By Dominic Reisig
We have rapidly become accustomed to dealing with kudzu bugs in our soybeans throughout the season. So the question is, where are they now?
We think the cold winter has knocked populations back. Many folks have noted dead bugs in overwintering spots. Furthermore, spots where kudzu bugs are showing up now are near traditional “hot spots” where they have overwintered.
Because of this, our greatest chance for kudzu bug infestations are going to be localized around these traditional hot spots. You probably shouldn’t expect kudzu bugs to show up at threshold levels in new spots this year.
Believe it or not, the kudzu bug migration into soybeans is in full swing. It is really wimpy compared to previous years. Our population levels are about 10 to 20 times lower than last year. Right now, kudzu bugs are moving into soybeans, mating and laying eggs. Nymphs have been noticed within the past weeks.
We can expect a few fields to hit threshold within a couple weeks. If you don’t find kudzu bugs at one nymph per sweep (one per “swoosh” of the net), you don’t need to treat.
It is especially critical to use a sweep net in situations like this year. We can expect most of our fields at risk for kudzu bug (which aren’t many) to be borderline situations. Many fields in the past were obvious treatment situations. Those fields were so full of kudzu bugs that you could smell them through the AC system pulling up to the field.
This year, you will find one nymph per sweep a lot easier and quicker using the sweep now than you would if you walked into a field and parted the canopy. Small, hairy green nymphs blend in with the stems and will be difficult to spot. Most fields won’t need to be treated for this insect!
Because we won’t be dealing with many kudzu bugs this season, we need to focus our efforts on the other pests that are around. These include the corn earworm/tobacco budworm, stink bugs and defoliators (loopers, armyworms, etc.).
The first pest we will likely have to manage is corn earworm/tobacco budworm. These insects can defoliate, but are more serious pests of seeds forming in the pod. They should never be sprayed at flowering, but should be controlled when pods are present (especially at R4 to R7). Thresholds vary with sampling method and row spacing; we suggest using the earworm/budworm online threshold calculator as a guide for treatment.
Corn earworm can usually be controlled with pyrethroids — unless there are resistant worms present. Resistant earworms and tobacco budworm should be controlled with a worm-specific insecticide (such as Belt, Blackhawk, Prevathon or Steward). Earworms and budworms are very difficult to tell apart without specialized training. Try pyrethroid as a first shot. If this fails, switch to one of the worm-specific materials listed above.
Stink bugs move in and out of soybeans throughout the season. You might notice a lot of them when soybean is flowering (R1-R2), but they do not cause yield loss at this point. Focus your control when the seed is forming (R5-R6). Seed producers should also treat at R7 to avoid quality loss. Like corn earworm/tobacco budworm, the thresholds vary with sampling method and row spacing. You can use the stink bug online threshold calculator to figure out when to treat. Green stink bug can be managed with a pyrethroid. Add in something like acephate (Orthene) or use acephate alone to kill browns.
Defoliators like soybean loopers and armyworms are more of a problem later on in the season. There are two reasons for this. One is that many are migratory pests that don’t overwinter here. So they can build as the season progresses. The second is that we often treat with a pyrethroid midseason. This is to manage things like earworms and stink bugs and is often needed.
The disadvantage is that we knock out all the beneficial good-guy insects, releasing these worms to eat foliage. You should only treat for defoliators when the canopy loss is 15% after bloom. For soybean looper, beet armyworm, and corn-strain fall armyworm, use a worm-specific insecticide (such as Belt, Blackhawk, Prevathon or Steward).