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. 

Introduction 

W 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, achieving 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 damage. Without effective controls, it is impossible to produce 

high quality corn throughout the season. 

This fact sheet discusses an integrated strategy for controlling these three caterpillar species using methods that meet 

current organic certification standards. Any grower interested in methods that are safe for the applicator and the environment may be interested in this approach. The components of this strategy are 1) monitoring to determine pest 

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

treatment of each ear with a microbial or botanical insecticide 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: 

# Introduction

# Corn Earworm

# European Corn Borer

# Fall Armyworm

# Putting it all Together

# Conservation of Natural Enemies

# SARE Research Synopsis

# References 

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.; however, 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 earworm over-winters and pressure may be greater than in 

the Northeast. 

GEOGRAPHIC RANGE:

Fact Sheet Practical applications for 

sustainable agriculture 

For the online version go to www.sare.org/publications/factsheet/0105.htm 

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 September. 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 devastating pest in lateseason corn anywhere in the 

Northeast. 

Adult moths have 

light tan scales 

and are about 1 1⁄4

inches in length. 

Distinctive features are a dark 

spot on the forewing, 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 1⁄2

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 

brown. 

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. Blacklight traps can be placed near corn fields, but not necessarily 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 trigger 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 

recommended. 

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 captures totaling two 

moths per week 

per trap indicate 

that a damaging 

population of corn 

earworm is present. Damage will 

increase as trap 

captures rise [1, 9]. 

Monitoring on your 

own farm provides 

the most accurate 

and timely information on corn earworm flights; however, 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 earworm. Recent research suggests that spinosad, 

which became available in an organic formulation 

(EntrustTM) 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 effecPhoto 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 population 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. 
Organic Insect Management in Sweet Corn SARE 3

tiveness of this material under a range of corn earworm 

pressures and spray intervals. Growers who would like to 

use this method should refer to existing publications on 

sprayer design and spray coverage for effective control of 

corn earworm [1, 9]. 

Control: direct silk applications 

An effective way to control corn earworm infestation in 

corn ears, which is especially suited for small to medium 

growers, is to apply a small amount of organically approved insecticide in oil directly to the silks of developing 

corn ears. A mixture of insecticide in oil applied directly to 

the silks at the neck of the ear penetrates the silk channel 

and acts as a barrier and a toxin. Caterpillars that eat the 

insecticide or contact the oil-coated silks die before they 

cause damage inside the ear. A similar technique, using 

mineral oil mixed with various toxins, was widely used by 

sweet corn growers in the 1940s before the development of 

synthetic insecticides. Research conducted from 1992-2002 

at the University of Massachusetts, Hampshire College, 

and on farms throughout New England has re-examined 

and improved this technique. Evaluation of other toxins, 

such as spinosad and neem, as well as other carriers has 

followed, and suggests that other materials used in the 

same way may be as effective. The following recommendations are based on this work. 

Application method 

This method involves walking through the stand of corn 

and treating the top ear of each plant. Only one application 

per ear is recommended. Treat each block when most ears 

are close to the ideal stage. It is cost-effective to treat only 

one ear per stalk. If silk emergence is very uneven throughout the field, it may be necessary to go through the stand a 

second time to treat late-emerging silks and achieve optimal control without tip fill problems. Apply 0.5 ml per ear 

(equivalent to five drops from an eyedropper) directly to 

the silk at the tip of the ear so that it will coat the silk channel. Higher quantities do not appear to give better control 

and may cause slightly oily ears at harvest. 

Tools: A hand-held applicator is needed to deliver oil to 

each ear. Oil sprays are phytotoxic and result in sticky 

brown husks. There is no way to avoid taking time to apply the oil to each ear. Eye droppers and converted oil cans 

can be made to work, but for commercial corn acreage durability, consistency, and ease of use are critical. The ZealaterTM (photo C), a hand-held applicator designed at the 

University of Massachusetts and Hampshire College expressly for this purpose, is being distributed by Johnny's 

Selected Seeds (207-861-3902). This device is durable, 

comfortable to hold and use, and delivers 0.5 ml of oil with 

each squeeze of the trigger. Tubing connects the device 

with a two liter bottle for the oil that can be strapped 

around your waist. 

