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Corn Earworm or Tomato Fruitworm

Closer Look Of The Corn EarwormAlso known as the cornworm or tomato fruitworm, this insect, in the caterpillar phase of its life, causes damage to fresh sweet corn by burrowing into the tops, or silks, of the corn and eating (also pooping all over) the kernels, making them undesirable to eat. It also interferes with the plants’ pollination and kernel development, leaving the corn deformed and open to attacks from other insects, mold and diseases.

In tomatoes, they chew a hole in the stem end, ruining the fruit, and in peppers they form small brown holes as they bore in and out of the developing fruit. They also chew buds and leaves, causing plants to wilt or be stunted. When the earworm attacks tomatoes, it is called the tomato fruitworm, but it is the same caterpillar that attacks corn.

In general, the damage is worst later in the season – August & September - when the second, and larger, hoard of corn worms hatch from your garden soil. This second wave is what really devastates corn and tomatoes, just as these vegetables are reaching maturity. Fruit and veggies harvested before late August will usually escape major damage, so planting early sweet corn can be a wise move, if possible.

Normally, this insect, in more northern climates, migrates from southern states, not being about to withstand cold winters. The adult moths fly northwards at night searching for corn stalks, being attracted by lights (so don’t have a light on in your garden).

The corn worm is considered the worst pest of corn and the second most destructive insect in the USA, attacking many of the most important field and vegetable crops. Once inside the corn silk, the caterpillar is difficult to destroy, so early detection and action is called for.


Corn Earworm Adult MothAdults are robust grayish-brown night flying moths whose wingspan is about one to two inches. The front wings are marked with dark-gray, irregular lines and a dark area near the wing tip. The female moths emerge from the ground, or fly in from southern states, normally at night, and begin searching for a place to lay their eggs. The green fresh silk on the tip of corncobs is the preferred place, but the leaves of corn, tomatoes or peppers are also acceptable. After mating with a male, the female lays her eggs and dies shortly afterwards.


Corn Earworm EggsThe female moths lay their eggs in the green silk tops of corn and also on foliage. Eggs are about 1/32 inch in diameter, being normally white or pale yellow in color but darken to brown or red just before hatching. Each female moth can lay a thousand eggs during her short lifetime, which accounts for the hoard of caterpillars that can develop. In about one week the eggs hatch, in the form of small but voracious caterpillars, and crawl into the corn silk to begin feeding on the top of the corn stalk.


Corn Earworm LarvaeThe full-grown larvae are caterpillars between 1 1/2-2 inches long. The color of these caterpillars varies widely and is not reliable for identification. In general, if you see a caterpillar in a corn silk, it is most likely the corn worm. Older caterpillars normally have distinctive stripes along the sides of their bodies, and wiskerlike spines on the top. Although the female lays several eggs on each stalk, only a single two-inch caterpillar survives, corn worms being highly aggressive and cannibalistic. They move very little and simply feed on the tips of fresh corn, defecating all over the place as well. After about two to four weeks the caterpillar is fully mature and drops to the ground, burrows down six to twelve inches, where it enters the pupae phase of its life.


Corn Earworm PupaCorn earworms overwinter as pupae in southern states, not being able to withstand the cold of northern winters. Come spring, they emerge from their pupa coverings and emerge as young adult moths (normally around May), beginning their northern migration. However, once the corn worm is present during the summer months, the larva drop from the corn silks, burrow into the ground and pupate for about two weeks. The adult moth then emerges and crawls to the surface to re-lay a new crop of eggs on corn silks and tomatoes. The cycle from egg laying to the end of the pupa stage is about one month.

Vegetables That Corn Earworm Like To Eat

Cabbage Lettuce Potatoes Squash
Corn Peppers Snap beans Tomato


Most home gardeners grow only a modest amount of sweet corn. If this is the case, then simply tying a paper bag over the corn stalks, after they have been pollinated and as they are maturing, is perhaps the easiest way to prevent damage from the corn borer. If this is too much to do, try clipping the silks together with a clothespin, as this might deter some attacks.

Hand picking the caterpillars is practical in a small garden. Simply open up a corn silk slightly and look for a large caterpillar. Use a caterpillar picker to remove the caterpillars if you like. Place them into a bucket of water with some soap added, as they will drown in this.

Carbaryl (Seven) is said to be effective against the corn worm. Apply this substance when 10 percent of the corn silks first appear, and every three days afterward for several weeks. Mix about two tablespoons per gallon of water, and spray the corn silks; don’t use a dust.

If sprayed when the eggs first hatch, BT, var kurstaki, is said to be effective against the insects. But once the caterpillars are over one half inch long, they are hard to control with BT.

Remember that it is the second generation of corn worms that normally does the most damage. Placing floating row cover around the base of your corn, or growing your corn under plastic, as we do, is also a good way to foil the insect. The reason being is that when the caterpillar drops to the ground, it won’t be able to burrow into the soil, and will probably die first, as corn worm larvae travel very little.

It is said that sprinkling ground lime on the silks when they first start to develop is effective, but we have never tested this. Also, if you plant peas or beans around the base of your corn stalks, the caterpillars have a difficult time entering the soil and maturing into new adults.

One trick for small home gardens is that you can wait until the corn silks have just developed, and then snip off the silks. When the female moth lays her eggs on the silks, you clip off the silks before the eggs have a chance to hatch. The corn ears will have been pollinated by then, and the eggs will drop of with the severed silks.

Squeezing an eyedropper full (about 20 drops) of mineral oil will normally suffocate young earworms, and if you mix the oil with a natural insecticide, such as pyrethrum, it is said to be even more effective. But do this only after the silks have matured, 4 to 7 days after the silks first appear, so you don’t interfere with the pollination cycle.

Pyrethrum paralyzes corn worms on contact, but must be applied directly to the caterpillar for it to work. Usually, two applications, 3 to 4 days apart, will control the insect. Finally, the powerful natural chemicals rotenone or neem will also control corn worms if nothing else seems to work.

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