A prolonged dry spell followed by heavy late summer rains and below average September temperatures have set the scene for Mid-South cotton defoliation conditions that are challenging at best.
“In some areas, we’re seeing regrowth from the top to the bottom of the plant, and these new, small leaves that are very close to the stem are very difficult to remove,” says Tyson Raper, University of Tennessee Institute of Agriculture Extension cotton specialist.
While we often think of cotton regrowth as something to worry about after defoliation, Raper says the flush of young leaves caused by late season rains could create more pre-defoliation headaches for producers.
“If a producer has much of this vegetative growth in the axillary buds, you’re looking at two applications to defoliate,” says Raper. “The first would target the large leaves high on the canopy. And the best way to target these small leaves would be increasing volume, increasing pressure and running fairly aggressive products. As temperatures drop, one of the PPO’s is going to be our only option.”
Raper kicked off UTIA’s first-ever Virtual Cotton Tour on September 2, 2020, with a presentation covering defoliation, as well as nutrient deficiencies and other ongoing research projects. A total of seven recorded presentations, covering a variety of cotton production topics remain available for viewing at the UT Crops YouTube channel or on the UT Crops News Blog (news.utcrops.com).
Cooler Temperatures Add More Complications
Dropping cotton leaves could be further compounded by cooler than normal September temperatures. In some parts of the Mid-South, nighttime lows are expected to spend the better part of a week below 60 degrees F, negating the effectiveness of certain defoliation products.
“Thidiazuron, the active ingredient in products such as Daze, Dropp, Freefall and Takedown, combined with a boll opener has excellent activity on juvenile and mature leaves,” says Raper, “but it requires overnight temperatures above 65 degrees to achieve the best activity.”
He suggests adding a tribufos product, such as Def or Folex, to thidiazuron to heat up the mix and create more injury to the leaf. Tribufos plus a boll opener is also a good option for defoliating cotton with little to no juvenile growth. However, Raper cautions tribufos alone will not provide much activity on juvenile growth and will not provide regrowth control.
“A thidiazuron plus tribufos plus boll opener mixture would be my preferred concoction if temperatures hold above 60 degrees, but I encourage producers to reach out to local extension agents to determine the best defoliation concoctions for their area weather conditions.”
“But if you’re seeing regrowth low on the plant, you have to address it with two applications. If you try to run a single application, you’re definitely going to see an increase in color and an increase in leaf grade when you get the picker out there.”