Cost: The cost of this method including labor and materials is approximately $100 to $120 per acre. To treat one 

acre requires about eight to ten hours of labor. Typical 

materials include about 0.5 lb dry Bt product, two gallons 

of corn or soy oil, and 1.6 cups of lecithin per acre. The 

price may change if other materials are used. 

Timing of application: Proper timing of the oil application is one of the most important factors in the successful 

use of this method. The best time to apply oil is when the 

tips of the silks have begun to wilt and turn brown, and 

pollination is nearly complete (Photo C). In western Massachusetts this generally happens five to seven days after 

silk growth starts- three to four days after the silk is fully 

grown, and about 14 to 21 days before harvest. Although 

caterpillars that are already in the ear may be killed by the 

Bt/oil application, the best control is achieved when it is 

present prior to larval entry. The Bt/oil barrier persists 

after application and continues to kill newly entering larvae [2].

Within a field, plants grow at different rates and begin silking at different times. In a relatively even stand, silk emergence is concentrated in a three- to four-day period. To 

determine the best time for oil applications, note the day 

on which 50% of the corn has begun to show silk, and 

count from that date. 

Photo C. 

Zea-later 

oil applicator being 

used to 

apply oil/Bt

treatment 

to corn silk. 
Organic Insect Management in Sweet Corn SARE 4

Applications made earlier than five days after silk do not 

appear to give better control and may result in a higher 

rate of “cone” tips (photo D). Cone tip develops when oil 

interferes with pollination of the silks that are attached to 

the tip of the ear, which are the last silks to develop. This 

results in unfilled kernels in the last half-inch of the tip. 

While partially-filled tips are a relatively common occurrence in sweet corn, the lack of kernel growth caused by oil 

is more pronounced. 

Oil applied later than eight to nine days after silk initiation 

can result in more feeding damage to the kernels caused by 

caterpillars that entered the ear prior to the application. 

There is a window between five and eight days after silk 

initiation that provides the best combination of corn earworm control and ear fill [3, 11]. 

This provides some flexibility in treating blocks of corn as 

they become ready. Since the development of corn varies 

greatly depending upon the temperature, one way to determine if the corn is ready to be treated is to carefully open 

some representative ears from the field. If the silks are all 

still attached to the kernels (photo E-1) then the corn is too 

young. The silks will be detached from the developing kernels if pollination of the kernel has taken place. If the silks 

are mostly detached, and connected only at the top 0.5” to 

1.0” of the tip, then the ear is ready to be treated 

(photo E-2). 

Materials 

Regulatory issues: Any material applied to your commercial sweet corn for caterpillar control must conform to 

two separate federal laws; three if you are organically certified. 

1) The Federal Insecticide, Fungicide and Rodenticide Act 

(FIFRA) regulates pesticides: all materials applied as a 

insecticide must be registered by EPA and have a pesticide 

label that includes sweet corn, or it must be exempt from 

labeling (FIFRA, Section 25b). Note: each state has its 

own labeling regulations, which may be more restrictive 

than FIFRA; some states do not allow the exemptions. 

Contact your state agency in charge of pesticides for instructions on the legal use of FIFRA exempt materials in 

your state (see National Pesticide Information Center

website for a list of state agencies in charge of pesticides). 

2) The Federal Food, Drugs and Cosmetics Act (FFDCA), 

regulates all materials applied to food crops; accordingly, 

the material applied to the corn ear must have a residue 

tolerance or have a tolerance exemption (section 408). 

3) A third federal law applies to organic farmers: the National Organic Rule. This law requires that materials used 

be allowed by the National Organic Program or the Organic Materials Review Institute (OMRI). 

The materials discussed below satisfy all of these criteria. 

Insecticides: Bacillus thuringiensis subsp. Kurstaki. Corn 

earworm larvae feed on silks as they move down the silk 

channel, then feed on the tip of the ear. Early in ear develPhoto E. De-husked corn ears during early silk. 1) Kernels 

have not been fertilized, ear is too young for oil treatment. 2) 

Only kernels at tip have not been fertilized. Oil should be applied at this stage. 

