Corn earworms infest many different plants, but corn is their favorite host. Corn earworm larvae prefer to attack ears of corn, but will also feed on the plant leaves and stalks. Young earworms are green with black hair on their bodies and have black heads. As they mature, the worms can grow to 1 to 1 1/2 inches (2.54 to 3.81 cm) long and are pale green and yellow, or shades of brown and pink.
Method 1 of 2: Check for Earworms
1Check your corn plants for earworms weekly when moth activity in your area has peaked. Some growers use pheromone traps to monitor the population. If your traps catch 20 to 30 moths a night for 3 to 5 nights in a row, begin your weekly checks.
- Check high-risk areas first if you are a high-volume grower. Check late-planted corn, fields that are flowering or have young pots, and those growing on elevated areas of the land. Corn grown on elevated areas or knolls is more vulnerable to egg laying.
2Keep an eye on the silk when it forms to see how many eggs the earworms lay. They lay eggs on the silk attached to the husks, which gives larvae easy access to the ears.
3Pick an area to check in several different spots throughout your fields. If you are growing several acres of corn, take at least 1 sample per 4 acres. If you are simply checking a home garden, only 1 sample is necessary.
4Lay a cloth or sheet of flexible material on the ground between 2 rows of corn. A 3-foot-long cloth allows you to sample 6 row feet if you check the plants on both sides.
5Bend each bordering plant over the sheet and beat it vigorously with your hand or a small stick.
6Count the number of earworms. Check the sheet to see how many worms are on it are at least 3/8-inches long. Worms smaller than that can not do plant damage and may not survive long enough to be a problem.
7Determine the number of earworms per row foot. If you used a 6-foot-row sample, you would divide the number of worms by 6. Your tolerance threshold is determined by row foot count and varies with the specific crop and the percentage of it under attack.
- If you are growing a small amount of corn for your own consumption even one per plant may be too many. Many large production growers usually have a higher threshold.
Method 2 of 2: Control Corn Earworms
1Choose a variety of corn that is known for being more resistant to earworm damage. Those that have a long, tight-fitting husk withstand attacks better than varieties with loose husks.
2Time the planting of your corn to minimize earworm damage. Corn earworm larvae is present all season, but is most abundant in late summer and early fall. Plant your corn crops early so they will be silking before the earworm population has peaked. Corn planted late, silks late, when many more moths are looking for places to lay eggs.
3Avoid over-use of pesticides, which also kill off beneficial insects that help keep the earworm population under control.
4Encourage or purchase lady bugs, damsel bugs, lacewings and minute pirate bugs, which feed on the eggs and small larva of corn earworms. Parasitic wasps, which attack the eggs, are also beneficial.
5Spray insecticides to control the earworms only if necessary and only when it is most effective.
- The timing of your chemical treatment is very important. Once the larva has gotten inside the corn ears chemical treatment is very difficult. Apply the insecticide when the corn plants are silking if you see a high number of eggs on the silk or if your plant check reveals an unacceptable worm count.
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- Since the eggs are laid on corn silk, damage from the larva is sometimes confined to the undeveloped kernels at the end of the ears of corn. However, left untreated the worms will continue to grow and eat their way through the ear. Holes seen further up on the corn shuck are typically emergence holes a worm made when it ate its way out.