Ambrosia beetles are a serious threat to mature trees in the landscape. When ambrosia beetles bore into trees, the tree is infected with a fungus that grows within the tunnels created by the beetles, and serves as a food source for both the adult beetles and their larvae. The fungus disrupts the flow of nutrients and water, severing the connection between the roots and the leaves. This causes wilting and dieback of branches, and in severe cases, can lead to the death of the entire tree, especially if the tree is already stressed.
And ambrosia beetles are attracted to weakened or stressed trees, making them particularly dangerous in landscapes that are not well-maintained or that have suffered from drought, disease, or other environmental stressors. Last summer I saw a few very large white oaks start wilting and then quickly die, all in a month from beginning to end. This was very surprising to me because white oaks are our longest lived oak species, known for being tough and well-adapted to this region.
One of the most significant challenges of managing ambrosia beetle infestations is that the beetles are difficult to detect. The tunnels they create are small and can be difficult to see, and the beetles themselves are only about 1/8 inch in size. It is much more common to find the sawdust created by these beetles in small piles around the base of the tree. The sawdust is extremely fine textured; more fine in texture than most sand. It’s so fine that it's almost a powder. Sometimes, the sawdust extrudes out of the hole in a stiff column like a pencil lead - this is a dead giveaway for ambrosia beetles. But by the time visible signs of damage appear, the infestation may be well-established and difficult to control. So, as they say, an ounce of prevention is worth a pound of cure.
To prevent ambrosia beetle infestations, it is essential to keep large old trees healthy and well-maintained. The best prevention is keeping the tree from becoming stressed. This means increasing the size of the mulch ring and removing grass to reduce competition. If we get a long period of drought this summer, consider watering your large old trees to keep their health up. Add a few bags of organic compost and water it into the mulch.
If you suspect that your trees may be infested with ambrosia beetles, it's best to consult with a certified arborist to properly diagnose the problem and quickly develop an appropriate treatment plan. I’ve seen large old trees die very quickly, so early detection and quick intervention can help prevent the spread of these damaging pests and protect the health and beauty of your trees.
Removing large old trees can be very expensive. I promise you, it is much cheaper to keep your trees healthy through mulch and compost, and some supplemental watering at a few key points during the hottest, driest part of summer. $50 of mulch and compost and an extra $20 on your water bill could prevent you from spending thousands of dollars to remove a large old tree.