Photo D. Sample of corn ears at harvest. Ear on right has 

cone-tip from oil application. The other two were not treated 

with oil; the tip fill of the center ear is incomplete, a condition 

that occurs in some varieties or under certain environmental 

conditions. Oil application does not always result in cone-tip.
Organic Insect Management in Sweet Corn SARE 5

opment the silk channel is several inches long (at harvest it 

ranges from 0.1 to 2 inches). Oil carries Bt down the silk 

channel where larvae ingest a toxic dose, cease feeding, and 

die before reaching the ear. Bt mixed with oil is more effective than Bt in water [4].Use a microbial Bt product 

that is registered and labeled for use in sweet corn, and use 

the lowest labeled rate for corn earworm or European corn 

borer. In trials using Dipel DFTM it was found that using 

a concentration of Bt that delivers Bt at the lowest labeled 

rate of 0.5 lb/acre produced better control than lower rates 

and as good control as higher rates [5]. This translates to 

approximately 3 tablespoons per liter of oil, for a plant 

population of 16,000/acre. 

If you are farming in accordance with organic certification 

standards, check with your certifier, the National Organic 

Program or the Organic Materials Review Institute to be 

sure that the Bt product you want to use is allowed. As of 

January 2005 there were no organically certified liquid Bt 

suspensions. For dry formulations the Bt must be dissolved in water first, and then added to the oil. To achieve 

a stable suspension of dissolved Bt in the oil an emulsifier 

can be added to the oil (see Emulsifiers, below). Because of 

the safety and regulatory status of Bt products and the 

long interval before harvest, use of Bt products in this 

manner is in accordance with pesticide and food safety 

regulations. 

Neem. Neem products also can be used as the insecticide 

in this method. The University of Massachusetts Amherst 

has conducted a trial using one product (Aza-directTM), at 

three concentrations of neem in oil: 1:1, 1:10 and 1:20, 

neem:oil (volume to volume ratio). All concentrations resulted in reduced ear damage compared to oil alone and 

there was no significant difference between concentrations 

[5]. Be sure that the label of the product indicates it is appropriate for use on sweet corn. 

Spinosad. Recent trials have shown that spinosad works 

well as an insecticide in the direct silk method. EntrustTM, 

the organic formulation of spinosad, is currently labeled 

for use in sweet corn and can be legally applied to corn 

silks using this method. Use a rate in the range recommended on the label (1-2 oz/acre; 1 oz = 6.3 Tablespoons). 

Since EntrustTM is a dry formulation, suspension in oil is 

best achieved when used with an emulsifier (see 

Emulsifiers, below).

Other. Other insecticides may be appropriate and effective; however, we have not tested their effectiveness nor 

determined the legality of applying them directly to the 

corn ears in this manner. If you want to try other materials, review the label and check with the manufacturer, the 

EPA or your state agency responsible for pesticide regulations (see Regulatory Issues, above). 

Oils:

Corn and soybean oils. Vegetable oil alone reduces the 

amount of caterpillar feeding damage in the tips of corn 

ears; however, it is most effective when used as a carrier 

for Bt [4]. The oil coats the silk channel and reaches the ear 

tip, increasing the effectiveness of the Bt. Water is not a 

good carrier because it beads up on the silk and does not 

fill the space within the channel. Both corn and soybean 

oils conform to all of the regulations listed above. It requires about 2.1 gallons of oil to treat one acre, applied at 

0.5 ml per ear of corn (estimating 16,000 ears/acre). Corn 

or soy oil may be available in certain formulations as a registered pesticide (see emulsifier/oil combos, below), or may 

be purchased in food grade form from grocery stores. Before using corn or soy oil check with your state agency in 

charge of pesticides to determine any legal restrictions on 

its use in your state. 

Petroleum-based oils. Highly refined petroleum oils, 

also known as narrow range mineral oils, have been shown 

to be effective as an oil carrier, but they have not been 

tested as extensively because their organic status has been 

inconsistent over the years. These oils must meet the 

regulatory requirements described at the beginning of 

this section. 

Emulsifiers: If you are using a dry insecticide formulation 

it is recommended that you use an emulsifier to insure a 

stable suspension in the oil. 

Lecithin. Add 5% volume of liquid lecithin to the oil before adding the dry material mixed in water (e.g. add 5 ml 

lecithin to 95 ml oil). Liquid lecithin is the consistency of 

molasses; we strongly recommend that you add it directly 

to the oil instead of measuring into a separate container 

first. Lecithin will mix readily with oil but will not mix 

directly with water, making cleanup difficult. 

