Gypsy Moths

There is a large population of gypsy moths (Lymantria dispar) thriving in New York this year. Their caterpillars are voracious eaters, and have been seen defoliating blueberries as well as strawberries. Gypsy moth caterpillars emerge looking small, fuzzy, and dark brown to black. As they eat foliage, the caterpillars grow and shed their skin. Every time a gypsy moth caterpillar sheds its skin, it gains an instar. For example, when it first hatches, the gypsy moth caterpillar is in its first instar. After it sheds for the first time, it is in its second instar.

Gypsy moth caterpillars take about 5 – 8 days to shed their skin and progress to the next instar. Male gypsy moths form pupas after five instars, and females form pupas after six instars. There is one generation per year.

Gypsy moths affect berry crops by eating the leaves, which will reduce the amount of carbohydrates the plants can send to developing berries and growing tissues. They can also sever berries and blossoms from growing points so that they do not become marketable fruit.

Managing gypsy moth caterpillars is easiest when they are in the first 3 instars. When the caterpillars are in the first 3 instars, their head capsules are black in color. When they age into the 4th instar, the head capsule becomes yellow in color. While young gypsy moth caterpillars typically feed during the day, older gypsy moth caterpillars usually feed at night. See photos of gypsy moths maturing from 1st to 4th instars at this link.

Managing Gypsy Moths

At this point in the summer, managing gypsy moth caterpillars is becoming more difficult due to the presence of caterpillars in the 4th instar and older. This post will look over the management options available at different points of the gypsy moth’s life cycle.

Managing instars 1-3

Bacillus thuringiensis, or Bt (trade name DiPel) is an organic pesticide that is highly recommended for gypsy moth control. This is because it has no impact on humans, aquatic life, or bees. It has a 4-hour re-rentry interval and a 0-day pre-harvest interval. If you are purchasing DiPel for gypsy moth control, keep this in mind:

1. Ensure that the DiPel that you have lists either “Bacillus thuringiensis subspecies kurstaki” (BtK), or “Bacillus thuringiensis subspecies aizawai” (Bt aizawai) as the active ingredient.

Spinosad, a combination of the chemicals spinosyn A and spinosyn B, is sold under many trade names (Captain Jack’s DeadBug Brew, Naturalite, Entrust). When wet, spinosad is highly toxic to most beneficial insects including honeybees. It is not toxic to honeybees after drying. Spinosad has a 4-hour re-entry interval and a 1-day pre-harvest interval.

Managing instars 4-6

If you are seeing caterpillars with yellow heads causing significant damage to your crop, organic control options are limited. A derivative of neem oil, azadirachtin (trade name Azaguard) can be used, although it is rather costly and may not fully eliminate the caterpillars in one application. Azadirachtin has a 4-hour re-entry interval and 0-day pre-harvest interval.

There are also several conventional options available. University of Wisconsin Extension has a useful Pesticide Guide for Gypsy Moth (Based on Life Cycle Stage) that can help you compare your options.

If the outbreak is not too severe, it may also be in your interest to wait until the moths pupate, emerge as adults, and produce egg masses in late summer.

Managing egg masses

Egg masses can be removed by hand, or sprayed with horticultural oils. In the pesticide guide mentioned earlier, University of Wisconsin Extension recommends Golden Pest Spray Oil which is an organic soybean-based pesticide.

Managing all instars beyond the berry patch

Growers with a tree line or forest near their property are likely getting more gypsy moth larva in their berry bushes. Gypsy moths mostly live off of landscape trees, hiding under the bark and eating the leaves. When they climb high up into the branches, the caterpillars can send out a string of webbing and catch a passing breeze. This is a way that they can parachute down into a berry planting.

By managing the trees near vulnerable crops (bushberries, strawberries) you can remove gypsy moths without spraying. Instead, you can attract them into a simple trap and then manually sweep them into a bucket of soapy water.

By wrapping strips of cloth around your tree trunks, you can create a trap for gypsy moth larva. These can then be killed before they migrate to your vulnerable crops. To be effective, you must walk by these traps at least once a day. This method can be used all summer long. Familiarize yourself with the appearance of egg masses and adults as well, and you also will be able to remove those during the daily walks. Here is a link with additional instructions and photos.

Resources:

Gypsy Moth Instars Visual Guide  | U.S. Forest Service (1-page PDF)

Gypsy Moth Life Cycle | Michigan State University

Pesticide Guide for Gypsy Moth (Based on Life Cycle Stage) | University of Wisconsin Extension

Gypsy Moth Egg Mass Identification | University of Wisconsin Extension

Gypsy Moth Barrier Band Trap | University of Wisconsin Extension