Sticky cotton's not new, nor is it limited to the western crop. Rather, notes Eric Hequet, the problem dates back to the 1940s, first occurring overseas, then in the U.S., and then worldwide.
“Indications are that 10 percent of the world's cotton production has some level of stickiness,” the assistant director of the International Textile Center at Texas Tech University, Lubbock, told those attending the recent Western Farm Press-sponsored Pima Cotton Production Summit at Visalia, Calif.
The most common cause of stickiness is from insect-specific sugars, Hequet noted.
“While cotton lint itself contains sugars, this is normal and generally causes no problem. Sugars from insect excretions are responsible for 90 percent to 95 percent of the contamination causing stickiness. Naturally-occurring stickiness that can be caused by weather conditions will usually disappear over time, but insect-caused stickiness is there forever; it won't go away.”
The stickiness problem is exacerbated, Hequet said, by the difficulty in detecting it in the field or in the ginning and spinning processes.
“Problems occur in spinning when these deposits accumulate on the machinery, causing yarn breakage, shutdowns, and loss of production. If there's only a slight level of stickiness, they may be able to continue spinning, but will still get imperfections in yarn and fabric.”
There are several different testing methods to detect sugars in cotton, Hequet said, but none is effective in predicting stickiness in the milling process. Some testing machines used by mills are very effective, but very expensive “and even the best instrumentation available still takes too much time and slows the process.”
And even though instrument testing can give good information about stickiness, “we still need to know the insect that caused the contamination.”
Trehalulose, sugar from whitefly excretions, becomes sticky at far lower temperatures, and thus more troublesome, than sugar from aphids, Hequet noted, although aphid sugar can cause milling problems in heavy concentrations.
“It's my sense, from the stickiness problems that we've seen, that there were a lot more whiteflies that should have been treated,” he said.
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