Liquid Bt’s with emulsifiers. If you are NOT certified 

organic you may be able to use a liquid Bt product and 

avoid the need for an added emulsifier. Liquid Bt products 

allowed for organic production may become available in 

the future. Check with OMRI for updates. 
Organic Insect Management in Sweet Corn SARE 6

Oil/Emulsifier combinations: Although more expensive 

than buying them separately, some organic crop oils come 

with an emulsifier already mixed into them, and are labeled for caterpillar control in corn. These can be either 

vegetable based or narrow range mineral oils. If you are 

organically certified 

use a product that has 

been reviewed by 

OMRI and is allowed 

in organic production 

(www.omri.org). Before applying any of 

these products, make 

sure that the product is 

labeled for use on corn 

and is registered in your state.

Carrageenan as an alternative carrier: The need for an 

emulsifier can be avoided with the use of carrageenan instead of oil. Carrageenan, derived from seaweed and exempt from FIFRA and food tolerance, can be used as an 

alternative carrier. Since it is water based, dry formulations of insecticides will mix readily, eliminating the need 

for an emulsifier; however, because of the water base it 

does not penetrate the silk channel like oil and must be injected well into the silk channel. Also, on its own carrageenan has little effectiveness against corn earworm, acting 

primarily as a carrier of the toxins. Further work is needed 

to evaluate carrageenan as part of this method, but it does 

appear to reduce or eliminate the cone-tip affect.

Other factors 

Sweet corn cultivars: Good husk coverage at the tip of 

the ear enhances the effectiveness of this technique. This is 

especially important where corn earworm pressure is extremely high. Look for cultivars that suit your climate and 

your market and also have a tight husk with a long extension above the ear throughout maturity. A tight husk protects the ears by holding the oil in a narrow channel, forcing caterpillars to encounter the oil and Bt to reach the ear. 

Another trait that contributes to success with the oil 

method is consistent plant development and ear maturity. 

Available sweet corn varieties change rapidly. Variety trials conducted in Maine in 1999, 2000 and 2001 [6] and in 

Maryland in 2003 [7] have identified some varieties that 

have good husk coverage. Of the varieties tested in Maine, 

Sweet Chorus, Sweet Symphony, Wizard (variable maturity), Bon Appetite, Delectable, Providence, Serendipity, 

Twilight, and War Dance (all se), and Jumpstart and 

SS#6082 BC (sh2) all had good tip coverage. Of those 

tested in Maryland, Temptation, Argent, and Frosty (se) 

and Punchline (sh2) had good tip coverage and a tight 

husk. 

Weed control: Since 

this method involves 

walking through a corn 

field and treating every 

corn ear, it is important 

that you have good 

weed control in your 

corn field. Tall weeds at 

the time of application 

interfere with access to each ear, thereby reducing the effectiveness of the control method.

Weather: One advantage of this method is that oil can be 

applied in windy or even wet weather. If it rains after the 

oil application, it is not necessary to re-apply the oil. We 

have found that the oil method works best in healthy, wellnourished, actively growing, sweet corn . Long periods of 

cold, wet weather or periods of drought that cause plant 

and eargrowth to slow sometimes result in poor control or 

may increase the cone tip effect.

European Corn Borer 

(Ostrinia nubilalis)

European corn borer is an introduced pest that has spread 

across much of eastern and central North America. The 

number of generations of European corn borer ranges from 

one per year in the extreme north to four per year in the 

Southeastern U.S. Most of the range within the U.S. has 

two generations per year; sometimes these co-exist with a 

strain that has one generation per year. There are two 

strains of European corn borer: the Iowa (E) and New 

York (Z) strain, which are present in different ratios in different regions. 

In northern areas, larvae over-winter in stalks of corn and 

other host plants, and pupate in the spring. In New England, adult moths emerge in late May or early June and 

mate in weedy or grassy areas. Fields that have been in 

field corn, sweet corn, or peppers for a long time will have 

higher pressure from European corn borer than other 

fields. 

Photo F. Caterpillar pests in sweet corn: european corn borer. 
Organic Insect Management in Sweet Corn SARE 7

About one week after flight begins, females start to lay flat, 

white egg masses on the underside of leaves in early corn. 

