Horticulture: September 1999 Other Horticulture Articles

There currently is great potential for a good pecan crop in most orchards in the Ardmore area, but a huge threat exists: the pecan weevil. Oklahoma - grown pecans have a reputation for good - quality nut meats, but also are known for containing larvae of the pecan weevil. The weevils have been so bad at times that the pecans from this area were severely discounted until there was not even a price offer for them.

Now is the time to protect your pecan crop from possible destruction by the pecan weevil. The first step is to identify a way to apply insecticide to control the weevil when or if a significant population exists. The sprayer most commonly used is a mist blower, while a handgun sprayer is acceptable for small acreage. Aerial application is a compromise, with a helicopter slightly preferred. Any of these technique is much better than allowing the pest to destroy the crop.

The next step is scouting to estimate the weevil population. One of the most effective techniques is trapping the adult weevil. Several traps are effective, but research shows that the Circle Trap catches the most weevils. The photograph at right shows the trap attached to the side of a pecan tree trunk. As the weevils crawl up the tree trunk, they are guided into the capture container for your observation.

The pyramid trap is accepted as the reference trap. It offers a more predictable outcome because of classic research performed on the trapping technique. In grazing systems, it is vulnerable to livestock since it is located on the soil surface; the Circle Trap has the advantage of being placed higher on the tree trunk.

Another scouting technique is to spray a tree in question and see what falls out onto a tarp located on the ground. Mix enough Sevin insecticide at the correct concentration to treat the tree or trees in question and then apply it. The weevils in the tree will fall to the ground within one hour of treatment. This technique is often used to verify trap catches because of its effectiveness.

As a last resort, shaking lower limbs of pecan trees by hand over a pickup bed can give some idea of whether the weevils are present. Also, looking at the nuts themselves can provide an indication of weevil activity. When the weevil bores a hole into a developing nut that is still in liquid or gel stage, the nut will abort and can be found on the ground within three days of being punctured. Weevil damage as represented by the nuts on the ground can be distinguished easily from other damage by the "tobacco stains" that developed from the fluids that ran out of the puncture hole.

After the meats solidify, the nuts remain on the tree and the weevil's tracks are visible around the drill hole. The point of entry is displayed in the photograph on page 2. The tracks can make the entry look much like a bull's - eye on a target. If you begin finding entries, it is often too late: there are usually eggs or maybe even larvae inside those nuts.

The preferred insecticide for adult weevil control is Sevin 80S. Refer to the label for the correct dosages and usage. The adult weevil is very sensitive to Sevin and will die quickly after coming into contact with a lethal dosage. The pesticide has a ten - day to two - week residual to keep the weevil in check. When the protection period has passed, scouting must begin because a second and, with very bad infestations, third application may be necessary to control the weevil.

The weevil is a threat from mid-July through early October. The weevil larva enters the soil where it pupates and remains two and sometimes three years. Some soils prevent the escape of the adult weevil until rainfall softens the soil. Dry periods can group the weevil concentrations for more specific control periods.

Timing of insecticide applications for the control of pecan weevil is site specific. For excellent control, orchards must be scouted individually; a neighbor's information may be useless. Neighboring orchards may have had rainfall yours did not have and may have a larger or smaller pest population because of past management. So watch each orchard specifically for proper weevil control.

For further information on trapping weevils and their control, obtain OSU Fact Sheet f-7190 or visit the Pecan Production web site: http://www.hortla.okstate.edu/pecan.

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