Recent moisture and warm temperatures have promoted vigorous growth in much of Oklahoma's cotton acreage, says Shane Osborne, Oklahoma State University Extension specialist, at the Oklahoma Southwest Research and Extension Center south of Altus.
Late last week Osborne said the area was receiving rainfall “with significant chances of rain predicted.
"Most cotton planted in early May that has been adequately protected from fleahoppers is beginning to or will soon be blooming. Traditionally, this has been the time most producers consider using a plant growth regulator (PGR). Determining the need for a PGR is the first step. Typically, we utilize internode length to help make this determination,” Osborne said.
“Counting the uppermost un-furled leaf as zero, count down five nodes on the plant. The distance between nodes four and five represents the most recently completed growth. This distance will not increase any more. All the nodes above the fourth are still growing and cannot be used to make this determination.
"If the distance between the fourth and fifth node is two inches or greater, a growth regulator may be used. If it is less than two inches, a growth regulator is not necessary as long as the fruit load on the plant is good. It is also important to remember that plant growth regulators are used primarily to promote earliness, crop uniformity and to control plant height. They accomplish this by helping the plant to maintain a growth habit that focuses on reproduction (fruiting), rather than vegetative growth. Although vegetative growth (development of the stalk and branches) is very important early in the season as it relates to yield potential, it can also be counterproductive later on, especially if early fruit-retention is low.
Osborne said significant loss of early-season fruit may result in vigorous vegetative growth before the plant's focus returns to reproduction.
“This is something to avoid. A heavy fruit load is always the best natural growth-regulator program. A well fruited plant will always maintain a steady growth pattern, compared to one that experiences fruit loss. The time it takes for the plant to recover from fruit loss and begin setting new fruit causes a significant delay in maturity.”
Those delays, he said, may result in significant yield loss. “As always, an early crop is the best crop. So, there are some things to remember when considering a PGR. First and foremost, never consider using a PGR unless you expect soil moisture conditions to remain good for the next 10 to 14 days and the crop is not experiencing any type of stress, including moisture, herbicide injury or disease.
"Secondly, remember mepiquat chloride accumulates within the plant so multiple applications have an additive effect. It is better to start out with modest rates and add more rather than over-supply an initial application.
Variety is also a consideration, Osborne said. "If you are using a variety for the first time and may be unsure of the growth habit, check with the seed company. All seed companies are familiar with the growth habits of their varieties and those characteristics are typically listed in annual variety guides. Usually the only time varieties exceed their known growth habit is when excessive nitrogen is present (usually when cotton follows alfalfa or peanuts). In those instances, above average growth can be expected and PGR strategies need to be more aggressive.”
The standard PGR strategy has been eight ounces per acre (of the traditional products containing mepiquat chloride) at first bloom, with a possible sequential application in 10 to 14 days if necessary.
“In recent years, several new products have become available, some of which require different rate structures. Two of the newer products available are Pentia and Stance. Pentia utilizes the traditional rate structure (similar to Pix or generic mepiquat chloride), while Stance requires a different rate structure due to its formulation. A typical PGR strategy in irrigated cotton, utilizing the traditionally formulated products (Pix, Pentia or Mepex) would be six to eight ounces per acre at first bloom with the possibility of a sequential four to eight ounces per acre application 10-14 days later.
"A typical Stance program in irrigated cotton would be two ounces per acre at first bloom with the possibility of a sequential two ounces per acre application 10 to 14 days later. In addition, it is very important for those using Stance for the first time to remember the lower rate structure in order to avoid an accidental overdose.
Osborne recommends a more conservative program for dryland cotton. “In dryland production, it is doubly important we make sure our crop will not experience any moisture stress in the next 10 to 14 days after application.”
He suggests lower rates in dryland cotton. “A good PGR strategy for vigorously growing dryland cotton is four ounces per acre (traditional Mepiquat chloride products such as Pix, Pentia and Mepex) at first bloom. If vigorous growth conditions still exist 14 days later, a second application may be warranted.
"If Stance is the products of choice, one-and-a-half to two ounces per acre can be applied at first bloom. It is important to remember that in dryland cotton PGRs should be applied only to vigorously growing cotton with good soil moisture and a favorable forecast.”
For help in determining PGR needs or to further discuss any of these topics, growers may call or go by the Research Center.
Osborne can be reached at 580-482-2120 or on his cell phone 580-471-7815.
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