Staying Out of "Tall Cotton"

Redefining plant-growth physiology

By Henry Gantz
hgantz@meistermedia.com

The on-line Urban Dictionary defines the term “tall cotton” as being wealthy, well off, well to do. As an example: “I just got my tax refund, and now I’m in tall cotton.”

For cotton growers, the literal and figurative terms for tall cotton are quite different. Opposites, in fact. While growers want to be in tall cotton financially, the do not want to be in tall cotton physically.

Most cotton varieties are indeterminate in growth habit, and vegetative and reproductive development occur at the same time. Vegetative growth is essential in supporting the development required for maximum yield potential, but excessive vegetative growth can lead to fruit abortion, delayed maturity, boll rot and harvest difficulties.

BASF introduced the mepiquat chloride-based plant growth regulator (PGR) Pix, in 1972. Pix would lead to a revolution in cotton management on par with transgenic traits and boll weevil eradication. But not at first. The problem initially with mepiquat chloride was that it was applied once, maybe twice, at high rates. Results were often erratic. But after delving a little deeper into the concept of Pix, it was found that lower sequential rates were hammer meeting nail. Pix eventually did what it was intended to do: Tricking the plant into channeling growth from stalk and stem to boll filling, and at just the right time.

Mepiquat chloride also concentrates the fruiting zone. In test plots, untreated and PGR-treated plants often had the same number of bolls, but the PGR-treated plants concentrated them on the lower, more productive part of the plants. Physiologically, lower bolls are bigger bolls.

Untreated check on the left. Stance-treated on the right.

Head East
Some of the rules that apply to PGR applications across the high heat-unit areas of the Cotton Belt, don’t necessarily pertain to the upper latitudes of North Carolina.

“Our problem in the early season is getting growth, not slowing it down,” says North Carolina Extension cotton specialist Dr. Keith Edmisten. “We don’t usually make a pinhead-square application. Our first application is made more toward matchead, or even a little later – at the at the ninth or 10th node.

“Most growers tend to be a little late with applications,” Edmisten continues. “They usually need to do something at the nine- to 10-node stage and then come back at early bloom.”

And even at that point, Edmisten advises growers to consider growing conditions, particularly moisture availability, before making PGR decisions.

Way Down Yonder
Speaking of latitude, Louisiana traditionally plants earlier and has a longer growing season than any of the Mid-South states. The most popular full-season variety in Louisiana, just as it is regionally and nationally, is Delta and Pine Land’s DP 555 BG/RR. Triple Nickel is a vigorous grower and requires more intense PGR management.

“It has forced us to rethink how we approach PGR management because it’s such an aggressive full-season variety,” says Louisiana Extension cotton specialist Dr. Sandy Stewart. “Applications at the eight- to 10-leaf stage have become much more the norm because of 555.”

DP 555 is a Bollgard/Roundup Ready variety, and EPA registration ends for Bollgard in 2009. Bollgard II varieties will take up the slack, and most will be stacked with the Roundup Ready Flex trait. “Some of the new Flex varieties don’t have the aggressive growth habits of 555,” Stewart continues. “As we transition into the Flex varieties, we’ll have to take another look at the approaches we use for PGR applications.”

Normally, Louisiana growers make the first application of a PGR at the eight- to 10-leaf stage, but, Stewart says, “I try to avoid thinking in terms of blanket rates – especially with Pentia, Mepex and other mepiquat chloride products. The biggest risk with mepiquat chloride is too high of a rate, too early, on pre-bloom cotton. If it turns dry, you can have stunting and induce early cutout. The first applications would usually be around eight ounces, but certainly no more than 10 ounces.”

Mepex is a 4.2% ai formulation of mepiquat chloride from DuPont Crop Protection, and Pentia is a mepiquat pentaborate product from BASF.

“Mepiquat is the base molecule in all of the PGR compounds, but what BASF did with Pentia was remove the chlorine ion and replace it with five borate molecules,” says Scott Asher, BASF Western Region Tech Service Manager. “This helps move the mepiquat molecule into the cotton plant quicker. This improved uptake results in a quicker rainfastness with Pentia – two hours as compared to four hours with other mepiquat-based PGRs.”

Asher adds that Pentia has provided consistent results in boll set and retention, which has resulted in an increase in earliness and an enhancement in yield.

Another refinement on mepiquat chloride is Bayer CropScience’s Stance. Stance contains 0.736 pounds of mepiquat chloride per gallon, plus an additional active ingredient that functions as an auxin transport inhibitor. Auxin is a hormone that reduces internode growth.

Stewart says Stance does not have as long of a lasting effect as straight mepiquat chloride, but that’s not necessarily a bad thing. “I like Stance in early applications,” says Stewart. “Maybe the PGR affects are not as long, but that gives you some built-in insurance. You can make a two-ounce early application, then if growing conditions are good, you follow that up with another PGR application. But if it were to turn dry after the early application of Stance, you might not have the stunting or early cutout if it were longer lasting.”

The Texas Two Step
The Costal Bend and Rio Grande Valley regions of Texas can be as different from the High Plains as Louisiana is to North Caroline. Two different regions; two different set of PGR recommendations.

Untreated check		PGR-treated

“The use of mepiquat products on the High Plains is going to be a different strategy than where we are,” says Dr. Robert Lemon, Professor and Extension Agronomist – Cotton, Texas AgriLife Extension in College Station. “One size is not going to fit all.”

Lemon says the best results he gets comes when the initial application of a PGR comes before bloom, ideally at 10-12 nodes. “If we wait until the bloom stage, it’s generally going to make it more difficult go manage the crop. As long as you have good moisture, we’ve done enough work to know that at that stage, a PGR application sets the plant up for a much better level of management. Generally, we would start applications with four to eight ounces, depending on moisture and variety.” 3:31

Moisture is also the driver on the High Plains, especially with the differences in dryland, center-pivot irrigated and drip irrigated. “A lot depends on our irrigation capacity,” says Dr. Randy Boman, Texas AgriLife Extension cotton specialist in Lubbock. “Very seldom will we use a PGR on dryland, but with the rain we had in ’07, there was a little bit used. In general, it’s going to be the (fields with) high-capacity pivots and drip that will require PGRs, and it can be somewhat varietal-dependent.”

In general, Boman says, FiberMax varieties tend to be smaller and more compact, “but that is not to say that FiberMax varieties won’t need a PGR. I think it will be more important on varieties from Delta and Pine Land, Phytogen and some of the materials from Dyna-Gro, Croplan Genetics and Americot.”

Typically the High Plains is noted for high-fruit retention, obviously depending on weather conditions. “Sometimes we have 80% to 90% fruit retention, and when you have that kind of fruit load, a lot of times on smaller-stature varieties you won’t need a PGR.”

GreenSeeker optical sensors measure plant health. Variable Rate GreenSeeker optical sensors measure plant health. Some of the first successful variable rate applications were made with PGRs. Although they work through the season, late-season variable-rate PGR applications are most common. “The early season challenge can be using aerial imagery to do it. The plants may be too small to show up if the resolution of the image is not high enough,” says Dr. Ed Barnes, Director, Agricultural Research at Cotton Incorporated. “Using GreenSeeker would be an approach, especially if you don’t have that growth. GreenSeeker runs right over the top of the plant,” he continues. GreenSeeker uses optical sensors for on-the-go measurements of plant health. “Another approach would be that if a grower knows that he has an area of weak soil and plants are small versus the rest of the field year in and year out. That would give him a static map, and usually – not always – you know that you don’t want to put PGRs there.