SUGGESTIONS FOR SCOUTING PECAN NUT CASEBEARER IN THE FIELD
(by Marvin K. Harris)
The Decision Window (see Figure 1) tells you when treatment may be needed to protect a harvestable crop, but it does not tell you if it is needed. About 3-5 days before the Decision Window occurs do the following:
Check 310 nut clusters (examine 31 trees, inspecting 10 clusters per tree) for: eggs, bud feeding and larval entries. Use flagging tape to mark a cluster when you find eggs or larvae. Write in permanent ink on the tape what you found (date & egg or larval condition). Then, when you check again a day or two later, you can both find new eggs and larvae and also easily see the progress those found previously have made since the last check. Update previous finds and flag new ones.
If you find more than 5 infested nut clusters before or when the Decision Window is reached, treatment is probably needed (see Figure 1). Note that you do not have to check the entire 310 nut clusters to make a decision to treat. If you encounter 6 or more infested clusters before checking is completed, you have already exceeded the threshold and can now concentrate on getting the treatment time exactly right. The best time to treat is when larvae are hatching (see Figure 2) but before most of them have begun entering the nuts. Consider use of a selective pesticide.
Finally, if you do decide to spray, the flagged clusters can be easily found again a day or two after spraying (when it is legal to re-enter the orchard--check the label) and you can see if the eggs/larvae flagged (see Figure 2) previously have died or if they have continued to develop. Obviously, if they do continue to develop for 2-3 days, you might get concerned about the effectiveness of the treatment and undertake some further investigation into the matter. Re-treat if needed.
Figure 1. PNC Sampling.
Figure 2. PNC Larva hatching (Fu, INIFAP).