dng hn. Cc thuc dng sa d xm nhp vo c th qua biu b cn trng v biu b l cy hn. Nhng biu b qu dy, thuc khng i qua c, hoc thuc ho tan trong biu b nhiu, b gi li biu b m khng i vo c bn trong, hiu lc ca thuc cng b gim. Xm nhp qua biu b, thuc s i tip vo mu v c mu di chuyn n cc trung tm sng.

Cc thuc xng hi li xm nhp vo l th, h thng kh qun v vi kh qun vo mu gy c cho cn trng. Cht c xm nhp qua ng h hp c tnh c mnh hn cc ng khc, do tc ng ngay n mu. Cng h hp cng mnh, kh nng ng c cng tng. V th, khi xng hi cc cn trng trong kho, ngi ta thng hoc rt bt khng kh, hoc bm thm CO2 vo kho kch thch s h hp ca cn trng.

Cc thuc tr su v c, c chuyn t ming n ng thc qun, ti thc n vo rut gia. Di tc ng ca cc men c trong nc bt v dch rut gia, thuc s chuyn t dng khng ho tan sang dng ho tan, ri thm thu qua vch rut hay ph v vch rut vo huyt dch, cng huyt dch i n cc trung tm sng. Nhng cht c cn li khng tan s b thi qua hu mn, hoc qua nn ma; mt phn nh cht c thm thu qua thnh rut trc, vo thnh


rut sau v b gi . Qu trnh bi tit cng chm, thi gian tn lu trong rut cng lu, lng cht c xm nhp vo c th cng nhiu, c ca thuc s mnh. pH ca dch rut nh hng nhiu n tan ca thuc. tan cng ln, nguy c gy c cng tng.

S xm nhp v di chuyn ca cht c vo trong c th loi gm nhm : Thuc tr chut c th xm nhp vo c th loi gm nhm bng c ba con ng : tip xc, v c v xng hi. Nhng do kh nng hot ng ca cc loi gm nhm ni chung v ca cc loi chut ni ring qu rng, nn kh dit chng bng con ng tip xc. Bin php dit chut v cc loi gm nhm ch yu l trn thuc tr chut vi thc n (lm b) ( con ng v c). Tc ng xng hi (ng h hp), ch c p dng trong cc khong khng gian kn (trong kho tng, trong hang)... D bng con ng no, cui cng thuc cng vo mu. Khi vo mu, thuc mt phn ph hi mu, phn khc c vn chuyn n trung tm sng, tc ng n chc nng sng ca cc c quan ny, chut b ng c ri cht.

S xm nhp v di chuyn ca cht c vo trong c th c di: Cht c cng c th xm nhp vo mi b phn ca thc vt, nhng l v r l hai ni cht c d xm nhp nht. B mt l v cc b phn khc trn mt t, c bao ph bi mng lipoit v nhng cht bo khc, c bn cht l nhng cht khng phn cc, nn thng d cho nhng cht khng phn cc i qua. V thn l nhng lp bn, thuc BVTV phn cc hay khng phn cc u kh xm nhp; nhng nu xm nhp c qua v thn, cht c s i ngay vo b mch v di chuyn n cc b phn khc nhau ca cy. Git cht c nm trn l, ban u xm nhp vo bn trong l nhanh, theo thi gian, nc b bc hi, nng git thuc s tng cao, kh nng ho tan ca thuc km, thuc xm nhp vo cy chm dn.

Cht c trong t xm nhp qua r l chnh ( cng c th xm nhp qua ht ging v nhng lng thn lp t mt) nh kh nng hp ph nc v cht ho tan. Cc cht phn cc d xm nhp qua r. Tc xm nhp thuc qua r thng lc u tng sau gim dn. Ring hai thuc tr c 2,4-D v DNOC li khc: lc u xm nhp nhanh, sau ngng hn ri li c mt lng thuc t r thot ra ngoi t. Mt di l c nhiu kh khng v t bo km, nn cc cht phn cc li d xm nhp. 1.3. Cht c phi tn gi trong c th sinh vt mt thi gian, nng nht nh pht huy tc dng: Cht c trong c th sinh vt bin i theo 3 hng:

- c ca cht c c th c tng ln: khi chng c bin i thnh nhng cht c tnh c cao hn. V d : MCPB ch pht huy tc dng dit c khi trong cy, chng chuyn thnh MPCA. Malathion c c km hn Malaoxon, mt sn phm oxy ho ca Malathion. Cc thuc tr su thuc nhm nereistoxin ( Cartap, Bensultap, Monosultap, Thiocyclam ) ch c hiu lc dit su khi chng c chuyn thnh Nereistoxin trong c th cn trng. Thuc tr nm Thiophanate methyl vo nm bnh s chuyn thnh carbendazim mi c c vi nm bnh.

- Cht c c th tr nn t c hn, thm ch mt hn tnh c: do cht c phn ng vi cc cht c trong c th, hoc di tc ng ca cc men phn hu thuc, hay nhng phn ng thu phn hay trao i khc.

Di tc ng ca men DDTaza, DDT chuyn thnh DDA hay DDE t c vi cn trng.Nhng cht c b thi nhanh ra ngoi do phn ng t bo v ca sinh vt cng khng gy c c vi dch hi.

Atrazin tr c nhiu loi c l rng v l hp cho nhiu loi cy trng khc nhau, nhng li rt an ton vi ng. V trong ng c men glutation tranferaza c kh nng kh Atrazin thnh hydroxysimazin khng gy c cho cy.


- c ca thuc c th khng thay i: Sunfat ng c c vi nm bnh khng thay i, d c xm nhp hay khng xm nhp vo

c th sinh vt. Cht c ch pht huy c tnh c khi chng t mt lng nht nh, tn ti trong c

th sinh vt mt thi gian nht nh. Vi hai iu kin , cht c mi c th gy hi cho sinh vt, bng cch phn ng vi protein, gy t lit h men, ngn cn s to vitamin, thay i trng thi keo, nht v kh nng nhum mu ca nguyn sinh cht, ph hu cc chc nng sng c bn lm cho sinh vt b ng c ri cht. Nng cht c cng tng, thi gian lu gi cht c trong c th sinh vt cng di, cng tc ng su sc n c th sinh vt. 2. CC HNH THC TC NG CA CHT C:

Sau khi cht c xm nhp c vo t bo, tc ng n trung tm sng, tu tng i tng v tu iu kin khc nhau m gy ra tc ng sau trn c th sinh vt: 2.1. Tc ng cc b, ton b: Cht c ch gy ra nhng bin i ti nhng m m cht c trc tip tip xc vi cht c nn gi l tc ng cc b ( nh nhng thuc c tc ng tip xc). Nhng c nhiu cht c sau khi xm nhp vo sinh vt, li loang khp c th, tc ng n c nhng c quan xa ni thuc tc ng hay tc ng n ton b c th gi l cc cht c tc dng ton b ( nhng thuc c tc dng ni hp thng th hin c tnh ny).

2.2. Tc ng tch lu: Khi sinh vt tip xc vi cht c nhiu ln, nu qu trnh hp thu nhanh hn qu trnh bi tit, s xy ra hin tng tch lu ho hc. Nhng cng c trng hp c th ch tch lu nhng hiu ng do cc ln s dng thuc lp li mc d liu lng thuc cc ln dng trc b bi tit ra ht c gi l s tch lu ng thi hay tch lu chc nng.

2.3. Tc ng lin hp: Khi hn hp hai hay nhiu cht vi nhau, hiu lc ca chng c th tng ln v hin tng ny c gi l tc ng lin hp. Nh tc ng lin hp, khi hn hp hai hay nhiu thuc khc nhau, gim c s ln phun thuc, gim chi ph phun v dit ng thi nhiu loi dch hi cng lc. C hai loi tc ng lin hp :

Tc ng lin hp gia cng: khi hiu ng ca hn hp bng tng n gin cc tc ng.

Tc ng lin hp nng cao tim th : khi hiu ng ca hn hp vt qu tng hiu ng ring ca tng cht cng li. Tc ng lin hp nng cao tim th cho php gim lng thuc khi s dng. Nguyn nhn: c th do l tnh ca thuc c ci thin tt hn, hoc cc loi thuc phn ng v chuyn ho thnh nhng cht mi c c hn v cui cng do kh nng nng cao hiu lc sinh hc ca tng loi thuc.

2.4. Tc ng i khng: Ngc vi hin tng lin hp l tc ng i khng, c ngha khi hn hp, cht c ny lm suy gim c ca cht c kia. Hin tng i khng c th c gy ra di tc ng ho hc, l hc v sinh hc ca cc thuc vi nhau.

Nghin cu tc ng lin hp v i khng c ngha rt ln trong cng ngh gia cng thuc v l c s cho hai hay nhiu loi thuc c hn hp vi nhau.

2.5. Hin tng qu mn: Cc c th xy ra hin tng qu mn khi tc ng ca cht c lp li. Di tc ng ca cht c, cc sinh vt c nhy cm cao vi cht c. Cht gy ra hin tng ny c gi l cht cm ng. Khi cht cm ng tc ng c vo c th vi liu nh cng c th gy hi cho sinh vt. Nu cht c xm nhp trc giai on tt


cng ca s cm ng, hin tng qu mn s khng xy ra v c th sinh vt li c th hi phc, c gi l hin tng mt cm ng.

