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Agricultural Innovations

Organic Insect Management in Sweet Corn

Scouting, thresholds and management methods for key caterpillar pests

By Ruth Hazzard and Pam Westgate

Department of Plant, Soil and Insect Sciences, UMass Extension Vegetable Program, University of Massachusetts Amherst.



hen customers flock to markets in search of sweet

corn, they want it to be of the highest quality --

sweet, fresh and worm-free. Yet, in ecological or organic

production of sweet corn, achiev ing worm-free corn is one of

the most difficult challenges. In the Northeast, three major

caterpillar pests -- corn earworm, European corn borer, and

fall armyworm -- invade ears and cause ugly feeding dam-

age. Without effective controls, it is impossible to produce

high quality corn throughout the season.

This fact sheet discusses an in tegrated strategy for control-

ling these three caterpillar spec ies using methods that meet

current organic certification standards. Any grower inter-

ested in methods that are safe for the applicator and the envi-

ronment may be interested in this approach. The compo-

nents of this strategy are 1) monitoring to determine pest

pressure and need for treatment a nd, if necessary, 2) a direct

treatment of each ear with a microbial or botanical insecti-

cide carried in vegetable oil to control corn earworm, 3)

Trichogramma releases and/or foliar applications of Bacillus

thuringiensis (Bt) or spinosad to control European corn

borer and/or 4) foliar applications of Bt or spinosad for fall

armyworm control.

Inside this fact sheet:




Corn Earworm


European Corn Borer


Fall Armyworm


Putting it all Together


Conservation of Natural Enemies


SARE Research Synopsis



SARE Agricultural Innovations are based on

knowledge gained from SARE-funded projects.

Written for farmers and agricultural educators,

these peer reviewed fact sheets provide practical,

hands-on information to integrate well-researched

sustainable strategies into farming and ranching

systems. The articles are written by project

coordinators and published by SARE.

Northeastern U.S. The methods presented in this fact

sheet were developed in the Northeastern U.S.; how-

ever, they can be used anywhere in North America

where these pests are a problem. The mix of caterpillar

pests and the timing of their infestation in corn depend

upon geographic location, requiring the use of localized

IPM scouting for each pest. This method has not been

extensively tested in southern regions where corn ear-

worm over-winters and pressure may be greater than in

the Northeast.


Fact Sheet Practical applications for

sustainable agriculture

For the online version go to

Sustainable Agriculture Research & Education

Organic Insect Management in Sweet Corn SARE 2

Corn Earworm (Helicoverpa zea)

The corn earworm is a widespread pest, which is also

known as tomato fruitworm, and cotton bollworm. In

southern areas of the U.S., corn earworm over-winters and

infests sweet corn throughout the season. Corn earworm

moths reach northern states through annual migrations,

invading late-season corn from mid-July through Septem-

ber. In New England, large numbers of moths can arrive

suddenly on storm fronts that move up the coastline and

river valleys. The

heaviest numbers

are found in

coastal areas, but

corn earworm

can be a devastat-

ing pest in late-

season corn any-

where in the


Adult moths have

light tan scales

and are about 1 ¼

inches in length.

Distinctive fea-

tures are a dark

spot on the fore-

wing, a dark band

near the margin of

the hind wing and,

in live moths, bright green eyes. Female moths lay single

cream-colored, globe-shaped eggs on the silk as well as

other parts of the plant. They are attracted to the odor of

corn silk; dried silks are less attractive than fresh silk as

egg-laying sites. They lay an average of five eggs per day

over their seven- to14-day life span. Eggs hatch in three to

seven days, depending on temperature, and newly hatched

larvae move directly down the silk and into the ears to feed

at the tip of the ear. Unlike European corn borer and fall

armyworm, earworm larvae do not tunnel through the

husk to reach the ear. Corn earworm caterpillars reach 1 ½

to 2 inches when full grown and have small bumps and

hairs that give the body a rough texture. They can be

brown, tan, green, or pink, with light and dark longitudinal

stripes (photo A). Their head capsule is always golden


Monitoring and thresholds

Trapping moths is a critical IPM tool for monitoring corn

earworm flight activity. Either blacklight or pheromone traps baited with corn earworm lures can be used. Black-

light traps can be placed near corn fields, but not necessar-

ily in them, and give a reasonable estimate of populations

up to one mile away from fields. Traps should be checked

daily, and capture of any corn earworm moths should trig-

ger treatment [1]. The pheromone trap should be placed in

freshly silking corn with the lure at ear height (photo B).

Lures are suspended in an opening at the base of the trap

and replaced every two weeks. Two traps per field, at least

50 feet apart, are


When the silk

dries, move the

traps to a new

block of corn in

fresh silk. Count

the moths captured

in each trap twice

weekly. Trap cap-

tures totaling two

moths per week

per trap indicate

that a damaging

population of corn

earworm is pre-

sent. Damage will

increase as trap

captures rise [1, 9].

Monitoring on your

own farm provides

the most accurate

and timely informa-

tion on corn ear-

worm flights; how-

ever, regional data

also can be used. Cooperative Extension systems in many

states maintain Helicoverpa zea trapping networks and

report captures regularly throughout the season. Contact

your county or state Extension system to determine what

information is available in your area.

Control: foliar spray applications

Foliar sprays of Bacillus thuringiensis (Bt ) will not control

corn earwor

m. Recent research suggests that spinosad,

which became available in an organic formulation

(Entrust™) in 2003, can suppress corn earworm if used on

a three- to four-day spray schedule, as in the same manner

that broad-spectrum insecticides are used in conventional

production. Further work is needed to evaluate the effec-

Photo A. Caterpillar pests in sweet

corn: corn earworm Photo B. Heliothis net trap with corn

earworm (CEW) lure in silking sweet

corn for monitoring arrival and popula-

tion of CEW. Note that the base of the

trap, where the lure hangs, is at the

level of the corn silks. Because of the

very heavy moth pressure at this site

(>50 moths per week), counting was

made easier by covering top with plastic

bag and inserting a vapor strip.


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