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Trees/How to get rid of Weeping Willow borers


QUESTION: I have two weeping willow, one is dead and will be cut down, once the borers started multiplying this tree was dead in 5-6 weeks.

The second WW is 75' away is starting to suffer the same damage from a wood borer. Had an arborist come out, said it needs to be sprayed to kill the borers. Now the WW has a dozen large European Hornets going after the borers.

What insecticide can be sprayed on the tree to remove the borers?


ANSWER: Borers will infest wounds and and can be controlled with the use of an insecticide called merit. Spray the area and the Merit will be absorbed by the bark and kill the insect in the tree. Or a newer product called Bayer Advanced Tree and Shrub Insect Control can be used by applying it to the soil around the tree and the roots will translocate the insecticide to the trunk limbs and leaves killing the borers. This product will give linger protection than the spray and is easier to apply. Check with your local nursery for this product. Here is a web link to this Bayer Advanced.

Borers normally attack trees that are under stress so I would also recommend that you fertilize the tree with 10-10-10 fertilizer at the rate of 1 lb per inch of trunk diameter scattered around the tree and watered in good. If you wait to fertilize just before a rain storm you do not need to water.

The wasps and hornets are feeding on the sap that is coming from the wounds created by the borer. The insecticide will stop the sap flow and the hornets will go away.

---------- FOLLOW-UP ----------


Great feedback, thank you. The Bayer solution has already been used. Not sure how to tell it's working unless I cut some bark away and see if the little buggers are still there. Any suggestions?

Check any wounds and if there is no sap running from the wounds then the borers are not active and the insecticide has done it work. New holes from borers will have sawdust or the sap running out. If none of this is present then you have controlled the borers. Do not cut into the bark this might create entrances for more borers.  


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Jim Hyland


I am an expert in Forestry, Forest Entomology, Forest Pest Control, and Forest Health. Extensive knowledge in Identification of insects and diseases of trees. Expert on Bark beetles and other insects that attack forests. Also a Registrated Forester with extensive knowledge in the management and care of forests.


34 years as State Pest Management Chief in a Southern state. Extensive knowledge in Forestry.

BS with major in Forest Management and Entomology
Registered Forester
Certified Pesticide Appicator

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