Eggs hatch in about one week, depending on temperature. 

Larvae feed in the whorl and in the succulent emerging 

tassel. As the tassel opens up, these larvae move downward, bore into the stalk and tunnel into ears through the 

side, base or tip. When moths are active during silking, 

they lay eggs on leaves near the ear and the larvae move 

directly into the ear after hatching. These larvae may tunnel through the husk or move directly down the silk channel at the tip of the ear. 

The moths are about 3⁄4” long and light tan or brown in 

color with yellow bands, and the male has darker coloring 

than the female. Larvae are either light colored or brown, 

with dark spots on each segment. The head capsule is dark 

brown and flattened in shape. Full-grown larvae are 3⁄4” to 

1" long and move fast when disturbed (photo F). 

Monitoring and thresholds 

Monitoring networks for European corn borer are maintained by Extension systems in many states and can be 

used to determine when flight begins in your region for 

each generation. European corn borer flight also can be 

monitored on-farm using blacklight or pheromone net 

traps. Consult your state Extension program to determine 

what type of traps are recommended in your area. Trap 

captures will tell you exactly when flight begins, when it 

peaks, and how high the population is [1, 9]. 

If you are using pheromone traps, consult your state Extension program to determine whether one or both E and 

Z strains are present. If both strains are present, use two 

traps: one baited with an E(II) lure, the other with Z(I), 

placed at least 50 feet apart in weedy borders of corn fields. 

Make sure the bottom of the trap stays close to the top of 

the weeds[1, 9]. 

Once flight is detected, blocks of sweet corn with newly 

emerging tassels should be scouted weekly by inspecting 

the tassels of 50 to 100 plants, in groups of 10, for the presence of European corn borer larvae and fresh feeding damage. This can be done in whorl stage corn by pulling the 

developing tassel out of the plant and inspecting it for frass 

and small larvae. Corn with emerged green tassels corn can 

be inspected for damage without removing the tassel. If 

more than 15% of the plants have one or more larvae present, then a spray should be applied because ear damage 

will be greater than 5% at harvest if European corn borer is 

not controlled. 

Control 

European corn borer can be controlled through releases of 

parasitic wasps that attack the egg stage, or with foliar 

sprays of Bt or spinosad that target larvae. During silking, 

oil applied to the silks for corn earworm control also will 

control European corn borer larvae that enter the ear 

through the silk channel, but may not give complete control of those entering from the side. 

Trichogramma releases

Trichogramma are small parasitic wasps that lay their eggs 

in the egg masses of host insects. Trichogramma larvae 

feed and pupate inside the egg, killing the egg and preventing hatch. Trichogramma ostriniae lays its eggs in European corn borer egg masses, and is the species that has 

shown the highest level of European corn borer control in 

field trials, reducing larval infestations enough to avoid the 

need for sprays. A closely related species, Trichogramma 

brassicae, is commercially available and also will suppress 

European corn borer. 

Since Trichogramma control European corn borer by 

parasitizing egg masses, they should be released just as the 

moths start to lay eggs, when the corn is in the four- to sixleaf stage. Knowing when European corn borer flight begins, reaches a peak, and ends in a given field is key to the 

proper timing of Trichogramma releases. You can use regional information about flight activity from your state or 

county Extension program and target your releases to that; 

however, to coordinate timing on your farm you should 

monitor flight activity in your own fields. 

Release rates and number of release locations within the 

field vary depending upon the species. Consult a supplier 

of beneficial organisms for more details; orders should be 

placed in advance of the growing season. We recommend 

releasing the species Trichogramma ostriniae, which is 

available through IPM Laboratories (www.ipmlabs.com; 

315-497-2063). 

Foliar sprays: European corn borers can be adequately 

controlled with one to three sprays per block of corn. If, 

when you scout, you find that 15% (or more) of the ears 

have live larvae or fresh feeding damage, spray once with 

Bt or spinosad. The ideal time is just before or during tassel emergence but before silking and before larvae move 

into the ear or stalk. Use a spreader-sticker for better control. Scout again in five to seven days, looking for live larvae, and use a second spray if the infestation is still over 

15%. Shorter spray intervals should not be necessary, but 
Organic Insect Management in Sweet Corn SARE 8

be sure to scout again within a week after the first spray. 

