Herbicide Resistance

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Herbicide Resistance. Discussion Topics What is resistance? What causes resistance?. Terminology. Mode of Action Codes ACCase inhibition ALS inhibition Microtubule assembly inhibition Synthetic auxin PS II inhibition, not groups 6 or 7 PS II inhibition, not groups 5 or 7 - PowerPoint PPT Presentation

Text of Herbicide Resistance

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Herbicide Resistance

Discussion Topics

What is resistance?

What causes resistance?

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Terminology

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Sites of ActionInhibition of ACCaseInhibition of ALSInhibition of PS IIPS I electron diversionInhibition of PPOBleaching: inhibition of carotenoid biosynthesis at PDSBleaching: inhibition of HPPDBleaching: inhibition of carotenoid biosynthesis, unknown targetInhibition of EPSPSInhibition of glutamine synthetaseMicrotubule assembly inhibitionInhibition of long-chain fatty acid synthesisInhibition of cell wall synthesisInhibition of lipid synthesis; not ACCase inhibitionSynthetic auxinsInhibition of auxin transportUnknown
WSSA Code Site of Action1Inhibition of ACCase2Inhibition of ALS5Inhibition of PS II22PS I electron diversion14Inhibition of PPO12Bleaching: inhibition of carotenoid biosynthesis at PDS27Bleaching: inhibition of HPPD13Bleaching: inhibition of carotenoid biosynthesis, unknown target9Inhibition of EPSPS10Inhibition of glutamine synthetase3Microtubule assembly inhibition15Inhibition of long-chain fatty acid synthesis20 and 21Inhibition of cell wall synthesis8Inhibition of lipid synthesis; not ACCase inhibition4Synthetic auxins19Inhibition of auxin transport17Unknown

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From 2011* NC AgChem Manual (>150 entries)Table 8-11. Herbicide Modes of Action.Brand names Active ingredient(s)Chemical familyMode of ActionAAtrexatrazineTriazine5AccentnicosulfuronSulfonylurea2AimcarfentrazoneTriazolinone14AlachloralachlorChloroacetamide15AlanapnaptalamPhthalamate semicarbazone19ArrowClethodimCyclohexadione1AtrazineatrazineTriazine5Assure IIquizalofopAryloxyphenoxy-propionate1Axiomflufenacet + metribuzinOxyacetamide + triazinone15 + 5BackdraftGlyphosate + imazaquinGlycine + imidazolinone9 + 2* Revised annually.

Mode of Action Codes

ACCase inhibition

ALS inhibition

Microtubule assembly inhibition

Synthetic auxin

PS II inhibition, not groups 6 or 7

PS II inhibition, not groups 5 or 7

PS II inhibition, not groups 5 or 6

Lipid synthesis inhibition, not ACCase inhibition

EPSP synthase inhibition

Glutamine synthase inhibition

Carotenoid biosynthesis inhibition at PDS

Carotenoid biosynthesis inhibition, unknown target

PPO inhibition

Inhibition very long-chain fatty acids

Unknown MOA

Auxin transport inhibition

PS I electron diversion

Inhibition of HPPD

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Herbicide Resistance Defined

(WSSA definition)

Inherited ability of a biotype* of a weed to surviveand reproduce following exposure to a dose of herbicide normally lethal to the wild type.

*Biotype is a subset of the population having

some genetically controlled characteristic not

common to the population as a whole

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Herbicide Resistance Defined

(WSSA definition)

Inherited ability of a biotype of a weed to surviveand reproduce following exposure to a dose of herbicide normally lethal to the wild type.

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Herbicide Resistance vs Tolerance

Resistance: herbicide used to kill that weed; it no

longer does; we have selected for

resistance.

Example: Hoelon and ryegrass

Tolerance:the herbicide never did kill that species.

Example: 2,4-D and ryegrass

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Cause of Herbicide Resistance

Herbicides do not create resistance.

Herbicides can select for resistant

individuals already in the population.

