Spongy moth (Lymantria dispar dispar, formerly gypsy moth) is a non-native insect pest that defoliates many species of forest, ornamental, and orchard trees. High populations of larvae affect the aesthetic and recreational value of an infested area. Most healthy trees can withstand a single year of moderate-to-severe defoliation, but two to three years of heavy defoliation can result in branch or whole tree mortality. High populations of spongy moth caterpillars release large amounts of frass, which can become a nuisance to homeowners.
Sign and Symptoms
In spring and summer, there will be egg masses found on tree bark and outdoor objects (ex: furniture to firewood). Spongy moth is the most destructive in the larvae stage (caterpillar) and symptoms can include leaves with holes or completely defoliated trees.
A variety of sampling methods have been developed for assessing spongy moth populations and forecasting potential damage to host trees. Sampling methods have been developed for each stage of the spongy moth life cycle:
Larvae: Burlap or sticky bands placed around the main stem of the tree can be used to trap spongy moth larvae and pupae. Spongy moth larvae seek shelter under the bands during the later feeding stages and often will pupate under these bands. Larval densities can vary greatly from day to day, and even during the day.
Adults: Female spongy moth adults do not fly but attract the male moths by releasing pheromone. This pheromone has been synthetically reproduced and is used to lure male moths to a variety of sticky or bucket-like traps. This is an effective method for detecting the presence of low level spongy moth populations and is widely used in the United States and Canada (Gage et al. 1990). Because this pheromone is so efficient, spongy moth pheromone traps are less effective during periods of high populations when they tend to become saturated with moths.
Egg Masses: Spongy moth lay their eggs in masses of up to 1,000 eggs on the stems and branches of trees, as well as on the forest floor and objects in July and August each year. They will remain in the egg mass until hatch begins sometime in April or May the following year. This provides the longest period for assessing spongy moth populations and is considered the most reliable method. Egg masses are easily counted, especially following leaf fall in the autumn, and old egg masses are generally easily distinguishable from new egg masses allowing for more accurate counts of the current year population.
BioForest recommends monitoring spongy moth populations annually and applying TreeAzin once per season, as needed. Treatments target first and second instar larvae and occur post-bloom, during, or just after egg hatch to inhibit early instar larval development and limit the amount of damage to the tree. This typically occurs mid-May to early June (weather and region-dependent). Refer to BioSIM maps as a guide for starting treatments.
TreeAzin controls spongy moth populations by inhibiting larval development, therefore, decreasing the amount of foliage consumed. There will be some foliage consumed post-treatment as TreeAzin is not a contact insecticide and must be ingested by the caterpillar.
An in-depth look at using TreeAzin systemic insecticide for spongy moth control. Join our technical specialist, Elsa, as she goes over the product's mode of action, dose rate and application methods.
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