-Mt s cht c khi xm nhp vo c th sinh vt, khng lm cht sinh vt , nhng ph hoi cc chc nng sinh l ca tng c quan ring bit, lm sinh vt khng pht trin c bnh thng, nh cn trng khng lt xc c pht trin, cn trng khng c hay t v c t l trng n thp, kh nng sng st km v.v... Hin tng ny mang tn tc ng d hu.

Ngoi ra, cht c c th lm cho sinh vt pht trin km, ci cc, gy nhng vt thng c gii nh hng hot ng h men v cc h sng khc. 3. NHNG NHN T LIN QUAN N TNH C CA THUC BVTV 3.1. Lin quan gia c tnh ca cht c vi c ca chng :

a. Lin quan gia cu to, tnh cht ho hc n c ca thuc BVTV: Trong phn t cht c thng c nhng gc sinh c quyt nh n c ca

thuc . Cc gc sinh c c th ch l mt nguyn t hay mt loi nguyn t ( nh Hg, Cu... trong cc hp cht cha thu ngn hay cha ng); hoc cng c th l mt nhm cc nguyn t ( nh gc -CN c trong cc hp cht xianamit; hay gc -P=O (S) trong cc thuc ln hu c) biu hin c trng tnh c ca cht .

Cc thuc BVTV c ngun gc khc nhau, nn c ch tc ng ca chng cng khc nhau:

Cc thuc tr su thuc nhm ln hu c v cacbamat km hm hot ng h men cholinesterase; pyrethroit li km hm knh vn chuyn Na+ v hp cht Cyclodien km hm knh vn chuyn ion Cl- ca h thn kinh ngoi vi; cn Fipronil v Avermectin li km hm s iu khin GABA v.v...Mt s thuc tr bnh dicarboxamide ngn cn qu trnh sinh tng hp tryglycerin; benzimidazol ngn cn s phn chia t bo ca nm bnh; cc cht khng sinh v acylamin li km hm sinh tng hp protein. Mt hp cht c hot tnh sinh hc mnh, thng l cc hot cht c c cao. Cc cht c c cc ni i hay ni ba, cc phn t d t gy hay d phn ng, lm tng c ca thuc. iu ny cng gii thch ti sao cc thuc thuc nhm pyrethroid c kh nng tc ng nhanh, mnh n cn trng n vy. Hay i vi du khong, c ca thuc i vi sinh vt cng ph thuc nhiu vo hm lng hydratcacbon cha no cha trong cc phn t ca chng. Hm lng ny cng cao, cng d gy c cho sinh vt, ng thi cng d gy hi cho cy trng.

S thay th nhm ny bng mt nhm khc, hay s thm bt i mt nhm ny hay nhm khc c trong phn t s lm thay i c v c tnh c ca hp cht rt nhiu.

S clo ho ca naphtalen v benzen lm tng tnh c ln 10-20, ca phenol ln 2-100ln. Ethyl parathion v Methyl parathion hon ton ging nhau v cng thc cu to c khc chng

Ethyl parathion c 2 gc etoxy C2H5O trong khi Methyl parathion c 2 gc metoxy CH3O. Tng t Fenitrothion v Methyl parathion c cng thc cu to hon ton ging nhau, nhng Fenitrothion c thm gc CH3 vng nitrophenyl. Mc d c s khc bit nhau rt t nh vy nhng chng khc nhau rt ln v phng thc v kh nng tc ng n cn trng v c ca thuc i vi sinh vt.


Ch tiu Ethyl parathion Methyl parathion Fenitrothion Cng thc cu to

S C2H5O P-O- -NO2 C2H5O

S CH3O P-O- -NO2 CH3O

S CH3 CH3O P-O- - NO2 CH3O

Phng thc tc ng

Tip xc, v c, xng hi, thm su mnh

Tip xc, v c, xng hi, thm su

Tip xc, v c, thm su yu

Tc ng n cn trng

Rt nhanh v mnh Nhanh Chm

c LD50 ( mg/kg)

Qua ming: 2mg/kg Qua da: 50mg/kg

Qua ming: 6mg/kg Qua da: 50mg/kg

Qua ming:250mg/kg Qua da: 2500mg/kg

c LD 50 vi ong mt 24h

c vi ong 0,07-0,14g/con

c vi ong 0,07-0,10g/con

c vi ong

LC50 vi c 96h

5mg/l 1,5mg/l 1,7mg/l

Hai thuc DDT v Dicofol c cng thc ho hc rt ging nhau ch khc nguyn t H c trong DDT c thay bng nhm -OH trong Dicofol; nhng DDT c tc dng tr su cn Dicofol li ch c tc dng tr nhn hi cy trng. H

Cl - - C - - Cl

C-Cl3

OH

Cl- - C - - Cl

C-Cl3 DDT Dicofol

S thay i nh trong cu trc phn t cng c th lm thay i c ca thuc. Thuc

666, mt thuc tr su c thuc nhm Clo hu c, c 8 ng phn, nhng ch c ng phn c hiu lc tr su mnh nht. Trong nhm pyrethroid, cc ng phn quang hc c c rt khc nhau. Thuc Fenvalerat c 4 ng phn quang hc khc nhau, nhng ng phn Esfenvalerat c c gp 4 ln cc ng phn khc gp li. Cc cht c mun pht huy kh nng gy c ca mnh phi xm nhp c vo trong t bo. Tnh phn cc v khng phn cc ca cht c cng c ngha ln trong kh nng xm nhp ca cht c vo trong c th sinh vt. Cc cht c kh nng phn cc, phn b khng ng u trong phn t v d tan trong cc dung mi phn cc, trong c nc. Cc nhm phn cc ph bin trong cc hp cht hu c l cc cht c cha nhm hydroxyl, carbonyl v amin. Chng rt kh xm nhp qua cc t bo v qua cc biu b sinh vt. Th tch phn t ca cc cht cng ln th kh nng xm nhp ca chng vo t bo cng kh. Nguyn nhn l ng knh cc l nh trong lp lipoproteit ca mng t bo gii hn s xm nhp ca cc cht phn cc vo t bo. Mc in ly ca cc phn t cht phn cc nh hng rt ln n tc xm nhp ca cht c vo t bo. Nhng ion t do, ngay c khi th tch phn t ca chng nh hn kch thc


ca cc l trn mng nguyn sinh, cng xm nhp km, thm ch khng xm nhp c vo t bo. L do: b mt ca cht nguyn sinh c s tch in, trn thnh cc l mng nguyn sinh cht xut hin lc y cc ion cng du v ht cc ion khc du, quyt nh kh nng xm nhp nhanh chm ca cc cht ny vo t bo. Cc cht phn cc li d xm nhp vo cy qua h thng r, bng s ho tan trong nc v c cy ht. Biu b sinh vt c cu to bng cc lipit, d cho cc cht ho tan trong cht bo i qua. Cc cht khng phn cc nh cc hydratcacbon li d tan trong lipit. Kch thc phn t cng ln, th ho tan ca chng trong cht bo cng tng. Cc cht c khng phn cc i vo t bo khng qua cc l nh ca mng nguyn sinh cht m ho tan trong lipit ca mng xm nhp vo mng t bo. Nhn chung, nhiu thuc BVTV l cc cht hu c, nn chng d dng xm nhp qua biu b vo c th sinh vt. Nhng loi thuc ny thng c phun ln l v gy c bng con ng tip xc. Nhiu loi thuc BVTV c kh nng xua ui cc loi ng vt nn c kh nng bo v cy trng v nng sn. V d : Thuc TMTD c kh nng xua ui di, chut chim bo v xoi hay cc loi ht ging khc. Tng t, cc thuc trong nhm pyrethroid cng c tc dng xua ui cn trng, nn gim kh nng hi phc qun th cn trng. b. Lin quan gia c tnh vt l ca thuc BVTV n c ca chng : Cc sn phm k thut cc dng lng, dung dch, bt hay cht kt tinh, c hm lng cht c cao. Chng rt c vi ngi, ng vt mu nng, cy trng, mi sinh v mi trng. Do c c cao, nn lng thuc tiu th trn mt n v din tch rt thp (khong 0,5-1kg a.i./ha, thm ch ch 6-12g a.i./ha), nn rt kh trang tri u trn n v din tch. Chng c bm dnh km, t tan trong nc v khng thch hp cho vic s dng ngay. V vy cc hot cht thuc BVTV thng c gia cng thnh cc dng khc nhau, nhm ci thin l tnh ca thuc, tng bm dnh v trang tri ca thuc, to iu kin cho thuc s dng d dng, an ton, hiu qu, gim nhim mi trng, t gy hi cho thc vt v cc sinh vt c ch khc.

c im vt l ca thuc BVTV c nh hng rt ln n c ca thuc v hiu qu phng tr ca chng. Nhng c im vt l l:

Kch thc v trng lng ht thuc : nh hng rt nhiu n c ca thuc. Ht thuc c kch thc ln, c din tch b mt nh, thng kh ho tan trong biu b l ( tc ho tan ca vt cht t l thun vi tng din tch b mt ca chng), gim kh nng xm nhp. Ht thuc c kch thc ln kh bm dnh trn b mt vt phun nn thng b ri vi tht thot nhiu, gim lng thuc tn ti trn vt phun. i vi cn trng, kch thc ht thuc ln, s kh xm nhp vo ming cn trng, lng thuc xm nhp vo c th cn trng b gim, hiu lc ca thuc do th cng gim theo. Vi cc thuc bt thm nc, khi pha vi nc to thnh huyn ph, kch thc ht ln lm cho huyn ph d b lng ng, kh trang tri u trn b mt, d lm tc vi phun, rt kh s dng.

