Opening bolls immediately after a freeze

• By Tyson Raper •

open bolls
Photo courtesy University of Tennessee

The forecast lows for Thursday, Friday, Saturday and Sunday nights in Tennessee have bounced around over the past few days, but this morning they included a 26, 28, 28 and 31 degrees. I’ve passed many fields with a large percentage of large bolls in the upper canopy still closed. Today (10/29) is the day to make any last-ditch effort at opening those bolls; it is likely all bolls remaining closed after this weekend will freeze shut.

If you have a large percentage of bolls still closed, your best option is ethephon. Remember the season-allowed rate of our standard 6 lb ethephon products is 42 oz/acre. It would be wise to apply all of the remaining ethephon allowed by label (up to 42 oz/acre) now.

While 48 hours is a short time period to allow that product to work, it is the best boll opening material we have and it represents our best shot at opening the remaining bolls.

For those who do not have any room for more ethephon, paraquat can also provide boll opening by drying the boll walls and encouraging the boll sutures to rupture. Paraquat is almost always rated as a poor boll opener, and you should expect all remaining leaves on the plant to be stuck after this application.

According to Drs. Guy Collins and Keith Edmisten at North Carolina State University, 8 to 11 oz/ac of a 3 lb paraquat product would be the best rate but expect the response to this application to be inconsistent. I would also include ethephon with this paraquat application if you can.

Note that aggressive applications like this can result in increased chances of bark if harvest is delayed; every effort should be made to harvest acres which receive paraquat within 7 days of the application to attempt to minimize the chances of bark entering the basket/accumulator.

If you decide to run ethephon and any leaves remain in the field, I would suggest including a defoliant or desiccant. Any product which encourages defoliation will also result in a release of ethylene which can further enhance boll opening.

Aim/ET/Sharpen with surfactants would be great options if juvenile growth is present. If mature leaves remain, Folex would be my preferred product. My recommendations would be near the upper limit for each of these products and my surfactant choice would be hot.

Dr. Tyson Raper is University of Tennessee small grains and cotton specialist. He may be reached at

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