Agronomic Crop Insect Scouting

David Owens, Extension Entomologist, owensd@udel.edu

Hemp
Corn earworm can be found in flower buds. EPA has approved a couple of products that have worm efficacy: Gemstar, Surtivo Ultra, Crymax and Spear Lep. The first two products are viruses. They are most effective on small larvae, and are sensitive to UV light, so if you use them, spray late in the day. Spear Lep’s label requires the addition of a low rate of B.t.k (like Crymax) for efficacy. Bt is going to be most effective on small worms, 3rd instar or smaller. Use a good amount of water carrier and pressure to reach the worms that are hiding in and underneath of flowers. The full list of EPA approved insecticides for hemp can be found here: https://www.epa.gov/pesticide-registration/pesticide-products-registered-use-hemp

Soybeans
Continue scouting for defoliators, podworms, and stink bugs. Defoliator thresholds are 10-20% defoliation through R6, the full pod stage. While most defoliators present are green cloverworm, soybean loopers are widely present. Green cloverworm tends to feed in the upper canopy, but soybean loopers tend to start in the middle canopy, so be sure to push plants back to assess the entire canopy. Green cloverworm can be controlled by pyrethroids, while soybean looper cannot. Although earworms have been relatively quiet, continue scouting double crop fields for them. Double crop fields may still have flowers present, which is going to attract egg laying females. I was putting in some ballpark figures for earworm thresholds in NCSU’s calculator: https://www.ces.ncsu.edu/wp-content/uploads/2017/08/CEW-calculator-v0.006.html) and it looks like 1.75 to 2.5 earworm in 15 sweeps will justify a treatment.

Sorghum
Several sorghum fields we have been looking at are moving into the hard dough stage. This is good. These fields should be safe from sugarcane aphid yield damage. As these fields dry down, sugarcane aphids are going to leave them. Scout any late fields! This aphid can reproduce extremely quickly and natural enemies often do not keep up, especially in fields that did not have corn leaf aphid prior to flowering. Thresholds for flowering sorghum to soft dough are 30% infested plants with honeydew present in localized areas. The latest fields may exceed that threshold. The only two effective products are Transform and Sivanto. Sivanto can be applied at 4 fl oz per acre, Transform at 0.75 oz.

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