Gypsy Moth: What We Know Today….

Last year the oldest standing Oak at the Quabbin Reservoir died due to repeated attacks by the Gypsy Moth.

The affect of repeated defoliation on trees is widely known, but Gypsy Moth outbreaks have not been as severe in New England since the widespread outbreak in the early 1980’s.

Rainy springs during 2018 and again in 2019 are likely to limit the worst outbreaks in 2019, but while coverage is patchier this year, there are still areas that will sustain significant damage based on egg counts. Both the virus and the fungus that may control GM during rainy springs, do so only after the major damage has already occurred.

This particular tree was at least a few hundred years old, and represented one of the few trees on the grounds when the reservoir was built in the 1930’s. Loss of the tree’s leaves depletes nutrient reserves and the tree is incapable of restoring its leaves and sustaining life after the attack.

This tree could have been saved. Systemic, trunk injection of low dose insect controls which are sealed in the tree can preserve most leaves on the tree even when severe outbreaks occur. In the central Ma area during the fall of 2016, many trees had tens of thousands of egg masses each carrying up to 500 eggs ready to hatch.

In research done during the fall of 2016 we injected these trees with several treatment options.

Treatments were done during colder temperatures in late October, but our research indicated that we would have seen better controls had we injected in September, especially for white oaks (the G. M. preferred oak species).

We learned several lessons from this research. We were able to retain 78% of leaves during heavy infestation using TREE-äge G4 ®. It is best to treat a bit earlier in the fall, because movement of the insect control up the trees may be a bit limited by loss of leaves in the fall, and colder temperatures, impeding liquid movement.

We learned that the white oaks were not able to retain leaves as well as their red oak neighbors, however during the usual Refoliation and recovery period in September, after insects had died, they refoliated at approximately 75% of regular leaf cover, while untreated red oaks which had completely defoliated gained by no more than 25% of leaves.

No trees died during the complete defoliation potential event on this TREE-äge treated property while adjacent untreated properties lost several mature oaks.

Timing of spring applications via injection is more time sensitive because hatch outs coincide with leaf emergence, so damage to young leaves is more significant. Some just-in-time injection applications can be effective against this pest but have a more limited treatment duration. One such product is ACE-jet® insect control.

During this particularly wet spring, it is important to know that none of these injected Arborjet treatment chemistries are affected by rain or wind; but for the future, we recommend earlier, preventative treatments such as fall applications, to enhance the narrow window for spring control.


Rob Gorden

Director of Urban Forestry and Business Development