Managing Proper Defoliation Timing
From Cotton Grower Magazine – August/September 2016
With boll set rapidly increasing across the Cotton Belt – and open bolls not far behind – it’s time for growers to start thinking about proper defoliation timing for fall harvest.
The exception, as usual, comes in the Coastal Bend and southern parts of Texas, where cotton harvest is well underway, if not complete. Early news out of the Rio Grande Valley and coastal areas around Corpus Christi has been promising, with reports of 2½ to 3 bales per acre on some dryland fields, says Gaylon Morgan, Texas A&M AgriLife Extension cotton specialist.
But what about those acres in other cotton-growing areas? According to Morgan, a lot depends on the approach growers want to take regarding defoliation, plus the environment they’re growing in. And, are they defoliating primarily for yield or quality?
“When we get to defoliation timing, it’s about selecting the correct time to get the leaves off,” he says. “There are different methods that people use when making that choice, including heat units, nodes above cracked boll or percent open boll. There are a lot of rules of thumb with cotton, and there are many ways growers can move forward with it and be successful.
“One of the main reasons we use defoliants or harvest aids is to gain an overall timely harvest and get the cotton out of the field before bad weather occurs that may degrade color, but also affect length, strength and other fiber characteristics.”
Morgan also suggests growers keep nitrogen management in mind, especially in areas like West Texas with shorter growing seasons. Studies by Randy Boman at Oklahoma State have shown a direct correlation between higher nitrogen rates and lower micronaire.
“There’s a point where growers can maximize yields and have decent quality cotton, too,” points out Morgan. “Pounds still pay the bills. But quality is more important than it has ever been.”
Defoliation timing can certainly help growers manage fiber quality, especially micronaire. But, adds Morgan, it’s also a fact that some varieties are just easier to defoliate than others. Although the variety decision was made months ago, it’s something that growers need to think about when prepping for harvest and planning for next year.
“Growers need to be aware of the level of leaf hairiness on their varieties,” he says. “The higher the leaf hairiness, the more prone those varieties may be to higher leaf grades if adverse weather conditions occur and growers are pushing the limits with early morning or late evening harvesting.”
With this year’s cotton economics, Morgan understands that some growers may be looking to save a little money and rely on a single application of defoliant before picking. But more often than not, a second shot is needed to manage regrowth or knock the last leaves off of the plant.
For growers who are stripping cotton, two passes are generally needed – one to defoliate and the other to desiccate the crop – in order to minimize the amount of leaf going into the stripper and help preserve quality. The more leaf and plant material in the lint, the more lint cleaning is required, which can increase fiber breakage and decrease lint quality.
But in spite of good planning, there’s still one uncontrollable factor that growers may have to deal with at harvest.
“Regarding defoliation, weather trumps all,” adds Morgan. “If we have a bad harvesting season – whether it stays wet or humidity stays high – that trumps pretty much anything else growers can do. We’ll just have to deal with it at that point.”