Like the four horsemen of the apocalypse, four pests of our native pinyon trees are on the move. Three beetles and a moth have launched their attack on our pinyon trees in the Delta County and surrounding area. These include the pinyon tip moth, pinyon ips beetle, mountain pine beetle and the pinyon twig beetle. While always around, only sometimes do they cause serious problems, at least to the trees they infest.
Now I know that the four horsemen reference comes straight out of Revelations, the last book of the Bible. But if your trees are the target of one of these pests, then you know how serious they can be, even causing death to trees that may be approaching 1,000 years old.
I personally have a pinyon tip moth infestation, which I wrote about in my June 19 column. I think I have gained the upper hand on this pest but I did suffer much twig terminal damage before control was achieved. But new growth is and will compensate. PTM larval feeding girdles the terminal causing the observed dieback. Rarely do PTM infestations kill a tree. They overwinter as young larva and begin feeding mid- to late-May. Moths fly primarily from late June through August. If you have this pest, I would spray with a pyrethroid insecticide mid-May and again in early July.
The next pest is the pinyon ips beetle. Its damage is characterized by reddish boring dust in bark crevices and at the base of the tree. They can have pitch tubes like the mountain pine beetle but are significantly shorter. Their extensive feeding galleries beneath the bark cause girdling and death of small to large branches, even whole trees. There are two to four generations a year. The goal is to cover the woody parts of the tree with a pyrethroid insecticide so that when the adult beetle starts boring in, it dies. If this is your pest, then I would spray in April and again in June and September. These are preventative sprays.
The second beetle pest is the pinyon twig beetle, one of the representatives of the bark beetle group. By tunneling under the bark of small limbs and twigs, their girdling kills the infested wood. Like the PTM, the PTB has two to four generations a year, but can kill the tree. Damage symptoms of the PTB can at times look like damage due to the PTM. April, June and September sprays with a pyrethroid insecticide should control this pest.
The fourth and final pest is the mountain pine beetle. It rarely attacks pinyons but when it does it can be devastating. This bark beetle usually becomes a problem when conditions are just right and then develops into an epizootic, a fancy word for an outbreak. Old age of a tree and stress such as drought conditions are key factors, but once an epizootic gets moving, even healthy trees are attacked. Outbreaks usually happen no more often than every one to three decades. Evidence of an infestation of the MPB are the reddish pitch tubes, up to one-half inch high at each entry point. These will be found on the largest branches and tree trunk. There is one generation per year, with larvae overwintering beneath the bark. Adult emergence occurs as early as the first part of July through September. Pyrethroid insecticide sprays such as those containing permethrin or bifenthrin, should be applied in late June as a preventative application.
So there you have it. Four pests that differ somewhat as to their attack and damage symptomology, but all able to inflict some pretty extensive damage, even death, to our long lived native pinyon trees. Even though we had great winter and spring moisture seasons, our pinyon trees are still affected by drought stress. I water my trees every 75 days and they are doing quite well. Any step you can take to prevent or relieve stress on a tree is a good step in avoiding bark beetle problems. Also, any infested dead branches or whole trees should be removed from your property.
Jim Leser retired to Cedaredge after a career with Texas A&M University Extension in entomology. He is a member of the Cedaredge Tree Board and a Colorado Master Gardener.