Extension Agent: Shuckworms on pecans

Aug. 17, 2010 at 3:17 a.m.

Hickory shuckworm infestation in a pecan can cause poor kernel quality because the worms destroy the network of nutrient-carrying capillaries in the shuck.

Hickory shuckworm infestation in a pecan can cause poor kernel quality because the worms destroy the network of nutrient-carrying capillaries in the shuck.

By Joe Janak The hickory shuckworm is an important mid- to late-season pest of pecans. Shuckworms are tiny - to -inch larvae, which tunnel in the shuck, interrupting the flow of nutrients and water needed for normal kernel development. Infested nuts are scarred, late in maturing and of poor quality. Damaged shucks stick to the pecan shell and fail to open, creating "sticktights" that reduce harvesting efficiency.

Biology: The seldom seen shuckworm moths are dark brown to grayish-black and about -inch long. They are active in spring before pecan nuts are available, but now, when pecan nuts are present, deposit eggs singly on the nuts. The egg is attached to the shuck with a creamy, white substance visible on the shuck surface. The tiny larva hatches in a few days and burrows into the shuck to feed for about 15 to 20 days.

Spraying before shuck penetration is important for control. Mature larvae are about -inch long, and cream colored with light brown heads. Pupation occurs in the shuck, and the moth soon emerges. Several generations are completed each year. Shuckworms overwinter as full-grown larvae in old pecan shucks on the tree or the orchard floor.

Control: Pecans are most susceptible to hickory shuckworm damage during the water through gel stages of the nut. If your pecan trees have a history of shuckworm damage, treat with an insecticide when pecans reach the half-shell hardening stage. The half-shell hardening stage is described when the nut shell, which matures from the tip toward the base, is hard half way to the base of the pecan. This is tested with a knife slicing across the nut. Hardening usually occurs about Aug. 10-18 each year and many nuts are at this stage now. If you are a bit late and you had shuckworm problems in the past, the recommendation is to spray the nuts as soon as possible, which will catch later arriving moths. A second application 10-14 days later may be needed.

A number of insecticides are labeled with research showing the best control with Intrepid and Confirm for commercial use and Spinosid, Malathion and Sevin for homeowners, but the latter one may cause aphid population increases. Removing and destroying old shucks and dropped nuts, where shuckworms overwinter, can reduce shuckworm infestations for next year.


We get many calls about "my pecan is dying," and in some cases, it is true. Callers note that their pecan trees are shedding bark and dying. Most cases of this are simply the natural process of trees growing and shedding bark. As a tree grows, the trunk circumference gets larger while the existing bark, which is dead tissue and doesn't grow, stays the same size. So many people see cracks between the bark and this is then followed by the bark sloughing off the tree - a normal process. This makes room for new bark, which has a rusty-colored appearance, directly under the old bark. If the bark really sloughs off all the way to the wood, the wood would be a cream colored, hard wood, similar to pine lumber. This almost always is not the case, and it is simply a good growing tree normally shedding bark.

Joe Janak is a Victoria County extension agent.



Powered By AffectDigitalMedia