Causes of High Micronaire in Cotton

  • An increased incidence of high micronaire cotton in both the 2012 and 2013 crops has concerned growers.
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  • When cotton plants produce more carbohydrates than are necessary to support plant development, the excess carbohydrates allow cotton fiber cell walls to thicken, resulting in high micronaire fibers.
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  • High micronaire is generally associated with anomalies such as drought stress, water stress, or extremely high yields.

What is Micronaire?

Micronaire (mic) is a measurement of the thickness of the cell walls of a cotton fiber. When cotton begins to bloom, cells that will eventually form fibers elongate into the boll. Final fiber length is reached about 16 to 20 days after formation. Once fibers are fully elongated, the fibers begin to thicken from the inside out. Carbohydrates produced through photosynthesis allow cellulose to be added to the cotton fiber walls, thus increasing both thickness and strength.1

Cotton buyers and textile manufacturers prefer a micronaire range of 3.8 to 4.5, and a fiber length of 1 1/8 inch. Thicker or thinner fibers cause problems in both spinning and uniform dying of yarn. Buyers discount the value of both high and low micronaire cotton.

High Mic in 2012

“We had some reports of high mic cotton in 2012, and we’re hearing a few reports of high mic cotton this year,65533;? says University of Georgia Extension cotton agronomist Guy Collins. “The physiology behind high mic cotton is fairly simple. When the plants produce more carbohydrates than are necessary to support plant development, the excess carbohydrates are available for fiber cell walls to thicken. Several things can lead to the availability of excess carbohydrates.65533;?

“Last year we had some exceptionally high-yield cotton,65533;? Collins says. “In some areas, essentially every boll on the plant reached full maturity, and growers harvested 3 to 3.5 bales per acre. Good growing conditions allowed the plants to continue to produce carbohydrates to fully develop many of the upper bolls, resulting in more high mic fibers.65533;?

“We generally associate high mic cotton with drought-stressed crops, where dry weather causes only the bottom crop to be retained,65533;? Collins continues. “With fewer bolls being set on the middle and upper nodes, the majority of the harvested crop consists of the more fully mature lower bolls, which may be high mic.65533;?

High Mic in 2013

Excess rainfall instead of drought set up the potential for high mic cotton in some situations in2013. Excessive rainfall actually had a similar effect that we normally see in some drought conditions, where only the lower, higher mic bolls are retained.

“With fewer bolls on the plant, fibers in the bottom bolls used the available carbohydrates to develop more high mic fibers,65533;? Collins says.

Management Considerations

One key to avoiding high mic grades is to be timely with defoliation and harvest. The less mature fibers in the upper bolls, blended with the more mature fibers in the lower bolls will reduce the average mic for the crop.

“The main goal should be to capture as much yield as possible,65533;? Collins says. “With the advent of more round bale harvesters, growers may be able to defoliate and harvest in a more timely manner, as peanut and cotton harvest can now be conducted simultaneously.

Planning for 2014

“Growers should not necessarily base their 2014 management decisions solely on what they have experienced this season,65533;? Collins says. “Some growers are seeing some high mic cotton and others are seeing mic within the normal range. The weather we have experienced this season is like none other that I’ve seen.65533;?

“Growers need to look at multi-year data, and look for trends in yields and fiber quality across a number of different locations as they select cotton varieties. I would not let the unusual growing conditions necessarily influence my variety selection,65533;? Collins says.

1Dodds, D., Cotton micronaire-potential problems exist this year, plan accordingly. (verified 10/25/2013).
Personal interview with Guy Collins, University of Georgia Extension cotton agronomist.​