May is traditionally the time when pecan producers get worked up about Pecan Nut Casebearer (PNC). PNC can cause significant damage if uncontrolled. Some producers may decide to utilize the crop loss from PNC as a natural thinning technique. Although a nice idea in theory, what if the PNC takes 60% of the crop instead of 30%? Hence the dilemma: to control or not to control. I advocate monitoring as a way to keep on top of PNC.
In some areas, the pecan nut casebearer completes two to three generations per year. Overwintering larvae develop into moths that emerge from May to June. After tree pollination, female casebearer moths begin laying eggs on pecan nuts. These eggs result in first-generation larvae that feed on pecan nuts and generally cause the most damage. Second-generation PNC begin appearing in July. Larvae feed primarily on pecan shucks. Little damage is created from second-generation larvae. Third-generation PNC hatch 30 to 40 days later and feed for a short time (if they feed at all) on shucks. Each small larva forms a tightly woven, protective silken case (hibernaculum) near a bud or leaf scar for overwintering. These larvae emerge from hibernacula in the spring and feed by tunneling into shoots. Pupation of the overwintering generation occurs in these tunnels formed from feeding, and adults emerge the following spring to deposit the first generation of eggs on pecan nuts.
Egg-laying by PNC generally begins in May. 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 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.
Nut clusters with eggs should be tagged with a ribbon or tape and checked daily to determine egg maturity. Insecticides should be applied within one to two days after the eggs hatch.
Pheromone-baited traps for PNC are available. The pheromone 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.
For images of PNC and the damage it causes visit this link: http://www.insectimages.org/browse/subthumb.cfm?sub=2612&start=1