Nov 11, 2020Weather Breaking, But Don’t Relax Yet
Now that the temperatures are where they should be for mid-November, insect pressure in general has begun to subside. But don’t become complacent, particularly in produce crops near harvest. Below are my thoughts on the status of local pest pressure based on field observations, trap counts and PCA reports.
Beet armyworm: Populations have finally subsided, and spray intervals have lengthened. Larval numbers are down, along with trap counts. This isn’t surprising given the return to more seasonal temperatures and the intensive spraying over the past 2 months that provided areawide suppression. But they are still out there.
Cabbage looper: Where did all the loopers go? Long time passing. First time, in a long time, that I have not been able to conduct a looper efficacy trial. I saw them on my melons in August, but literally have only seen one or two since then. Be careful though, with warmer weather forecast for next week they could surprise you. Similarly, don’t relax with Corn earworms. Although trap captures have been down the last few weeks and no recent reports of larvae in head lettuce, it only takes a couple of these dudes at harvest to ruin your day. (see Areawide Insect Trapping Network)
DBM: Trap counts have been unusually low this fall, and larval populations have been scarce. But trap counts increased markedly over the past two weeks (see Areawide DBM Trap Network). Counts were highest adjacent to organic brassica crops, and transplants not treated with Verimark. It is advisable to closely examine your earliest plantings a little more closely until harvest, looking for feeding signs in terminal leaves. Remember, DBW hatch on outer leaves but quickly migrate to the growing point.
Whitefly: Areawide, whiteflies have been spotty, but have recently had reports of fields requiring control for whitefly adults and nymphs, particularly in brassica transplants. Efficacy trials on direct-seeded broccoli at YAC have shown that Exirel has been the most effective foliar product against nymphs (with good adult activity too), and Sivanto, Venom and PQZ have shown consistently good adult knockdown.
Thrips: Western flower thrips populations have slowly been building on romaine at YAC, and areawide traps indicate adult movement has sharply increased in the past week. Because of the potential for INSV to move into the desert on coastal transplants, it is advised that PCAs keep thrips populations suppressed as much as possible in early fields (particularly transplanted lettuce originating from Salinas). It might be worth making an extra spray just to prevent secondary spread to adjacent fields. Also, stress to your growers to disc under recently harvested lettuce/spinach field ASAP. Remember the key to thrips control is to maintain larval populations at low levels. The cryptic or thigmotactic behavior of thrips often makes them difficult to find on lettuce plants. So, when scouting if you find a few, there are probably a lot more that you don’t see within the plant.
Aphids: Large colonies of aphids have been showing up on organic brassica transplants for a few weeks now. They clearly hitched a ride on the transplants. They may soon be spreading to adjacent fields. We’re also beginning to pick up green peach aphids on our sticky trap sooner than we usually do. This may be a good sign. With the desert being very dry and a La Nina forecasted, aphid may be forced into our valleys without the chance to build up to large numbers in the desert landscape. Stay vigilant though, proper ID is important for the selection of the most cost-effective insecticide. Like thrips, it’s best to “nip colonization in the bud”.
Name that pest
How many aphid species are present in the image below? Name them.To contact John Palumbo go to: jpalumbo@ag.Arizona.edu