Following pollination, as we advance into the growing season, those tiny nutlets on terminal branches of pecan trees are potentially exposed to feeding by pecan nut casebearer (PNC) caterpillars. The adult moths of this species emerge out of their overwintering stage in the spring and are often active in pecan orchards from mid-April onwards. No other known host plant of this insect exists, so they always stay in the pecan orchard. The first generation of the moths is more serious as the females lay eggs on small nutlets, and the caterpillars coming out of these eggs can feed on multiple nutlets in a cluster. It takes about 4-5 days for eggs to hatch. PNC eggs are somewhat difficult to locate at first, but once your eyes are trained, they become easier. It is important to know what eggs look like and the damage symptoms from caterpillar feeding (Figure 1).
Figure 1. Adult PNC moth (left), eggs: whitish when fresh and then turn orange/pink before hatching (middle), nut damage as indicated by webbing and black granules as result of feeding.
The challenging part of PNC control is that once caterpillars enter the nutlets, insecticide application becomes ineffective. There is a short window between the emergence of a caterpillar from egg to nut entry. Therefore, an insecticide chemistry that has longer residual activity must be applied around the time when the majority of the eggs are present on the nutlets and ready to hatch. Once these newly emerged caterpillars start crawling and chewing on any tissue, they will be exposed to the insecticide-treated surface and should die.
I am sure most pecan growers are familiar with the pheromone trap used to monitor PNC flight activity (Figure 2). These traps are an important part of PNC management as they provide the “biofix” date. The “biofix” is considered a developmental event in an insect’s life cycle. In the case of PNC, it is the date when moths are captured in pheromone traps for two consecutive days. This year, we collaborated with several dedicated county agents (Berrien-Ben Reeves, Brooks-Michasia Dowdy, Ware-Scout Carter, Wilcox-John Bennett, Montgomery-Lauren Staney, Tatnall-Derrick Bowen, Burke-Cliff Collins, Houston-Morgan Stickland, Colquitt-Jeremy Kichler & Tanner Wilson and Sumter-Chelsea Lopez) to monitor the ‘biofix’ date. I am grateful for the input from Andrew Sawyer-Area Pecan Agent and Joe LaForest-UGA Tifton Campus, who provided invaluable help with both logistics and technical aspects, making this effort a success. I hope I can expand this list to include several other counties next year.
Figure 2. Commonly used pheromone trap (left), FMC’s “smart” trap also a pheromone trap with a camera and remote connectivity (center), PNC moths captured on sticky card (right) (shared by Ben Reeves).
Most of us put out these pheromone traps after mid-April and continued monitoring every day until yesterday. It is quite a commitment to check these traps every day, and for that, the effort of the county agents participating in this project is really commendable. In addition to our traditional delta traps, there are 50 more “smart” traps from FMC Corporation spread across the region from which we can see the PNC activity. Based on the data from the county agents, our observation here at the Ponder farm, and the “smart” traps, the “biofix” was reached within the last 2-3 days. That means, if we had “biofix” according to the model, it is predicted that we should see 25-50% eggs between 12-15 May (Figure 3). It is recommended that you should start sampling nut clusters for eggs and damaged nutlets during this period. Also, if you are considering a preventative application based on this “biofix” date, you could make an insecticide application between 10-14 days following the “biofix” date.
Figure 3. PNC forecast model prediction for South Georgia (Tifton) based on 30th Ap
I also want to share that we have seen more PNC moths on traps across the region than last year. For example, last year, we captured 4 moths on each trap placed for 25 days, whereas in the previous three days in April alone, this number was as high as 52. Through my communication with county agents and looking at the data from the FMC’s “smart” traps, I am convinced that our observation at the Ponder farm is a pretty good indicator of what is found in other areas, too. I am also sharing a figure provided by FMC (Courtesy: Erica Rudolph, Blaire Colvin, Madison Lane) showing last year’s and this year’s trap capture trend, and it is clear that during the last three days (28th, 29th and 30th) in the month of April (Figure 4), PNC capture has increased tremendously and surpassed last year’s capture during this time.
Figure 4. Comparison of PNC capture on smart traps between the Year 2023 and 2024 in South Georgia. (Solid blude line for 2024 and dotted blue line for 2023).
So, what does all this mean to the overall risk of PNC damage to our pecan crop this year? This is hard to predict definitively. Higher moth captures do not always reflect higher nut injury. Besides, one needs to consider the crop load, variety, and input level. When crop load is high, some nuts drop due to PNC damage, which could, in turn, be helpful to thin out. Similarly, some varieties naturally shed nuts in the middle of the season. If it is a low-input crop, one can sacrifice a portion of the nut drop. Thus, the decision to invest in a PNC application depends on some of the abovementioned factors and does not apply to all operations. That being said, I am concerned after seeing a comparatively higher number of PNC moths on the traps this year and recommend using scouting and preventative application of insecticide in the timeframe mentioned here.
