Excessive moisture has been and continues to be an issue in much of North Carolina’s cotton acreage, impacting both the cotton crop itself as well as complicating field access for needed inputs like herbicides, growth regulators and nitrogen. The short term outlook doesn’t look any better.
Unfortunately, most of our cotton insect pests don’t mind this excessive moisture a bit. All of the succulent wild and cultivated host vegetation could translate into a more prolonged insect season, especially in view of our generally late cotton crop that could be attractive to pests for a longer period. With our generally weak root systems in many areas of the state, we will also be more susceptible to drought if conditions turn dry.
Plant Bug Update
Some areas of the state report low square retentions rates, though in some cases with plant bug levels only about half or less of the 8 per 100 sweep threshold recommended for pre-blooming cotton. This appears to be more common in fields with saturated soils, with square loss due at least in part to excessive moisture. In other areas, mostly in the far eastern region of our cotton production area, plant bugs are prevalent – sometimes to the tune of 2-fold or more the threshold level. Once cotton has begun to bloom, a 2.5 foot black beat cloth (either purchased or homemade) is the sampling device of choice. The black background is better for spotting the small bright green nymphs than the white sweep net (see video here). Like stink bugs, plant bugs are often more abundant in lusher, more rapidly growing fields or field areas. Beat both rows into the center of the ground cloth between the rows, using a threshold of 2-3 plant bugs per sample.
Stink Bugs Coming to a Cotton Field Near You?
Stink bugs also appear to be particularly abundant on both wild and cultivated hosts such as field corn, with brown stink bugs presently being particularly common. Despite some persistent anecdotes to the contrary, remember that stink bugs, especially the adults, are not regarded as a significant pest of cotton until the first appearance of new bolls during the initial week of bloom, as documented in this research article. Even during the first week of bloom when young bolls are scarce, our suggested threshold is 50% internal warts or damage. This would be a particularly good year to scout carefully and frequently for stink bugs and to make use of the dynamic threshold that varies by week of bloom.
Although spider mites most often thrive under dry conditions, we have had several calls this week about building mite levels from wet areas of the state (I guess that doesn’t rule out much). In one case, the light stippling leaf dots and reddening had progressed to the point of lower leaf defoliation with mites on most plants. That’s not a bad definition of a threshold level of mites.