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Resistant individuals initially rare

Initial frequency of resistance: 1 in 100 thousand

1 in 1 million

1 in 10 million

1 weed/4.3 square feet = 10,000 weeds/acre

= 1,000,000 weeds/100 acres

Frequency of 1 in 1 million equal to one resistant

plant per 100 acres

0X 1/4X 1/2X 1X 2X 4X 8X 16X 32X

0X 1/4X 1/2X 1X 2X 4X 8X 16X 32X

0X 1/4X 1/2X 1X 2X 4X 8X 16X 32X

Hoelon-susceptible biotype

Hoelon-resistant biotype, Union Co.;

Treated with Hoelon

Group 1, ACCase inhibitor

Hoelon-resistant biotype, Union Co.; Treated with Axial

Group 1, ACCase inhibitor

Example of Cross Resistance

Italian ryegrass

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0X 1/4X 1/2X 1X 2X 4X 8X 16X 32X

0X 1/4X 1/2X 1X 2X 4X 8X 16X 32X

0X 1/4X 1/2X 1X 2X 4X 8X 16X 32X

Hoelon-susceptible biotype

Hoelon-resistant biotype

Treated with Hoelon

ACCase inhibitor, Group 1

Hoelon-resistant biotype

Treated with Osprey

ALS inhibitor, Group 2

0X 1/4X 1/2X 1X 2X 4X 8X 16X 32X

Example of Multiple Resistance:

Italian Ryegrass

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Quiz

Multiple resistance is greater concern

than cross resistance.

Why?

Discussion Topics

What is resistance?

What causes resistance?

What is the extent of resistance?

What species have resistant biotypes?

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ACY 2008

ALS inhibitors

PS II inhibitors (triazines)

ACCase inhibitors

Glyphosate

DNAs

Ureas/amides

Auxins

Arsenicals

Thiocarbamates

PPO inhibitors

Carotenoid biosyn. inhibitors

Nitriles

Herbicide Resistance in US by Site of Action*

Paraquat

HPPD inhibitors

*Current as of Dec. 6, 2010

Resistance reported with 14 SOAs and 76 species;

128 species by SOA combinations, due to multiple resistance

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Glyphosate-resistant biotypes in U.S.

Glyphosate-resistant biotypes in U.S.

Glyphosate-Resistant Weeds in the US

7 Broadleaf weeds 5 Grasses

Palmer amaranthItalian ryegrass

Tall waterhempRigid ryegrass

Common ragweedJohnsongrass

Giant ragweedGoosegrass

Hairy fleabaneAnnual bluegrass

Horseweed

Kochia

Examples of glyphosate multiple resistance in USPalmer amaranthglyphosate and ALS inhibitorsHorseweedglyphosate and ALS inhibitorsglyphosate and paraquatCommon ragweedglyphosate and ALS inhibitorsGiant ragweedglyphosate and ALS inhibitorsHairy fleabaneglyphosate and paraquatTall waterhempglyphosate, ALS inhibitors, and PPO inhibitors

Glyphosate-

Resistant Weeds

in NC

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Discussion Topics

What is resistance?

What causes resistance?

What is the extent of resistance?

What species have resistant biotypes?

Impacts of herbicide resistance?

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Impacts of Herbicide Resistance

Increased cost of weed management; reduced profitability

Increased complexity of weed management

Fewer herbicide options

Fewer crop options

Compromise conservation tillage

Impacts of Herbicide Resistance

Increased cost of weed management;

reduced profitability

Increased complexity of weed management

Fewer herbicide options

Fewer crop options

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Impacts of Herbicide Resistance

Increased cost of weed management; reduced profitability

Increased complexity of weed management

Fewer herbicide options

Fewer crop options

Compromise conservation tillage

Impacts of Herbicide Resistance

Increased cost of weed management;

reduced profitability

Increased complexity of weed management

Fewer herbicide options

Fewer crop options

Compromise conservation tillage

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Discussion Topics

What is resistance?

What causes resistance?

What is the extent of resistance?

What species have resistant biotypes?

Impacts of herbicide resistance?

Basics of resistance management

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How does herbicide resistance develop?

Prerequisites for Resistance

At least one resistant plant must be present

2.Selection pressure must be put on that resistant plant

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Herbicide Resistance Management

The focus must be on

reducing selection pressure.

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Diversity in management options reduces

selection pressure on herbicides.

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Weed Management in Cotton: Before RR

Conventional tillage

PPI and PRE herbicides

Early POST or POST-directed herbicides

Late POST-directed herbicides

Cultivation

Weed Management in Cotton: with RR

No-till or strip-till

No cultivation

No PPI herbicide; little to no PRE

Multiple in-crop Roundup applications

Very little other chemistry

Herbicide Resistance Management

(Reducing selection pressure)

Minimize seed bank; avoi