Why Are There Holes in My Pecans?
Many people had problems last season when harvesting pecans and discovering white larvae inside instead of a pecan. The pecan weevil was a common pest problem late last season. By the time most people discovered the problem it was 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. Larval feeding within the nut causes the second type of damage. 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. 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 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 question is how to control the pecan weevil. Because the adult weevils are emerging from the ground during August in search of pecans to puncture, that is the time when you want to control them. You want to control the adult weevils as they are emerging from the ground because they cannot be reached once they are in the nut or while they’re 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. 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. Several techniques can be used to monitor for when the adults emerge from the soil. A simple way to monitor is inspecting nuts that have dropped to the ground for puncture holes.
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 an insecticide that contains the active ingredient carbaryl. If you want to try to avoid 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 lookout for the pecan weevil. With an understanding of the pecan weevil’s life cycle and knowing when to watch for the weevils emerging from the ground you may prevent the disappointment of opening pecan shells during harvest just to find those white worms enjoying your pecans instead of you.
Reminder: A growing program this year is the “Sampson County Friends of Horticulture”. This program offers monthly “How To” Horticultural Seminars. Please call (910) 592-7161 for more information. Please call the Sampson County Cooperative Extension Center at (910) 592-7161 with your horticultural questions and to register for any upcoming events. Be sure to check out the Ask An Expert Widget at sampson.ces.ncsu.edu for any questions you may have.