Ngi ta bit rng, tc ri ca cc phn t thuc c tnh theo cng thc : 2gr2 v = --------- (D-a) 9 Trong : v= Vn tc ri t do ca cc ht (cm/gy) g= Gia tc trng trng (981cm/gy) r= Bn knh ht cm


= nht ca khng kh ( 10-30oC vo khong 0.000076-0.000086) D= T trng thuc bt a= T trng khng kh ( 0.001225) V gia tc trng trng g, nht ca kh quyn , t trng khng kh a c th xem nh

nhng hng s, nn tc ri hay lng ng ca ht thuc ph thuc ch yu vo ln ca ht v t trng ca thuc bt.

T cao h, thi gian ri ca cc ht c tnh bng cng thc:

h t = ------- vt Trong : t = Thi gian ri ca ht thuc (gy) h = cao vt = Vn tc ri t do theo hng thng ng. T hai cng thc ny ta thy: Thuc c ht to, nng chim u th, tc ri ca cc ht

s ln, , thi gian ri ca thuc xung b mt vt phun ngn, thuc khng bay xa khi ni phun. Ngc li, trong thuc c nhiu ht nh, nh, thi gian ri ca thuc s di, thuc d b cun xa khi ni phun. y l c s cho dng thuc bt-ht ra i.

Iwada (1973) cho bit: dng my bay ln thng phun thuc cao 5m, thuc bt c c ht < 44m, b gi cun i xa khi ni phun 250m; trong khi cao 8m, thuc ht bt mn c c ht 105-297m ch b gi cun i xa khi ni phun thuc 50m.

Hnh dng ht thuc nh hng nhiu n bm dnh v tnh c ca thuc. Ht thuc x x, nhiu gc cnh d bm dnh trn b mt vt phun hn cc ht thuc trn lng.

Trong huyn ph v nh tng l lng ca cc ht thuc lu s gip cho s phn tn cht c tt, nng cao c c ca thuc, ng thi cng gim kh nng gy tc bm.

Kh nng bm dnh ca thuc l mt trong nhng nhn t ko di hiu lc ca thuc. Thuc c bm dnh tt, t b tht thot do ra tri, chng c tc hi ca m , ma v gi, lng thuc tn trn cy nhiu hn v lu hn.

Tnh thm t v kh nng loang ca git thuc cng nh hng ln n hiu lc ca thuc. Khi phun lng, hnh dng ht nc thuc v kh nng loang trn b mt vt phun (thc vt v dch hi) ph thuc vo mt h thng gm 3 pha: cht lng, khng kh v b mt ca vt phun; trong hin tng b mt ng mt vai tr quan trng. Trn b mt vt phun, git cht lng c hnh dng khc nhau, tu theo mi tng tc ca nng lng b mt gia cc pha. Trng thi git cht lng trn b mt vt rn c xc nh bng cong ca b mt git cht lng, c biu th bng gc to ra bi b mt cht rn v ng tip tuyn vi b mt git cht lng ti ni git tip xc vi vt rn.

1 = 90o < 90o

> 90o 2 3 ______.________ ____________ __________.____________________

Nghch xc Cng xc


S 1- Cc hnh dng git thuc ri trn b mt vt phun Ti y, c 3 lc tc ng ng thi: 1 sc cng b mt ca cht lng v khng kh; 2

sc cng b mt gia cht rn v khng kh; 3 sc cng b mt gia cht lng v cht lng. Tu mi tng tc gia 3 lc ny m gc c to ra gia b mt cht rn v ng tip tuyn vi b mt git cht lng ti ni git tip xc vi vt rn c 3 kh nng nh hnh 1.

Trong , hin tng git cht lng lm t b mt vt rn c gi l s cng xc ( gc < 90 o) v hin tng cht lng khng lm t c b mt vt rn gi l hin tng nghch xc ( gc > 90 o ).

Harkins Cheng v Young ra cng thc biu hin mi nng lng b mt gia cc pha nh sau:

2 - 3 cos = ---------------- 1 Mun cho thuc loang dnh tt, phi tc ng lm sao cho gc nh i, hay ni cch

khc gi tr cos phi ln ln. Mun vy, phi tng hiu s ca 2 - 3 hay gim gi tr ca 1. Gi tr ca 2 & 3 rt kh thay i v chng ph thuc vo bn cht b mt vt phun v bn cht thuc. S thay i d thc hin nht l gim sc cng b mt gia cht lng v khng kh 1 . y l l do khi gia cng thuc ngi ta phi thm cc cht hot ng b mt.

tin cho ngi s dng, cc nh sn xut gia cng thuc BVTV thnh cc dng khc nhau ph hp vi mc ch s dng. Cc dng khc nhau ca thuc BVTV cng c kh nng gy c khc nhau. Thng thng c i vi ng vt mu nng v thc vt ca thuc dng sa cao hn nhng thuc dng bt... c. Lin quan gia cng tc ng ca thuc BVTV n c ca chng :

Cng tc ng ca cht c n c th sinh vt ph thuc vo nng , thi gian tip xc v mc tiu dng ca thuc BVTV.

Nng ca thuc BVTV l lng cht c cha trong dng thuc em dng, hoc lng ho cht c trong khng kh. Nng ca thuc BVTV c th hin bng phn trm trng lng ca hot cht/ trng lng ca sn phm ( i vi sn phm) hay phn trm trng lng ca sn phm / trng lng nc ( i vi dch phun); hoc c biu th bng g trng lng hot cht/ n v th tch. Nhn chung, nng cng cao, cng d gy hi cho sinh vt.

Di tc ng ca nng cht c, c th sinh vt c phn ng vi cht c khc nhau. nng thp, trong mt s trng hp, chng cn kch thch sinh vt pht trin tt, ngc li nng cao, chng gy hi c khi lm cht sinh vt. V d : Ngi ta dng 2,4-D nng thp kch thch sinh trng cho mt s cy trng; nhng nng cao, 2,4-D li l loi thuc tr c. Khi cn trng tip xc vi thuc tr su nng thp, nhiu ln, trong thi gian di chng nhng cn trng khng b tiu dit m chng cn dn hnh thnh tnh chng thuc, gy kh khn cho vic phng tr cn trng. Mc tiu dng l lng thuc cn thit x l cho mt n v din tch hay th tch. Mc tiu dng ph thuc vo cc loi dch hi, loi cy ( cy c tn l rng, cn dng vi lng thuc nhiu hn c th trang tri u trn cy),vo tui cy ( cy ln cn phun vi lng thuc nhiu hn), tnh hnh sinh trng ca cy ( cy cng xanh tt, pht trin mnh cng cn lng


thuc nhiu hn) v cc dng thnh phm ( dng thuc ht cn lng nhiu hn thuc bt thm nc v dng dung dch). Khi phun thuc ln cy dng lng, lng dung dch phun trn n v din tch cng mang c tnh ca mc tiu dng. Ngoi ra, khi s dng thuc dng dung dch, lng nc dng nhiu hay t, cn ph thuc vo cng c phun ri ( khi dng bm ng c, lng nc c th gim i, nhng nng thuc phi tng ln tng ng so vi dng cc bm tay, nhng khng c thay i mc tiu dng).

Qui m s dng v s ln phun thuc : S ln phun thuc cng nhiu, qui m dng thuc cng rng, nh hng ca thuc BVTV n mi trng cng mnh, c bit l cc thuc tr su. Ngoi ra, khong cch gia cc ln phun cng ngn, cng d to iu kin cho thuc tch lu trn b mt vt phun, d gy nhim vi mi trng.

Thi gian hiu lc ca thuc cng di, c ca thuc i vi mi trng cng tng. Cng mt nng , thi gian th hn triu chng ng c, gy cht hay qut ng cho sinh vt cng ngn, th loi thuc cng c. 3.2. S lin quan gia c im ca sinh vt vi c ca thuc BVTV:

Phn ng i vi cht c mi loi sinh vt u tun theo qui lut sau y: Cc loi sinh vt c phn ng rt khc nhau i vi mt loi thuc. Cng mt loi

thuc, cng mt liu lng, mt phng php x l, thm ch trn cng mt im x l, nhng c loi sinh vt ny b thuc gy hi, loi khc li khng hay t b hi.

