A one-year study by weed scientists at the University of Tennessee showed no significant differences in yield or quality in plots of 15-inch cotton planted at a wide range of seeding rates.
But scientists were quick to point out that additional research is needed to further refine optimum planting rates for 15-inch cotton. “Under the best conditions, you can get by with the lower populations,” said Larry Steckel, a weed scientist with the West Tennessee Experiment Station in Jackson, Tenn. “If you plant when it's cold and wet, it might be better going with the higher population. But with the higher seed and technology costs, the lower part of the range is where you'd like to be.”
Ideally, 15-inch cotton is a good fit in west Tennessee because of the region's rolling hills, short growing season and marginal soils, especially with the recent development of a 15-inch-row spindle harvester. The picker should increase harvesting speeds over stripper harvesters used in ultra-narrow-row cotton (7.5-inch spacing) and could reduce bark and other trash discounts that occur with stripper-type harvesters.
Advantages of 15-inch cotton include quicker canopy closure, earliness and possible consolidation of equipment for grain and cotton operations.
The objectives of the UT research were to evaluate the seeding rates needed to achieve uniform stands, sufficient earliness and optimum lint yields. Researchers also looked at mepiquat chloride strategies for 15-inch cotton and 15-inch cotton following wheat.
The research was conducted in 2005 at the West Tennessee Research and Education Center in Jackson. All plots were planted no-till using a John Deere 7300 planter with finger pick-ups and all plots received 80-60-90 (N-P-K) at planting. None of the studies received moisture from supplemental irrigation. The plots were harvested with a John Deere 9930 harvester retrofitted with 15-inch heads.
Researchers looked at four seeding rates — 35,000, 52,000, 75,000 and 95,000 plants per acre. The variety DP 444 BG/RR was planted May 16 and received one mepiquat chloride application at early bloom.
Plant stands were adequate for each of the four seeding rates tested. Yield was numerically but not significantly greater with seeding rates of at least 52,000 plants per acre. Seeding rates in excess of 52,000 plants per acre did not result in significantly greater yields. Earliness was not affected by seeding rate, possibly because the variety used, DP 444 BG/RR, is extremely early, regardless of management style.
Although plant stands in the lower seeding rates were adequate, missing plants resulted in slower canopy closure and more weed competition. Lower seeding rates may be effective if good conditions are present at planting and precise planting equipment is used, researchers said. There were no significant quality differences between the treatments.
Researchers also looked at four mepiquat chloride strategies for 15-inch cotton:
- Untreated check.
- Low dose strategy of 4 ounces of mepiquat chloride applied at matchhead square, followed by 4 ounces 10 days later, followed by 8 ounces at early bloom.
- Medium dose strategy of 16 ounces at early bloom.
- High dose strategy of 8 ounces at matchhead square, followed by 16 ounces 10 days later, followed by 16 ounces at early bloom.
No significant yield or quality differences were seen among the treatments. A significant reduction in plant height was noted in plots receiving low and high rate multiple applications beginning near matchhead square. Applications made near bloom resulted in slightly taller plants but did not affect yield.
The study indicates that growers could get by with low doses, noted Steckel. “The 15-inch cotton is almost self-Pixing. But a lot depends on the variety.”
Earliness was enhanced slightly with heavy use but did not result in greater overall yields. Harvest was not affected by plant height in this study, suggesting that growth management may not be as critical as with UNR cotton.
To evaluate 15-inch cotton after wheat, DP 444 BG/RR was planted June 20 after wheat harvest, at a planting rate of 52,000 plants per acre. Sequence was applied at 4-leaf followed by Envoke. Researchers looked at six management strategies:
- Untreated — no plant growth regulators or insecticides.
- 16 ounces of mepiquat chloride at early bloom, followed by 3.2 ounces of Mustang Max at near cutout.
- 5 ounces of Bidrin at the eighth node, 2 ounces of Centric 10 days later, 16 ounces of mepiquat chloride at early bloom and 3.2 ounces of Mustang Max near cutout.
- 8 ounces of mepiquat chloride at matchhead square, 8 ounces of mepiquat chloride 10 days later and 16 ounces of mepiquat chloride at early bloom, followed by 3.2 ounces of Mustang Max near cutout.
- 5 ounces of Bidrin and 8 ounces of mepiquat chloride at node eight, 2 ounces of Centric and 8 ounces of mepiquat chloride 10 days later, 16 ounces of mepiquat chloride at early bloom and 3.2 ounces of Mustang Max near cutout.
- 5 ounces of Bidrin and 4 ounces of mepiquat chloride at node eight, 2 ounces of Centric and 4 ounces of mepiquat chloride 10 days later, 18 ounces of mepiquat chloride at early bloom and 3.2 ounces of Mustang Max near cutout.
Adequate plant stands were achieved for cotton planted after wheat harvest, due in part to good moisture at planting and adequate rainfall thereafter. Researchers expected aggressive mepiquat chloride applications to result in better overall yields, but the data suggested that early applications of insecticides were more important.
Researchers explained that because of the later planting, the fruiting period occurred during a period of heavy tarnished plant bug and stink bug infestations. Applications made during this time resulted in greater overall yields.
Defoliation was delayed because of wet field conditions and yields were hindered somewhat by a killing freeze that occurred prior to defoliation. The cotton was mature at the time of the killing freeze and timely defoliation may have led to better results. “It had some real issues. Planting that late is really pushing your luck,” Steckel said.
In another study, Steckel researched various over-the-top weed control strategies in 15-inch cotton planted in a Roundup Ready Flex variety. “We found that going with two shots of glyphosate, one at the first node and another shot of glyphosate with a pint of Dual at the fourth node was a good treatment. We really didn't need a lot of follow-up after that.
“One thing I liked about the 15-inch cotton was that it shaded the ground a lot quicker than 38-inch rows, and that's a mode of action. For example, Palmer pigweed needs three things to germinate — water, heat and light. When we get the ground shaded a lot quicker, it cuts down on the herbicides we needed to apply.”
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