Are the outsides of your pinyon pines turning brown? As a Master Gardener and member of the Cedaredge Tree Board I get the opportunity to make house visits for troubling plant problems.
One of the most vexing problems I am seeing is the "browning" of the terminal growth of pinyon trees and in some cases their death.
Pinyon pines are naturally drought-resistant, so when this tree species dies, I get very concerned. There are a lot of people in the Surface Creek area who live in the pinyon pine-juniper zone and still others who add pinyons to their landscape. This is an important issue to many of them.
There are several problems that can develop with pinyon pines. Biotic agents include pinyon twig beetles, Ips bark beetles, pinyon pitch mass borers and black stain root fungus. Since 2007, I have lived in the Cedaredge area and have not observed any problems with Ips bark beetles. I have, however, seen damage from twig beetles and have been monitoring them with a special trap since 2009.
While trap catches of twig beetles has been high this year, I have yet to find damaging infestations in pinyon trees that have brown branch terminals. For more information on these twig beetles go to http://wci.colostate.edu/Assets/pdf/TwigBeetle.pdf.
This leads me to two other factors that appear to be responsible for the "browning" of our pinyon pine trees. These abiotic or environmental factors include drought and winter desiccation. Some people have called this pinyon pine decline. But no matter what you call it, stricken trees can die slowly over several years. Affected trees have distinct symptoms that separate this problem from other problems commonly seen on pinyons. This environmental-related problem is not due to bark beetles, black stain root disease or other common problems. Environmental stresses such as winter drought followed by a hot summer may trigger the decline.
We have been experiencing drought conditions in western Colorado for a number of years which more than likely have stressed our native pinyon trees. Pinyon pines and junipers are the dominant tree species across much of western Colorado. They have long been known to be capable of withstanding one or two years of drought and have grown in many areas at moderate elevations. They are thought to have expanded their range over what has been a wetter-than-normal century.
Most of the problems I am observing with native pinyons are associated with older trees growing in shallow soils with associated poor water-holding capacity. In addition, large pinyon trees are known to have 2-6 times greater mortality than small pinyons. Since junipers are 6.5 times less likely to suffer drought mortality as compared to pinyons, our native pinyon–juniper woodlands could become more dominated by juniper, a species that is typical of lower elevations and more arid conditions. To see this outcome you only need to visit the Four Corners area or the west side of Interstate 25 between Walsenburg and Trinidad.
Piggybacked on the problems pinyons face from drought has been increased winter desiccation, a factor most prevalent this year in our area and the Grand Junction valley.
If the "browning" problem is limited to the outer part of your pinyon pines, this is probably mostly due to winter desiccation. Evergreens can lose considerable moisture on sunny winter days. If the soil doesn't contain enough moisture to replace the loss, needles — starting from the outside and moving inward — dry out and turn brown. In some cases the soil may be moist but the roots can't absorb it. The ground might be frozen or the roots damaged. To avoid winter desiccation, provide adequate moisture to the trees throughout the year, including during winter.
What our problem pinyon trees need right now is some tender loving care. I would provide additional watering to affected trees, but not too much and certainly not more than once per month to get them through this stressful period. If new growth is evident through the production of new "candles" then you should be alright. This advice holds true for trees you purposely planted in your landscape as well. Also, do not fertilize these problem trees. This will further stress them.
For more information on pinyon pine insects and diseases, go to: http://www.ext.colo
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 master gardener.blog comments powered by Disqus