V d: Dung dch booc c th dit tr nhiu loi nm v vi khun gy bnh cho cy, nhng li c hiu lc km hoc khng dit c loi nm phn trng (Erisiphales). Thuc tr c Ethoxysulfuron c kh nng dit tr mnh c ci lc v c l rng; nhng li t c hiu lc tr c ho tho, c bit l c lng vc nc v khng gy hi la. Thuc Buprofezin c hiu lc tr cc loi chch ht cao, nhng t gy hi cho cc su ming nhai.

Nhn chung, cc loi k sinh thin ch thng mn cm vi thuc tr su hn cc loi cn trng v nhn gy hi.

Mi loi thuc ch dit c mt s loi sinh vt, nn ngi ta chia thuc BVTV thnh cc nhm khc nhau tin cho vic s dng nh thuc tr su, tr bnh, tr c... Cng mt loi sinh vt, tnh mn cm ca loi sinh vt cc giai on pht dc khc nhau cng khng ging nhau vi tng loi thuc. V d: giai on trng v nhng ca cn trng thng chng thuc mnh hn giai on su non v trng thnh; c non thng chng chu thuc km hn c gi ( do kh nng xm nhp ca thuc vo c gi km hn vo c non v kh nng trao i cht ca c gi cng km hn c non).

Tnh mn cm ca cht c cn c th bin i theo ngy m. Nhng cn trng hot ng ban ngy thng km mn cm vi thuc hn vo ban m. Ngc li, nhng cn trng hot ng ban m li c kh nng chng chu vi thuc mnh hn ban ngy.

Gii tnh cng nh hng n s chng chu ca thuc. Thng thng kh nng chng chu ca con c km con ci.

Tnh mn cm ca cc c th sinh vt trong mt loi, cng giai on pht dc vi mt loi thuc cng khc nhau. Khi b mt lng rt nh cht c tc ng, c nhng c th b hi rt nghim trng, nhng c cc c th khc khng b hi. l phn ng c th ca sinh vt gy nn do cc loi sinh vt c cu to khc nhau v hnh thi, c trng v sinh l sinh ho khc nhau. Nhng cn trng i n, sinh trng trong iu kin kh khn thng c sc chng chu vi thuc km.


Hin tng ny l do mt hay nhiu nguyn nhn sau y gy nn: -Cc loi sinh vt c kh nng t bo v khc nhau trnh s xm nhp ca thuc vo

c th sinh vt. Loi gm nhm c v gic v khu gic pht trin, h thn kinh ca chng kh hon thin nn chng c tnh a nghi, t bo v bng cch khng n hay n t b, nn ma hay t gy nn ma tng b c ra ngoi.

-Gia cc loi sinh vt c cu to khc nhau v cu to gii phu, dy mng ca biu b; th ng ca l, l c lng hay nhn bng, dy lp sp, nng su ca r v.v... nh hng nhiu n kh nng xm nhp ca thuc vo c th sinh vt.

-Tnh trng sinh l v hot tnh sinh l lc b ng c cng nh hng n kh nng chu ng cc loi thuc ca sinh vt. Sinh vt c trng thi sinh l tt, c kh nng trao i cht mnh, kh nng thi loi cht c ra khi c th mnh th kh nng chu ng cht c ca cc loi ny tng. Ngc li, khi hot tnh sinh l cao s to iu kin cho thuc xm nhp vo c th nhiu hn, nn mn cm ca sinh vt i vi thuc cao hn.

-Thnh phn h men trong c th sinh vt c nh hng quyt nh n tnh chng thuc ca dch hi. Cc loi sinh vt c h men phn hu cc cht c thnh cc cht khng c, mn cm ca loi ny i vi cht c cng gim i nhiu. 3.3. nh hng ca iu kin ngoi cnh n c ca thuc BVTV :

Yu t ngoi cnh nh hng trc tip n l ho tnh ca thuc BVTV, ng thi nh hng n trng thi sinh l ca sinh vt v kh nng sinh vt tip xc vi thuc, nn chng nh hng n tnh c ca thuc cng nh kh nng tn lu ca thuc trn cy.

a. Nhng yu t thi tit, t ai : Tnh thm ca mng nguyn sinh cht chu nh hng mnh m ca iu kin

ngoi cnh nh pH ca mi trng, nh sng, nhit , m v.v... Do tnh thm thay i, kh nng xm nhp ca cht c vo t bo sinh vt cng thay i, ni cch khc, lng thuc BVTV xm nhp vo t bo sinh vt nhiu t khc nhau, nn c ca thuc th hin khng ging nhau.

i a s cc thuc BVTV, trong phm vi nhit nht nh (t 10-40oC), c ca thuc vi sinh vt s tng khi nhit tng. Nguyn nhn ca hin tng ny l: Trong phm vi nhit thch hp, khi nhit tng, hot ng sng ca sinh vt ( nh h hp dinh dng...) tng ln, ko theo s trao i cht ca sinh vt tng ln, to iu kin cho thuc xm nhp vo c th mnh hn, nguy c ng c ln hn. Hiu lc ca cc thuc xng hi kh trng kho tng tng ln r rt khi nhit tng.

C loi thuc, khi nhit tng ln, lm tng s chng chu ca dch hi vi thuc. Khi nhit tng, hiu lc ca thuc s gim. Nguyn nhn ca hin tng ny l: s

lng nhit trong mt phm vi nht nh, lm tng hat tnh ca cc men phn hu thuc c trong c th, nn lm gim s ng c ca thuc n dch hi. V th, vic s dng thuc DDT nhng ni c nhit thp li hn nhng ni c nhit cao.

Mt s loi thuc tr c, nhit cao lm tng kh nng phn hu ca thuc, hiu lc v thi gian hu hiu ca thuc do th cng b gim.

Nhit thp, nhiu khi nh hng n kh nng chng chu ca cy vi thuc. Khi phun 2.4D v cc sn phm cha 2.4D hay Butachlor cho la gieo thng, gp rt di

ngy, b cht hng lot. Nguyn nhn l do nhit thp, cy la khng ra r kp, mm thc khng pht trin thnh cy, li tip xc vi thuc lin tc, nn b cht.


Nhng cng c trng hp, tng hay gim nhit ca thuc cng khng nh hng nhiu n c ca thuc (nh CuSO4.5H2O).

Nhit cng nh hng mnh n bn v tui th ca sn phm. Nhit cao lm tng phn hu ca thuc, lm tng s lng ng ca cc git hay ht cht c trong thuc dng lng, gy phn lp cc thuc dng sa, dng huyn ph m c.

m khng kh v m t cng tc ng n qu trnh sinh l ca sinh vt cng nh c cu cht c. m ca khng kh v t lm cho cht c b thu phn v ho tan ri mi tc ng n dch hi. m cng to iu kin cho thuc xm nhp vo cy d dng hn.

C trng hp m khng kh tng, li lm gim tnh c ca thuc. c ca pyrethrin vi Dendrolimus spp. gim i khi m khng kh tng ln. Khi m tng, kh nng s khuych tn ca thuc xng hi b gim, dn n gim hiu lc ca thuc xng hi.

Nhng ngc li, m cng nh hng rt mnh n l tnh ca thuc, c bit cc thuc th rn. Di tc dng ca m, thuc d b ng vn, kh phn tn v kh ho tan.

Nhit v m nh hng nhiu n cht lng ca thuc, nn khi bo qun nh sn xut thng khuyn, thuc BVTV phi c ct ni rm mt cht lng thuc t b thay i.

Lng ma va phi s lm tng kh nng ho tan thuc trong t. Nhng ma to, c bit sau khi phun thuc gp ma ngay, thuc rt d b ra tri, nht l i vi cc thuc dng bt, cc thuc ch c tc dng tip xc.V vy khng nn phun thuc khi tri sp ma to.

nh sng nh hng mnh n tnh thm ca cht nguyn sinh. Cng nh sng cng mnh, lm tng cng thot hi nc, tng kh nng xm nhp thuc vo cy, hi lc ca thuc do vy cng cao. Nhng mt s loi thuc li d b nh sng phn hu, nht l nh sng tm, do thuc mau b gim hiu lc. Mt khc di tc ng ca nh sng mnh, thuc d xm nhp vo cy nhanh, d gy chy l cy.

Nhng c loi thuc, nh 2,4-D, phi nh nh sng, thng qua qu trnh quang hp ca cy, thuc mi c kh nng di chuyn trong cy v gy c cho cy.

Paraquat ch c hot ho, gy cht cho c di tc ng ca nh sng.

c tnh l ho ca t nh hng rt nhiu n hiu lc ca cc loi thuc bn vo t. Khi bn thuc vo t, thuc thng b keo t hp ph do trong t c keo v mn. Hm lng keo v mn cng cao, thuc cng b hp ph vo t, lng thuc c s dng cng nhiu; nu khng tng lng dng, hiu lc ca thuc b gim. Nhng nu thuc c gi li nhiu qu, bn cnh tc ng gim hiu lc ca thuc, cn c th nh hng n cy trng v sau, nht l vi cc loi cy mn cm vi thuc . Ngc li, cng c mt s loi thuc nh Dalapon, vo t, thuc b phn hu thnh nhng ion mang in m, cng du vi keo t, b keo t y ra, thuc d b mt mt do b ra tri.

