Time is drawing near to begin monitoring for Pecan Nut Casebearer (PNC). If producers have not ordered PNC pheromone traps it is time to do so. As a general rule for southern and central Oklahoma, traps should be in the orchard by the first week of May. The key to using pheromone traps is to get them out early in order to detect the onset of flight. The initial date of collection, when moths are captured (on 2 consecutive nights) will act as a biofix for predicting egg laying (oviposition).
Adult casebearer moths are gray to dark gray, have a dark ridge of scales on the forewings, and are about 1/3 inch in length.
Eggs are small and oval shaped (0.36 X 0.65 mm). The first generation of eggs are laid singly at or near the calyx lobes of nuts after pollination. PNC eggs are white when first laid, then gradually change to a red color three to five days before hatching. As the larvae grow and move to developing nuts, they will bore into the base of one or more nuts.
Black excrement (frass) and silk at the base of nuts indicates larval entry. They remain within the nut and feed for four to five weeks. Full-grown larvae will pupate inside the pecan and emerge as moths 9 to 14 days later.
In Oklahoma, egg-laying by PNC begins around the end of May in southern counties and ranges to June 15 in northern parts of the state. Excessive rainfall or cold temperatures may delay development of the overwintering generation.
Scouting for PNC eggs should begin one to two weeks before nut entry by larvae. This requires looking for eggs on the nuts and using a hand lens to determine the maturity of eggs. To determine infestation levels, nut clusters should be examined. A cluster is infested if any eggs are found, or evidence of larval entry (damage) is observed.
Examine 10 nut clusters per tree across several trees. If 2 or more clusters are infested before 310 clusters have been examined, an insecticide application should be made as soon as possible. If less than two clusters are found infested, sampling should be repeated in two to three days.
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First generation PNC generally cause the most damage. Larvae tunnel into nutlets shortly after pollination and can potentially destroy all nutlets in a cluster. The most effective control method is a well-timed insecticide spray. Whenever possible, biological insecticides (B.t.) or insect growth regulators (IGR) should be used for controlling PNC instead of synthetic pyrethroids, carbamates, or organophosphates.
The latter materials, while effective, can result in reduction of parasite and predator populations. Due to loss of beneficial organisms, this increases the possibility of rapid population growth of aphids and spider mites.
Insecticides should only be applied if the nut load and infestation level warrant a treatment.
Pheromone-baited traps for PNC use pheromone (sex attractant) that mimics the chemical emitted by female casebearer moths and attracts males to a sticky trap. Trap captures can be used to detect the arrival of PNC into an area, aid the grower in estimating population numbers, and provide a signal of when first significant nut entry by larvae may occur.
As a general rule, oviposition will start 7 – 10 days after first capture and nut entry starts 12 – 16 days after initial catch. Monitoring should begin in early to mid-May to identify a biofix and prepare for the flight in late May/early June.