When cotton blooms, it’s time to switch sampling and thresholds for plant bugs. This previous article covered management of plant bugs pre-bloom. There is no magic switch point, but once cotton blooms for a couple weeks, monitoring square retention becomes a less reliable way to make treatment decisions, as does the sweep net.
For this reason, we recommend a threshold of 2-3 plant bugs per drop cloth sample (1 per row foot) during the bloom. During early bloom, consider using both a sweep net and a drop cloth for sampling.
You can visit the cotton scouting guide for detailed information and a video for how to use the drop cloth correctly.
Remember that plant bugs will feed on larger squares and small bolls during bloom. The feeding on the large squares can result in dirty blooms. You should never treat based on the presence of dirty blooms, but they are an indicator that you should use your drop cloth in the field and scout.
Once threshold is reached during bloom, it would be a good idea to switch away from a straight neonicotinoid product. Options are many, but you could pick up plant bugs and stink bugs both with pyrethroids and Bidrin.
In the Midsouth, they have found that mixing Diamond with pyrethroids has lengthened their spray intervals. They have also found that back to back sprays within 4-5 days of the first spray has improved control over back to back sprays made one week apart.
AgFax Weed Solutions
The take home for us is to rotate chemistry and to scout more frequently, even twice a week. If you chose to apply Diamond, keep in mind that it is an insect growth regulator and that only immature insects grow. So it will only be active on nymphs, not adults. If you want to kill adults, you will need to mix in some other knock down product.
Finally, keep in mind that many of these products are harsh on beneficials. That could mean more spider mites, aphids, or bollworms later in the season.
We have a Section 18 for Transform this year. This would be a great insecticide to try in your rotation to manage plant bugs, while preserving beneficial insects.
More on insecticide recommendations and efficacy can be found here.