⋅ BY AMANDA HUBER ⋅
After being behind much of the season in growing degree days, conditions in late July and August allowed the cotton crop to catch up in many areas of Georgia.
“Between severe weather, plant bug problems galore and deer damage, it has been a tough go,” said Camp Hand, University of Georgia Extension cotton specialist. “In mid- to late-July, the crop turned a corner and looks really good. We have great yield potential out there, and my hope is that we can get it in the basket and to the gin.”
As the crop approaches defoliation, Hand offers these points to keep in mind.
→ Pull the defoliation “trigger” at the right time. “There are many ways to determine the appropriate time to defoliate your cotton crop – 60% to 75% open boll, four nodes above cracked boll and the ‘sharp knife’ method,” said Hand, who recommends using at least two methods to determine the correct timing.
To determine percent open boll, count the number of open bolls and the number of unopened, harvestable bolls. Divide the number of open bolls by the total bolls and multiply by 100. For NACB, count the number of nodes from the uppermost first position cracked boll to the uppermost first position harvestable boll. When that number is four, on average, it is time to defoliate.
“For the ‘sharp knife’ method, cut into the uppermost boll you intend to harvest and look for a black seed coat with developed cotyledons inside. Also, you want the lint to string out,” Hand said. “Keep in mind that deer damage and severe plant bug infestations that were not controlled will likely delay maturity, thus checking your fields is of paramount importance!”
→ Use the correct products and rates to accomplish your intended goals. Hand said, there are three main goals in defoliation – removal of juvenile and mature leaves, regrowth prevention and boll opening. “Determining your goals, as well as the environmental conditions surrounding defoliation, will assist in the decision on products and rates.”
Products and rate recommendations can be found beginning on page 143 of the 2023 UGA Cotton Production Guide, which can be found at www.ugacotton.com/production-guide/.
→ Control regrowth. One of the best things you could do to manage whiteflies in the coming year is to defoliate your cotton crop in a timely manner, Hand said.
If the bottom crop is ready to defoliate, but conditions have caused it to start regrowing and blooming, is it worth waiting on this top crop? Hand said it is probably best to defoliate it.
“Investing more money to try to make a top crop doesn’t seem worth it for a couple of reasons. One, you probably have enough money tied up in the crop already, and waiting on that top to finish will cause the bottom crop to deteriorate.
“Secondly, if regrowth is allowed to keep going, that young growth is like cotton candy to whiteflies. They will keep feeding and reproducing and will contribute to a greater population going into the winter time and next year,” Hand said.
→ One shot versus two? “In Georgia, we primarily use one shot for defoliation, and it works very well,” Hand said. “Rarely will I recommend a second shot unless something went wrong on the first.”
→ Use more water. Hand said, “A higher sprayer output in gallons per acre works better than a lower sprayer output with respect to defoliation, even if you decide to use dicamba nozzles. Shoot for 15 GPA if you’re defoliating with a ground rig to get defoliant down in the canopy.”
→ Keep defoliants on target. “It is imperative to apply all pesticides, including defoliants, responsibly,” Hand said. “Keep the lessons from ‘Using Pesticides Wisely’ trainings at the forefront of your mind.”
Producers should keep in mind what is around fields, the wind speed and direction at the time of and after application and keep the spray booms 24 inches above the crop canopy. Use nozzles that produce larger droplets with a higher spray output.
“It is important to reduce pesticide drift in general, but also from the standpoint of protecting the chemistries we use,” he said.
If defoliation is still a few weeks away, the question then becomes whether fungicides may be needed to protect yields. UGA Extension plant pathologist Bob Kemerait says areolate mildew is one disease that can affect cotton later in the season.
“Growers within four weeks of defoliating their cotton need not worry about managing areolate mildew,” he said. “Where it occurs in a crop with defoliation a month or more away, and weather is favorable for continued development and spread of the disease, a fungicide may be beneficial to protect yield.”
Just as timely use of a fungicide protects hundreds of pounds of lint, timely defoliation and harvest are key to producing a high-quality crop.
In a final tip, Hand said, only defoliate what you can come back and harvest in about 10 to 14 days to help preserve crop yield and quality.