Issue: August 23, 1999

Juniper insects killing twigs

There are a lot of branches dying on my pine trees. It is not the whole branch that dies, but only the six inches or so at the end. What can I do to solve this?

The sample you sent was of juniper, not pine. I am aware that many people call all evergreen conifers "pines", but in this case it is important to recognize the difference because different pests infest pines and junipers.

In your case the problem is either a beetle called the juniper girdler or a small caterpillar called the twig pruner.

A little information about your potential pests. According to Bob Cain, NMSU Extension Forest Entomologist, the twig girdler feeds in the phloem and cambium zone under the bark of the twig before moving to the pith in the center of the twig. The twig pruner goes directly into the pith and feeds there.

Bob states that these insects are more common in forested areas than in the urban landscape, but occasionally there will be problems in the home landscape. The management treatments recommended by Bob Cain are the same for both insects. He recommends that you remove the branch tips as they die. There is no effective chemical control recommended and the damage done is usually only cosmetic. The form and density of the juniper is not altered significantly by these insects.

Pinyon sawfly

The needles on my pinyon trees seem to be eaten. Most of the needles on several branches are totally gone, or eaten down to stubs. There are some little worm-like things that seem to be causing the problem. I have sprayed with Bacillus thuringensis because I don't like to use chemical insecticides.

Dr. Bob Cain, NMSU Extension Forest Entomologist, said that the pinyon sawfly is active now. It can occasional strip the all the needles from the tree, but more often only strips the needles from one or two branches. These larvae are the juvenile form of a sawfly, in the order Hymenoptera, the wasps, ants, and bees. The sawfly is not the larvae of a moth or butterfly, it is not in the order Lepidoptera, the moths and butterflies.

Bacillus thuriengensis (BT) is effective only against members of the Lepidoptera, so the Bacillus thuringensis is not effective agains sawflies. Since you prefer not to use chemical Bob recommends that you blast them out of the tree with a strong jet of water. Most of these insect larvae will not successfully return to the tree. Those that do succeed will be dispersed through the tree and the damage will be much less apparent. If you have ponderosa pines, Bob says that there may be some sawfly on them as well. The water jet method of sawfly management is the first line of defense against this pest for homeowners. If the infested trees are large or the infestation is more extensive, some may wish to use chemical insecticides. In this case, contact your local Cooperative Extension Service Office for recommendations of appropriate chemical controls.