Hm lng cht dinh d ng c trong t, c th lm gim hay tng c ca thuc BVTV. Theo Caridas (1952) thng bo, trn t trng u tng c hm lng ln cao, s lm tng hiu lc ca thuc Schradan. Hackstylo (1955) li cho bit, trn t trng bng c hm lng m cao, hm lng ln thp lm gim kh nng hp thu Dimethoate ca cy.

pH ca t c th phn hu trc tip thuc BVTV trong t v s pht trin ca VSV t. Thng thng, trong mi trng axit th nm pht trin mnh; cn trong mi trng kim vi khun li pht trin nhanh hn.

Thnh phn v s lng cc sinh vt sng trong t, c bit l cc VSV c ch cho ph nhiu ca t, c nh hng ln n s tn lu ca thuc trong t. Thuc tr su, tc


ng nhiu n cc loi ng vt sng trong t. Ngc li, cc loi thuc tr bnh li tc ng mnh n cc vi sinh vt sng trong t. Cc thuc tr c, tc ng khng theo mt qui lut r rt.

Nhiu loi vi sinh vt c trong t, c kh nng s dng thuc BVTV lm ngun dinh dng. Nhng thuc BVTV c th b cc vi sinh vt ny phn hu v s phn hu cng tng khi lng vi sinh vt c trong t cng nhiu. Ngi ta d dng nhn thy mt qui lut i vi thuc tr c:

Ln u dng thuc tr c, thi gian tn lu ca thuc trong t rt lu. Nhng nu cng dng loi thuc tr c y nhiu ln, th cng v sau, thi gian tn lu ca thuc trong t ngy cng ngn li, thuc cng b phn hu mnh hn. Hin tng ny l do, cc loi vi sinh vt thch ng c vi thuc, sn ngun dinh dng pht trin mnh vi s lng ln nn phn hu thuc mnh hn. Ngi ta cng nhn thy, nhng loi thuc t b keo t hp th, d b vi khun phn hu, ngc li b keo t hp ph nhiu li b nm phn hu.

b. Nhng yu t v cy trng v iu kin canh tc Khi iu kin canh tc tt, v sinh ng rung tt s hn ch c ngun dch hi nn

gim c s gy hi ca dch hi. Trong phng tr c di, tnh hnh sinh trng v pht trin ca cy trng v c di mang

mt ngha quan trng. Khi mt cy trng cao, cy pht trin mnh, cy cng gi, cng cnh tranh vi c di mnh, nhiu khi khng cn tr c. Nhng trong tnh hung nht nh phi phng tr, phi tin hnh ht sc thn trng, m bo k thut thuc khng dnh ln cy trng, gy hi cho cy. Nhng khi c di pht trin mnh, vic phng tr c di cng kh khn, lng thuc dng cng nhiu, cng d gy hi cho cy. Ni chung, thc vt cng non cng d b thuc tr c tc ng. cha k mt s thuc tr c ch c th dit c c di khi cn non.

Butachlor, Pretilachlor, Mefenacet, Bensulfuron methyl ch dit c trn rng la khi cy c cha c qu 1.5 l tht. Thuc Dual 720EC khng c hiu lc tr c, khi c ln.

Di tc ng ca thuc BVTV, cy trng c bo v khi s ph hi ca dch hi, s sinh trng v pht trin tt. Khi cy sinh trng tt, s to ngun thc n di do, dch hi c thc n, cht lng thc n li tt nn dch hi pht trin mnh, c sc chu ng vi thuc tt hn. Mt khc, khi cy sinh trng tt, cy pht trin rm rp, c li cho dch hi n nu, thuc kh trang tri ng u, kh tip xc c vi dch hi, lng nc thuc cn nhiu hn, vic phng tr dch hi tr nn kh khn hn, hiu qu ca thuc b gim nhiu.

Trong iu kin cy trng sinh trng tt, s lng dch hi sng st do khng hay t c tip xc vi thuc, s sng trong iu kin mi thun li, t b cnh tranh bi cc c th cng loi, ca cc k sinh thin ch, ngun thc n di do, cht lng tt, d hnh thnh tnh chng thuc, gy bng pht s lng. Di tc ng ca thuc, tnh a dng ca sinh qun b gim, c v chng loi ln s lng. Khi cc loi k sinh thin ch b hi, d lm cho dch hi ti ph, c th pht thnh dch, gy hi nhiu cho cy trng. Khi dng lin tc mt hay mt s loi thuc phng tr cc loi dch hi chnh, s lm cho cc loi dch hi th yu trc kia nay ni ln tr thnh dch hi ch yu, c coi l xut hin mt loi dch hi mi. Tt c nhng hin tng ny u xut hin Vit nam nh: tnh chng thuc ca su t hi rau h thp t; s bng pht s lng ca ry nu hi la; s xut hin loi dch hi mi l nhn trn ch. Nhng hu qu ny u do qu lm dng thuc BVTV, khng ch n k thut dng thuc gy nn.


Mi quan h gia 3 nhn t thuc BVTV, sinh vt v ngoi cnh ( s 2) l rt mt thit, tng tc ln nhau, nhn t ny l tin cho nhn t kia hay ngn cn nhn t kia pht huy tc dng.

THUC BO V THC VT -Bn cht ho hc;

-c tnh vt l -Cng tc ng

DCH HI IU KIN NGOI CNH -c tnh sinh vt hc -iu kin thi tit, t ai -c tnh sinh thi hc -iu kin canh tc, cy trng

S 2 Ni dung mi quan h qua li gia 3 yu t : Thuc, Dch hi v iu kin ngoi cnh

tc ng n hiu lc ca thuc BVTV.

CU HI N TP 1/ Nhng iu kin c bn thuc BVTV pht huy c tc dng? 2/ Cc hnh thc tc ng ca cht c v ngha ca chng? 3/ Nhng yu t lin quan gia c tnh ca thuc BVTV n c thuc? 4/ Nhng yu t lin quan gia c im ca sinh vt n c ca thuc BVTV ? 5/ Anh hng ca iu kin ngoi cnh n c ca thuc BVTV?


CHNG III THUC BO V THC VT, MI TRNG & HU QU XU CA

CHNG GY RA CHO MI SINH. Gip hc vin thy r tc ng ca thuc BVTV n mi trng sng v hu qu xu ca chng gy ra cho mi trng. Nhng bin php ngn nga thuc BVTV gy hi cho mi sinh mi trng. 1.TC NG CA THUC N MI TRNG V CON NG MT I CA THUC Trong qu trnh sn xut, vn chuyn, bo qun v s dng, thuc BVTV tc ng n mi trng bng nhiu cch khc nhau, theo s :

S 3 - Tc ng ca thuc BVTV n mi trng v con ng mt i ca thuc ( Theo Richardson, 1979; Dn theo Phm Vn Bin v cng s, 2000).

Thuc BVTV, bng nhiu con ng khc nhau, chng s b chuyn ho v mt dn. S mt i ca thuc BVTV c th xy ra do cc yu t sinh hc v phi sinh hc sau y:

1.1. S bay hi: Da theo kh nng bay hi, cc thuc BVTV c chia thnh 2 nhm: bay hi v khng bay hi. Tc bay hi ca mt loi thuc ph thuc vo p sut hi ; dng hp cht ho hc v iu kin thi tit ( gi to, nhit cao d lm cho thuc bay hi mnh).

1.2. S quang phn (b nh sng phn hu): Nhiu thuc BVTV d b phn hu khi tip xc vi nh sng mt tri , nht l tia t ngoi.

Cc thuc tr su Permethrin thuc nhm pyrethroid d b nh sng phn hu. Thuc tr c 2,4-D b nh sng phn hu to sn phm cui cng l acid humic.

Khng kh

Thuc bo v thc vt t

Nc

Thc S dng S dng

Thc phm

Tn d

ng Ngi

Khng kh

Thuc bo v thc vt t

Nc

Thc vt

Thc phm

ng vt Ngi


1.3. S cun tri v lng tri: S cun tri l hin tng thuc BVTV b cun t trn l xung t do tc dng ca

nc ma hay nc ti, hay thuc trn mt t cun theo dng chy i ni khc. S lng tri l hin tng thuc BVTV b ko xung lp t su bi nhiu yu t. C hai qu trnh ny ph thuc trc ht vo lng nc ma hay nc ti, c im

ca thuc v c im ca t. 1.4. Ho long sinh hc: Sau khi phun thuc, hoc sau khi thuc vo cy, cy trng vn tip tc sinh trng v

pht trin, din tch l tng, chi mi xut hin, khi lng cht xanh trong cy vn tng. Nu lngthuc BVTV trn cy khng b phn hu th t l % lng thuc trong cy vn b gim. S ho long sinh hc s gim kh nng bo v ca thuc, nhng cng lm gim lng cht c c trong sn phm, gim nguy c gy c cho ngi v gia sc. Trn nhng cy non c tc sinh trng mnh, ho long ca thuc cng nhanh.

1.5. Chuyn ho thuc trong cy : Di tc dng ca men, cc thuc BVTV trong cy b chuyn ho theo nhiu c ch.

Cc phn t thuc c th b chuyn ho thnh nhng hp cht mi c cu trc n gin hay phc tp hn, nhng u mt /gim/tng hot tnh sinh hc ban u.

