More Bark Beetle Attacks?

With the persistence of this drought, we may see more bark beetle attacks. For the first time, I witnessed two Ips engraver attacks on the same property. The two attacks occurred four weeks apart. The scenario required for Ips attacks is not usually reoccurring. Because they attack only stressed trees, Ips usually leave the scene and are done. Could it be that stress from the drought is causing trees to release the stress pheromones that attracts the beetles?

Ips Engraver Beetle-UGA

There are a few species of beetles that cause problems in pine stands. The Southern Pine Beetle and Ips Engraver Beetle bore into trees and induce the blue stain fungus. This fungus clogs the vascular tissue of the tree and kills it. The difference in the two species is that Ips beetles rarely if ever attack a healthy tree. Pheromones (chemical signals) from a dying or distressed tree are picked up by Ips beetles. These are usually lightening struck trees. Once Ips beetles show up, they only attack a few trees and leave. Sometimes I see 3 trees in a stand killed and as many as 8 trees killed last week.

Symptoms/Signs

Other than a tree that suddenly dies,  the most common sign of an Ips attack is pitch tubes on the side of the tree. Once the adult beetle bore into the tree, the tree exudes sap to counter the beetle. The sap piles up and look like pieces of bubble gum attached to the tree. The center of the tube contains a hole through which the adult beetle enters the inner bark. If no hole is present in the pitch tube, the beetle attack was unsuccessful.

Boring dust and pitch from Ips attack

Holes in pitch tubes where adult beetles entered the tree

An addition to the presence of pitch tubes, the adults construct egg galleries in the inner bark. These galleries are in certain shapes. Ips usually follow the wood grain, and have a “Y”- or “H”-shaped gallery patterns. I took my knife and scratched some outside bark away to find a few galleries.

Egg galleries of Ips beetle attack

Management

A common question is should we cut the trees down? Shortly  after the initial attack, needles at the crown turn yellow then brown. This happens quickly. Once we notice the trees are dead, the Ips beetles have already moved out. UGA Extension Forestry Specialist Dr. David Moorhead says in a pine stand, we actually do more damage cutting down a few dead trees than if they are left alone. The only time we would cut down trees is for 1) astetic reasons or 2) they pose a risk if fallen.

We can also use insecticides, but the issue is Ips attacks are difficult to predict and they enter the tree high up – you would have to cover the tree. The third beetle species is black turpentine beetles. They attack trees at the base and move about 5 feet high. However, their risk is minimal since they do no carry blue-stain fungus.

Cross section view of blue stain fungus