Warm weather has affected the agricultural community across the board, whether producers are growing row crops or pecans. Fortunately, there has been some relief where recent rainfall predictions have materialized, providing much-needed moisture.
Earlier this month, some pecan growers applied imidacloprid to manage phylloxera galls. By now, the results of those applications should be visible, with a noticeable reduction in gall formation on leaves.
At this stage, pecan trees have developed nut clusters at the ends of branches. These young nutlets are particularly vulnerable to an important insect pest this time of year: the pecan nut casebearer (PNC). Each year, growers face the same question: Will PNC cause damage, and is an insecticide application necessary? Unfortunately, there is no simple answer. Like many of you, my recommendations are based on observations and available data.
Figure 1. Delta traps with PNC phermone lures installed in early April (left), sometime budmoths are captured along with PNC on the sticky surface, but easy to distinguish the two species (right).
To monitor PNC activity, pheromone traps have been deployed since mid-April (Figure 1). Trap data indicate that moth emergence varies by location. For example, the first captures occurred on April 18 in Tifton, April 23 in Tattnall and Colquitt counties, and April 27 in Dougherty County. Once moth activity is detected, the next step is to scout for eggs on the tips of nutlets to determine whether treatment is warranted. However, identifying these eggs can be difficult and time-consuming.
Figure 2. Pecan nuts at thier early stage, which is susceptible to damage by PNC (left), PNC egg on tip of a nut, usual place for laying individual egg (center), and damaged nutlets by PNC indicated by the black granular frass and webbing.
At the UGA Ponder Farm, moths were first captured on April 18. Since then, nut clusters have been monitored almost daily, but no eggs have been found until yesterday in the same block as the traps. The presence of eggs indicates that females have begun laying, and within about five days, larvae will hatch and begin feeding on young nutlets (Figure 2). Once larvae enter the nuts, damage has already occurred, and insecticide applications at that point will provide limited control.
For growers with a history of PNC infestation or with trap counts relatively high (around 10 moths per day in many locations), it may be time to consider an insecticide application. Timing is critical and will vary by location due to differences in moth emergence. In general, applications are recommended 10–14 days after capturing PNC moths on two consecutive nights in pheromone traps.
The first generation of pecan nut casebearer (PNC) moths—currently being captured in pheromone traps—is the most important to monitor. Larvae from this generation feed directly on young nutlets and can cause significant damage. In contrast, later generations are typically less harmful because the nuts have already grown larger and are less susceptible to injury. As a result, multiple insecticide applications for PNC are generally not necessary.