Cc thuc tr su, tr nm ln hu c b phn gii qua tng bc v sn phm cui cng l acid phosphoric khng c vi nm bnh v cn trng.

Thuc tr c 2,4-DB trong cy c 2 l mm ch c th dit c khi chng b oxi ho thnh 2,4-D. Thuc 2,4-DB s khng dit c nhng loi thc vt khng c kh nng ny.

1.6. Phn hu do vi sinh vt t (VSV): Tp on vi sinh vt t rt phc tp, trong c nhiu loi c kh nng phn hu cc

cht ho hc. Mt loi thuc BVTV b mt hay mt s loi VSV phn hu (Brown, 1978). Thuc tr c 2,4-D b 7 loi vi khun, 2 loi x khun phn hu. Ngc li, mt s loi VSV cng c th phn hu c cc thuc trong cng mt nhm

hoc thuc cc nhm rt xa nhau. Nm Trichoderma viridi c kh nng phn hu nhiu loi thuc tr su clo, ln hu c, cacbamat,

thuc tr c ( Matsumura & Boush ,1968) Nhiu thuc tr nm b VSV phn hu thnh cht khng c, n gin hn (Menzie, 1969). Theo Fild v Hemphill (1968); Brown (1978), nhng thuc d tan trong nc, t b t

hp ph thng b vi khun phn hu; cn nhng thuc kh tan trong nc, d b t hp ph li b nm phn hu l ch yu. Cha r nguyn nhn ca hin tng ny. Khi dng lin tc nhiu nm, mt loi thuc tr c trn mt loi t th thi gian tn ti ca thuc trong t ngy cng ngn. Nguyn nhn ca hin tng ny c Kaufman v Kearney (1976) gii thch nh sau: Khi thuc mi tip xc vi t, cc loi VSV t c s t iu chnh. Nhng VSV khng c kh nng tn dng thuc tr c lm ngun thc n s b thuc tc ng, nn b hn ch s lng hay ngng hn khng pht trin na. Ngc li, nhng loi VSV c kh nng ny s pht trin thun li v tng s lng nhanh chng. Trong nhng ngy u ca ln phun thuc th nht, s lng c th v loi vi sinh vt c kh nng phn hu thuc trong t cn t, nn thuc b phn hu chm. Thi k ny c gi l pha chm tr (lag period). Cui pha chm tr, qun th VSV t thch ng vi thuc, dng thuc lm ngun thc n, s pht trin theo cp s nhn, thuc tr c s b mt i nhanh chng. Thi k ny c gi l pha sinh trng ( grow period). Khi ngun thc n cn,


VSV t ngng sinh trng, chuyn qua pha nh v ( stationary period) hay pha ngh ( resting phase). y xy ra 2 kh nng: -Nu VSV c tip thm thc n ( thm thuc), s lng VSV t tip tc tng, pha chm tr b rt ngn li. S ln s dng thuc tr c cng nhiu, thi gian mt i ca thuc cng nhanh. t c c tnh ny c gi l t hot ho (activated soil). -Nu qun th VSV t khng c tip thm thc n ( khng c bn thm thuc), chng s chuyn sang pha cht ( death phase) hay pha suy tn (decline phase). Tc suy tn tu thuc vo loi VSV: Mt s b cht, mt s chuyn sang dng bo tn (n 3 thng hoc lu hn) ch dp hot ng tr li. C trng hp VSV t phn hu thuc, nhng khng s dng ngun cacbon hay nng lng c trong thuc. Qu trnh chuyn ho ny c gi l ng chuyn ho (co-metabolism) hay l ng oxi ho (co-oxydation)(Burns, 1976). S phn hu ca DDT , 2,4,5-T trong t l s kt hp gia hai hin tng chuyn ho v ng chuyn ho. Hot ng ca VSV t thng dn n s phn hu thuc. Nhng c trng hp VSV t li lm tng tnh bn lu ca thuc trong t. Khi thuc BVTV xm nhp vo trong t bo VSV, b gi li trong , khng b chuyn ho, cho n khi VSV b cht ra; hoc thuc BVTV b mn gi cht m mn l sn phm hot ng ca VSV t- trnh c s tc ng phn hu ca VSV t (Mathur v Moley, 1975; Burns, 1976). Ngoi VSV, trong t cn c mt s enzym ngoi bo ( exoenzyme) cng c kh nng phn hu thuc BVTV nh cc men esteraza, dehydrogenaza... C rt t cng trnh nghin cu v s phn hu thuc BVTV ca cc enzym ngoi bo. 2.THUC BO V THC VT V MI TRNG SNG: 2.1.D lng thuc BVTV: a.nh ngha

D lng l phn cn li ca hot cht, cc sn phm chuyn ho v cc thnh phn khc c trong thuc, tn ti trn cy trng, nng sn, t, nc sau mt thi gian di tc ng ca cc h sng (living systems) v iu kin ngoi cnh ( nh sng, nhit , m v.v...). D lng ca thuc c tnh bng mg (miligam) thuc c trong 1 kg nng sn, t hay nc (mg/kg).

Nh vy, d lng thuc BVTV bao gm bt k dn xut no ca thuc cng nh cc sn phm chuyn ho ca chng c th gy c cho mi sinh, mi trng. D lng c th c ngun gc t nhng cht x l vo t hay trn b mt vt phun; phn khc li bt ngun t s nhim ( bit hay khng bit ) c trong khng kh, t v nc.

/ Tnh bn (persistent) l thi gian thuc BVTV c th c pht hin bng phng php ho hc hay sinh hc sau khi x l thuc. Thi gian tn ti ca d lng thuc tu thuc vo loi thuc, s ln phun thuc, lng thuc dng v iu kin ngoi cnh. Thi gian ti thch ca hiu lc sinh hc ph thuc vo bn cht ca thuc v yu cu ca sn xut. Ni cch khc, hot tnh sinh hc ca d lng cn chm dt ngay sau khi hiu lc sinh hc mong mun t c.

Mt s thuc BVTV c hot tnh sinh hc vt qu thi gian mong mun, c th gy c cho cy trng v sau hoc cc i tng khng phng tr. Nhng thuc nh vy mang tn l nhng thuc c / tnh bn sinh hc (biological persistent).


b.D lng thuc BVTV trn cy trng v nng sn: Thuc BVTV tn ti trn cy v nng sn mt thi gian l iu cn thit bo v cy

trng v nng sn chng li s gy hi ca dch hi trn rung, trong qu trnh vn chuyn v bo qun. Nhng d lng cng l ca thuc c trn nng sn, s l ngun gy hi cho ngi tiu dng. D lng thuc thng c trn cy trng nng sn v ch gy hi khi chng vt ngng cho php. Chng c chia thnh:

-D lng biu b (cuticule residue): gm nhng cht tan c trong lipid, nhng khng tan c trong nc, tn ti lp biu b.

-D lng ni b (sub-cuticule residue): gm nhng cht tan c trong nc, nhng khng tan trong lipid, tn ti di lp biu b.

-D lng ngoi b (extra cuticule residue): gm nhng cht khng tan c trong lipid v nc, tn ti bn ngoi biu b.

Ch tiu lng tiu th hng ngy c chp nhn (Acceptable Daily Intake- ADI) cho bit lng thuc BVTV c php n hng ngy trong thi gian sng m khng gy hi cho sc kho ngi tiu dng.

ADI c tnh bng s mg thuc c trong nng sn c cung cp cho 1kg th trng ngi trong mt ngy (mg/kg/ngy).

i khi trong nghin cu d lng, ngi ta cn dng ch tiu liu cp tnh tham kho (Acute reference dose - ARfD ): l lng cht c c trong thc n, nc ung, c tnh bng mg / kg th trng, a vo c th trong thi gian ngn ( thng trong mt ba n hay trong mt ngy), m khng nh hng mt cch ng k n sc kho ngi tiu dng. Liu cp tnh tham kho (ARfD) biu th tnh c cp tnh khc vi Tr s tiu th hng ngy c chp nhn (ADI ) biu th s ng c mn tnh.

Mc d lng ti a cho php ( Maximum Residue Limit MRL) hay Mc d lng chu ng c (Residue Tolerance Level -RTL) l gii hn d lng ca mt loi thuc, c tnh bng mg/kg, c php tn ti v mt php l, hoc xem nh c th chp nhn c trong hay trn nng sn, thc n gia sc m khng gy hi cho ngi s dng v vt nui khi n cc nng sn .

D lng ti a cho php ca thuc c tnh theo cng thc: ADI x th trng trung bnh/ngi MRL = mg/kg Lng thc n tiu th trung bnh / ngi/ ngy Thuc cng c cng c MRL cng thp. Nu d lng ca mt loi thuc trn nng sn

thp hn MRL th cho php nng sn c php lu hnh trn th trng. Th trng trung bnh/ngi mi quc gia, mi dn tc cng khc nhau. Lng thc n tiu th trung bnh /ngi/ngy l ch tiu ht sc quan trng tnh

MLR. Lng thc n tiu th trung bnh /ngi/ngy ph thuc vo c cu ba n cng nh tp qun sinh hot ca ngi dn tng nc. V th, vi tng loi nng sn gi tr MRL khng ging nhau vi mt loi thuc cc quc gia khc nhau.

