Plant bug, stink bugs and bollworm infestations often start peaking about the same time every year.  The last 10 days of July and the first 10 days of August is a critical window.  The reality is that these pests really tend to occur at their highest numbers beginning about 3-4 weeks after first bloom, so the crunch time will vary depending upon the maturity of your crop.  We currently are in an insect lull in many areas, but intensive scouting will be required for the next several weeks as the money part of the crop (bolls) are being produced.  The presence of bollworm eggs is being reported for flowering cotton in our southern most counties and those along the Mississippi River.

Below are some treatment thresholds to keep in mind between first flower and NAWF5 + 350 DD60s.  A general rule of thumb is that it takes about 18-22 days to accumulate 350 DD60s in normal summertime temperatures.  I believe these thresholds are aggressive and there is no need to “shave” them despite the relatively good price of cotton.

1)  Tarnished plant bug – an average of 3 or more per drop cloth or 15 per 100 sweeps.  The drop cloth is my preferred sampling method in cotton during crunch time because it is better at finding nymphs, which will often compose the vast majority of the population.

2)  Stink bugs – 1 per drop cloth or if 20% or more of thumb sized bolls show internal evidence of stink bug feeding.  I touched on monitoring boll injury from stink bugs last week.  Tip – consider counting stink bugs as equivalent to 3 tarnished plant bugs when making treatment decisions if both pests are present.

3)  Bollworms – for Bt cotton including WideStrike and Bollgard II, treat when 4 or more larvae are found per 100 plants.  Do not count very small larvae in Bt cotton (< 1/4-inch long) to allow the Bt toxins time to work.  Treatment is sometimes suggested when 2% or more boll damage is found and larvae are still present. 

Except in unusual circumstances, treatment based solely on the presence of “worm” eggs is discouraged, again to give the Bt technologies a chance to work.  Some eggs may even be those of tobacco budworm, a non-threat to Bt cotton.  High egg counts (>30% of plants) should be considered, and this is truer for WideStrike varieties because they typically do not provide the same level of bollworm control as Bollgard II varieties.  Certainly, the presence of high egg counts should cause you to chose a pyrethroid insecticide as a tank mix partner if you need to spray for plant bugs or stink bugs is needed.

Some go to treatments for crunch time are listed below.  These options are expected to provide control of plant bugs (including clouded plant bug) and stink bugs.  Options having a pyrethroid component will also help to control bollworms if they are present.

Some preferred treatment options for plant bugs/stink bugs in blooming cotton.

* Pyrethroids might include Asana XL, Baythroid XL, Brigade (bifenthrin), Declare, Karate Z, Mustang Max and others.  With the possible exception of bifenthrin products, do not expect synthetic pyrethroids to provide adequate control of tarnished plant bugs if used alone.

Several premixes such as Brigadier, Leverage and Endigo contain a neonicotinoid component (imidacloprid or Centric).  UT suggests avoiding further use of neonicotinoid insecticides after first bloom as a resistance management tactic to preserve this class of chemistry.  However, you might consider their use if neonicotinoid insecticides have not been used for several weeks, thus not exposing consecutive generations to the same mode of action.