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|Hickory shuckworm larva feeding inside pecan nut
University of Missouri
Mature larvae of Hickory shuckworm, Cydia caryana, overwinter in pecan shucks found on the ground or the tree and emerge as moths in mid-May. Spring development of hickory shuckworm coincides with that of native hickory trees, which set fruit two to three weeks earlier than pecans. First-generation moths oviposit on hickory nuts, phylloxera galls and on pecan foliage, although those larvae hatching on pecan foliage rarely survive. Few pecan trees are infested with first-generation hickory shuckworm because most moths die before pecan nut set. Second-generation larval feeding in the interior of the nut, which occurs from mid-July until shell hardening in mid-August, causes premature nut drop (see above image). In newly dropped nuts, you often can detect a chalky, white deposit at the larval entry point. This deposit is the scales of the female moth, placed to protect and seal the egg to the shuck. The hickory shuckworm larva creates a paper-thin "window" in the shuck before pupation, which protects the pupa and provides an easily torn exit hole for the adult moth.
The third-generation moths typically emerge in early August. After shell hardening, the larvae mine tunnels in green shucks, which attaches the injured portions of the shucks to the shell (sticktights). Such third-generation shuckmining also delays nut maturity and inhibits proper kernel development.
Eggs are minute, white and flattened and usually are laid on the shucks. Larvae have five pairs of prolegs, are creamy-white with brownish heads and are three-eighths of an inch long when mature. Adult moths are dark-gray nocturnal flyers, three-eighths of an inch long with a wingspread of one-half inch. Pupae, dark-brown and up to one-third inch long, are found within the shuck.
Scouting and control
Second-generation hickory shuckworm rarely causes economic damage to native pecans. You should focus on controlling the third-generation moths, which often emerge at the same time as pecan weevils (early August). If pecan weevil emergence is delayed by drought conditions, you can apply an insecticide at the shell-hardening stage of nut development in mid-August. Adequate control of the third-generation often translates into lower hickory shuckworm populations in subsequent years.
George S. Smith and Maureen H. O'Day
Department of Entomology, University of Missouri-Columbia
Kansas State University