Liu khng gy hiu ng ADI = mg/kg/ngy H s an ton


H s an ton thng thng l 100. Trng hp loi thuc th nghim c kh nng gy ung th th h s an ton c th ln n 500 hay 1000.

Lin quan n h s an ton, ngi ta dng ch tiu Xc nh ri ro ch n ( Determination of dietary rish) v c tnh theo cng thc:

Ri ro ca ch n = Triu chng x Q* Trong Q* biu th mc tim nng gy ung th ca thuc tr dch hi. Tr s Q*

cao l thuc c tim nng gy ung th mnh ( to khi u c hay lnh tnh) do d lng thuc tr dch hi c trong thc n.

Liu khng gy hiu ng (No effect level = NEL hay No effect = NEF) hay Liu khng quan st thy hiu ng ( No observed effect level = NOEL): liu lng ngng ca mt cht c ( c tnh bng mg cht c th nghim/kg th trng ca con vt th nghim/ ngy (mg/kg/ngy), khi cho cc con vt th nghim n hng ngy m khng gy ra bt k phn ng no khc thng v hnh vi, sinh l, bnh l ca cc con vt th nghim ( khng gy nguy him cho ng vt th nghim).

Cn mt khi nim khc Liu khng quan st thy hiu ng xu (No observed adverse effect level = NOAEL): liu lng ngng ca mt cht c khi cho cc con vt n hng ngy lin tc trong nhiu ngy, nhiu thng m khng quan st thy c bt k mt biu hin xu khc thng ca cc con vt th nghim (t n, hot ng km, run ry, v.v...). Liu khng quan st thy hiu ng bt li cng c tnh bng mg cht c/kg th trng/ngy.

Thng Liu khng quan st thy hiu ng xu c liu lng ngng cao hn Liu khng gy hiu ng .

D lng ti a cho php ca thuc hn hp c tnh theo cng thc: DA x100 DB x100 DC x100 MRL = + + + ...... 100 MRLA MRLB MRLC Trong thuc hn hp, mi thnh phn c c ch c l khc nhau v hn hp c

c tng theo cp s nhn th tr s MRL c tnh theo cng thc: DA x100 DB x100 DC x100 MRL = x x x.... 100 MRLA MRLB MRLC Trong D-d lng xc nh c ca cc thuc A,B,C.... Tr s MRL ca mi loi thuc i vi tng cy trng v vt nui c qui nh khc

nhau cc nc. MRL ca thuc c trong thc n thng nh hn nhiu so vi gi tr MRL do y t qui nh.

Trong thng mi quc t, ngi ta cn dng ch tiu Gii hn kim dch (Limit of Quarantification - LOQ ): Mc d lng thuc c trn nng sn, c tnh bng mg/kg, cho php hng ho c nhp vo mt quc gia hay mt khu vc xc nh . LOQ c vai tr nh MRL, nhng ch c gi tr trong thng mi.


Mc d lng c ngun gc bn ngoi ( Extraneous Residue Limit- ELR) l d lng thuc tn lu trn cy trng v nng sn do s nhim bn mi trng gy nn ( do x nghip ho cht hay cc nguyn nhn khc khng lin quan n vic dng thuc BVTV).

c.Cc bin php nhm gim thiu d lng thuc BVTV trn cy trng v nng sn: -Bo m thi gian cch ly ( Preharvest interval PHI): L khong thi gian tnh bng ngy t ln x l cui cng n khi thu hoch. Thi gian cch ly l thuyt l khong thi gian t ln x l thuc cui cng n khi thu

hoch m ti thi im , d lng ca thuc trn cy ch bng hay thp hn d lng ti a cho php.

Trong thc t, m bo an ton cho ngi v gia sc, ngi ta thng ko di thi gian ny thm mt s ngy na ( thng l gp i) v c tn l thi gian cch ly thc t.

Thi gian cch ly c th thay i t mt vi ngy n mt vi tun tu theo loi thuc, tu loi nng sn c phun thuc v tu quc gia. Thu hi nng sn cha ht thi gian cch ly l rt nguy him. Ngi v gia sc n phi nng sn c thu hi khi khng bo m thi gian cch ly, s d b ng c bi thuc BVTV v cc sn phm chuyn ho ca chng.

-Phi s dng thuc ng k thut: Nn nh, thi gian cch ly c xc nh trn c s nng v liu lng thuc BVTV dng mc khuyn co. Nu dng thuc nng v liu lng cao hn liu khuyn co, th d c bo m thi gian cch ly cng khng c ngha, v d lng ca thuc trn cy vn cao hn d lng ti a cho php, vn c kh nng gy ng c cho ngi v gia sc.

-Nn chn cc loi thuc t c, t bn trong mi trng, mang tnh chn lc cao tr dch hi.

- Chn dng thuc, phng php x l v thi im x l thch hp gim s ln phun, gim lng thuc dng v gim thiu s nhim cy trng v mi trng.

-Chn cy trng lun canh thch hp gim d lng ca thuc BVTV c trong t v gim nguy c gy c cho cy trng v sau. 2.2. Thuc BVTV trong t v nc D x l bng phng php no , cui cng thuc BVTV cng i vo t, tn ti cc lp t khc nhau, trong cc khong thi gian khng ging nhau. Trong t thuc BVTV thng b VSV t phn gii hay b t hp ph ( b st v mn ht). Nhng c nhiu loi thuc c thi gian phn hu di, khi dng lin tc v lu di, chng c th tch lu trong t mt lng rt ln.

Thi gian tn ti ca thuc trong t c gi l bn ho hc (chemical persistent). Bao gi tnh bn ho hc cng di hn bn sinh hc. Nhiu hp cht ho hc c th tn ti di dng lin kt khng gy c tc ng sinh hc, hoc tn dng thng thng, nhng lng thp, tuy c th pht hin bng phng php ho hc, nhng khng th hin hiu lc ca chng vi sinh vt. nh gi kh nng tn ti ca thuc trong t, ngi ta thng dng ch tiu Thi gian bn phn hu (half life), c k hiu bng tr s DT50 ( Disappeared time - DT : thi gian b bin mt): l khong thi gian tnh bng gi, ngy, tun, thng, nm k t khi hot cht c a vo t n khi hm lng ch cn mt na lng thuc a vo.


Tr s DT50 ca mt loi thuc ph thuc vo bn cht ho hc, cc phn ng ho hc c th xy ra, mc hot ng ca VSV t v cc nhn t mi trng (tnh cht t, nhit v m t, iu kin thi tit). Tuy nhin trong nhng iu kin xc nh, tr s DT50 kh n nh. Cn c vo tr s DT50, Briggs (1976) chia bn ca cc thuc BVTV thnh 4 nhm: -Rt bn DT50 > 26 tun -Bn lu DT50 6 - 26 tun -It bn DT50 2 - 6 tun -Khng bn DT50


- S c mt lu di ca mt loi thuc BVTV trong t c th km hm s phn hu cc thuc BVTV khc. -Thuc BVTV c th gy nhim b mt t v mch nc ngm.

iu kin ng rung ( field conditions) l cc yu t tc ng n s nhim bn mch nc ngm. Gm: - nghing ca mt t: Lm nc trong t rt nhanh, tng kh nng cun tri thuc, d gy nhim bn thuc trn din rng.

-c tnh vt l ca t: Nhng t tht nh, thnh phn ct nhiu, t mn, kh nng hp ph v gi thuc km, thuc trong t b ra tri nhiu, tng kh nng gy nhim mch nc ngm.

-S thm v ra tri: Thuc trong t ct, t mn , nhiu l hng, kh hp ph thuc, d b thm v ra tri. S ra tri tng ln khi c ma ro v ti nc qu nhiu. Tc hi ny cng th hin khi b kh hn ko di.

-Mc nc ngm: Mc nc ngm cao kt hp vi kh nng hp ph ca t km d gy nhim mch nc ngm.