With Bt use at least two-thirds the maximum label rate as 

low rates can result in lower 

levels of control. 

If European corn borer 

moths are active (e.g., pheromone trap captures >7 per 

week) and laying eggs during 

the period when ears are 

forming, an additional spray 

during silking can help reduce the number of small 

borers that move directly 

into the ear after hatching. If 

possible, this spray should be 

applied at ear height. 

Sprayer design and needs depend on how much sweet 

corn acreage you grow and how important spraying is in 

your operation. For growers with small acreage, it may be 

practical to use a backpack mist blower, walk through the 

corn and cover two or three rows in each direction with a 

concentrated solution. Tractor-mounted boom sprayers 

that can be lifted as corn grows are well suited for moderate to large acreage and should be configured for over-thetop coverage of the tassel as well as coverage of the foliage 

and ear zones. Drop nozzles are recommended.9 Bt and 

spinosad products can be used whenever European corn 

borer or fall armyworm are the target pests, regardless of 

the time of season or stage of crop growth. 

Fall Armyworm 

(Spodoptera frugiperda) 

Like corn earworm, the fall armyworm is a summer migrant to the colder regions, over-wintering in Florida and 

other southern states. Fall armyworm moths, which are 

about 3⁄4”to 1” long with clear hindwings and mottled 

brown forewings, migrate into New England and other 

northern areas in mid to late summer. The females lay 

scale-covered eggs on many types of plants, with a preference for whorl-stage corn. 

Eggs hatch in two to 10 days 

and larvae feed deep in the 

whorl as well as in tassels 

and ears. Like European corn 

borer they eat through the 

side of the corn ear; however, 

unlike European corn borer, 

fall armyworm leave behind 

a large, messy opening. Larvae are smooth, brown or 

dark green with lengthwise 

stripes, and the head capsule 

is dark with a distinctive light-colored marking in the form 

of an inverted Y. Full-grown larvae reach 1 1⁄2 inches. 

(photo G). 

Monitoring and thresholds 

Watch whorl-stage corn for signs of ragged feeding damage and scout for larvae in the whorl and the emerging tassel. Feeding damage from fall armyworm is more obviously destructive than that of European corn borer; however, if you find only feeding damage and no larvae, it is 

likely that the infestation is over and larvae have pupated. 

The scouting method and threshold for fall armyworm are 

the same as for European corn borer: if 15% of plants are 

infested with either larvae, controls are needed. 

Control 

Foliar sprays are the only effective means of control for fall 

armyworm at this time. Bt products that contain Bt aizawi

or Bt kurstaki and have fall armyworm listed on the label 

may be used. Spinosad is also a good alternative. Spray to 

control fall armyworm during whorl stage if they are 

above threshold. For tassel stage, see thresholds and methods described for European corn borer, above. 

Photo G. Caterpillar pests in sweet corn: fall armyworm.

Table 1. Recommended treatments for each caterpillar pest.

*Oil reduces damage that results from any caterpillars that enter through the ear tip, including ECB; other methods 

are needed to achieve integrated control of ECB. 

**Spinosad only; not Bt; suppresses CEW only if used in intensive spray program. 

Pest Oil Treatment Foliar Spray Trichogramma 

release 

Corn earworm(CEW) X X** 

European corn borer (ECB) X* X X 

Fall armyworm (FAW) X 
Organic Insect Management in Sweet Corn SARE 9

Putting it all Together 

Depending upon location and the time of the season, it is 

possible to have one, two or three of the key caterpillar 

pests in a single planting of sweet corn. European corn 

borer and fall armyworm may be feeding at the whorl or 

tassel stage and can move into ears during silking. Some 

enter ears through the tips and some through the side. 

Corn earworm enters only through the tip, and only during silking. An integrated strategy is needed to address 

each pest, at the appropriate growth stage of the corn. 

The following approach has provided effective control of 

all of these pests in experimental trials in Massachusetts 

(see table 1): 

Whorl stage: Scout for fall armyworm. If infestation is 

greater than 15%, spray with Bt or spinosad. If using 

Trichogramma, start releases at this stage. 

Pretassel/tassel stage: Scout for European corn borer 

and fall armyworm. If infestation is greater than 15%, 

make a foliar application of Bt or spinosad; scout and make 

a second application, if needed, five to seven days later.

