David Owens, Extension Entomologist, owensd@udel.edu
Soybean
Small earworms continue to be reported in double crop fields. While some fields appear to be at threshold, the worms are still very small, and it is possible that many of them will not make it to the 3rd instar, or approximately ¼ inch. It takes worms about 5-6 days from egg hatch to reach the 3rd instar. If you are seeing only very small worms, you may want to think about rescouting early next week before pulling the trigger. Also take a look at the NCSU threshold calculator as a useful tool for decision making: https://www.ces.ncsu.edu/wp-content/uploads/2017/08/CEW-calculator-v0.006.html.
Stink bugs continue to be reported in some fields. Pay attention to soybean growth stages! R4 – R5 is the most susceptible stage for stink bug damage. This is when there are pods present on at least one of the upper four nodes. R5 is when those upper pods have the beginning of seed. At R6 when the seed in those upper pods is touching each other and the pod is full, stink bugs are less likely to cause significant yield injury, so thresholds can drift upwards. At R7 when the plants begin to senesce and pods start changing color, thresholds are at least double. Pay attention to the species present, as green stink bugs are fairly easy to control with pyrethroids, while brown and brown marmorated stink bugs are best controlled with bifenthrin.
Sorghum
We found our first sugarcane aphids in a southern Sussex sorghum field at boot/early head emergence. Aphids were only found on a single lower canopy leaf, but they were thick. White sugarcane aphid is a yellowish white color, smooth body, and small, black cornicles. Pay attention to late sorghum for this pest. It tends to build up in low canopy leaves first. White sugarcane aphid should be scouted frequently, at least weekly, if not more so. At the boot stage, thresholds are 20% infested plants, while flowering to dough stage is 30%. The only effective materials for white sugarcane aphid are Sefina, Sivanto and Transform.
Do not confuse white sugarcane aphid with corn leaf aphid, which is fairly abundant this year. Corn leaf aphids tend to build up large colonies on the flag leaves. However, I have often observed these aphids to disappear once the head emerges. There are also a lot of parasitoids and predators that go after them. Beneficials are much less effective on white sugarcane aphid, but at least they will be present in fields with corn leaf aphid. For these reasons, I think of corn leaf aphids as beneficial, kickstarting our predator complex without persisting in fields or doing any significant damage.
While looking at leaves for aphids and their tell-tale honeydew slicks, Beat heads into buckets to determine if the field is above threshold for armyworm, earworm, or webworm. Webworms seem to be a bit more abundant this year, but are less of a concern because they are much smaller than other worms, and thresholds are double that of an earworm threshold.