The same bollworm flight affecting soybean is occurring in cotton. The areas affected are spotty but more widespread.  There have been many calls about heavy (20-70%) egg lays in some fields. Bollgard II appears to be holding up well, but the presence of 2-3 day old larvae at a level of 5-25% plants infested plants has been reported on WideStrike varieties (e.g., PHY375 WRF).  Of course, any non-Bt cotton should be carefully monitored for both bollworm and tobacco budworm.

Tarnished plant bug infestations are all over the board, ranging from below threshold to 6-7 times threshold (20+ per drop cloth).  Stink bug infestations are generally low to moderate with some exceptions.  The presence of threshold levels of plant bugs or stink bugs makes insecticide selection an easy one in the presence of a significant bollworm flight.  Applications should include a pyrethroid, and the best treatments will include a tank mix partner such as Orthene/Acephate (0.33 – 0.5 lb/a), Bidrin (2-4 oz/a), Diamond (4-6 oz/a), Vydate (6-8 oz) or Dimethoate (6-8 oz).  There are other options that can also be considered including Endigo (4-5 oz) and Leverage 360 (3.2 oz).

I’ve included some test data from two tests rated this week that show the relative performance of selected treatments.  In the first table you will see several “go to” treatments.  In this high pressure situation, virtually no treatment brought TPB populations below treatment level (3 per drop cloth) after a single application.  In heavy pressure scenarios, you are almost always better off making two applications rather than trying to clean up a field with high rates using a single application.  Reminder – two applications at a 5 day interval should be expected when TPB infestations are high (exceeding threshold by 3-4 fold).  Tightening up the spray schedule for two consecutive sprays can often prevent chronic infestations and a third trip across the field.

Numbers of tarnished plant bugs 5 days after treatment (Haywood Co., 8/1/11).

Numbers not followed by a common letter are significantly different (P < 0.05, LSD).
* Discipline = Bifenthrin 2E.

The table below makes the point that using only a pyrethroid insecticide (is this case Declare) will not provide satisfactory control of tarnished plant bugs.  The possible exception is bifenthrin (e.g., Brigade, Fanfare, Discipline, etc.), and I would not recommend this product alone when pressure is high.  You will also note that adding a medium rate of Vydate improved control considerably, and you would expect a similar response with other potential tank mix partners such as Acephate, Diamond and Bidrin.

Numbers of tarnished plant bugs 5 days after treatment (Haywood Co., 8/1/11).

Numbers not followed by a common letter are significantly different (P < 0.05, LSD).
* Declare 1.25 EC = Gamma-cyhalothrin;  Transform 50 WG = sulfoxaflor (not labeled for use at this time).

Treating for Bollworms: If plant bug and stink bug populations are below treatment level, the decision to treat should primarily be based on larval counts.  Treatment would be recommended anytime larval counts exceed 4-5% infested plants prior to NAWF + 350 DD60s (see below).  Assuming we are talking about Bt cotton, you should generally NOT consider very small larvae when making treatment decisions, allowing the Bt traits time to work.  However, don’t totally ignore the presence of many small larvae.  You should be able to use one of many synthetic pyrethroid insecticides on Bt cotton with good success.  However, I would lean toward using a bifenthrin product (e.g., Brigade, Fanfare, Discipline) if plant bugs are present.

When should I quit spraying for plant bugs, stink bugs and bollworms?  The easy answer is when the field reaches node above white flower (NAWF) = 5 + 350 DD60s.  Under the extreme heat, this may be as little as 12-14 days after reaching NAWF5.  In reality, you can probably start relaxing the threshold for tarnished plant bug a few days sooner.  I get several calls each year asking about whether another application is needed, but without seeing the field or knowing the date of NAWF5, all I can do is make an educated guess.  Here are a couple of signs you have reached or past this point: 1) the terminal has shed most the squares and small bolls and 2) you have a hard time finding a first position white flower, and when you do, it is only 1 or 2 nodes below the terminal.  The bugs will often let you know.  Populations of plant bugs usually drop quickly as the food supply drops off and the bolls become hardened.