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Milberger's Nursery and Landscaping
3920 North Loop 1604 E.
San Antonio, TX 78247

Three exits east of 281, inside of 1604
Next to the Diamond Shamrock station
Please click map for more detailed map and driving directions.

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Questions for the Week

by Jerry Parsons, Ph.D.
Horticulture Specialist, Texas Agricultural Extension Service in San Antonio

The pecan nut casebearer is the number one insect threat to pecan production in Texas. This nut feeder can account for significant crop losses over many years on unsprayed trees. With proper timing of a labeled insecticide, economic losses can be minimized for commerical pecan producers. For homeowners, spraying may be too expensive and, luckily, unnecessary.

In some seasons when pecan production is expected to be heavy, the nut damage and consequent nut abortion caused by the casebearer is beneficial to avoid over-production. Too many pecans on a tree can cause limb breakage and poor quality nut production. Pecan trees are alternate-bearing which means the trees produce a heavy crop one year followed by a light-to-non-existent crop the next year. During what is expected to be a heavy crop year is when you need the casebearer's "help" to thin the crop to prevent tree damage and improve the nut quality.

Normally, this insect is found damaging nuts within a two week period in May. This two-week time frame will normally occur around the first week of May in South Texas, the second week of May in San Antonio and South Central Texas, and the third week in May in the Hill Country.

If you want to attempt to control this insect, the timing of the insecticide application so crucial to effective casebearer control is signaled by the appearance of hatched eggs. Insecticides currently labeled for the casebearer do not kill the eggs. They only kill larvae that feed on treated leaves, buds and nuts. An insecticide applied before larvae hatch will not work unless the residual lasts until the larvae finally hatch. Since the larvae hatch over a week-long period or more, a second application is recommended 7 days after the first.

To determine when to spray, inspect pecan clusters for casebearer eggs. Casebearer eggs will be located on the puffed end of the young pecan nutlet. The egg will resemble a small grain of sand.

Tag clusters that have eggs. Return to those eggs daily until the first egg hatches. Once the egg is laid, it will gradually turn from white to red in a three to five day period before it hatches.

After hatching, the larva feeds on developing buds and shoots for two to three days before entering a nut. Apply your insecticide so that you have coverage on your trees by the third day after the first egg hatching. By using this method of timing, you will obtain the full residual effect of your insecticide treatment.

A variety of pesticides can be legally used on the pecan nut casebearer. Among those recommended are Sevin and Malathion. Sevin and Malathion are familiar vegetable garden insecticides and are effective controls for the pecan casebearer if timely applications are made.

When spraying to control this damaging pest, be sure to add zinc and the fungicide benomyl (systemic fungicide) to the mixture. This will prevent leaf rosette and fungus scab damage. Zinc must be applied as a spray on foliage to be effective, since zinc soil applications are quickly rendered unavailable for plant uptake in alkaline soils. The wet-able powder zinc sulfate or a liquid formulation can be used. Zinc sulfate sprays should not be applied close to peach or plum trees since defoliation can occur. If peach or plum trees are growing near pecan trees, a liquid formulation of zinc must be used and will not cause any defoliation if mixed according to label instructions.

Insecticide and fungicide can be mixed in the same spray. If zinc sulfate is used, it is better to mix and spray the zinc source in a separate application.