1 - Environmental stresses can make trees susceptible to insect attack.
Yard and Garden September 7, 2013
Q.
Trees are dying everywhere. The canyons are brown and you can see pinon pines that are dying everywhere. Most are toast and the bark beetles have them. However, I am seeing lots of pinon pines and even more junipers dying in yards, planted windbreaks, etc. I try to tell folks that this was not an overnight thing and a quick fix. The last 5 - 7 years have been devastating to trees if you are not a "meticulous" tree care taker and supply lots of water in summer and winter both. I do not see beetle or borers holes, I do not see scale, but recently the junipers have started to get brown spots and they expand from outside in and eventfully the whole trees is brown and dies. I have researched the "wall borer" and some have dug up some trees and found borers in the roots. As I understand, you cannot tell if you have them unless you see the roots and imidacloprid is the systemic of choice to deal with them. I also see junipers dying from the ground up. The bottom half is grey dead already and the top half is gradually dying. That seems like lack of water to me. Can you expand on pinions and junipers and what you are seeing and what if anything can be done to some that are not toast yet?
From an NMSU County Extension Agent
A.
This county agent and others around the state are diagnosing numerous tree problems. As stated above, the past several years have been imposing stress on trees. The winter of 2011, the prolonged deficit in precipitation, and in many cases, improper irrigation, have stressed trees to the point that they are dying. These stresses have increased the susceptibility of trees to insects, hence the agent's discussion of borers and bark beetles. The ultimate cause of the problem is environmental stress. However, to answer the insect questions, Dr. Carol Sutherland, NMSU Extension Entomology Specialist, has provided information in response to this question. After discussing the impact of drought and the winter of 2011 in weakening trees, Dr. Sutherland stated, "For junipers in your area, there are mites, aphids, foliage-feeding beetles, leaf-tiers, leaf-miners, twig and bark beetles, flat-headed wood borers, carpenter ants and sawflies; the beetles, probably from several families and genera, are quick to take advantage of any kind of juniper and just about any size tree. For pinon pines, there are all of the above (but different genera and species) PLUS thrips, cone and seed beetles, borers and moths, foliage-feeding caterpillars, gall-formers, scales, webworms, cicadas, pitch-nodule moths, round-headed borers and powder-post beetles. The beetles again are key pests. For bark beetles, they also introduce blue stain fungus and brown stain fungi which will kill the tree if the beetles do not." Dr. Sutherland goes on to say, "As for junipers with yellow patches of foliage, I would bet Phloesinus bark beetles are at work there. Some species act as twig beetles and others attack the trunk. These are the primary bark beetles that attack juniper, and they can kill, especially when drought, old freeze damage, poor / thin soil, slope and orientation to the prevailing winds and sun are added in. If the bark is girdled externally or internally or both by bark beetles, water, minerals, and sugars cannot move throughout the tree. This kills the tree. With these beetles, their small size, 2 - 3 mm, makes for very small holes in the rough juniper bark. These holes are often difficult to see." Dr. Sutherland also identified another potential insect causing problems, "The genus Prionus, a cerambycid, or long-horned beetle, has really chunky, legless larva. Prionus larvae tend to mine the very base and large roots of a tree. Their life cycles can take 3 - 5 years according to one source. They are not that picky about hosts and will mine in conifers as well as broadleaf trees. Adults are rusty red to almost black, 2.5 - 3 inches long with stout chewing jaws, long antennae." These and other insect problems are often results of environmental stress. Whenever possible, gardeners should minimize stress by irrigation. In the case of extreme winter cold, or summer heat, proper irrigation may minimize the damage. However, there will always be insects ready to exploit any weakened trees and tree removal and replacement will be necessary.
Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.
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