Pecan Nut Weevil and Crop Thinning
One of the biggest pests for pecans is the pecan nut weevil. If you’ve ever been disappointed to find empty nuts on the ground with a small hole pierced in the shell, you know what kind of damage they can cause. Mid to late July is the time of year this pest usually shows up, typically just after a heavy rain.
Spraying a mature tree for this pest is not practical for most homeowners. Soil applied products just don’t work well for this pest. Fortunately, the behavior of the weevil allows us to use a simple option to help control the population. Adult weevils crawl up the tree trunk to feed. You can successfully capture a good percentage of these insects as they begin their climb if you install circular weevil traps on the trunk. While capturing some of these insects will not eliminate nut damage, it will reduce it significantly. Even if you do have the equipment or resources to spray the entire tree, the traps can help you get a better idea of numbers to help determine if spraying is warranted. Just because weevils are bad one year doesn’t mean that will be the case the following year.
For more information on the pecan nut weevil including building your own traps, see OSU Fact Sheet #EPP-7079 Biology and Control of the Pecan Weevil (PDF / Mobile) . The Botanic Garden at OSU has a nice example of a weevil trap. On your next visit, look for the chicken coop and you’ll find the weevil trap close by, easily accessible for close inspection.
Another helpful tip for insuring a good crop, and one that might seem counterproductive until you’ve seen the results it can yield, is to thin the pecans. A tree can only put so much energy into producing a crop. In years like this when we have high numbers of immature nuts, this means it is unlikely they will fully size and mature. Removing some of the excess now is a good way to do this.
If you are seeing large numbers of clusters with 5-6 nuts a cluster, thinning will likely be helpful. Commercial growers can simply give their trees a short shake but obviously that is not an option for the homeowner. You can thin the crop using a frailing pole. These long bamboo poles are often used as a harvest aid but they will work for thinning as well. If you don’t own (or can’t locate) a bamboo pole, a long piece of pvc pipe works fairly well for this purpose.
Thinning is not an exact science so it’s hard to know just how many to remove. I suggest starting with about 25% of the nuts you are able to reach. Two notes of caution: pecan trees are notorious for dropping limbs-take care that you don’t dislodge a large limb and hurt yourself. And two, be wary of any overhead electrical lines in the area.
If you thin, try to keep notes on your efforts. Come harvest time, this might help you to better determine if your efforts were worthwhile.
For more information on this or any other horticultural topic, you can contact Keith Reed, the Horticulturist in the Payne County Extension office. Keith can be reached via email at firstname.lastname@example.org, phone at 405-747-8320, or in person at the Payne County Extension office, located at 315 W. 6th in Stillwater.
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