Issue: May 20th
Juniper branches turning brownQuestion:
My cedars are turning brown on one side. I just noticed this; it seems to have happened overnight. The branches that are turning brown also have a grayish covering on them. What is wrong and what can I do?Answer:
There are several things that can cause "junipers" to turn brown. You called them cedars, a commonly used name for our junipers, but from the picture you sent, they are junipers.
I have been observing this problem all over New Mexico as I have traveled doing programs. Your problem is spider mites, and it seems to be especially severe this year over much of New Mexico. I have seen it in the southern, eastern, and northern parts of our state.
Spider mites are small (almost microscopic) creatures that feed on the sap of many of our plants. There is a type of spider mite that really loves our junipers (often called cedars). As they draw the juices from the plants, the infested part of the plant turns brown. Their populations can build up very rapidly so the damage can seem to appear overnight.
The grayish coloration you mentioned and which shows in your photo is the webbing produced by these mites. Even though these pests are called spider mites, they are not spiders and their webbing is not like that of spiders. It doesn't spread across large areas, it isn't for trapping insects, and it certainly isn't pretty as are some of the orb weaver spider webs. It is just a web material coating the twigs. The mite webbing maintains a higher humidity in the mites' environment and protects the spider mites from predators. This webbing also catches dust and begins to look very dusty.
The fact that this year has been dry has been helpful to them. A good rain storm will wash them from the plants, preventing major damage. This year such rain storms have been very infrequent and the spider mites have had an excellent opportunity to build up damaging populations in our junipers.
Regarding the solution to your problem, you can try washing them out of the juniper with a strong stream of water from the garden hose. In other words, you can make your own rain storm. If you will do this several times a week for a while, you can probably solve the problem. However, the damage that has already been done may remain apparent. If there is sufficient damage to some of the branches, they may die, even if the mites are eliminated. Other branches may be damaged enough that the evidence of the mite attack will remain until sufficient growth occurs to cover the areas that were damaged.
If you don't trust the water to do the job adequately or if you have tried washing the mites from the plants without success, you may wish to try a miticide. Mites are not insects and many insecticides are not effective in controlling them. In fact, some insecticides may increase the problem. Look for a product labeled to control mites and follow the directions on the label.
Many other plants are also subject to spider mite attack, so be watching other plants in the landscape for evidence of the mites. Look for the webbing and look for stippling and discoloration of the foliage as evidence of the mites' presence. If you detect the problem early, you can prevent most of the damage that they cause, and you can use the less environmentally impacting water treatment to solve the problem.Top of page
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: firstname.lastname@example.org, office: 505-865-7340, ext. 113.
Please copy your County Extension Agent and indicate your county of residence when you submit your question!