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January 11, 2014

1 - Twig girdler beetles and other insects may be observed in New Mexico conifers as a result of the very dry conditions early last year

Yard and Garden January 11, 2014

Q.

I have 2 Leland Cypress trees; they are approximately 7 years old. They are shedding only the tips of their branches. The tips have broken off and lie on the ground around the trees. I took a few to a local nursery and they could find nothing wrong - no bugs or anything that appeared to be the cause. I hope you can shed some light on this. And if there is something I can do to prevent this I would like to know. This is the first year this had happened.

-Patricia McE.

Via University-Wide Extension

A.

What you have described sounds like your tree may be infested with twig girdler beetles. These are very small beetles whose larvae feed on the critical phloem and cambium layers just below the bark. In the case of the twig girdler, they usually feed in a tunnel just under the bark and in a circle around twigs. The result is the death of the ends of the twigs. These dead twigs often turn brown or dull green and then "flag". Flagging describes the tips that partially break and hang downward from the ends of the rest of the twig looking like flags. In time as a result of snow and ice accumulation, or wind, they finish breaking free from the twig and fall to the ground. The dry weather earlier in 2013 may have stressed to the trees making them attractive to beetles. Under stress conditions many trees produce chemicals that attract insects whose natural job is to remove stressed or dying trees from the environment, making room for new trees. In the natural environment, that is a good thing, but in our landscapes it is usually not appreciated by gardeners.

There are some other insects, cypress bark beetles and cypress scale insects that may also be involved. They are also attracted to trees that have been stressed. The twig girdlers may be diagnosed by looking at the twigs where the “flags” broke free or where they are still hanging on the tree. Look for a band of damaged tissue and slight narrowing of the twig at the point of separation. You will probably not find insects at this time. The broken tips that have fallen will also not reveal insects.

If the cypress trees are affected by cypress bark beetle or cypress scale insects there will be larger portions of the tree and larger branches affected and turning brown. You may find some signs of tunneling under the bark (check this in any branches that begin dying) if the problem is caused by bark beetles. Scale insects will show up as a whitish, cottony accumulation under bark plates or in cracks and crevices in the branches. What you have described sounds like the twig girdler, but look for signs of other problems as well. Even twig girdler beetles can cause problems for larger branches and may even kill whole trees if their populations are great enough. There are insecticides labeled for managing these insects, be sure to read product labels for chemicals to confirm that they will control these pests. However, first confirm the diagnosis by contacting your local NMSU Extension Service office. They can also direct you to the products currently recommended for controlling the insects that they have positively identified.

Cultural practices to help avoid these problems in the future include proper irrigation in extremely dry times such as we experienced last winter. Your NMSU Extension agent can also provide information regarding proper placement of irrigation water and irrigation frequencies.

For more gardening information, visit the NMSU Extension publications Web site at http://aces.nmsu.edu/pubs/_h, or to read past articles of Yard and Garden go to http://aces.nmsu.edu/pubs/periodicals.html

Send your gardening questions to:

Yard and Garden, Attn: Dr. Curtis Smith
NMSU Agricultural Science Center
1036 Miller Rd.
SW, Los Lunas, NM 87031.

Curtis W. Smith, Ph.D., is an Extension Horticulture Specialist emeritus with New Mexico State University's Cooperative Extension Service. NMSU and the U.S. Department of Agriculture cooperating