Early silk stage: If corn earworm moths are present, use 

the oil method to control all caterpillars that enter through 

the tip. If European corn borer flight is high during silking, 

apply Bt or spinosad. 

Conservation of Natural Enemies 

Sweet corn is a favored habitat for beneficial insects that 

feed on caterpillar eggs and small larvae, corn leaf aphids, 

and sweet corn pollen and help suppress pest populations. 

These natural enemies include ladybeetles, insidious 

flower bugs, lacewing larvae, parasitic wasps, and indigenous Trichogramma species. The methods described here 

conserve these natural enemies. Studies conducted to 

evaluate the effects of Bt and spinosad on a range of beneficial insects and non-target organisms have shown that both 

have low toxicity, although spinosad shows somewhat 

more negative effects than Bt [10]. 

SARE Research Synopsis 

With funding from SARE and from the Organic Farming 

Research Foundation (Santa Cruz, CA) the organic caterpillar control methods outlined in this article were tested 

on eight commercial vegetable farms throughout New 

England from 1999 to 2001. During the project, grower 

Farm Location

Total 

Veg. 

Acres

Acres of 

SweetCornMarkets

3 Years; Average

Flight / Night

% Clean Ears

All 3 Years

 ECB CEW No 

Oil

Oil 

Treated

1 Maine 36 2 Wholesale 1.6 4.9 67.1 82.7

2 Rhode Island 16 2.5

Wholesale

Farmstand

CSA

4.7 11.7 9.1 38.8

3 Southern VT

CT River Valley 50 12 WholesaleFarmstand 12.3 1.0 65.8 76.7

4 Southern VT

CT River Valley 30 10 Farmstand 4.7 1.3 77.8 92.2

5 Western MA

CT River Valley 18 4 CSA 2.7 2.3 63.0 87.0

6 Central MA 30 6 Farmstand 4.4 9.0 50.1 73.4

7 Western MA

CT River Valley 38 4.5 Wholesale 5.7 0.4 60.2 84.9

8 Central CT

CT River Valley 22 1

Farmstand

Farmer’s

 Markets

1.4 1.2 22.5 47.5

Table 2. Data for each of the participating farms. 

The average nightly moth captures, during the corn’s susceptible period, over the 3 year project for European corn 

borer (ECB) and corn earworm (CEW) are included, as well as the average percent of corn ears that had no caterpillar damage in the oil treated and control corn plantings. 
Organic Insect Management in Sweet Corn SARE 10

interest and input guided the development of the ZealaterTM applicator device and further studies on the timing 

and longevity of the oil treatments. Of the eight farms that 

participated in the project, six continue to grow sweet 

corn; all of these farms have continued to use the control 

methods outlined above. 

For three growing seasons (1999-2001), three blocks of 

corn per year were planted on each farm to test the effectiveness of the Bt foliar sprays for European corn borer 

(ECB) and fall armyworm (FAW), combined with oil 

treatments to the silks for corn earworm control (CEW). 

All of the ears in one half of each planting were oiled for 

CEW control while the other half was not, regardless of 

the pest pressure. When foliar applications were applied, 

all corn in the planting was treated. All corn plantings 

were scouted for ECB and FAW damage and traps were 

monitored for ECB, FAW and CEW pressure. At harvest, 

100 oiled corn ears and 100 non-oiled ears were scored for 

damage and caterpillars. Any caterpillar damage to the kernels, however slight, rendered the ear non-marketable for 

the purposes of this study. 

All farms showed significant improvement in the quality 

of the ears between the oiled and the non-oiled ears of 

corn. Four out of the eight farms were able to achieve a 

three-year average of over 80% clean ears with the oil 

method (table 2), with improvements each year of the project (figure 1). A significant portion of damage on some of 

the farms was due to poor control of the ECB pest with the 

foliar spray due to poor timing, too few sprays, or lack of 

spray when called for [11]. Other farms, such as Farm # 2, 

struggled with very high CEW pressure and poor weed 

control (table 2). See the full report for more detailed results and individual farm profiles. 

