Agronomic Crop Insect Scouting

David Owens, Extension Entomologist, owensd@udel.edu

Soybean

Continue scouting all double crop soybean, especially those planted after the beginning of July, for corn earworm. Reports came in this week from Bridgeville, Gumboro, Galestown, Dorchester, Selbyville, Frankford, and Millsboro. This year’s flight into soybeans has been more intense than usual. On August 23, we dropped a spray trial in a field near Roxanna where worms averaged 1 every 4 sweeps. One week later, the average worm count is 1 per sweep. Pyrethroids initial knocked earworms back, but residual activity has been poor and treated plots are now back above threshold. A report was received earlier this week of a severe pyrethroid failure on Delmarva, with many loopers also present in sweep samples. Do not rely on pyrethroids alone. Even though they are extremely cheap, they do not provide sure efficacy or peace of mind. In our spray trial, a mid-rate of Besiege zeroed out worms. Other chlorantraniliprole containing products would have similar efficacy, including Elevest and Vantacor (which used to be Prevathon). The other advantage of these products as well as a new product for soybean, Denim, is that they will also help reduce the possibility of flaring up soybean loopers.

Pay attention also to other pod feeding pests. Stink bugs are still active and bean leaf beetles are increasing, which is typical for this time of year. The most widely used threshold for stink bugs in the mid-Atlantic is 5 bugs per 15 sweeps. In tall canopy beans, it may be justifiable to use a slightly lower threshold as a surprising number of stink bugs can hide deep in the canopy. Once we start moving into the full-seed full-pod stage of growth, stink bugs are not going to have as strong of an impact on yield and thresholds can drift upwards (it should be noted that quality may still be impacted). Once soybeans are senescing, the threshold doubles. I think a slightly lower threshold is justified for Plenish soybean. Most double crop fields are a bit earlier in their pod filling stages and do not have as full of a canopy.

Sorghum

Late planted sorghum is heading and should be scouted for earworm. To sample sorghum heads, shake heads vigorously against the side of a bucket (sweep net will work in a pinch). This dislodges worms. If you are near 1 worm per head, pay attention to Texas A&M’s headworm calculator. Note that fall armyworm and earworm should be classified together, and sorghum webworm should be counted as a half-worm. It is smaller and less damaging than earworm and armyworm. The calculator can be found here: https://extensionentomology.tamu.edu/sorghum-headworm-calculator/.

Also scout for white sugarcane aphid. Spotty, low-level infestations have been observed in plots in Georgetown and in late planted fields south. Thresholds used in southern states are 30% infested plants with localized areas of honeydew and established aphid colonies from flowering to dough stage. The only effective insecticides registered for sorghum are Sivanto Prime and Transform. Sivanto has a 2ee recommendation for 3 to 7 fluid ounces. There is some data suggesting that 2 fl ounces is quite effective. Transform is also effective, but requires adjuvants.

Hay Crops

Scout for true armyworm in grasses and for blister beetles feeding on weeds, especially pigweeds. If hay is being sold or fed to horses, blister beetles should be scouted for carefully to ensure that they do not end up in the hay. For alfalfa, continue scouting for potato leafhopper.

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