September 19, 2001
With Alabama cotton producers eyeing their most promising crop in the past four to five years, defoliation and harvest timing become even more important, says Dale Monks, Auburn University Extension cotton specialist.
“This is the time of year when producers must decide when to terminate the crop and begin picking,” said Monks at the recent Alabama Cotton Field Day in Belle Mina. “Cotton bolls that are open can lose weight, and quality can decrease due to yellowing or spots, especially under wet conditions.”
Open bolls can deteriorate under wet conditions that last for several weeks, he adds. “Cotton that is defoliated early but not picked for several weeks also may be more vulnerable to tropical storms,” he says.
Cotton fields across Alabama are at different stages, says Monks, and each field must be considered individually. There are several methods, he says, that can be beneficial in determining when a boll is mature enough to open and harvest without affecting yield and quality.
“We suggest using several tests for determining boll maturity. The first test is to drive down the road. If your neighbor is defoliating, then your options are to wait, treat or get out of the truck and look. Remember — each field and farm is different, so the decisions should be made on a field-by-field basis,” he says.
Another, more scientific method of determining boll maturity is to cut open the last boll you expect to harvest, says Monks. If the boll is mature, it'll be difficult to slice with a sharp knife, he adds.
Light brown to tan
“The seed coat should be light brown to tan in color, with cotyledons formed in the seed. Also, there should be no gelatinous material inside the seed. If a boll is immature, it'll be easy to slice a cross-section, and the seeds will be gelatinous and not well formed,” he says.
Another method, says Monks, is “nodes above cracked boll.” “Find the uppermost first-position boll that is cracked. Then, count the nodes above it to the last boll you expect to harvest. If the nodes are four or less, all bolls should be mature. If nodes are five — depending on how bolls were set — the crop still could be mature. If nodes above cracked boll number six or greater, a harvest-aid application will result in yield and quality reductions.'
Growers also can count open bolls and green bolls they expect to harvest, he continues. “If the percent open bolls is 60 or greater, and there are no fruiting gaps, harvest aids can be applied. But this method doesn't work as well if there are large will work fine if the plant is fruited uniformly.”
The science or art of defoliating cotton is a “moving target,” says Monks, and there are four basic factors which can help to determine the success of a defoliation program. These include temperature, crop maturity, coverage and materials used.
“Most products work best under normal, ‘warm’ conditions. Cooler temperatures can slow the activity of most products, and hotter temperatures can increase the efficacy, causing leaves to ‘stick’ in some situations. Once you stick a leaf to a plant, the only way to get it off the plant is with a picker. When temperatures are in the 60s or 70s, it may be necessary to bump up the rate of the harvest-aid material or to use a combination product.”
Adequate coverage is essential, he says, for most harvest-aid products to work satisfactorily. The thicker and more rank the cotton, the more difficult adequate coverage becomes, he adds.
Crop maturity also is essential to a successful defoliation program, notes Monks. Cotton that is naturally mature, he says, is much easier to defoliate than immature cotton.
The selection of the right harvest-aid materials is an equally important factor, he says, with product combinations generally working better than single products.
“Growers will have a few new products from which to choose this year. FreeFall, from Griffin, is a new harvest-aid with the same active ingredient as Dropp. LeafLess — a Uniroyal product — is a Dropp-Harvade combination. There's also Boa, a paraquat product from Griffin. And one new product that just recently received clearance is Aim from FMC. This is brand new chemistry, with a rate range of two thirds to one ounce. You need to be careful with this product from the standpoint of warmer temperatures and sticking leaves.”
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