Pecan Pests

— Written By and last updated by Sue Nichols

Pecan trees are common in eastern North Carolina. One of the most devastating insects on pecans is the pecan weevil. Pecan weevils damage nuts in two ways. First, they feed on the young nuts in late summer, causing some to drop early still in their husks and never complete development. Second, they lay their eggs inside the pecans still on the tree. Within a few days cream-colored grubs hatch from these eggs and begin feeding on the nut. By the time the pecan drops to the ground, the grub has eaten most of the nut. Then they drill a small hole in the top of shell and crawl out. If you have ever picked up pecans that had a hole in the top of the shell and were empty, or found grubs inside pecans when you cracked them open, then you have experienced pecan weevils. Though their damage will not become evident until later in the year, now is the time to control this pest.
The life cycle of the pecan weevil has four stages. Pupae develop underground. They remain in the soil for one to two years. Adult weevils emerge from the soil from August through September, usually coming out after a significant rain. The female chews holes into the nut and then lays her eggs. The larvae hatch and feed on the nut. After reaching maturity the larvae leave the nut falling to the ground where they burrow into the soil to pupate and emerge as an adult the next August. It is a continuous cycle with one generation taking one to three years.
If you have a pecan tree whose nuts have been damaged by pecan weevil in the past two years it is most likely your tree will be damaged again this year. So you need to take control measures. Pecan weevils can be controlled by spraying liquid applications of carbaryl (commonly sold as Sevin) on the ground underneath trees out to the drip line, as well as up the trunks of pecan trees as far as you can reach, beginning in mid August and continuing every seven days through mid to late September. Dust forms of Sevin (carbaryl) are not as effective as liquid sprays for controlling pecan weevil.
This control method will greatly reduce the number of nuts lost to pecan weevil. To minimize the number of sprays needed, pecan tree owners can monitor weevil populations by tying burlap cloth around the trunks of pecan trees in layers. Check the burlap each day for weevils and begin spraying when they are found. Pecan weevils are a type of beetle. The adults are brown in color and less than ½” long, with a long, narrow, curved snout protruding from the front of their body. Stop spraying when weevils are no longer being found on a regular basis. Later in the season, when mature nuts begin to fall, pick up pecans daily and discard infested nuts away from the tree to lower future weevil populations.
You can also use Tanglefoot a sticky substance painted on the base of the tree to monitor and trap some beetles. As with all insecticides, follow the label recommendations.
Pecan scab is another common and severe pecan problem in our area. This fungal disease causes leaves and shucks to become covered in black spots. Severely infested shucks will not properly release pecan nuts. Tree’s whose leaves are covered in spots often have poorly filled out nuts. Treating for scab is not practical for most homeowners and requires several fungicide applications starting in early summer. Fungicides must be sprayed throughout the tree, which requires special equipment. Overall, there is little homeowners can do to reduce scab disease in established pecan trees. When planting new trees, always select varieties resistant to scab, such as Cape Fear, Sumner, or Elliot.
Other common pecan problems include poor pollination, biennial bearing (bearing a heavy crop one year and little to no crop the next year), and stink bug damage, which causes dark bitter spots to develop on the nuts. Fall webworms also commonly feed on pecan trees, forming large tent like webs on the ends of branches. Webworms typically are a cosmetic issue on larger trees. On small trees you can prune or knock the web out.
Pecans can be a rewarding growing experience if you manage them properly. For more information call the Extension Master Gardeners Monday, Wednesday, or Friday from 1-3 p.m., 252-237-0113 or email any time at wilsonemgv@hotmail.com.