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When To Take A ‘Chill Pill’

Cotton, Cutout And Termination Of Insecticide Applications

Scott Stewart
IPM Specialist
University of Tennessee Extension

Cotton becomes less sensitive to injury from tarnished plant bugs and other pests as it matures. Below are data from a multi-state study done in the Mid-South on Bt cotton. It shows that terminating insecticide application for tarnished plant bug too early can cause substantial yield loss.

The data pretty consistently showed throughout the Mid-South that insect management during the first four weeks of bloom was critical, and you can relax … but not necessarily quit … after this time.

It is important to continue battling plant bugs, bollworm, fall armyworm and some other pests until a field has accumulated 350 DD60s after cutout. The word “cutout” is synonymous with Nodes Above White Flower 5 (NAWF) and occurs when a field averages five or fewer nodes above the uppermost first-position white flower. I really like “starting the clock” when the field drops below NAWF5. My reasoning is some fields will ride NAWF5 for a week or two, and we want to put those fruit in the picker basket.

Some Specific Guidelines
Once cutout is reached, you need to manage your cotton crop for insect pests for another 16-20 days under typical temperature conditions. After this time, insecticide applications for most pests can be terminated. Here are some specific suggestions to help you make decisions on whether to quit spraying insecticides.

Insecticide tankmixes are often suggested once cutout is reached because we are often dealing with a complex of pests. One of my favorite recommendations is acephate (0.67-0.75 lb) plus a full rate of a pyrethroid insecticide. This is not a great choice for spider mites but is otherwise good at cleaning up a combination of plant bugs and stink bugs. It also generally provides decent suppression of bollworm infestations and some suppression of fall armyworm.

Once cutout is reached, I suggest increasing the threshold for tarnished plant bugs from three to five bugs per drop cloth. Applications for plant bugs can be terminated about 250 DD60s after cutout. This normally takes about 10-14 days.

Plant bug applications can be terminated about 250 DD60s after cutout.

Applications for bollworm, stink bugs, fall armyworm and spider mites may be needed for about another seven days after this point (approximately NAWF5 + 350 DD60s). This is the time you can take a “chill pill” on spraying insecticides. Both fall armyworm and spider mites can potentially cause yield loss beyond NAWF5 + 350 DD60s. However, this almost always occurs when infestations were already present in the field. You can’t walk away from fields just because they hit NAWF5 + 350 DD60s if significant pest problems are present.

A Final Reminder
We typically expect Bollgard 2 to provide better bollworm control than WideStrike cotton. The reverse is true of fall armyworm. WideStrike 3 cotton should provide good control of both pests. I recommend treatment for fall armyworms when four or more larvae are found in 100 blooms and/or bolls or when 10-20 larvae are found per 100 plants. They can be easy to miss if you are not checking white and pink blooms or behind the bracts of medium sized or larger bolls.

A tip off that you are dealing with fall armyworm (and not bollworm) is the presence of bract feeding and feeding scars on the sides of bolls. Also, think fall armyworm if you are regularly finding multiple larvae in flowers.

Contact Stewart at 731-267-6085 or sdstewart@utk.edu.