Sign and symptoms in

crops

Dr. Kumara Thevan

FIAT, UMK

Overview

• Affected plant parts

• Diseases

• Diagnosis plant pest (beneficial &

pest insects)

• Pest infestation (assessment)

• Stored product pest

Pest damage to crop plants

Vegetables

“Tomato, are you health or not?”

• Environmental stress• Nutritional deficiency

• Chemical injury

• Insect damage

• Infectious Disease: fungi, viruses, bacteria, nematodes

Nutrient Deficiencies

Iron

Calcium Molybdenum

Magnesium

Disease triangle

HostSpecies

Cultivar

Age

Pathogen

fungi

bacteria

nematodes

viruses

EnvironmentTemp, RH, wetness

Symptoms & Signs

Symptom

Expression of a disease by the plant

Sign

Visible presence of a pathogen

Symptoms

Galls

Leaf spots

Wilthttp://www2.dpi.qld.gov.au/horticulture/17902.html

Mottling, distortion

Signs: pathogen structures

Anthracnose

Tomato

Clemson University –

USDA Cooperative Extension Slide Series

www.ipmimages.org

Cabbage white mold mmk

Anthracnose

squash

Clemson University –

USDA Cooperative Extension Slide Series, ,

www.ipmimages.org

Alton N. Sparks, Jr., The University of Georgia, www.ipmimages.org

Vectors: whiteflies, aphids, thrips

Diagnosing Plant Pests

• The best way to control insects and

diseases to prevent them before they

get a foot hold in your garden.

• How?

Beneficial Insects

• Ladybug larvae are equally relentless predators.

…

• The Praying Mantis is anotherwidely-recognized insectpredator.

Lacewing Larvae

• They are miniature monsters when

viewed at close range. They are

deadly enemies of small caterpillars,

aphids, and other soft-bodied insects.

Chrysoperla carnea

Appearance

• Approximately 12–20mm long.

• Adults are pale green and have long

antennae and bright, golden eyes.

• They have large, transparent, pale

green wings and a delicate body.

Plants that attract LadybugsAchillea filipendulina - Fern-leaf yarrow

Achillea millefolium- Common yarrow

Ajuga reptans - Carpet bugleweed

Alyssum saxatilis - Basket of Gold

Anethum graveolens - Dill

Anthemis tinctoria - Golden marguerite

Asclepias tuberosa - Butterfly weed

Atriplex canescens - Four-wing saltbush

Coriandrum sativum - Coriander

Daucus Carota - Queen Anne's lace

Fagopyrum esculentum - Buckwheat

Foeniculum vulgare - Fennel

Helianthus maximilianii - Prairie

sunflower

Penstemon strictus - Rocky Mt.

penstemon

Potentilla recta 'warrenii’ - Sulfur

cinquefoil

Potentilla villosa - Alpine cinquefoil

Tagetes tenuifolia Marigold - lemon

gem

Tanacetum vulgare - Tansy

Taraxacum officinale - Dandelion

Veronica spicata - Spike speedwell

Vicia villosa - Hairy vetch

Lifecycle

• Oval shaped eggs are laid at the end of long

silken stalks. These single eggs start off green

and turn grey after a few days.

• The active larvae are grey or brownish. They are

alligator–like with well–developed legs and large

pincers with which they suck the body fluids from

prey insects such as aphids.

• Adult lacewings feed on pollen and also need

nectar or honeydew as food before laying eggs.

Habits• Adults are active fliers, particularly during the

evening and at night.

• considered an important predator of mealybugs

• feed on (among others) several species of aphids,

spider mites (especially red mites), thrips,

whiteflies, small caterpillars and beetle larvae.

• often used as a biological integrated insect control

program.

Plants that Attract Lacewings

Achillea filipendulina - Fern-

leaf yarrow

Anethum graveolens - Dill

Angelica gigas - Angelica

Anthemis tinctoria - Golden

marguerite

Atriplex canescens - Four-

wing saltbush

Callirhoe involucrata - Purple

poppy mallow

Carum Carvi - Caraway

Coriandrum sativum - Coriander

Cosmos bipinnatus - Cosmos

white sensation

Daucus Carota - Queen Anne's

lace

Foeniculum vulgare - Fennel

Helianthus maximilianii - Prairie

sunflower

Tanacetum vulgare - Tansy

Taraxacum officinale - Dandelion

Wasps

• many Small Wasps are important parasites of otherinsects. Adult parasites range in size from very small.

• range in size from 2 to 15 mm

• Larvae of most parasites develop inside the bodies oftheir prey, but some feed externally or pupate outsidethe host's body. These parasites are important insuppressing populations of many insects. They areimportant for control of loopers, cutworms, andaphids.

Common Pests

Spider mites

Aphids

Mealy bugs

Thrips

Cabbage Looper

Potato Beetle

Tomato Horn Worm

Squash Vine

Borer

Pest infestations

• Incidence

• Severity

Incidence

• The incidence of the pest (or damage

symptoms) is generally the proportion

of plants in a sample which are host

to the pest (or which show damage

symptoms), and is usually expressed

as a percentage.

