Author: H. C. Ellis, Extension Entomologist
The adult is a small moth with a wingspread of 10 to 12 mm. Forewings are deep brownish-black, tinged with purple. Larvae are 7 to 10 mm long, creamy to dirty white with brown heads.
Before shell hardening, larvae tunnel into nuts, causing them to drop. Entrance holes can often be detected by a white stain around the hole. (Figure 14) After pecan shells harden, larvae tunnel in the shucks and prevent kernels from developing properly. (Figure 15) Heavily infested nuts are likely to be poorly filled and mature later than pest-free nuts. Injured portions of the shucks may stick to the nut shell interfering with processing and staining the shells.
Shuckworms overwinter as larvae in shucks on the ground or in trees. Moths may begin to appear in mid-February but most moths of the overwintering generation emerge in April. Small numbers of overwintering generation moths may continue to appear well into the summer. The spring emergence generally coincides with that of the nuts of native hickory, which set 2 - 3 weeks earlier than those of pecan. Only late emerging moths of the spring brood lay their eggs on pecan. Few pecan nuts become infested with shuckworms before June. The greatest amount of damage is done after the pecan shells harden, when populations have built up. Starting in June, populations increase rapidly with successive generations. There are 4 - 5 generations per year in southern Georgia.
When to Control
If blacklight traps (BLTS) are used for sampling, place at least two per orchard. Operate traps at least three nights per week and check after each night’s operation, beginning in early June. Apply shuckworm control when there is an increase in the number of shuckworm moths in BLT catches for three consecutive trapping periods and when the number of captured moths reaches seven (7) in any one BLT; or when four or more moths are caught in any BLT for three trapping periods. Pheromone traps for hickory shuckworm are also available. If pheromone traps are used, treat according to the guidelines provided with the traps.
If traps are not being used, treat based on past orchard history, experience, or schedule. If an orchard has a past history of high incidence of nut drop caused by hickory shuckworm prior to shell hardening, apply a shuckworm spray during June. Begin regular shuckworm sprays at 2 shell hardening (August 1-15) and repeat at two week intervals until shuck split if shuckworm activity continues. This is not necessary where pecan weevil sprays are being applied.