Unfortunately, gypsy moth caterpillars can devour a tree’s leaves quite quickly if not controlled. But we have good news! These pests RARELY kill a tree directly- it would take a few seasons of defoliation or other stressors before a tree will start to suffer. With proper pest management and watering, we can help you and your trees survive the onslaught of caterpillars this season.
In July/August, female gypsy moths will climb up trees and structures ( patio furniture/wood piles etc) and begin to lay egg masses. These eggs will endure the winter months and, once the weather warms, begin to hatch into the larvae stage (caterpillar). Depending on the season –this can be mid April to late June—you will notice damage to your tree as the caterpillars feed on leaves. In late June to early July they will pupate, and in July-August begin their moth stage once again. There is only one generation of moths per year.
Only the caterpillar stage feeds on tree leaves, but they can eat very quickly—and there are usually thousands of them. Most of the feeding happens at night, or on cool days, as caterpillars do not like extreme heat and fear predatory birds during the day. They will begin their descent at dawn from the top of the tree in search of a safe spot, and will ascend at dusk.
Knowing these habits helps us with effective treatment. We find it best to follow all three recommended treatments.
- Banding Tape; Wrap the tree at about chest-height with banding sticky tape. Tanglefoot and GreenEarth produce effective products, stocked here at the greenhouse. As the caterpillars climb up and down the tree, they get stuck as they pass over the tape. You may have to replace the tape or sticky trap a few times a season, depending on how severe your infestation is. The tape can also be applied for the control of female moths in August, as female gypsy moths cannot fly. As they crawl up the tree to lay eggs, like the caterpillars, they will get stuck to the tape.
- BTK SPRAY; This spray is an effective biological control that can be used to control the population of ANY caterpillar. Safe for humans and pets, it begins to deteriorate in sunlight within 5 days of application so it does not stay in the environment. This spray needs to be applied to as much of the leaf surface as possible, as the caterpillar needs to ingest it for it to work.
How does it work? ” The highly alkaline environment of the caterpillar’s gut triggers the bacterium to release a crystalline protein called an“endotoxin” that poisons the insect’s digestive system”*. Re-apply once a week if you notice you still have some caterpillars, as it will deteriorate within a week. The younger the caterpillar, the more effective the spray will be.
- Maintenance; Unfortunately, female gypsy moths can lay their eggs anywhere they can reach. If you have had an issue this season, check old wood piles, lawn furniture, dead trees or any other structure near the infested tree, as they could have laid eggs. Scrape off any egg masses into warm, soapy water, before disposing of them. Spray trees with a combination dormant spray ( lime sulfur and horticultural oil) in fall to kill any egg masses on tree trunks. Keep infested trees well watered during summer as to ensure they do not go through any drought stress.
*excerpt from https://extension.entm.purdue.edu/GM/PDF/GMquestions.pdf
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