When cotton blooms, it’s time to switch sampling and thresholds for plant bugs, says Dr. Dominic Reisig, an entomologist with North Carolina State Extension.
In a June 24 post to the NC State Extension Cotton page, Reisig dives deeper into recommendations, but here are a few highlights from his post ‘Switch Up Scouting and Spraying for Plant Bugs During 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.
- At this time, he recommends a threshold of 2-3 plant bugs per drop cloth sample (~0.5 per row foot) during the bloom. During early bloom, consider using both a sweep net and a drop cloth for sampling. Recently published work done in North Carolina supports the fact that net profits will be higher when these thresholds are used.
- 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 with pyrethroids, Othene, and Bidrin.
- In the Midsouth, they have found that mixing Diamond with pyrethroids has lengthened their spray intervals. Note that pyrethroid resistance has been documented in both the Midsouth and North Carolina. Pyrethroids alone should be used with caution, but they will be more effective when tank-mixed with other insecticide classes. Remember, many of these products are harsh on beneficials. That could mean more spider mites, aphids, or bollworms later in the season.
- Researchers in the Midsouth 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. The take home for us is to rotate insecticides, tank mix multiple modes of actions among insecticides, and scout more frequently, even twice a week.