Nghin cu s dng thuc BVTV mt cch hp l cho cy trng nc l rt cn thit trnh thuc gy hi cho cc sinh vt thu sinh, gy nhim b mt t v mch nc ngm. Cn tnh n kh nng gy nhim do gi cun thuc i xa hoc lng thuc b mt trc tip trtn nhng cnh ng c phun hay ti. Cn la chn k thuc BVTV v phng php dng thuc gim thiu mc nhim cho vng ngp nc, ca sng v vng ph cn, gim tc hi ca thuc n cc loi ng vt hoang d v cc loi thu sinh. Dng thuc sai k thut, lm ln, v, to iu kin cho thuc vo t v mch nc ngm nhiu hn. 3. HU QU DO THUC BO V THC VT GY RA CHO QUN TH SINH VT: 3.1.Hu qu do thuc BVTV gy ra cho qun th sinh vt gy hi Trong vng x l, sau mi t dng thuc, bn cnh cc c th dch hi b cht, cn nhiu c th, do nhiu nguyn nhn vn sng st. Chng pht trin trong iu kin mi. Tc ng ca iu kin sng mi n sinh vt rt su sc, ko di, thm ch n cc th h sau. Qun th sinh vt b chuyn bin theo cc hng khc nhau. Nhng c th dch hi sng st, sau khi tip xc vi thuc, nu khng c ch ng mc, s gy cho con ngi khng t kh khn, thm ch c trng hp tr thnh tai ho i vi sn xut v mi sinh.

a.Phn ng ca dch hi i vi cht c liu lng thp Dch hi cn sng st sau mi t x l thuc, do khng b trng thuc hay trng liu di mc gy cht (sub-lethal dosis), s pht trin trong iu kin khc trc: mt qun th gim, cy trng sinh trng tt hn, dch hi hng ngun thc n di do, c cht lng cao, thay i sc sinh sn, c im sinh l ca c th trong qun th; mt thin ch v vi sinh vt c ch t, nn dch hi d hi phc s lng. Di tc ng ca liu di mc gy cht, dch hi s pht trin mnh , gy kh khn cho vic phng tr. Rp o Myzus persicae l mi gii truyn bnh virus hi khoai ty. Dimethoate, Thiometon v mt s thuc tr su khc, tuy c hiu lc tr rp ny cao, nhng khng hn ch c s ly lan ca bnh. Nguyn nhn ca hin tng ny: Rp b ng c thng hot ng mnh ln v phi mt 3 5 gi sau, rp mi cht. Trong thi gian , thi gian rp ly bnh.


Dng mt s thuc hoocmon tr c, lm tng mc sinh sn ca rp. Chut rng n ht tng bch c tm thuc chut liu di liu gy cht, lm cho qun th chut a phng tnh nht b, khng chu n bt k loi ht no khc. lm cho hiu lc tr chut ca thuc b gim. Nhng cng c hin tng, liu lng thp, thuc BVTV li c li cho vic hn ch s pht trin ca dch hi. Sc n rp ca b ra Semiadalia undecimnolata khi mi tip xc vi Primicarb liu thp b gim xung, nhng sau li tng mnh, hn hn nhng con khng c x l. Mt s cht khng sinh nh norobioxin, ampixilin, actinomyxin D, pactamyxin di liu gy cht, lm gim sc trng ca nhn Tetranychus urticae. Khi ng c mt s thuc tr chut chng ng mu brodifacoum liu thp, hot ng ca chut tr nn chm chp, d lm mi cho cc ng vt sn mi.

b.Tnh chng ( khng) thuc BVTV: Tnh chng/khng thuc ca dch hi l hin tng ph bin nhiu loi sinh vt, trn

nhiu a bn khc nhau (ngoi rung, trong kho tng v nh ; nng thn v thnh th; trn cn v di nc). Nhng tnh chng thuc c hnh thnh mnh nht cn trng v nhn.

Hin tng chng thuc c nu ln u nm 1887. Nhng hin tng c m t k u tin l hin tng chng lu hunh vi ca loi rp sp Quadraspidiotus pezniciosus Comst (1914). Gia nhng nm 80 ca th k 20 c trn 100 loi nm v vi khun; khong 50 loi c di; 12 loi chut; 447 loi cn trng v nhn ( trong c 264 loi cn trng v nhn hi nng nghip ) hnh thnh tnh chng thuc. u tin, nhiu loi cn trng v nhn ch chng thuc clo, ln hu c v cacbamat, th nay cc nhm thuc mi nh pyrethroid, cc cht trit sn, cc cht iu khin sinh trng cn trng, cc thuc vi sinh vt cng b chng. Nhiu loi dch hi khng nhng chng mt loi thuc, m cn c th chng nhiu loi thuc khc nhau. Nhiu loi thin ch ca cn trng v nhn gy hi, mt s loi c sn, c p mui... cng hnh thnh tnh chng thuc. Nm 1977 c ti 70% s thuc khng sinh v 90% thuc tr bnh ni hp b nm v vi khun chng li. C di cng hnh thnh tnh chng thuc. Hu ht cc nhm thuc tr c u b c di chng li. Ring Paraquat, n nay, c 18 loi c chng thuc ny.

Vit nam, loi su t Plutella xylostella hnh thnh tnh khng nhiu loi thuc trn phm vi c nc. Hong Trung (2004) xc nh c mt s dng mt Tribolium castaneum chng Phosphin v mt Rhizopertha dominica khng c Phosphin v DDVP. Ngoi ra, cn mt s loi cn trng v nhn khc cng b nghi hnh thnh tnh chng thuc nh su xanh da lng Helicoverpa exigua hi bng, mt s dng rp o Myzus persicae H ni, mt s dng ry nu Nilaparvata lugens ng bng sng Cu long v.v...

tr dch hi chng thuc, bin php u tin l phi dng nhiu thuc hn, chi ph tng ln v mi sinh mi trng b u c nhiu hn.

Tnh chng thuc ca dch hi l mt tr ngi cho vic dng thuc ho hc phng tr dch hi v gy tm l nghi ng hiu qu ca cc loi thuc dng. Cc thuc tr dch hi mi ra i khng kp thay th cho cc thuc b dch hi chng.

Dch hi chng thuc gy nhng tn tht to ln trong nng nghip v trong y t nhiu nc v ngy cng tr nn nghim trng. Nhiu chng trnh phng chng dch hi trong nng nghip v y t ca cc t chc quc t v khu vc, da ch yu vo thuc ho hc b tht bi. T 1963, T chc Nng lng th gii (FAO), T chc Y t th gii (WHO) thnh lp mt mng li nghin cu tnh chng thuc ca dch hi v bin php khc phc.


nh ngha tnh chng thuc ca dch hi : l s gim st phn ng ca qun th ng hay thc vt i vi mt loi thuc tr dch hi, sau mt thi gian di, qun th ny lin tc tip xc vi thuc , khin cho nhng loi sinh vt y chu c lng thuc ln c th tiu dit c hu ht cc c th cng loi cha chng thuc. Kh nng ny c di truyn qua i sau, d c th i sau c hay khng tip xc vi thuc (WHO,1976) .

Ch s chng thuc( resistance index- Ri) hay h s chng thuc (resistance cofficien = Rc) l ch tiu xc nh tnh chng thuc ca dch hi. Ch s / h s chng thuc l:

LD50 ca loi dch hi b nghi l chng thuc Ri (Rc) = LD50 ca cng loi dch hi nhng cha tng tip xc vi thuc Loi dch hi nhng cha tng tip xc vi thuc c gi l ni mn cm (sensible

strain). Mun c c ni mn cm nhiu khi phi nui / cy dch hi trong mi trng nhn to, cch ly hon ton vi thuc BVTV.

Nu Ri (Rc) 10 c th kt lun ni chng thuc hnh thnh. Nu Ri (Rc) < 10 th ni mi ch trng thi chu thuc. Ri (Rc) c th t ti tr s hng trm thm ch ln n hng ngn. Theo Nguyn nh t (1980): Tr s chng thuc Ri (Rc) ca qun th su t X n vi Methyl

parathion ln n 251.5; ca qun th su t Thu lnh vi Trichlorfon258.3; ca qun th su t Ph din vi Diazinon 117.4

Cn phn bit 3 khi nim: Chng thuc hay khng thuc; Chu thuc v Quen thuc. -Tnh chu thuc ( tolerance) : l c im ring ca tng c th sinh vt, c th chu

ng c cc liu lng thuc khc nhau. Tnh chu thuc ca tng loi sinh vt ph thuc vo tng c th, trng thi sinh l v khng di truyn sang i sau. Tuy nhin, tnh chu thuc cng c th l bc khi u ca tnh chng /khng thuc.

-Tnh quen thuc( accoutumance): Hin tng xy ra trong mt i c th c tip xc vi thuc (cht c) vi lng cao dn v cui i, c th c th chu ng c lng thuc cao hn rt nhiu so vi ban u. Nhng con chu ca c th li khng chu c lng thuc . cn trng v nhn cha c hin tng ny.

Nhng c th chu thuc v quen thuc ch chu c lng thuc thp hn nhiu so vi c th chng/ khng thuc.

c im ca s hnh thnh tnh cc qun th dch hi khng thuc: -S hnh thnh tnh chng thuc ca cc loi sinh vt, phn no ph thuc vo

mc s dng thuc. Vic s dng lin tc, nhiu ln, t thay i loi thuc, dng thuc trn qui m ln d gy nn hin tng chng thuc.

Mt thc trng kh ph bin: Khi nng dn thy mt loi thuc c hiu qu tr mt loi dch hi no , h thng dng thuc , cho n khi thy hiu lc ca thuc b gim. tng hiu lc, ngi ta tng nng , lng thuc dng,phun thm nhiu ln, thm ch hn hp thuc vi cc loi thuc khc, dn n tnh trng dch hi cng nhanh chng thuc.

-S hnh thnh tnh chng ca cc loi khc nhau i vi cc loi thuc BVTV khc nhau l khng ging nhau.


Trong 364 loi chn t chng thuc th b Diptera c 133 loi ; b Coleoptera - 56; Hemip

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32. Giáo Trình Sử Dụng Thuốc Bảo Vệ Thực Vật - Nguyễn Trần Oánh, 171 Trang