Winter moths, what of it?
Did you see these guys banging up against your windows during the winter?
Attracted to the light and warmth of the cozy living room in which you were hunkered down against the cold, winter moths (Operophtera brumata) have to brave the brutal conditions in order to procreate. Adult winter moths emerge around Thanksgiving and may continue to appear until December if temperatures remain mild. Males will find females by following the trail of pheromones to a tree where females are racing up the trunk, at which point they will mate and then the female will continue scurrying up the bark and begin to lay eggs. Both males and females die soon after egg deposition, but this still leaves 150 eggs per pair to possibly hatch and begin feasting on your trees and shrubs at bud break.
Caterpillars will emerge in early spring and attempt to enter flower and leaf buds almost immediately, then become free-feeding, causing damage which will persist throughout the growing season. The leaf damage seen below limits the amount sunlight collected by chlorophyll needed to photosynthesize and produce energy, and most trees will not leaf out a second time. Winter moth population sizes appear to vary by region, season, weather conditions etc., in other words some years are worse than others and some areas of the country get hit hard while in other areas winter moth doesn’t exist. The caterpillars enjoy a wide variety of host species, including but not limited to; oaks, maples, basswood, elm, ash, crabapples, apple, blueberry, rose and cherry. Population size and potential for damage is very hard to predict but if treatments are timed right and applied correctly a herd type immunity phenomenon can be observed.
Winter moth eggs remain on the bark, in crevices or under lichen and are tiny and difficult to identify. Eggs can potentially be managed with a horticultural oil trunk spray are but are present in late winter to early spring, when affected regions will still be experiencing temperatures too low for appropriate product use.
Caterpillars can begin hatching in late March and continue through the third week in April. Newly hatched caterpillars are about one millimeter long and will attempt to force their way in between bud bracts and scales, if buds are still too tight they produce a long strand of silk and balloon away on a wind gust. They can enter swollen buds and remain happily inside feeding on leaf and flower tissue. Once the caterpillars become “free feeding”, meaning they are now roaming around the foliage, they are the easiest to target. There are several products that will effectively control caterpillars, but some are better than others in that they are not only effective but narrow spectrum and naturally derived. Two products that fall into this category are BT (Bacillus thuringiensis) and Spinosad products. BT is a bacterium specifically toxic to Lepidopteran (butterflies and moths) larvae, it works best on very young caterpillars and must be ingested to be affected. Spinosad products are derived from a bacterium which has been subjected to fermentation in order to extract the active ingredient. Spinosad is our product of choice because it controls caterpillars of all ages and works on contact.
Both products need to be applied by a licensed, trained specialist as directed by your arborist and carefully timed to avoid hurting communities of beneficial insects while effectively targeting winter moth caterpillar populations. Beneficial insects include pollinators such as bees and butterflies, whose colonies are dwindling. Plant healthcare specialists are trained for proper application which targets pests while protecting beneficials. Do not hesitate to make an appointment with your arborist to discuss your needs and concerns, timing is everything when it comes to winter moths.