Issue: May 22, 2004

Locust trees dying

I have four Purple Robe locust trees in my yard. Two of them are doing just fine. As of the date of this question, one has not produced any leaves this year. It is four years old and has been fine until this year. The other one is also four years old, and it has sparse leaves on only one side of the tree. I was wondering if you had any advice or knew of any reason why this would be happening. Both trees are flexible and are green inside but are just not blooming at all.

Daren C.

Farmington, NM

I am getting similar questions from all parts of New Mexico. In most cases, the problem can be traced back to improper irrigation during the drought. In some cases, there was no irrigation supplied to the trees. In other cases, the trees were watered but in a manner that did not benefit the tree. Changes to our landscapes, conversion from traditional lawns and water intensive landscapes, have also had a negative impact on trees.

There may also be borer insects involved, but these are often a secondary problem. Many types of borers are attracted to trees that are under stress. Drought stress is one such stress and may be responsible for borer damage in many trees. One of our county agents reported to me that he was receiving samples of locust borers. Any wood damaged by borers may need to be pruned out, but first check for life in the branches as described below.

While it is possible that at least one of two affected trees may survive, the other may not survive. Look for supple twigs that have a bright green cambium layer under the bark. If the twigs retain a viable cambium layer, the tree may recover totally if properly irrigated (see below). If the twigs are dead but there is healthy cambium, the may be new growth from the branches. You will need to prune off any dead wood. Prune dead wood in the summer after the new growth has developed and revealed the dead tissue. If there is so much dieback that the tree will not look good, you may prefer to remove the tree.

Proper irrigation is important to protect the remaining trees. When a tree is newly planted, it is necessary to apply water at the base of the tree because the roots are in the planting hole. As the tree grows, roots extend outward and irrigation must move outward with the root extension. Once the tree is established, the roots that absorb water are located in the soil below the farthest extent of the tree's branches (the dripline) and beyond the dripline. Watering at the base of the trunk is an inefficient use of water and of little benefit to an established tree.

If the soil around the tree is so compacted that water runs off rather than soaking in, you may need to aerate the soil. You can create channels that allow water to permeate the soil by carefully pushing a spading fork into moistened soil and pulling it back to "crack" the soil. If the spading fork encounters a root, remove it, move to the side, and start again. This should be done in a circle around the dripline of the tree and outward.

For more information about proper tree irrigation, contact your local Cooperative Extension Agent. For a new, colorful brochure, contact the Water Use and Conservation Bureau of the New Mexico Office of the State Engineer (1-800-WATER-NM, or www.ose.state.nm.us).

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.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!