Tips for Managing Cotton Growth in Variable Weather Conditions

I’ve been fielding questions lately on managing plant growth after Hurricane Barry’s deluge, coupled with the “cool” temperatures forecast for this week (week of July 22). Most of these discussions have led to someone mentioning “cotton likes it hot,” followed by a comment indicating cotton growth may slow this week.

I do not believe it will. Instead, I’m concerned it may be difficult to slow down.


Many are reporting a decent physiological square shed after the cloudy conditions last week. If you add all these factors up, it appears – in football terms – that the crop may be deep into the secondary, and we don’t have the best safety.

It is true that cotton likes a long growing season, and we typically make better crops when we have more heat units. Good years, however, are typically not associated with blistering mid-season heat. Instead, they are associated with warmer springs and falls.

High humidity and 95+ degree daytime temperatures result in plant stress. Cotton is pretty good at handling that stress, but most scientific literature suggests ideal growing temperatures fall around 86 degrees during the day and 68 degrees at night. Those temperatures closely match our current forecast. Couple that with another good rain across much of West Tennessee on July 22 PLUS a decent environmental square shed, and you have all the required conditions for excessive vegetative growth.

Just a few things to keep in mind right now:

  • The most commonly used 4.2% mepiquat chloride products have a rainfast period of close to 8 hours.
  • Using more expensive products like mepiquat pentaborate or mepiquat chloride + cyclanilide or incorporating an adjuvant can reduce that rainfast period.
  • If rain falls within a few hours of your application, monitor growth closely and be ready to re-apply.
  • Watch the fourth and fifth internodes down from the top of the plant. These are the internodes that represent current growing conditions.
Tips for Managing Cotton Growth in Variable Weather ConditionsPhoto: University of Tennessee

With a little luck, we should see developing bolls begin to slow vegetative growth in the coming weeks, but don’t expect that slowed growth to occur now.

The take home: Expect aggressive PGR applications to be warranted on many acres this week.