Missouri Cotton News
AUGUST 1999

Many of the fields have been severely drought stressed and may have lower cotton bolls popping open. Some of the cotton bolls may open prematurely. Early reports on the cotton micronaire testing show very low values. This indicates that the fiber is immature and will possibly result in low fiber strength, short staple lengths and lower than expected yields.

Cotton fibers elongate for the first fifteen to twenty-one days after flowering. Water is required to make the fiber elongate. Water stressed crops during this critical period could result in the fiber length being short. If rain occurs or the crop is irrigated, the plant starts producing more sugar. This sugar is deposited in the form of cellulose on the inside of the fiber wall. With shorter than normal fiber, the cavity will be small and the fiber will have a larger than average diameters. This translates into a high micronaire, which may be 5.0 or greater. A large portion of the cotton crop across the Cotton Belt has been dry and may have a high micronaire rating. Large amounts of high mike cotton, could result in higher than normal price discounts. Past discounts have been two to six cents.

In these fields the Hal Lewis Method of timing defoliation may be particularly valuable. The back page is an explanation of this method. This is another tool to use along with a sixty percent open cotton crop or the top harvestable boll within four nodes from the top open boll to help determine the proper defoliation time.

The Hal Lewis Method requires hand ginning and micronaire testing. This service is offered here at the Portageville Delta Center for a fee of $10 per sample. If you have a question on boll sampling, please give me a call or come by the station. I will be happy to demonstrate taking a sample and explain how this process works.

1. Sample Cotton Field.
   1. Sample at least 4 areas which are representative of the field.
   2. Hand pick all the open 1st position bolls from the 1st, 4 fruiting branches. Seedcotton should be open, fluffed and dry when picked, seed should crack.
   3. Sample at least 8 plants from each area.
   4. Use a clean paper bag for the sample, label the bag precisely for field name or number, date of sample, % open and any other pertinent information.
   5. Mix seedcotton thoroughly in the bag prior to ginning.

(The more thoroughly the field is sampled the more accurate the test.)

2. As a service to area cotton producers, the University of Missouri Delta Research Station will be offering a Micronaire testing service. The Delta Center will gin and determine the Micronaire on the field samples for a fee of ten dollars. The results will be determined as soon as possible, or no more than one working day. Leave seedcotton samples with Dave Dunn, the soils lab manager.
3. Find the % open at which you need to defoliate and then lookup the average Micronaire value of the field in the Micronaire Prediction Chart. The values listed in the chart are based on the assumption that fall maturation temperatures (temperatures which occur after the 1st four 1st position bolls open) will be average. If fall maturation temperatures are hotter than normal the Micronaire may be higher than the values listed in the chart. The values listed in the chart are based on normal fall temperatures and are accurate to within ± 0.3 of the Micronaire unit depending on whether fall maturation temperatures are cooler or hotter than normal.

Sampling bolls from higher fruiting positions will give unreliable results.

Using other estimates of fiber maturity such as slicing green bolls and nodes above the last cracked boll can improve timing, quality and yield.

*Revised with permission by Delta Center Staff.

Bold area = Desired Range, Average Maturation weather
Maturation weather cool, subtract 0.3 Mic units
Maturation weather hot, add 0.3 Mic Units

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