Cankerworms are everywhere right now! While their normal lifecycle makes them a regular occurrence each year, there are some years where everything lines up for an abundance of these annoying defoliaters. Guess what this year looks to be?
Cankerworms are also called inchworms but they are really caterpillars. They are called inchworms because of the way they pull up the rear of their body and use it to gain momentum to thrust the front of their body forward. These caterpillars can vary in color but are predominately marked with green, pale-yellow or brown stripes along the lengths of their 1 inch bodies. They also just happen to look like the tassles of oak pollen, ew!
Larvae hatch from eggs just about the time that buds are breaking and leaves are developing on the trees in spring and fall and feed for 3 — 4 weeks. Cankerworms can quickly work to defoliate broad leaf trees. Established, older trees may still experience some defoliation but will generally put out a fresh flush of foliage and not sustain long-term damage. All this being said, I did recently find some cankerworms happily munching away at my prized blue hibiscus petals!
Not cool, inchworms, not cool! Bt Bacillus thuringiensis is an organic spray that can help control cankerworms, although is best to know that this spray like most insecticides tends to work best when cankerworms are still young when they are around a half inch long. There are two species of cankerworms--fall and spring cankerworms. The fall cankerworm emerges from the soil as an adult moth after a hard freeze.
Male moths emerge a few days before the females. Mating takes place as the females crawl up tree trunks in search of small twigs in which to lay their eggs. Shortly after the eggs are deposited, the males and females die. The eggs stay on the tree and hatch the following spring. Newly hatched cankerworms spin silk threads that allow them to blow from tree to tree and they reach full-grown length in about four weeks. Larvae then fall to the ground to pupate in the soil before becoming adults later in the season.
Spring cankerworms differ from fall cankerworms in a few ways. First, the pupae in the soil do not emerge as adult moths until early spring. Second, the eggs are deposited in loose clusters in the bark and are not easily seen. It lays its eggs after the first major spring thaw.
Small holes in the new leaves are often the first sign of damage. As the cankerworm larvae eats, the holes become larger until only the leaf veins remain. During high populations, cankerworms can completely strip trees.
Most trees grow back their leaves by early July. However, their growth is slower and they are less able to fight potential new diseases and other insect attacks. The best way you can control adult cankerworms is to band your trees before larval cankerworms become a problem.
Banding your trees with Tanglefoot is an environmentally acceptable way to keep adult cankerworms from climbing the tree to lay eggs. You should band your trees by mid-March to control the spring cankerworm and by mid-September or before the first hard frost to control the fall cankerworm.
Encourage your neighbours to also band their trees because cankerworms can travel on their silken threads as larvae. A tree is normally very tolerant of some defoliation and control efforts are unnecessary when only a few larval cankerworms are present. Several pesticides are effective for treating cankerworms when applied at the correct time. Examples of active ingredients of pesticides are:. Use the bacterial insecticide Bacillus thuringiensis, whenever possible.
Always follow all label directions completely. The label is the final authority for use of the product. Trunk banding is a method, where sticky barriers are applied to tree trunks to trap cankerworms. This method is NOT recommended. This method does not work very well, even in areas where most trees have been banded. The sticky material used for trunk banding is expensive, messy to work with and spoils the appearance of the trunk.
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