South Carolina Cotton: With Insects, Shift Your Focus Now

Tarnished Plant Bug. ©Debra L Ferguson Stock Photography

Drake Perrow, consultant in Calhoun County, reported that he observed beet armyworms on pigweeds at noticeable numbers.

William Hardee, county agent covering Horry and Marion Counties, reported that “brown and southern green stink bugs are bad in {his) area. Seeing some ear curl on corn and leaves wilting in tobacco. No soybean and cotton news…but be on the lookout at least.”

I am hearing of separate reports of squares on the ground and plant bugs being present, and that is scaring a lot of folks. We don’t need to panic and all spray every field. That would not be good.

Every field needs to be scouted to determine if plant bugs are there and are part of the problem. Many of the dropped squares, I bet, were caused by physiological shed – too much hot, dry weather followed by too much rain at once.

We will cover plant bugs more below. I also found corn earworm in non-Bt corn ears today (6/14).

Cotton Insects: Shifting Focus

Although thrips have been an extended pest this season, we will shift our focus this week to tarnished plant bugs, aphids, and spider mites.

Spider mites should have been knocked back pretty good by the rains we had this past week, but don’t stop looking for them, since it doesn’t take long to develop problems with them again. More rain in the forecast for next week. Hopefully, that will continue to help with spider mites.

Tarnished plant bug (TPB) is likely becoming more of an issue, and we want to survey this season to see where we are in the state with importance of this pest. It is not as bad a problem for us here in the Southeast as it is for growers in the Mid-South.

But, there has been more concern in recent years, and some of that is valid. I had one plant bug trial last year, and we exceeded threshold for TPB in that test.

There were no statistical differences in yield in that trial, but we did make a little more cotton in the sprayed treatment. If that numerical increase was real, I am estimating/guessing that it might have been 50 to 70 pounds/acre of lint.

That was one trial, and the focus was on TPB. It was planted near corn, a crop interface that can heighten the risk of TPB problems in adjacent cotton.

Key Points On Ratings, Scouting

Cotton that has squares on it needs to be rated for square retention, but that does not always tell you what you need to know. In that trial last year at 8 to 9 nodes, square retention was between 70% and 85% the first time we checked it. Retention of squares was over or at 90% the next two weeks we checked it at 10 and 12 nodes, respectively.

That is when we exceeded the threshold of 8 TPB per 100 sweeps, so you have to go look for the bugs. You cannot just check square retention and think all is well or that it needs to be sprayed.

Check squaring cotton now for adult TPB, and only consider treating if you exceed 8 TPB/100 sweeps.

Get sweep nets from sweepnets.com ($47 each), gemplers.com ($78 each) or anywhere else you can find them for sale.

You will most likely only see adults in samples now on pre-bloom cotton. We didn’t start detecting nymphs until July last year when we switched over to using a black drop cloth for sampling. Get drop cloths from greatlakesipm.com ($24 each) or anywhere else you can find them for sale.

Switch to a drop cloth when cotton gets big enough to sample with a drop cloth (plants tall enough to bend over the cloth and shake out insects).

Sweep nets are most useful only when the cotton is really too small for a drop cloth, and they are really only good for counting adults. When nymphs are present, you want to use the drop cloth to detect them.

Cotton Aphids: Take Plant Disease Into Account

Cotton aphid is capable of transmitting a virus to cotton that has been detected here in the Southeast, and we will be focusing on that a little here and more next week.

The disease that shows up after infected aphids feed on cotton is called cotton blue disease. It gets that name because one of the symptoms is darkened leaves that almost look blue. Other symptoms can include tightly stacked nodes, cupped and crinkled leaves, and other discolorations.

Photo: Alabama Cooperative Extension Cotton blue disease. Photo: Alabama Cooperative Extension (Click image to enlarge)

The disease was found last season in numerous counties in Alabama, some counties in Georgia, and two counties in South Carolina. We plan to survey across the state this season for incidence of the viral pathogen.

Cotton aphids can transmit the virus very quickly if infected with it, so it is impossible to prevent this pathogen from being transmitted to a given field. We will be researching this season to see if we can slow the spread of the virus by treating for aphids.

Don’t panic about this issue! We have a lot of questions to answer before we start trying to spray all of the aphids we see and cause bigger problems with other pests or at least our wallets.

I suspect that we have had this virus for some time and that we often see selected plants with severe symptomology. So, my stance has not changed on aphids…I think they are mostly food for our beneficials in the field and allow beneficials to build and exert pressure on bollworms that get through the Bt technology later.

Do not worry about aphids unless they get really bad on young cotton or continue to stress cotton that might already be under stress. Let’s keep an eye out for aphid infestations and watch out for disease symptomology.

Soybean Pests: 4- and 6-Legged

Once again this week, deer continue to be a problem, especially in early soybeans (planted mid-April) in my planting date study.

I cannot spray any more repellents on my plots because we don’t want to kill the insects that we want to count. We put fence posts and Plot Saver tape around that test today. You can get that from plotsaver.com.

We still have plenty of grasshoppers and threecornered alfalfa hopper (TCAH). So far, those are the most numerous insects in our sampling, but I also easily saw stink bugs in the field today on April planted soybeans that were blooming.

It could be a big stink bug year. I easily saw them today when I just glanced at some corn.


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