I was looking out the window the other day, and I saw a black caterpillar crawling along the edge of the window frame. I recognized at once what type of caterpillar it was. The gypsy moth caterpillars have hatched out.
Gypsy moth caterpillars have been in our area for many years. In the late 1970s and early ’80s, their numbers skyrocketed and most trees were defoliated by the large numbers of caterpillars that were eating. By late June in that time frame, the leaves had been stripped of foliage and the oak trees and the maple trees had the appearance of trees in the fall. This can tell you how destructive this caterpillar can be in your yard.
Oaks would appear to be the favorite food of the gypsy moth caterpillar. Once the caterpillars get to be big enough to be easily seen by most people, you will notice thousands of the caterpillars feeding on the oak leaves.
Gypsy moth caterpillars are unusual in that they do a lot of their feeding during the evening. As the morning comes, many of them will climb down from the tree and stay on the lower trunk or even hide in the grass to keep out of the sun.
This characteristic ultimately led to the demise of the caterpillars in the early ’80s. There is a disease that was released in the ’20s that finally infected the caterpillars. It appears when moisture conditions are right in the soil. As the caterpillars got sick, they spread the infection to other caterpillars.
If memory serves me correctly, in 1982 or 1983, this disease became so widespread that the gypsy moth caterpillars were all but eliminated for about 30 years. Each spring, you would see a few caterpillars around, but they soon became infected and the damage to trees was minimal.
The caterpillar population began to rise in 2015 and 2016 when very dry spring weather allowed the disease to go dormant.
I was looking at trees last spring, and as you may remember, we had a fair amount of rain during the season when the gypsy moth caterpillars were active. I noticed that many of the caterpillars feeding were soon dying from the reactivation of the disease.
With the rainy days that we have been having, I would assume that the disease would be active again this month. If this is the case, the disease will kill many of the caterpillars off. Fewer caterpillars mean fewer moths to mate and lay egg masses on the trees.
Here’s hoping that Mother Nature will control the caterpillars on your trees.
You may find that the gypsy moth caterpillars will feed on some of your trees and on some of your plants. If this does happen, the most effective spray that you can use to control the caterpillars is a product called Bt, short for Bacillus thuringiensis. The bacterium attacks and kills just caterpillars. It is sprayed onto the foliage of the plants, and as the caterpillar eats the foliage, it soon gets sick and stops feeding. Within a few days, the caterpillar dies.
Bt is safe to use around birds and most pollinators. Keep in mind that this product can kill the caterpillar stage of most butterflies.
Now is the time to keep an eye on your trees and other plants, and if you see signs of the gypsy moth caterpillar feeding and not getting sick, you can then do an application of Bt to control this caterpillar.
Well, that’s all for this week. I’ll talk to you again next week.
Tim Lamprey has worked in the lawn and garden industry for 45 years.