South Carolina: Soybean Pests Have A Healthy Appetite Right Now

Velvetbean caterpillar on soybeans. Photo: Jennifer Bearden, University of Florida

Charles Davis, county agent in Calhoun County, found stink bugs in his observations but reported “damage was hard to find in the fields” he walked. Charles also reported that “a lot of final growth regulator and insect sprays are going out this week as a parting shot. On the non-insect side, I see a lot of boll rot in some fields but also a lot of mildew.

“Hopefully, we will get some better weather this week. Cotton is opening fast. Some fields showing severe potassium deficiency are nearly defoliated and most bolls are open.”

Cotton Insects: Check For Stink Bugs

Captures of bollworm moths in pheromone traps have started going down, as has activity in the field. Despite a late flurry of activity from the species, additional injury in the field will subside very soon, and only later- planted cotton would need a look for bollworm at this point.

Where bollworms leave it, stink bugs will take it. I call August “Stink Bug Month” for a good reason, but stink bugs don’t have calendars and go elsewhere just because it is September. Stink bugs can feed on hard pecans right through the shell, so they can certainly feed on bolls and seed until the picker comes through the field.

That said, adult stink bugs have a choice, and they usually choose to leave cotton when there are no more soft bolls on which to feed. They move on to soybeans and finish off the season there.

However, any immature stink bugs remaining in cotton don’t have a choice. They don’t have wings, so their only option is to continue feeding, and some of my early research showed that large nymphs can cause as much damage as adults.

Pressure from stink bugs has increased lately in cotton and soybeans. Keep using the dynamic boll-injury threshold for stink bugs to finish the season. Most fields are probably getting close to the 6th or 7th week of bloom.

Soybean Insects: Make No Mistake, They Are Present

Defoliation has contined to accumulate this week, as velvetbean caterpillar (VBC) , soybean looper (SBL) and green cloverworm (GCW) gang up on unprotected soybeans. I have some soybeans that will be completely defoliated next week.

If you have yet to notice VBC moths flying around, just look and I bet you will flush and see them as you move through the field. VBC moths will be the ones with their wings out to the sides when at rest, and there will be a line going across the wings.

With VBC, It doesn’t take long to go from an egg deposited on a soybean leaf to a large caterpillar with a belly full of sunlight-capturing leaf material. If you have not sprayed an insecticide in a couple of weeks, you certainly need to check for SBL, VBC and GCW, and other defoliating species.

You need to identify the species because SBL can be more difficult to control, as you know. A more expensive material will be needed if you still see small SBL while sampling. Use a drop cloth and a hand lens to identify the small caterpillars, as those are what you will deal with soon.

So far this season, data from my insecticide efficacy trials have indicated that we are controlling VBC and GCW with just about anything sprayed, so it is good to know that VBC are back to normal and susceptible this season (at least those that migrated into my area).

Apparently, we are also good with the lep-specific insecticides we recommend for SBL control. I have not seen anything in the data that indicate we have a problem with appropriate insecticides recommended for SBL. And, at least for another week, podworm (same species as bollworm or corn earworm) might still be in the mix. I found these two in soybeans this week – podworm and SBL close on the shake sheet sample.

Finally, stink bugs and grasshoppers continue to reproduce in and damage soybeans. We have sprayed some soybeans twice with a very good insecticide for stink bugs, and they continue to hatch out from egg masses that are not killed by insecticides.

Grasshoppers continue to do the same. See our Pest Management Handbook for more details and recommendations on insecticide choice for all of these insect pests.




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