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Question from Ryan Davis, Arthropod Diagnostician, Utah Plant Pest Diagnostic Lab -
There is a housing development to the south of Moab that is experiencing pinyon dieback. I suspect that the mortality is due to infestation from Ips confusus, but my guess is that drought stress is adding to this issue. What are your thoughts on reducing drought stress on pinyon pines to reduce their attractiveness to bark beetles? Would you have specific recommendations for irrigating pinyon pines (frequency, drip type, amount of water, etc.)? They want to keep their trees alive and I have given them many options to accomplish this, but I don't see insecticide applications to all trees every year as a good, sustainable solution. One aspect of an overall program would be to reduce drought stress on the pinyons.
Answer from Dr. Mike Kuhns, USU Extension Forester and Professor -
Ryan,
This exact thing happened all over central and southern Utah and throughout the Four Corners area about 15 years ago. If I had a few valuable pinyons I would consider spraying the trunks or soil applications of something appropriate (dinotefuran?) to ward off the beetles for awhile. But I also would irrigate in the hotter and drier part of the summer and maybe the fall as long as things stay abnormally dry. How much to irrigate is hard to say, but when they irrigate they should apply enough to have the water get down a foot deep or more. They can check how deep it is going by occasionally pushing a probe in in a non-rocky area. It will penetrate easily until it reaches dry soil.