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How to Avoid Another Devastating Year of Winter Moth Infestation

Mar 29, 2018 06:00AM ● By Pamela Johnson
The winter moth (Operophtera brumata, of the insect order Lepidoptera—moths and butterflies—and the family Geometridae for the bug geeks) is an invasive species that is now a major problem in Massachusetts. Infestation is expected to be even worse this year than in previous ones. Some of the more common trees that the winter moth targets are maple, oak, ash, birch, beech, apple, cherry, pear and rose.

Most people notice winter moths around Thanksgiving (late Nov. to early Dec.) when adult moths emerge and the males begin to fly. At this point in their life cycle, there is no effective treatment for the moths, but they don’t do any damage at this time either, because they’re not feeding. At this stage, the male moths are able to fly; the female moths are flightless because, although both sexes have wings, the females’ wings are very small and therefore ineffective for flight.
Female winter moths have to climb the side of the host tree to lay their eggs on the trunk and branches. After the eggs are laid, the adults die and the eggs remain on the stem of the tree throughout the winter and into spring.

The caterpillars begin to emerge from late March to early April, and this is when the attack begins. After the winter moths emerge from the eggs, they spin a silk thread and drop down from the tree and are carried by the wind to a feeding spot, in a process known as ballooning. At this early point in their life the leaves have yet to emerge so they will squeeze their way into a bud on the tree and begin feeding on the swollen bud. As the plant continues to grow, the caterpillar grows as well and continues to eat the plant’s leaves until the end of May to the beginning of June.
Obviously, this is the time period when the insect does the most damage to your plants. In many cases, all of the leaves are destroyed, leaving the trees completely defoliated, which is obviously very detrimental to the trees’ long-term health. Many healthy, well-rooted trees can withstand being defoliated; while the trees have enough reserve nutrients to push out new leaves, they have enough reserve for only one year. If the defoliation occurs year after year, the tree will eventually be unable to recover. After a few years of this level of stress on the tree, it will start to show signs of dieback throughout the canopy, such as, a loss of leaves or a thin canopy, and eventually it will die.
It is during this time in the moths’ life cycle that control and treatment are most effective. One of the best methods of treatment is with a Spinosad product that works by attacking the nervous system of the winter moth. Treatment is effective if the moth has direct contact with the chemical or it feeds on treated foliage.
If left untreated, winter moths will continue to eat until fully grown, into the beginning of June. Once they are done feeding, they will drop down from the tree into the soil and immediately spin a cocoon and pupate. When they are in their pupate stage there is no control, except for a few natural predators. This is where they will stay for most of their life cycle. They do not emerge from the soil until around Thanksgiving, when the cycle of devastation begins again.
For more information or to have your trees sprayed to prevent winter moth damage, contact a local licensed arborist.

Written by Ryan Anzivino, Certified Arborist # NE-6914A, of Bellingham-based, family-owned Outdoor Maintenance Co. Office tel: (508) 883-3564; cell: 508-498-4397.