Topic Tuesday: Corn Earworm
Suwannee County is home to a vast array of diversified crops, such as peanuts, soybeans, hay, vegetables, and orchard crops. One important harvested crop is corn for grain and silage. Growing conditions can be tough for corn and on top of that, diseases and pests can greatly impact the crop. One major pest seen in corn is the corn earworm and it is labeled as quite a costly pest, attacking the harvestable portion of the corn, the kernels. Read on to find out more about corn earworm.
What are Corn Earworms?
Corn earworms are commonly found throughout the United States and are active throughout the year in areas with tropical and subtropical climates, such as Florida. They are most active in the summer months here in Florida and they complete their life cycle in 30 days. Corn is the most common host for corn earworms, but can be found on other crops as well, such as tomato, cabbage, lettuce, potato, pumpkin, spinach, squash, sweet potato, watermelon, and many others.
The corn earworm starts as an egg deposited on corn silks or leaf hairs. The egg color starts as a pale green and will become yellow, then gray. Eggs are about 0.5 to 0.6 mm in diameter and height. Females can lay around 500 – 3000 eggs and the eggs will hatch in three to four days, producing larvae.
Larvae will first look for a food source, which is usually the reproductive parts of the plant. Only one larva is typically found on one ear of corn because as the larvae mature, they become aggressive and kill other larvae. The corn earworm larva has a light brown colored head and the body is usually tan or brown in color with a dark brown stripe and tan stripe along its back. The body has numerous black thorn-like microspines as well.
The pupa stage is next, where mature larvae will drop to the ground and burrow into the soil. There they will pupate for around 13 days.
Finally, the corn earworms will enter the adult stage. Here they look like moths and vary in color. The forewings are usually yellowish brown and have a dark spot. The back wings are usually creamy white and have a small dark spot. The moth size can vary from 32 – 45 mm. Adults will start to lay eggs three days after emergence and continue till death. Adults prefer to lay eggs in fresh silking corn, but dry silk is also a possibility. Females can lay up to 35 eggs per day starting the cycle all over again. The adults may survive 5 – 15 days.
Corn earworms are nocturnal, so most active during the night. Young larvae will start by feeding on corn silk, affecting pollination. Eventually, the larvae will move to the kernels, where they will feed on the tip of the corn ear or move further down the ear, decreasing yield potential. If a corn earworm finds an ear that has not produced silk yet, it may burrow into the ear directly. Corn earworms usually feed on one ear but can also leave that feeding site and search for another, spreading the damage. Larva can also damage young, developing leaf tissue when the corn is in whorl-stage, decreasing its growth and yield potential.
- Practice crop rotations
- Plant trap crops
- Monitor field for eggs and larvae
- Set up traps to monitor and control for moths
- Use resistant varieties – the most effective approach
Insecticides can be applied to foliage in liquid formulation specifically near the ear zone to reach the eggs and larvae on the corn silks. Applications can be made at two to six-day intervals. Unfortunately, corn earworms have become resistant to certain insecticides due to frequent use, so using different modes of action are important
For proper management practices of controlling corn earworms, refer to the Vegetable Production Handbook of Florida for application information on products labeled for use
Always remember to read the label before applying any chemicals in your field.
UF/IFAS Extension in Suwannee County is an Equal Opportunity Institution.