Little can be done to remedy an existing Ambrosia Beetle outbreak because the insects (and the fungi they introduce and feed on inside the tree) are not treatable with pesticides. While some treatment options exist to coat the bark in an insecticide to try to kill new beetle arrivals before they colonize the tree, these chemicals are not beetle-specific and risk harming other organisms, including beneficial insects. The timing of their application might depend on the exact species of beetle present as well (they can be challenging to ID), since the applicator would need to know when to expect adult beetles seeking hosts. We are not aware of a biological pesticide that would be useful in this situation.

The majority of Ambrosia Beetle species target stressed trees, even if symptoms of that stress are not yet obvious. Typically, this stress results from root zone soil conditions like drought or oversaturation. Both occurrences can be typical of trees growing in developed landscapes, especially since the construction of the original building(s) damaged the soil with compaction and likely altered the soil grade and drainage patterns as well. While some of these impacts are less directly responsible for any impacts on forest trees adjacent to home sites, impacts of climate change and other region-wide suburban contributors to tree stress could still be harming them over time. Tree decline can take months, years, or even decades to manifest as overt canopy loss and tree death, so it's hard to say when any changes in the tree's health began.

Not all mature trees with Ambrosia Beetle infestations are doomed, and often multiple overlapping or sequential events work to bring about tree demise, meaning that Ambrosia Beetle, while perhaps weakening a tree, is generally not be the sole cause of tree death if it does succumb. Some species of oak and other native canopy trees have more tolerance to drought or soil wetness than others, so if replanting (which we encourage), consider using a mix of species for better resiliency. We have received a number of oak decline queries in recent years, and there hasn't been a sole factor responsible. We have several web pages about tree decline (including for oaks) that might be of interest:

• What Causes Trees and Shrubs to Die?
• Why Oak Trees are Declining or Dying
• Browning and Defoliation of White Oaks

If you haven't done so already, it wouldn't hurt to have any trees of concern evaluated by a certified arborist. While they won't necessarily be able to intervene to remedy every existing problem, they can help confirm a diagnosis and look for sources of tree stress that might be mitigated to improve its prognosis.

Miri

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