Sep 30, 2020Don’t Forget to Rotate Chemistries when Fighting Beet Armyworm
Wow. What a September this has been. This is the heaviest beet armyworm (BAW) pressure I’ve seen in probably 20 years. Similar reports coming in from PCAs as well. Seedling stands have required earlier and more frequent treatments, particularly in the Dome Valley/Wellton areas. PCAs have noted the need to spray more frequently due to overlapping egg lays and plants outgrowing insecticide residual. It seems to be slowing down a bit in the past few days though. They’ve been heavy here in the Yuma Valley at the Ag Center too. I recently lost about an acre of experimental lettuce plots to BAW waiting to spray. I was a few days late. Note: under ideal conditions (~86 F), BAW larvae will develop through all 5 instars in 5-6 days. Broccoli also hit hard, pretty beat-up. Good news is, we haven’t found any diamondback moth larvae on the broccoli yet. However, areawide pheromone traps indicated a significant increase in DBM moths last week captured in traps in or adjacent to transplanted cauliflower and cabbage (see graph below).
Fortunately for local PCAs, several insecticide alternatives are available that provide excellent residual activity on these pests (see my last 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), 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 and Diamondback Moth in Desert Produce Crops.
Name that Pest Sep-30-2020
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu