An old television commercial once had the tag: “It's not nice to fool Mother Nature.” But when it comes to better managing when and where you can harvest cotton with harvest aid treatments, “Mom” probably doesn't mind.
“There are many benefits that can be expected from a good defoliation job,” says Mississippi State University cotton agronomist Will McCarty. “Defoliation improves harvest efficiency in fields with large green plants. Defoliated fields tend to dry out faster, permit more harvesting hours per day and allow harvesting sooner after rain.”
Mike Friemel, who harvested his third cotton crop in 2003, likes to manage his harvest around when he combines corn. He farms several thousand acres of cotton and corn near Groom, TX.
His rotation is grown primarily under center-pivot irrigation, with dryland cotton in most of the corners. Since corn must be harvested when it's naturally matured and dried down, he can choose when to harvest cotton thanks to boll openers, defoliants and desiccants.
“We've been growing corn a long time and usually know how to manage our production and harvest since we have our own storage system. But with the addition of cotton, timeliness is much more important,” says Friemel. “I depend on a crop consultant (Justin McGee) to help coordinate both corn and cotton harvest. Corn harvest dictates most of our cotton harvest aid program, since we don't have the manpower to do both at the same time.”
McGee recommends what most growers or consultants do — start with an application of a boll opener. “We start with a 1.5 pt. of Prep (ethephon) every year, then it's a matter of what we will add to it, depending on the conditions we're facing,” he says. “If cotton is too green, I feel the defoliant Ginstar works best. If the weather is cool and wet, then we might go with Prep and Def. We then follow those applications with Gramoxone Max, (formerly Cyclone, a paraquat-based desiccant). If the crop is late and we're still cutting corn, an application of Ethephon prior to frost may be all that's necessary.”
In Friemel's Ginstar program, he might start with 1.5 pt. of Finish defoliant tankmixed with 8 oz. of Ginstar, then followed by 1 pt. of Gramoxone. Weather permitting, he can harvest five days later.
Randy Boman, Texas A&M cotton agronomist in Lubbock, where mostly stripper-varieties are grown, says the yield and condition of the cotton should determine the type of harvest aid material chosen. “If leaves are beginning to shed and have reddish to purple pigmentation, they'll drop off the plant easier without detrimental ‘leaf stick,’ which occurs when the leaves don't drop and are frozen on the plant,” he says. “If the leaves ‘stick,’ then lint quality can be reduced due to increased leaf content in the fiber.”
For lower yielding cotton of less than one bale/acre, Boman usually recommends paraquat-based desiccants, such as Gramoxone Max. “If plants are large and there are a lot of leaves remaining, sequential applications of low rates of desiccants are sometimes used to promote defoliation and reduce leaf sticking,” he says, noting that the use of desiccants should be discouraged when seedling wheat is close to targeted cotton fields. “Drift from desiccants can cause severe damage to developing small grain plants grown for cover or harvest.”
For stronger yielding cotton, Boman says tank mixes of Ethephon and defoliants are effective in higher yielding cotton to open bolls and drop leaves.
“Warm temperatures of about 80°F are normally required to obtain the maximum boll-opening response,” he says, “although higher rates of Ethephon are still effective under cooler conditions.” Tank mixes of Harvade, a sodium chlorate defoliant and 1 pt./acre of crop oil concentrate (COC) have performed well in medium-yielding cotton and have good desiccation activity on morningglories. A sequential paraquat application will likely be required for stripper harvesting.
Roundup can also be used in a tankmix with various defoliants to achieve late-season control of weeds and to reduce populations of perennial grasses and vines.
Boman and McCarty see “nodes above cracked boll” (NACB), as a solid tool to help time harvest aid application.
A recent Beltwide cotton harvest aid project determined that if the uppermost first position-cracked boll is within three nodes of the uppermost harvestable first position boll, then no lint weight will be lost if a defoliant-type harvest aid is applied at that time.
“However, if the uppermost harvestable first position boll is four or more nodes above the uppermost first position cracked boll,” says Boman, “then potential for some lint loss exists. The lint lost potential increases as the NACB increases.”
Micronaire reduction generally follows a similar pattern when using the nodes above cracked boll criterion. “If applying desiccants, more bolls must be mature in order to reduce the risk of fiber weight loss or reduction of micronaire, thus two to three NACB would be a better target,” says Boman.
McCarty warns that defoliation may have some disadvantages and limitations. “When plants are defoliated, the fiber and seed development essentially stops,” he says. “Therefore, if too many bolls are immature at the time of application there can be a reduction in yield and quality associated with the treatment.”
For the NACB system to work, fields should be mapped regularly to make data reliable. “This is one of several techniques to help in timing decisions,” says McCarty. “It should be used accordingly to validate or supplement other techniques. A physical examination of the bolls should precede any application of defoliant.”
|Finish 6 Pro||Bayer CropScience|
|Def||Bayer Crop Science|
|ET 2.5%||EC Nichino America|
|Dry formulations include Dropp from Bayer CropScience and Freefall from Griffin LLC.|
|SOURCE: RANDY BOMAN, TEXAS COOPERATIVE EXTENSION, LUBBOCK.|