South Carolina Cotton: Bollworm Decisions Looming

Photo: Texas AgriLife Extension

We still have plenty of aphids. Hopefully, though, the fungus will start helping us on a widespread scale. However, many folks are still calling and texting about aphids, so the problem is certainly lingering.

Spider mites could become an issue in some fields, particularly those that keep missing rains. So, don’t forget your hand lens when you go scouting. At least look for the stippling on upper surfaces of leaves. But, you are a little late on noticing spider mites at that point.

Bollworm and stink bugs should be the focus for the remainder of the season. Counts of bollworm moths in our pheromone traps continue to increase, and folks are reporting eggs at 20 to 40 per 100 plants in some areas.

Eggs were easy to see in some of my plots yesterday, as were bollworm moths and tobacco budworm (TBW) moths. We caught a good many TBW moths in pheromone traps this past week, so some of the eggs could be from TBW.

Because all Bt cotton provides a very high-dose strategy for controlling TBW, none of the eggs from TBW will survive. So, this is where the danger in spraying on eggs comes in…you might be treating for a high proportion of TBW eggs that will die due to the Bt toxins.

There is no need to kill TBW twice. Without a reliable test kit for the eggs, we have to assume that some of the eggs are from TBW in the system. For example, using some very crude math and extrapolation, my traps caught about 1.4 times as many bollworm moths as TBW moths this past week. So, you could roughly estimate that 1 out of 3 moths flying around was TBW. If TBW moths are in the system, it can complicate spraying for bollworm on eggs.

The best way to scout for bollworm in cotton is to use all available ways to assess their density in the crop. Count eggs and pay attention to any pheromone trapping data in your area that might indicate proportions of TBW or bollworm. Eggs should be counted on the top 20% of the plant and around each bloom. Look for larvae in terminals, squares, blooms, on top of bolls under bloom tags and on the sides of bolls. Look for injured squares, blooms, and bolls.

Bollworm Scouting Guidelines

Here is the language on scouting for bollworm in Bt cotton in SC:

  • In transgenic cotton varieties that contain Bt endotoxins, an insecticide treatment should not be needed before first bloom.
  • Transgenic Bt cotton varieties that have two or more Bt genes have increased efficacies against bollworms; however, under potential situations of very heavy pressure from bollworm, some Bt technologies can incur significant injury and losses if not protected with supplemental/timely application(s) of insecticide.
  • To control escaped worms in Bt cotton, an insecticide treatment should be applied when 3 or more larger (>0.25 inch) worms are found per 100 plants or 5% of small bolls are damaged. Also, entire plants can be examined for eggs to determine pending pressure.
  • Insecticide application can be justified if peak egg lay approaches 1 egg per plant. On each plant, a scout should examine a white bloom, a pink bloom and the two smallest bolls.
  • If dried blooms (bloom tags) adhere to small bolls, remove them and look for larvae boring into the boll tips.

Across The State

Mitch Binnarr, representative with Corteva Agriscience, reported that he was checking some cotton in Dillon and Marlboro Counties this week and found that aphids were still an issue, with treatments being made. He also said that stink bug injury was present in older cotton, with treatments being made, and that trap captures were up for bollworm in southern North Carolina and bollworm eggs were being found on bloom tags.

Another report out of Hartsville indicated that bollworm egg activity was trending up in cotton. So, much activity is being reported from the northern portion of the Coastal Plain in South Carolina this week.

Tom Smith, a local consultant, reported more green stink bugs, plant bugs (although sporadic), leaffooted bugs and bollworm activity in cotton (moths and eggs). He also added that aphids seem to be “diseasing out” in the crop.

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