Q: Bore-infested plum tree is oozing sap and losing leaves. Is there an insecticide for the borers?
Wednesday, December 30, 2015
Q: I have an ornamental purple leaf plum tree that has become infested with what I believe to be borers. Many tiny holes (pinprick size) cover some limbs. Many of the holes ooze sap, so that the tree is covered in little globules of sap. The limbs worst hit have no leaves. Can I save the tree? What do I do? Should I cut off the worst limbs and try to save the still healthy ones? Is there an insecticide for the borers? Even more importantly, how do I protect the rest of my tree?
A: There can be many insects and borers that affect plum and fruit trees. If the borers wound the trees, there can be sap bleeding or oozing. The branches that have no foliage can be checked to see if they are alive by scratching the thin bark away with a thumbnail. If green cambium is beneath, the branches are alive. If the branch is dried and hard and bark can't be scratched like a wooden dowel, the branch is dead.
All dead branches can be pruned off at any time. If branches that have sap oozing are mostly dead, they can pruned off. If the shape of the leaf crown is so badly deformed by pruning, it may make sense to remove the tree.
There are insecticides that will kill borers. They need to be preventative to kill borers as they eat through the bark to lay their eggs, and to kill the larvae that feed beneath the bark. Trunk and branch drenches soak into the bark and can kill beetles that eat through the material. Soil drenches or trunk injections need to be taken up by the tree and will kill borers as they enter the bark and cambium. Follow label directions.
The best way to protect trees is to keep them healthy. In California, many properties have cut water to their lawns, and also their trees. Water-stressed trees are more susceptible to insect attacks.
Responder: Gordon Mann, RCA #480, Auburn, CA