GOSHEN, Ind. — When my children were in their early teens, it seems like all they did was eat and grow. As they reach adulthood, the rate at which they consume food and grow has slowed considerably. Most other animals have similar patterns in their growth habits.
Gypsy moth larva, for instance, have been eating away at tree leaves in many parts of the area. When the caterpillars are ½ to 1 inch in size, they are eating machines, just like young teenagers. A single caterpillar can consume 11 square feet of foliage in their five weeks as a larva. And because there are usually thousands of caterpillars at a site, whole neighborhoods can be defoliated quickly.
The gypsy moth larva I saw last week were up to 2 inches in length, meaning they are wrapping up their intense eating phase and are creating pupa (cocoons) now. They will be in the pupa for 10 to 15 days, then emerge as moths. Neither the pupa, the adult moths, or the egg masses that will be laid do any actual harm to the trees. However, they do represent the next generation that will cause defoliation next year.
There’s not much sense in spraying insecticides on larva once they begin to cocoon. Instead, pick the pupa off and throw them in soap water. They will attach pupa to anything sitting still outdoors. Trees, playground equipment, the siding on your house, grills, fences, trailers, cars, boats, firewood; it is all fair game. They are very good at hiding their pupa cases, so look under loose bark or hidden spots for pupa cases.
Gypsy moth over winter as eggs. A single egg mass, about the size of a quarter, can have 500 to 1000 eggs inside. Once these tan colored masses begin to appear, it’s a good idea to pick them off and destroy them. Use a knife or paint scraper to gently scrape all of the eggs into a jar.
Don’t just scrape egg masses onto the ground or try to crush them with your shoe as they will survive to hatch next spring. Any parts of the egg mass you are unable to scrape off can also hold surviving eggs. Eggs can be killed by soaking in soapy water for 2 days before discarding them in the trash.
Another technique to destroy egg masses is to spray them with a vegetable oil or horticultural oil labeled for gypsy moth egg masses (available at lawn and garden centers). Do not use motor oil, mineral oils, or other oils not labeled for gypsy moth. Spray the oil onto the egg mass until it is soaked. Spray what you can reach. Unfortunately the egg masses are often laid high up into the tree, out of reach for most homeowners. Tree care companies can often treat the egg masses later in the fall with their equipment.
Finally, plan ahead for 2019. If you have gypsy moth, chances are your neighbors do to. Because the caterpillars do not respect property lines, a coordinated group effort is often much more effective than a small group of random households trying to protect their own trees.
A coordinated effort may mean spraying in early May days after the caterpillars hatch from the eggs, and before the damage is done to the trees. Aerial applications of Bacillus thuringiensis can be used over large areas (5 acres or more), but there will need to be coordinated by and managed by a home owners association or something similar.
For smaller plots or areas where coordination efforts prove fruitless, spraying the ground around affected trees, or using injections into the trees, can be effective. These efforts, of course, are best done when the young caterpillars are just beginning to feed.
Need more information about gypsy moth? Check out Purdue’s gypsy moth web page at extension.entm.purdue.edu/GM/index.php.
— Jeff Burbrink, Extension Educator, Purdue Extension Elkhart County
For more news from Indiana, click here.