Issue: July 27th, 1998

Sudden peach tree death

My peach tree suddenly died. It bloomed beautifully this spring, there were a lot of peaches forming, but now the peaches are all shriveled and the leaves have turned crisp. The leaves are green but crumble when you touch them. What happened? I didn't use any herbicide or fertilizer.

t is likely that your peach tree has been killed by peach tree borers. This is the greatest pest of peaches, cherries, plums, and other stone fruits in New Mexico. This borer is the caterpillar of a moth that looks a lot like a black wasp. So if you see a black wasp-like creature with one or more yellow stripes or bands around its abdomen flying around your stone fruit trees, anticipate problems. However, even if you don't see them, if you live in New Mexico (or many other parts of the U.S.) you can expect to have this pest cause problems at some time.

The female moth has a single, broad orange band while the male has narrow bands. Both are dark blue with clear wings. Their larvae are small, yellowish to whitish borers which feed on the cambium layer of tissue just beneath the bark of the trees.

Evidence of peach tree borer infestation is an accumulation of gummy sap and sawdust at the base of the tree. These moths attack at ground level, or just below or above ground level. Initially, sap exudes from the tree at the point of infestation. This sap gels into a gummy mass, then later hardens. Boring dust, large sawdust, produced by the borer and frass are often mixed with the sap. There may be a foul odor as the sugar in the sap begins to ferment.

The borers work around the tree near the soil level, in time girdling the tree. When the tree is girdled, the food produced in the leaves is cut off from the roots. The roots starve, then when the roots die, no water is available to the top of the tree which appears to die suddenly. In actuality, the tree has been slowly dying as the roots slowly starved.

In some cases, the borer may not completely girdle the tree but may cause damage to the bark and cambium in a portion of the trunk. In such a case, with only one or a few borers active in the trunk, the top of the tree may die in sections, one branch at a time. A zone of dead bark will be found at the base of the tree, but the tree will not be completely girdled.

Treatment for the peach tree borer has become more difficult as one of the more effective products, Paradichlorobenzene, is no longer available in New Mexico garden centers. Rather than this product which fumigated the base of the tree, killing the borers under the bark, now we must use one of the borer sprays labeled for use on peach trees to prevent borer infestation.

Transplant iris now

A friend has a lot of pretty irises and has offered some to me. Is it safe to transplant them now? She is moving and I must transplant them now. It is very hot, and I am afraid it is too hot to transplant them.

Late July and early August are the best times to transplant an iris. They are inactive now and can best handle the transplanting. In the fall they will grow new roots, and in the spring they will produce new leaves and flowers. They will do best if you transplant them now.

Before moving the irises, prepare the planting site by working the soil well. Add a moderate amount of compost or other organic matter to the soil. Be sure to incorporate a source of phosphate into the soil. This may be super phosphate or colloidal phosphate. In our calcareous soils, bone meal is not an effective source of phosphorus for plants.

When you plant the irises, do not bury the rhizomes. Place them on the soil surface with soil covering only the bottom half of the rhizome. It is okay to trim the leaves at this time.

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!