Defoliating cotton when less than 60 percent of the bolls are open can help reduce micronaire levels without sacrificing yields, says Virginia Tech's cotton specialist. Virginia got a head start on the rest of the southern Cotton Belt when researchers began looking at early defoliation as a way of battling high micronaire and low fiber strength in 1997.
Today, fiber quality is a major issue facing the cotton industry.
In three years of tests, Jim Maitland, Virginia Tech Extension cotton specialist and Charles Swann, Extension agronomist, found that defoliating when the bolls are less than 60 percent open can help lower micronaire readings without sacrificing yields. In many cases, the yields increased. Maitland presented the findings at the recent Southeast Cotton Conference in Raleigh.
The impetus for the study came in 1996. That year, Virginia cotton growers were bringing high micronaire and low fiber strength cotton to the gins. Maitland lists the usual culprits for the high mike readings: environment, early-maturing varieties and genetics. A dry spell in July 1996 also contributed to the high-mike readings.
Taking into consideration the environmental factors, as well as the fact that some varieties tend to produce high-mike cotton, Maitland and Swann set out to see if they could improve the situation by defoliating when less than 60 percent of the bolls were open.
In the first year of the study, the Virginia Tech researchers used Delta and Pine Land Co.'s 451. In 1998 and 1999, they also used Stoneville Pedigreed Seed's 474.
In 1997, the researchers defoliated the crop when 30 percent, 40 percent and 58 percent of the bolls were open. They used four treatments, including Finish at a quart per acre; Finish at a quart and a half per acre; and Dropp, Folex and Prep. Harvest followed 10 to 14 days after the use of harvest aids,.
In 1998, using both Delta and Pine Land 451 and Stoneville 474, they repeated the regime at 30, 40 and 58 percent open bolls. In 1998 and 1999, they went with the Finish application at a quart and a half.
Almost down the line, early defoliation contributed to lower mike and increased yield. Defoliating at 30 percent open bolls lowered the mike reading from 5.2 to 4.8; at 40-percent open bolls, the mike reading decreased to 4.8; and at 60 percent, the reading hit 4.7.
In 1998, at 30-percent open bolls, both the Stoneville and the Delta and Pine Land varieties were already operating at a discount based on mike readings above 5.0. In untreated plots, the Delta and Pine Land variety had yields of 829 pounds of lint per acre. A harvest-aid treatment meant an increase in yield to 1,118 pounds of lint per acre. “We were able to reduce the mike reading while not decreasing the yields,” Maitland says.
Research in 1999 was literally a wash due to hurricanes.
“When you know you have high-mike varieties, you can defoliate early,” Maitland says.
“A lot of early maturing varieties will set bolls fast — that was the cause of some high-mike cotton in Virginia in 2001,” Maitland says. “We had a tremendous boll-set early in the season and in July we didn't get any rain. The result was we had some mike readings of 5.1 to 5.4 this year along the North Carolina-Virginia line.”
In short, where there's a possibility of high micronaire, growers can defoliate at 30, 40 and 60 percent bolls open.
Research continues on early defoliation in Georgia, North Carolina and South Carolina.