South Carolina: Cotton, Soybean Insects Plenty Active

Bollworm burrowing into cotton boll. Photo: University of Tennessee

Jonathan Croft, county agent in Orangeburg County, reported that he “checked soybeans on the edge of Calhoun and Orangeburg Counties this morning [yesterday] and found about 50% threshold on soybean looper and kudzu bug nymphs. Also picked up a few immature green stink bugs and a few velvetbean caterpillars. These were in beans setting pods. No podworms. In some beans behind wheat just at full bloom stage grasshoppers were only the insects worth mentioning, and defoliation was minimal.”

I also spoke with consultants Drake Perrow and Fleming McMaster this week, and they were seeing some of the same things I have been noticing this past week.

There were many bollworm moths flying around in cotton and soybeans this week, and stink bug numbers have increased in both crops. I saw this Pima cotton bloom in one of my trials this week. Rare find.

Cotton Insects

Bolls are opening on the bottom of cotton plots I planted in April. So, counting graduate school, the end of my 28th insect season is near.

Captures of bollworm moths in pheromone traps increased, and numbers this week were higher than they have been all season and certainly higher than last year.

I stated last week that the rainstorms would wet the soil and likely release additional moths from their pupal cells underground. That prediction came true, and as the rains continue, I expect the flight to continue.

Keep a watchful eye on 2-gene Bt cotton. The technology seems to be holding up this season, but we have recently observed square and boll damage over threshold in 2-gene Bt cotton. Moths are undoubtedly depositing more eggs, and there are still positions on the plant to protect.

The eggs are difficult to locate, but get out and try to find them on terminals and near squares and blooms. We will probably see caterpillars causing injury next week.

Counts of bollworm eggs at or exceeding 20 eggs per 100 plants should get your attention. If 3 or more larvae are found per 100 plants or damage to squares and bolls exceeds 5-6%, treatment thresholds have been met.

We are halfway through the “stink bug month” of August! Numbers of mating pairs of stink bugs were up this past week, and you know what that means. I saw the big 3 – southern green, green, and brown stink bugs.

We have them all in cotton here in South Carolina. Stink bugs should be the focus of insect management efforts in cotton now and into September. Bolls are relatively safe from stink bug injury when they reach about 21-25 days from bloom – about a full-size boll.

Soybean Insects

As foliar diseases crank up during these wet and cloudy thunderstorm days, thoroughly scout your soybean fields for insects to see if a tank mix of fungicide and insecticide is in order.

With input costs up and commodity prices down, everyone is trying to minimize costs, for sure. Potential, you can save a trip or two across the field, if everything lines up.

Defoliation is increasing, as are populations of soybean loopers. I saw moths of soybean looper (SBL) and green cloverworm (GCW) this week, so we are still observing many different species in the field.

I mentioned last week the importance of being able to tell these two species apart when they are small caterpillars.

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Make sure you can do that. Again, small GCW “loop” when they crawl and look just like SBL. You have to look very closely with magification to properly identify the two. Costly materials are needed for control of SBL, but you can control GCW easily with a pyrethroid.

Velvetbean caterpillar (VBC) is in the mix also, but this migratory species has yet to arrive in large numbers like they did last year. That is probably coming, though, within the next few weeks.

Watch this complex of defoliating caterpillars, and don’t let defoliation exceed 30% before mid-bloom or 15% after that.

Estimate defoliation at least weekly. Use a sweep net or a drop cloth to make counts of insects to see what species you have, as insecticide choice depend on proper identification of species.

Podworm moths (same as bollworm) were abundant in soybeans this week, so they might also be a factor next week as larvae feeding on pods.

As pods develop, stink bugs should be the focus of insect control in soybeans. They are our number one soybean insect pest group.




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