Harvest aid decisions have changed significantly for West Texas cotton farmers over the last 10 to 20 years.
New chemistry and new varieties offer growers more options to open bolls and drop leaves, but the capricious nature of weather and the gremlins that often thwart even the most thoroughly thought-out defoliation schedule continue to make the chore interesting.
Crop maturity, medium-to short-term weather predictions, and variety play crucial roles in cotton defoliation, says Billy Warrick, Extension agronomist at the Texas Extension and Research Center in San Angelo.
He discussed defoliation challenges at the recent Concho Valley Cotton Conference at San Angelo.
Last season provided plenty of those challenges.
“Squares were out of kilter,” Warrick says. Mis-formed squares affected flowering and “we lost early squares.” Unusually hot conditions during May and June affected plants season-long.
“We had about 20 days of temperatures topping 100 degrees in May and early June; on open soil around cotton plants they probably hit 120 degrees.”
He says plants developing under stress conditions produce tougher leaf surfaces, which may affect harvest aid performance.
Other in-season conditions also affect how those materials work. Maturity delays, too much nitrogen fertilizer, insect damage, and excess plant growth affect defoliation. Irrigation and rainfall late in the season, when the plant needs to shut down, also create challenges.
“If nutrients are not pulled down to a low level and then rain comes, regrowth is likely,” Warrick says.
Cool temperatures at the end of the season also slow the cotton plant's response to harvest aid materials. “Increased rates may be necessary.”
Variety selection also has changed the way farmers look at defoliation. “We've seen a lot of changes the last few years. Twenty years ago, we were planting 75 percent stripper cotton varieties; now we plant less than 20 percent stripper types. Picker cotton is easier to open.”
Warrick says farmers have more chemical options for defoliation. “Know the products. Evaluate the crop needs and understand the chemistry in each product.”
He says desiccants such as paraquat work best when applied late in the afternoon so it can spread over the leaf surface and activate with morning light.
Materials such as Ginstar, Blizzard, Resource, ET, and Aim are light sensitive and, if applied under cloudy conditions, do not perform well. “It's best to apply these materials on bright, sunny days.
“Focus on coverage,” Warrick says. “We have no systemic materials, so coverage is critical for best performance. We've had some problems with adequate coverage the last few years. Nozzle type, nozzle size, flow rate, pressure, and height of application are important considerations. It's a challenge to get the material into the canopy, so we need to use plenty of water and adequate pressure.”
Adjuvants may improve coverage and performance.
Warrick says farmers must be cognizant of environmental conditions, such as humidity and temperatures, as they prepare to apply harvest aids. “Humidity is best on the high side. And we need warm daytime and nighttime temperatures.
“Be aware of wind speed and direction — drift is a concern with high-pressure applications, so be aware of sensitive areas and don't apply harvest aids when wind blows toward those areas.”
He says farmers should be prepared to stop applications if wind shifts or becomes too strong for safe application.
Crop maturity poses a critical challenge. “Maturity affects product performance, so target a maturity range for harvest aid application. Performance will be better when the crop is in the target range. Farmers should select the uppermost boll they intend to harvest and time applications when that boll is ready.”
Warrick recommends looking for a tan seed color inside bolls as a guideline for that top harvestable boll.