Once larvae reach 2.5 cm or greater and develop those distinctive Yellow markings on their head capsule, they are no longer susceptible to B.t.K (Bacillus thuringiensis Kurstaki).
But not all of the larvae are that far along in development. In the spring, Gypsy moth eggs will hatch sequentially, over a period of 14-21 days, meaning we can often find larvae of distinctly different sizes (instars) on the same tree. If the majority of the larvae have hit this threshold, its time to switch from B.t.K to another product.
For a list of pest control products registered for Gypsy moth, click HERE.
Check the rules around pesticide licensing and application by clicking HERE.
Gypsy moth can significantly impact tree health, especially where defoliation is greater than 50% of the canopy. While it is true that deciduous broadleaf trees will use stored reserves to produce a new flush of leaves, the amount of energy required to produce a new set of leaves is tremendous, and is especially taxing on tree health during hot, dry seasons. Because evergreens store carbohydrates in their foliage, defoliation by insects such as Gypsy moth can be devastating to plant health and lead to dieback or even mortality. Young trees are most severely impacted since they have smaller storage reserves.
Mid-late instar caterpillars will usually rest during the heat of the day, creating an opportunity for manual removal for homeowners and landscape service providers.
By providing burlap skirts around tree trunks for the caterpillars to congregate in, you can attract more caterpillars and create a greater opportunity for manual removal for the remainder of the feeding period.
We expect larval feeding to continue for another 10-20 days.