The timing of the oil/Bt application can be critical to the 

success of this method and the development of the corn 

ears. In one timing experiment conducted over two growing seasons, different plots received one oil application on 

day 3 to 11 after 50% of the field showed first silk. The 

percent cone tip at harvest decreased linearly with the day 

of treatment application in both years. The best combination of effective insect control resulting in the highest rates 

of marketable ears with the least degree of cone tip was 

achieved by application on days 5 to 7 after 50% of the 

field showed silk. This window is likely to vary by a day 

or two depending upon the temperature. 

In another timing experiment, we examined the effectiveness of the oil treatment relative to when the CEW larvae 

Percent Clean Corn Ears in Each Year 

on All Farms

0

10

20

30

40

50

60

70

80

90

100

99 00 01 99 00 01 99 00 01 99 00 01 99 00 01 99 00 01 99 00 99 01

1 2 3 4 5 6 78

Farms and Years

% Clean Ears

Oil

Control

Figure 1. Average percent of harvested ears that were clean (no damage to kernels) on each farm in 

each year of the project in control (green) and oiled (yellow) ears.
Organic Insect Management in Sweet Corn SARE 11

References 

1. Adams, R. G. and J.C. Clark, eds. 1996. Northeast Sweet Corn Production and Integrated Pest Management Manual. 

University of Connecticut Cooperative Extension. 120pp. 

2. Cook, R. A. Carter, P. Westgate and R. Hazzard. 2003. Direct silk applications of corn oil and Bacillus thuringiensis as 

a barrier to corn earworm larvae in sweet corn. HortTechnology 13:509-514. 

3. Cook, R., A. Carter, P. Westgate, and R. Hazzard. 2004. Optimum timing of an application of corn oil and Bacillus 

thuringiensis to control Ledpiopteran pests in sweet corn. HortTechnology 14(3): 1-8. 

4. Hazzard, R.V., B.B. Schultz, E. Groden, E.D. Ngollo, and E. Siedlecki. 2003. Evaluation of oils and microbial pathogens for control of Lepidopteran pests of sweet corn in New England. Journal of Econ. Ent. 96(6): 1653-1661. December. 

5. Hazzard, R. and P. Westgate. 2004. Integrated Caterpillar Control in Organic Sweet Corn, Part 3: Evaluating oils and 

emulsifiers, and spreading the word. Organic Farming Research Institute Final Report. 

6. Handley, D., and M. Hutton. 2003. Early sweet corn variety trials. Proceedings from the New England Vegetable & 

Berry Conference and Trade Show & Fruit Meeting. Manchester, New Hampshire. pp158-163. 

7. Dively, G., and T. Patton. 2003. Field evaluation of ear tip coverage and OMRI-approved Entrust insecticide for control of ear-invading insect pests. University of Maryland. http://www.mdipm.umd.edu/programs/dively.htm. 

8. User Guide: Biological Control of the European Corn Borer with Trichogram Releases. Insecterra Inc., Quebec, 

Canada. 

9. Ferro and Weber. 1988. Managing Sweet Corn Pests in Massachusetts. University of Massachusetts Extension, University of Massachusetts Amherst. 6 pages. 

10. Kovach, J, C. Petzoldt, J. Degni and J. Tette. A Method to Measure the Environmental Impact of Pesticides, Table 2, 

List of Pesticides. New York State Integrated Pest Management Program, 

http://www.nysipm.cornell.edu/publications/EIQ.html.

11. Hazzard, R. A. Carter, and P. Westgate. 2003. Implementing a Bio-intensive Strategy for Caterpillar Control in 

Sweet Corn. NE SARE final report. grant # LNE99-118. 

SARE Fact Sheet #01AGI2005 

entered the silk channel. In two seasons, oil, Bt or oil+Bt

was applied on day 5 after 50% silk. Newly hatched CEW 

larvae were then applied to those oiled ears and to nonoiled ears on day 3, 6, 9, 12, 15, or 18. Ears were picked 

and examined four days after each larvae application. Both 

oil and Bt-treated ears had fewer larvae and less feeding 

damage than the non-treated ears. Oil and Bt, alone or together, provided protection to the ears up through the end 

of the experiment at 22 days after 50% silk. When the larvae were applied to the silk two days before the oil treatment, damage was not significantly less in treated ears 

compared to untreated ears. 

This fact sheet is based on a SARE-funded project. 

For more information, please visit www.sare.org > 

Project Reports > Search the Database

for project # LNE99-118