Should you stop treating cotton for insects?

• By Dominic Reisig •

bollworm feeing on boll
A bollworm feeds on a cotton boll — photo courtesy Texas A&M AgriLife Research

Should I treat this cotton for bollworm eggs, plant bugs or stink bugs? This is not a one-size-fits-all answer, but here are a few scenarios to consider.

1) Delayed cotton with low yield potential The good news is that this cotton is likely insect-safe. We consider bolls to be safe from plant bug and stink bug feeding once they hit 5 nodes above white flower (NAWF) + 250 cotton growing degree days (GDD) and bolls to be safe from bollworms once they hit 5 NAWF + 350 GDD.

Jeff Gore at Mississippi State University recently shared some data that 5 NAWF + 250 GDD was equal to about 2-3 NAWF in their environment. That means a lot of this cotton that’s blooming out the top isn’t susceptible to these pests.

2) Delayed cotton with high yield potential It’s important to check out the boll load in this situation. Keep in mind that August 25th was the last effective bloom date. That means on average there is a 50% chance that lint from today’s bloom will make it into the picker.

I wouldn’t worry about losing squares from plant bugs at this point. If there are bolls smaller than the diameter of your thumb, then it will be important to protect these from plant bugs and stink bugs. Plant bugs prefer smaller bolls in this category and stink bugs prefer larger bolls in this category. Both can cause injury to the boll through seed feeding and by transmitting pathogens causing boll rot.

3) Cotton with bollworm eggs We are now entering the fourth generation of bollworms produced right here in North Carolina. With every generation, there are usually more and more in the system. So that means that some folks are noticing really heavy flights and some significant egg lay in cotton.

Fortunately, while these eggs may hatch, the larvae rarely get past the first or second instar stage. It’s always good to keep an eye on your cotton if it’s still bollworm-susceptible for those once in a blue moon scenarios.

However, I don’t think we need to roll out with more egg threshold sprays at this point in the season.

Dr. Dominic Reisig is an associate professor and Extension specialist, Entomology & Plant Pathology, at North Carolina State University. He may be reached at

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