Williamson County News Releases
Title: What's Wrong With My Pecans?
Date: October 15, 2001
Author(s): Ron E. Leps, County Extension Agent-AG, Williamson Co.
Holes In The Nuts
These are made by "redheads" – the larve of the pecan weevil. The weevil larve eat the pecan nutmeats during September and October and then bore a small (1/8" diameter) exit hole to escape to the ground to overwinter. They can be controlled by properly timed insecticide sprays. Pecan weevil are one of our worst pest problems but damage has been much lighter than usual this year.
Pecan Shuck Won't Open
The hickory shuckworm, a small white worm about 3/8" long, tunnels in the shuck and causes extensive damage to the shuck tissue. This can cause the shuck to remain tightly closed, or to only open partially if the damage is only at the base of the shuck. The shuck damage also results in poorly filled nutmeats. Properly timed insecticide sprays are essential for control. Destroy or plow under infested shucks to reduce the population of overwintering shuckworm larvae.
A condition termed "sticktight" can also result in failure to the shuck to open. Sticktight shucks gradually blacken as the nut approaches maturity in August and September. Affected shucks do not open and the nuts are very difficult to shake from the tree. Nutmeats in sticktight pecans are poorly developed. Sticktights are associated with tree stress - both drought and heat. Shuck disease is also a possibility, but no disease has ever been clearly linked to the disorder.
Pecan Kernels Are Poorly Filled
Several factors can be involved in this.
Drought stress can be a major cause.
Poor nutrition especially inadequate nitrogen and zinc fertilization also play a role.
Insect damage such as the shuckworm damage described above can cause the kernel to fail to develop. Aphids sucking sap from pecan leaves during the summer and fall also rob nutrition and the black mold that grows on the "honeydew" secreted by the aphids blocks sunlight and thus photosynthesis. Any such problem that interferes with energy production by the tree will result in poor nut fills.
Certain Varieties also fill poorly. Large varieties like Mahan and Mohawk are notories for poor kernel development.
Overbearing also can cause poor nutfill because of excess competition for nutrients.Black Spots on the Kernels
Black spots or streaks on the nutmeats are usually associated with stink bugs and related sucking insects that feed on the nuts. Feeding before shell hardening causes the nuts to drop, but nuts fed on after shell hardening remain on the tree and develop the black spots on the kernels. The taste of the nutmeats is usually not affected. The recommended spray schedule for hickory shuckworm and pecan weevil will usually keep this problem at a minimum.
Dark Kernels
Tannins in the seed coat determine the kernel color. Certain varieties such as Wichita and Mohawk are darker naturally, while others such as Sioux and Cheyenne are naturally light colored. Prolonged wetness at maturity will result in Kernel darkening so harvest promptly and air dry the nuts for at least 2 weeks in a well ventilated, shady location. Oxidation of the tannins will also cause darkening of the kernels so for longer storage (especially of shelled pecans) store them in tightly closed containers - preferably in the refrigerator or freezer.
Rancidity
Steps that slow darkening will also slow rancidity. Pecan kernels contain 60 to 75% oil (95% unsaturated). Oxidation of the oils causes the bad flavor associated with rancidity. Rancidity will be minimal if the nuts are promptly dried as indicated and stored in tightly closed containers in a freezer.
Extension programs serve people of all ages regardless of socioeconomic level, race, color, sex, religion, disability or national origin. The Texas A&M University System, U.S. Department of Agriculture, and the County Commissioners Courts of Texas Cooperating.
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