Diagnosis of Pest ProblemHow to scout and what to look for?

Dr. Ayanava MajumdarExtension Entomologist

Alabama Cooperative Extension SystemGulf Coast Research & Extension Center

8300 State Hwy 104, Fairhope, Alabama 36532Cell phone: 251-331-8416

PART 2

Types of Plant Problems

• Means “non-living “causes to the problem

• Uncontrollable abiotic: weather events, soil structure

• Controllable abiotic: pesticide injury (hot product mixtures), improper planting, fertilizer overdose, overwatering

Abiotic stressors Biotic stressors

• Caused by living organisms or “pests”

• Pest: an organism that cause injury and economic loss to humans or human property

• Plant injury: effect of pest on plants

• Damage: effect of pest in economic terms

• “All damage is injury but all injury is not damage!”

1. Define the problem:– Record the normal & abnormal

characters– Keep written notes & take pictures

(blogging?)– Examine entire plant in its

ecosystem– Look around: is something

affecting one plant or a group of plants?

Steps to diagnosis of plant injury

2. Look for patterns:– Nature is random!– If patterns exist on plant or a group

of plants…abiotic problem? (e.g., herbicide injury, storm injury to plants, etc.)

– Biotic sources affect plants randomly (e.g., insect, diseases)

– Biotic problems change location between years

Steps to diagnosis of plant injury

3. Scouting procedure:– If you have found the problem,

mark the problem area with sticks, garden stakes, tall flags, etc.

– Familiarize yourself with sampling techniques and sample preparation

– Take a closer look at plants, uproot plants if feasible

– Ask the experts before spending money on control!

Steps to diagnosis of plant injury

4. Delineate time-development:– Biotic problems may spread slowly in an area and a

pattern may appear– Abiotic problems develop faster and patterns are

obvious– Keep an eye on the marked area and sample

frequently to be able to “encounter” the problem (random)

Steps to diagnosis of plant injury

5. Determine the cause of injury:– Think broadly >> narrow

down to few causesOR

– Use the process of elimination to arrive at a solution

– Use all resources you have to ID insects, many on the web

– Find the economic threshold: doing nothing is also OK

Steps to diagnosis of plant injury

TOMATO INSECT PESTS(using identification skills acquired from Part 1)

Potato aphid: Long legs, antennae, and corniclesPink or green in colorVector of many virusesSluggish movement, persistent grip

Tomato aphid

Green peach aphid: Smaller that potato aphidHas over 800 plant hostsLime green in colorMove rapidly when disturbed, easier

to dislodge

Cornicles

Scouting for aphids

Cornicles

• Scout early in season, aphids have cornicles

• Search under leaves and stem

• Winged aphids may indicate migration

• Record the number of leaves with aphids present, then mark the area (distribution is highly clumped)

• ET = 50% leaves have aphid

• Watch for presence of ants that feed on honeydew

• Watch for ladybeetles and lacewings

Flea beetles

Strong thick hind-legs (arrow)Various colors (commonly black/striped)Jump when disturbedGenerally early season seedling pest

Scouting for flea beetles• Sample in mid-morning or afternoon

• Sample the seedling plants (6-10 inch height)

• Estimate the level of defoliation

• Estimate the number of adults with a sweep net and relate it to foliar injury

• ET = 5-10% foliar injury

Colorado potato beetle

Has many host plants, major pest of tomato

Has insecticide resistance (e.g., to Sevin in some areas)

Has high fecundity – so NE don’t work

Rotate chemicals, use alternative strategies

Scouting for CPB• Defoliation is less threatening on mature plants

• Beetle injury first on field margins

• Scout the short crop intensely (6 to 10 inch)

• Estimate the number of CPB on 10 plants

• ET = 5 beetles in short crop, 10% defoliation

Tomato fruitworm

Has many host plants, major pest of tomato

Has a brown head capsule + longitudinal stripes

Feeds with part of it’s body outside the fruit

Overwinters as pupa in the top soil

Scouting for tomato fruitworm• This is a major pest. Mark the location with flag & mark your calendars!

• Use pheromone traps for monitoring flight

• ET = scout intensely for eggs/larvae if 7 adults per trap

• Scout for larvae during fruit set.

• ET = one larva per plant or one fresh injury per plant

• Improve scouting technique with experience

Stink bugs

Has many host plants

Major pest of tomato and cotton

Piercing-sucking mouthparts

Early attack can destroy blooms and late attack destroy fruits

Scouting for stink bugs

• Can you smell them in field?

• Try sweep netting to sample adults mid-morning

• Scout intensively when fruit formation begins: 10 plants per location

• ET: 0.25 stink bugs average per 10 plants during the green fruit stage

• Much research on trap crops (alfalfa, clover, sorghum)

Leaf-footed bugs

• Related to stink bugs• Emerging problem in

vegetables and fruit production (Lousiana, Florida, California, Alabama)

• Interesting behavioral issues

• Trap crops may work!

Tomato hornworm

Caterpillar with Cotesia (parasite) cocoons

• Size is a problem in insect world!

• The caterpillars are rapid defoliators, fruit not harmed

• Adult = hummingbird moths OR Hawk moths

Sphinx /Hummingbird moth

Scouting for tomato hornworm

Leave these caterpillars alone!

