Weevils Gobble, Then They’ll Likely Fall Down
Q: What can I do now to reduce pecan weevil problems this fall?
A: Many people run into a problem in the fall when harvesting pecans of discovering a white worm inside a pecan shell. The pecan weevil is common pest problem on pecan trees. By the time most people discovered the problem it is too late to control. The pecan weevil is a pest to start controlling in August and September to prevent discovering problems later this year.
The pecan weevil causes two types of damage. The first type is when the adult weevils puncture the nuts in early August, causing the nuts to fall after two or three days. The adult pecan weevils are reddish-brown to gray beetles with long slender snouts and thin legs. The second type of damage is caused by larval feeding within the nut. The larva chews a circular hole through the shell, and, as nuts fall to the ground, it exits the nut, and burrows into the soil. Larvae are creamy white, legless grubs with reddish brown heads.
Understanding the life cycle of the pecan weevil helps explain why the weevils cause two types of damage. The adult weevils emerge from the soil from August through September. Often times they emerge from the soil when we have a significant rainfall of an inch or more. The majority of weevils fly to the tree trunk or tree canopy while a small number walk. After the female adult weevils puncture the nut in early August, the eggs are laid inside the developing pecan. At maturity the larvae exit the nut and burrow into the soil. They remain in the soil until the following August where they then pupate and emerge as adults. Then the cycle begins again with the adult weevils puncturing the pecan nuts.
Now that we know how those white larvae get into the pecan, the next questions is how to manage the pecan weevil. Because the adult weevils are emerging from the ground during August in search of pecans to puncture, this is the time you want to control them. You want to control the adult weevils as they are emerging from the ground because they can not be reached once they are in the nut or while their in the soil. The weevil’s emergence from the soil is during a two-month period of August to September, so monitoring for when the adults emerge from the soil is important. A simple way to monitor is by inspecting nuts that have dropped to the ground for puncture holes. Also keep in mind that the weevils usually emerge from the soil after a rainfall. A dry or hard soil provides a physical barrier to the adult weevils, delaying their emergence from the soil.
There are many traps available for monitoring the pecan weevil varying in cost and in the amount of labor required to set up. A homeowner can avoid the cost of a trap by wrapping burlap around the pecan tree three to four feet above the soil and tying it in place at the bottom. The remaining burlap is overlapped and then tied at the top. This causes the weevils to walk over each flap thus delaying their trip up the tree and allowing time for grower observation. If you did choose this monitoring method, you want to set it up just before August and monitor it daily for weevils to indicate when to start spraying. As you monitor for the weevils you can go ahead and destroy the weevils you do find on the burlap to provide some control. One downfall to using this monitoring method is that you only know how many are walking up the tree and since most fly to the tree, you may not be getting an accurate idea of when the adult weevils are moving to the tree.
If you decide to use insecticide to control the pecan weevil, applications should be made every 7 days from mid-August through mid-September using a carbaryl (Sevin) insecticide. If you want to try avoiding using insecticides or want additional control along with the insecticide, a good control method is to gather and destroy weevil-infested nuts as they fall to prevent the larvae from entering in the ground and hanging around until next growing season.
August through September is the time to be on the outlook for the pecan weevil. With an understanding of the pecan weevil’s life cycle and knowing when to watch for weevils emerging from the ground you may prevent the disappointment of cracking open pecan shells and finding a little worm enjoying your pecans instead of you.
For your gardening, landscape, and lawn questions contact the Wayne County Extension Master Gardener Volunteer Plant Clinic on Mondays and Wednesdays from 10 am to 1pm. The plant clinic is a free service open to any citizen in Wayne County that has home gardening questions. One can reach the Wayne County Extension Master Gardener Volunteer Plant Clinic by phone at 919-731-1433, e-mail at Master.Gardener@waynegov.com, or stopping by Room 100 of the Wayne County Extension Office (208 West Chestnut Street, Goldsboro). People contacting the plant clinic with questions are encouraged to bring samples and/or pictures that could help in reaching a solution. Extension Master Gardeners are trained volunteers with the Wayne County N.C. Cooperative Extension Service.
Recommendations for the use of chemicals are included in this article as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services does not imply endorsement by the North Carolina Cooperative Extension Service nor discriminated against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical. For assistance, contact an agent from North Carolina Cooperative Extension Service.
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North Carolina Cooperative Extension
Wayne County Center
P. O. Box 68
Goldsboro, NC 27533