Cotton Insects on the Decline?
This week we appear to be much closer to putting cotton insects in the rear view mirror. Only stink bugs remain a possible threat in some late cotton fields, with cotton aphids, spider mites and bollworms no longer able to inflict economic damage.
Even without using the stink bug card or web app for treatment decisions based on internal boll damage and week of bloom, if hardened off speckled bolls (including cracked and/or open bolls), outnumber small bolls in the top of plants by about 5 to 7 to one, stink bugs should no longer be an economic problem in those fields. In those situations, the internal boll damage treatment threshold (still based on the sampling of quarter-sized bolls) would likely be 50% or above. My guess is that less than 15% of our cotton acreage is still vulnerable to stink bug damage as of today. Often at this time of year, stink bugs tend to gravitate more to soybean fields.
Although the caterpillar toxin in early-planted WideStrike and Bollgard II cotton varieties tends to lose some of its effectiveness at this time of year, bollworm moth levels appear to be too low to create a problem in the coming days or weeks.
Beginning this coming week, I’ll begin the 29th and final year of our annual damaged boll survey. This year, our project’s boll damage assessments will target only 1) what kind (mostly bollworm vs. stink bug) and the amount of boll damage and 2) possible regional differences in boll damage. We will not be making comparisons between BGII and WideStrike bollworm efficacy this year. Past surveys have clearly demonstrated that in producer-managed cotton fields, BGII was more efficacious against bollworms than WideStrike, but the differences in bollworm damage between these technologies were very slight. Additional Bt genes available in commercial lines going forward (i.e., WideStrike 3) will render differences in caterpillar efficacy between competing technologies even more minimal. (That is, unless bollworm or budworm resistance to Bt genes develops!). It’ll be interesting to find out how much late season boll damage our producers experienced in 2013.
Article by Jack Bacheler, NCSU Extension Entomologist