• Minor problem in commercial production (foliar damage only)

• Visual location, scout & hand-pick when possible

• Monitor the level of Cotesia infested larvae

• There could be 3–4 generations per year, so late season buildup should be monitored

INSECT PESTS of COLE CROPS(using identification skills acquired from Part 1)

Crucifer family of crops (list)• Cabbage• Broccoli• Cauliflower• Mustard greens• Brussels sprout• Kale • Collard• Turnip• Radish• Horseradish

Cabbage looper vs. Imported cabbageworm

Cabbage looper (CL) Imported cabbageworm (ICW)

Note: no. of abdominal prolegs, larval shape, moth vs. butterfly

Damage by CL vs. ICWCabbage looper Imported cabbageworm

• Extremely mobile insect, move rapidly from plant to plant• Leaf margin >> area between viens >> leaf skeletonization

• Feed on terminal buds and soft leaves• Cabbage head is riddled with holes• Caterpillar stays camouflaged against the midrib

Diamondback moth

• Major insect on many crops

• Notorious for insecticide resistance

• Larvae are delicate, make silken web

• Larvae balloon from plant to plant

• Larva make shapeless holes, feeding in bunches

• Cause head deformation

Scouting for caterpillar pestsCabbage looper Imported cabbageworm

• Look for larvae with 2-pairs of prolegs

• Look for frass at the base of head

• Use pheromone trap to monitor pop.

• ET = 10 % defoliation

• Look for white/yellow moths early in the season• Caterpillars camouflage with leaf midrib• ET = 10% defoliation

Diamondback moth

• Scout early in season• Observe any deformation• Ballooning caterpillars?• ET = 10% defoliation

Cross-striped cabbageworm

• Have black/white markings with bright yellow stripe on side

• Feed in clusters (find the aggregations early)

• Larva feed on tender parts, esp. terminal bud

• Feed into the head

• Polyphagous insect• Have many wild hosts –

lambsquarter & redroot pigweed

• Creamish or light-green caterpillar, 4 pairs of prolegs

• Black spot on thorax just above the leg (circled)

• Moth has clear hindwings• Early instars feed

voraciously• Are attracted to weak plants

Beet armyworm

Damage to pepper plant

• Wide variety of crops damaged, major on soft-stemmed crops

• Moth lays eggs on low vegetation (mustard greens)

• Damage more plants that they eat (cause early & late season problem)

• Dry weather is favorable

• Types: solitary surface, climbing, army cutworms

• Larva curls into a C

Cutworms

• Early detection & treatment is important to prevent spread

• Scout for egg masses and caterpillars on 10 to 20 plants at different locations

• Use a sweep net to sample moths around field edges

• Use pheromone trap for monitoring moth activity

• ET = 2-3% plants with egg masses, 1 larvae per 20 plants, 10% or under defoliated plants

Scouting for armyworm & cutworm

Armyworm

Cutworm

Cabbage aphid

• Feed on a variety of weedy and cultivated host plants• Have piercing-sucking mouthparts• Remove cell sap and kill cells, feed on underside of leaves in dense colonies• Have waxy covering…difficult to control• Reduce plant vigor, stunting• Contaminate produce

Scouting for cabbage aphid• Turn over wrapper leaves to locate colonies• Notice any sudden increase in natural enemy populations (indicator species)• ET = if you find satellite colonies

Lacewing

Ladybeetle

Aphidus sp. - parasitoid

• Small insect that are quick to jump, large hindlegs

• Crucifer flea beetle – prefers cauliflower over cabbage

• Migrate from weedy borders

• Early season damage is most threatening

• Larvae feed on roots but not a problem

Flea beetles

Shot-holes in turnip leaves

• Scout early, seedling stages

• Get a hand-lens and a sweep net!

• Try sweep net sample during mid-morning or afternoon

• Watch for shot hole injury – may be intense on one part of the field (mark the area and keep watch on adult pop.)

• Watch for stunted plants and dig around the base

Scouting for flea beetles

• Fly is dark ash gray, ¼ inch, black stripes on back, bristly adult

• Eggs deposited at base of plant

• Maggots like cool, moist soil

• Feed on root surface, facilitate bacterial soft rot & black leg diseases

Cabbage maggot vs. Seedcorn maggot

• Fly is grayish, smaller than cabbage maggot

• No stripes on back

• Maggots prefer beans & cucurbits; may feed on seedlings of cole crops

Maggots are damaging!

Scouting for maggots• Adult emergence: 192 degree

days (base temp 42oF)

• Look for seedling damage by uprooting plants

• Look for your planting condition:

• scout if cool, dry soil

• scout if high organic matter

• Maggots are difficult to identify as immatures

Back to basics…• Scientific sampling protocols are not expensive• Sampling accuracy improves with experience,

correct equipment, and sample size• Draw a field layout >> start from border and

finish in the middle• Try to connect population level (e.g., using

sweep net, pheromone traps) with true crop injury…gain experience!

• Make treatment decisions at the right time using safest product available to you. Rotate chemicals.

Diagnosis of Pest Problem

QUESTIONS?