Even though the monsoon is officially over, and the temperatures/humidity has dropped, worm pressure remains steady in most growing areas. Here at the Ag Center, cabbage looper eggs and young larvae are especially abundant on all our crops (lettuce, cauliflower, broccoli and melons). Similarly, lots of reports of steady looper pressure from the field, and pheromone trap counts remain above average, particularly in the Wellton/Dome Valley area. This is quite a change from this time last year when we couldn’t find a looper. In contrast, armyworm pressure is about average for early October, but still troublesome on new stands. Again, this time last year beet armyworm pressure was the heaviest I’d seen in 20 years. Diamondback moth and corn earworm are active in pheromone traps, with only a few showing up so far. Bt don’t be fooled, they have been known to show up unexpectedly in numbers in mid-late October. Fortunately for local PCAs, several insecticide alternatives are available that provide excellent residual activity on these pests (see the Sept 22 update). Perhaps equally important, many of the products have unique modes of action (MOA) that can be alternated throughout the growing season. This is important because the most fundamental way to reduce the risk of insecticide resistance is to eliminate exposure of multiple generations of Leps to the same MOA. By using a different MOA on each subsequent spray application, you can minimize the risk of resistance by Lep larvae to these insecticide compounds. In contrast, repeatedly applying insecticide products with the same MOA for Lep control in the same area will significantly increase the risk of resistance. This is particularly important with the Diamide group of insecticides (IRAC group 28). These products can be applied as both foliar sprays and soil systemic treatments, and currently 7 Diamide products are for use labeled in leafy vegetables - all with the same MOA (Coragen, Durivo, Besiege, Minecto Pro, Verimark, Exirel and Harvanta). To avoid confusion among the Diamides, the IRAC group number (28) is placed on each label, adjacent to the product name. This is very helpful in avoiding repeated use of the same MOA. A complete list of all registered compounds and their MOA can be found at the IRAC MOA Classification Scheme. Furthermore, applying a Diamide product (i.e., Coragen/Verimark) to the soil at planting or as a tray drench, and then subsequently applying Diamide foliar sprays (i.e., Harvanta/Besiege) on the same field is not a good idea as it can expose multiple generations of Leps to the same MOA. For example, under ideal weather conditions, one could potentially expose 5-6 generations of BAW or DBM to the same MOA given the residual efficacy of the diamides. That’s not a good way to use these products if you want them to remain effective for more than a couple of years. Since the Diamides, as well as the other key products currently available (e.g., Radiant, Proclaim, Intrepid, Avaunt, Bts), are critical to effective management of Leps in leafy vegetables, PCAs should consciously avoid the overuse of any of these compounds. The most effective way to delay the onset of resistance by Leps in leafy vegetables is to consider the recommendations provided in the guidelines entitled Insecticide Resistance Management for Beet Armyworm, Cabbage Looper and Diamondback Moth in Desert Produce Crops.