Severity

• The severity of the infestation is a

measure of the size of the pest

population on the plants, or the extent

of the damage done, and is often

measured as so many insects per

plant, per bush, per 10 leaves, egg

masses per plant, etc.

Plant population assessment

• the three most widely used methods

employ between 4 (Raunkiaer, 1934),

6 (Braun-Blanquet, 1927) and 11

(Domin) abundance categories.

• categories of abundance are;

Economic threshold limits

(ETL)

ETL = cost of control ($/ha)

[commodity value ($/kg) x damage coefficient (kg/ha/#pest/ha)

Damage assessment

• extent of crop damage is usually

proportional to the numbers of insects

present:

*detectable but not of any economic importance.

Damage assessment

• With simple damage, such as leaf lamina being

eaten or apples infested with Codling Moth larvae,

damage can be expressed easily as proportion of

lamina destroyed or percentage of fruits infested

per tree. In some systems numbers of pests

present are correlated empirically against

expected loss of yield (percentage), on a scale of

no loss (0%) to total loss (100%)

Plant age/stage of development

• termed crop vulnerability.

• Many crops are only vulnerable to

certain pests at a particular time in

their growth (development).

Plant age/stage of development

• Generally the two most stressful

times for plants are the time of

establishment and the time of

flowering/fruit development, and at

these vulnerable times pest damage

is often most serious.

Oil palm- economic threshold

Symptoms:Soft-bodied insects covered by

shells or scales

Plant pest - Leaves

Symptoms:Twisting white or brown lines or

mines causing brown, dried-up blotches in

the leaves

Leaf miners

Plant pest - Leaves

Symptoms: Abnormal growths or galls on

buds

Gall midges, gall mites

Flowers and buds - Pest

Gall mites

• Symptoms: Rhizome bored

Banana Weevil (Cosmopolites sordidus)

Fruits - Pest

• Symptoms: Larvae in fruits

• Potential pest: Oriental Fruit Fly

Fruits - Pest

Symptoms: Small brownish-black shells

attached to the stems, sometimes with sticky

foliage

Scale insects

Trunks, branches, and stems

- Pest

Roots, bulbs, and tubers-

Pest

• Symptoms:Small holes in tubers,

onion bulbs, or other root vegetables

Slugs, wireworms

Damage to stored products

• On-farm storage is usually practised

for a while after harvest, particularly

on smaller farms, although this is

more typical of the tropical parts of

the world.

Types of pests

• Primary pests

• Secondary pests

• Fungus feeders

• Scavengers

Primary pests

• These insects are able to penetrate

the intact test of grains and seeds,

and include Trogoderma, Sitophilus,

Rhizopertha, Cryptolestes and

Ephestia spp.

Secondary pests:

• These are only able to feed on grains

already damaged by either primary

pests or physically damaged during

harvest; such as Oryzaephilus spp.

Fungus feeders

• A number of insects that are regularly

found in infested stored products are

actually feeding on the fungi growing

on the moist produce; but a few

species may be both fungus feeders

and secondary pests, such as some

Psocoptera.

Scavengers:

• These are polyphagous, often

omnivorous, casual or visiting pests

(as distinct from the resident or

permanent pests), such as

cockroaches, crickets, some beetles,

ants...

Types of damage

• Direct damage

• Selective eating

• Heating of bulk grain

• Webbing by moth larvae

• Contamination

Direct damage:

• direct weight loss or reduction in

volume.

• But this is not accurate as there is an

accumulation of frass, faecal matter,

dead bodies, etc.

Direct damage:

• All the insects and the rodents are

responsible for such damage.

• In some flour mite infestations

observed the final bulk of exuviae,

faeces and dried dead bodies

amounted to nearly 50% of the

original food volume

Selective eating:

• Some insects show preference for the

germ region of seeds and grains; thus

a fairly low level of damage will

severely impair germination of stored

seeds, and in food grains there will be

a serious loss of quality.

• This preference is shown by

Cryptolestes and Ephestia larvae.

Heating of bulk grain:

• Stagnant air becomes heated by

insect metabolism and ‘hot-spots’

develop.

• The moisture from the insects’ bodies

condenses on the cool grains at the

edge of the hot-spot, and the water

causes caking, leads to fungal

development, and may also cause

some grains to germinate.

Webbing by moth larvae:

• The pyralid larvae in stored products

all produce silk-webbing, which if

present in large quantities may clog

machinery and otherwise be a

nuisance.

Contamination:

Contamination:

• The presence of insects in the

produce, and dead bodies, exuviae,

frass, faeces, etc., causes a general

loss of quality and value; aesthetic

rejection of produce becomes even

more pronounced when prepacked in

transparent wrappings for

supermarket sale

How to know?

• Cross-infestation

• Regular inspection

Thank you!!!!!!!