Weather plays a critical role in harvest aid application timing decisions.
Applying cotton harvest aids used to be described as about as much “art as science.” That may no longer be the case as years of research and experience have shown growers some objective criteria to follow in deciding when to apply harvest aid materials.
It’s still somewhat of a balancing act, however, says Jason Ott, Texas AgriLife Extension agent for Nueces County.
“Once bolls mature and open, cotton plants may begin to resume vegetative growth, especially with additional rainfall and excessive soil nitrogen,” Ott says in his most recent weekly newsletter. “Any vegetative regrowth before harvest can lead to significant problems due to trash in the harvested cotton, lint staining and decreased color in picker-harvested cotton.” High moisture content also may be a problem.
Timing, he says, is critical. That’s where the balance comes in. “Proper timing of harvest aid applications can be thought of as a balance between allowing immature bolls to mature and preserving the lint quality of earlier maturing bolls,” Ott said. “Applying harvest aids too soon may halt development of green bolls that could contribute to yield, and could negatively affect fiber and seed quality.”
Scheduling options
Farmers have options to take some of the guesswork out of application timing. They can use the percent open boll equation, the sharp knife technique, or count nodes above cracked boll.
Most harvest aid labels refer to percent open boll, the percentage of open harvestable bolls. Product labels usually recommend applications when 50 percent to 70 percent of harvestable bolls are open. “This is not the most accurate method,” Ott says. “Research has shown that optimal application timing may range from 42 percent to 81 percent open boll, depending on distribution of fruit on the plant.”
A sharp knife is something of an old-school method of determining crop maturity. Growers select the uppermost harvestable boll and cut a cross section with a sharp knife. If the boll is difficult to cut (with maturing fiber) and the seeds have dark seed coats and fully developed cotyledons, the boll is mature.
“Very light colored seed coats and the presence of ‘jelly’ inside the seed indicate an immature boll.”
Ott says counting nodes above cracked boll (NACB) is also useful to schedule applications. “From the uppermost first position cracked boll, count the main stem nodes up to the uppermost harvestable boll. Sufficient research has shown that harvest aids applied at three NACB will not result in lint weight loss. If harvest aids are applied at NACB greater than four, yield loss can be expected.”
Weather factor
Weather also plays a role in proper harvest aid application and offers another area of uncertainty. Efficacy of harvest aides is significantly affected by environmental conditions, Ott says. “The most effective harvest aid applications are made under warm, sunny conditions with low soil moisture (but sufficient to maintain active growth).” Excess soil nitrogen also affects harvest aid efficacy. Application is also more effective on mature plants that are not producing new leaves.
Thorough spray coverage is critical, as is the appropriate spray nozzle. Uniform coverage and small spray droplets are best. “Total spray volume should be at least 15 gallons per acre for ground applications and five gallons per acre when aerially applied.”
Ott suggests several publications to help cotton harvest aid decisions, including “High Plains and Northern Rolling Plains Cotton Harvest-Aid Guide”.
Ott encourages Nueces County and other nearby cotton farmers to check harvest aid plots on the Claude Otahal Farm. For more information call (361)767-5223.
Another critical late-season cotton issue will be post-harvest stalk destruction. Texas Boll Weevil Eradication Foundation Program Director Larry Smith explained the need for removing cotton plants during the recent Producers Information Exchange Tour, a National Cotton Council and Bayer CropScience project currently in its 27th year.
“We have to be diligent to prevent re-infestation,” Smith said. “That’s especially difficult in a sub-tropical region (South Texas) because it freezes only about once in 30 years.”
He said three cotton plants that survive after harvest and into the winter are capable of hosting as many as 8,000 boll weevils, making cotton stalk destruction a crucial factor in the South Texas boll weevil eradication effort.
Volunteer cotton is common in harvested fields but smith said Boll Weevil Eradication personnel also look for cotton plants along roadways, railroad right of ways, gin yards and even in residential neighborhoods.
“We will try to take out every surviving cotton plant,” he said.
