Issue: January 26, 1998

Fruit tree pest control

When should I begin spraying my fruit trees, and what should I use?

This question is hard to answer because it gives too little information. What kind of fruit trees? What insect and disease problems have been a problem in the past? Don't apply products unless there is a problem to solve; you may create a real problem if you treat for a nonexistent problem. Is this an orchard or a few backyard trees?

I can safely assume from the address that this is a backyard "orchard" with a few trees. I will have to guess at the answers for the other questions. The fruit trees which have the greatest problems in New Mexico tend to be apples with codling moth or powdery mildew problems, cherry trees with peach tree borer or cherry fruit flies, or peaches and other stone fruits with peach tree borer problems. While there are other problems encountered in New Mexico, these are much more common than others. If you have different problems, be sure to contact your local Cooperative Extension Service office or Master Gardeners for assistance in diagnosing the problem. Many local nurseries may also be able to help.

Regarding apples, codling moth larvae are the worms in the apples. Use of a horticultural oil as a dormant spray now can help reduce the problem in the summer but will probably not eliminate the worms from the apples. A dormant spray will also help reduce other insect problems you will encounter in the summer. For homeowners, there are several products which must be used through the summer to prevent the worms in the apples. Some of these are organic insecticide materials, others are those called synthetic insecticides such as Diazinon(c) which has proven effective at codling moth control. Whichever product you choose, it may be necessary to reapply the product several times through the summer, some as often as every ten days to two weeks. Be sure to buy a product intended for use on the plants you have and intended for management of the problem you have identified. If powdery mildew is a problem, there are products labeled for use on apples which may be used if the problem is severe enough to require treatment.

Cherries don't get codling moths, but they are subject to fruit flies. Here in New Mexico the problem is the Western Cherry Fruit Fly. Not the kind of thing you want to find in a cherry after eating a handful without checking first. Actually, you can probably eat them without harm to yourself as long as you don't see them. Personally, however, once I have seen one, the cherries don't taste good any more. A dormant spray will not be helpful in solving this problem. Pesticides such as Malathion(c), Diazinon(c), or Sevin applied to the ground under the trees and to the leaves as the cherries approach full size can help. There are also some cultural techniques such as placing a sheet of clear plastic on the soil under the tree from the time the fruit begins to enlarge until after harvest. The reason for treating the soil with pesticides or plastic covering is that the fly pupae (cocoons) mature in the soil under the tree. They emerge from the soil as adult flies when the fruit is maturing. The female flies lay their eggs in the nearly ripe fruit where the maggots develop and destroy your appetite. Treating the soil under the tree will probably not be sufficient since you live in town with neighbors nearby whose trees are untreated. The adults can fly a considerable distance to get to your tree. Here in New Mexico the flies can receive quite an assist from the wind if it blows the correct direction. Again, choose your control products after carefully reading the label, then follow the label directions when using it.

The peach tree borer attacks all of our fruiting and ornamental stone fruit trees, those trees whose fruit have a pit such as cherries, almonds, apricots, and peaches. Their larvae borer into the tree at the ground level or just below the soil surface. If the tree is young or heavily infested, the borers can quickly kill the tree. Often they attack and weaken the tree, and subsequent attacks over the years result in the decline and death of the tree. The frustrating part is the tree will often die with a bumper crop of fruit shriveling on the tree. The chemical products for controlling peach tree borer are becoming less numerous. Dursban(c) is still labeled as a preventive spray to be applied at the base of the tree in late spring. It only prevents successful infestation by new peach tree borer larvae; it does not kill those already under the bark. Parasitic nematodes have proven to be a reasonably effective biological control measure with the benefit of "search and destroy" capabilities. These tiny round worms, if applied around the base of the tree, are able to travel a short distance in search of the borer larvae which they enter and kill.

In all cases, it is essential that you properly identify the pest problem and choose a management method appropriate for that problem on the specific crop you are treating. Then read and follow the directions on any product whether an organic pesticide or synthetic.

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!