Borers in Pine Trees

Q. I am losing portions of my pine trees at my home. All ten were planted from “live” Christmas trees we bought in the past either Mondale or Aleppo type. Out of the 10 trees, 3 are starting to show complete limbs that are dying. I trimmed some “dead” out of one tree this week and saw numerous small holes on it, so I hit it on the cement and this “worm-type bug” fell out. What is this creature and how did it arrive? Is it causing the damage I see in my trees? And finally, how do I get rid of them before they kill all my pines?  

Flatheaded borer found in pine trees

A. Pines are not a preferred tree of flatheaded borers, like the picture you sent. Flatheaded borers are a problem in many plants but usually not pines. Most of the time in heavy sap producers, like plum and apricot trees, the sap floods an area damaged by insects and “suffocates” invaders like these flatheaded borers. I am not sure if it’s an old tale or not, but I understand that sap that oozes from the damaged branches is first cloudy because of insect feeding, and then becomes translucent as the invader or borer is overwhelmed by the sap and dies.

Stress the Usual Culprit

My guess is that these trees had limbs stressed because of a drought problem and these stressed limbs attracted borers to these living, but stressed, branches. So first make sure that water is being delivered to an area equal to about half the area under their canopy. Next, when water is applied be sure it reaches a soil depth of about three feet to satisfy any drought condition they might be experiencing.

Remember pine trees, just like fig trees and palms, like to have their “tootsies” in water. The trees don’t have to be growing in it, but they like to access it during the hot season, even if the water is deep. They don’t like to be surrounded by a “dry” desert soil.

I don’t think “borers” are totally responsible for branch death, but finished them off when the trees became stressed.

What to do? 

Make sure at least half the area under the tree is getting watered. Plant other deep-rooted plants under the tree to deliver water to a wider area and to make sure. Make sure applications of water are to at least three feet deep. Use a four-foot-long piece of rebar after an irrigation is finished to judge how deep the water "wets" the soil. 

If increasing the water doesn't help, apply a soil drench of borer control insecticides to kill existing borers in the branches. Apply it in May after the tree finishes “flowering”.

Any soil drench containing imidacloprid in the active ingredients and for ornamental trees and shrubs will work and should be applied after the plant finishes flowering.