May 21, 2020
In late April, the trustees of the Oconee Hill Cemetery reached out to NUF; there were several trees that had recently died and needed to be removed.
Our arborist arrived expecting to give a quote for the removal, but while he was there, he noticed that the reason that these trees were dying was not due to their normal end of lifespan. There was evidence of Ambrosia Beetles on a number of the trees, which indicates that an infestation was the reason for the decline in canopy.
Ambrosia beetles are very interesting creatures. They are one of only a few species of insects that farms its own food. In the case of ambrosia beetles, the females bore into tree trunks, carrying a fungus with them that they “plant” in the tree’s vascular system. The unfortunate side effect is that in most cases this fungus clogs up the tree and ultimately kills it.
For a historic site such as Oconee Hill, which takes pride in the park-like setting, this was an important discovery. Ambrosia beetles generally attack stressed trees but occasionally even healthy-looking trees are at risk. In most cases, trees do not survive ambrosia beetle attacks unless they are identified very early and treatments begin right away.
The best way to prevent ambrosia beetle damage is to maintain healthy trees. Proper watering and mulching are great steps to take. Additionally, trees with limited soil area, compaction or other soil-related concerns benefit from soil care and fertilization.
In the case of the Cemetery, more extreme measures are taken. We know there is a presence of ambrosia beetles and we also know that many of the mature trees on the site are already stressed. To prevent further infestation, we use an insecticide applied to the base of the trunk of the tree. This is similar to a person using bug spray to prevent mosquito bites. It will not last forever, and there’s still a chance of bites, but it’s our best defense.
One of the stressors that is likely to attract Ambrosia Beetles is phytophthora canker. This “root rot” fungus also can be treated to improve the health of the tree and ALSO prevent the ethanol produced by the fungus from attracting the damaging ambrosia Beetles.
The presence of phytophthora canker is also a good indicator that there will be ambrosia beetles, if they are not already present. Studies have shown that one is a good indicator of the other.
Phytophthora looks almost like a bleeding wound on the tree. It often presents as a dark canker on the roots or the trunk of the tree. Evidence of the stress on the tree also can be seen in the canopy of the tree in the form of dieback or chlorosis.
Several other clues indicate to an arborist the presence of Ambrosia Beetles. One common sign is “frass.” The frass looks like sawdust at the base of the tree and can even be seen as what looks like toothpicks coming out of the tree. This is the refuse of the beetle as it bores to the xylem to deposit fungus that it feeds on.
With the preventative treatment and proper soil care, the character and aesthetic of Oconee Hill Cemetery should be preserved for many future generations. The care of the trees is imperative to this endeavor.
