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Late-season management called key to sticky cotton

The San Joaquin Valley's coveted reputation as a producer of high quality cotton fiber is flirting with potential disaster, and this year's harvest will have a tremendous impact on how the industry views San Joaquin Valley cotton.

One thing is certain, however, the quicker cotton is out of the field and into the bale, the less susceptible lint will be to becoming sticky.

Late season infestations of whitefly and aphids throughout the central valley last year created significant problems with sticky cotton. The resulting outcry from mills worldwide sent an ominous message that growers simply cannot afford to ignore: Either solve the problem or lose the premium.

“I think we all got hit by surprise last year,” says Bob Hutmacher, University of California's statewide cotton specialist. “For the most part, we skated through the season without much pest pressure, started thinking about defoliation and harvest, and then got hammered with aphid and whitefly in some areas. I think, as we head into defoliation this season, we need to really pay attention to what's going on, perhaps put a little more thought into defoliation strategies and be a little more conscientious about getting that crop out of the field.”

Aphids and whiteflies secrete sugars that are deposited on the plant. If lint is exposed during an infestation, the sugars will contaminate the fibers, resulting in sticky cotton.

Costly to mills

“Mills can lose millions of dollars in lost production time when sticky cotton slows down the spinning process,” says Earl Williams, president of the California Cotton Ginners and Growers Associations. “It's quite clear why they want to avoid the problem, and it's certainly understandable why they would simply stop buying cotton — or at least heavily discount it — from an area that has a reputation for sticky cotton.

Sticky cotton briefly became a significant issue in California during the mid-1990s, but quickly vanished from the radar screen. Whether it was better scouting and management techniques, superior products or simply less pressure, the problem seemed to have all but disappeared.

In addition to many new, effective chemistries on the market for whitefly and aphid control, University of California researchers have developed highly effective management strategies in recent years to deal with late season whitefly and aphid infestations.

Larry Godfrey, Extension entomologist with the University of California at Davis, says it is particularly important for growers to move from a mid-season management strategy to a late-season management strategy as soon as bolls begin to crack and there is exposed lint in the field. During mid-season, a threshold of 50-75 aphids per leaf can be tolerated before triggering a pesticide application, but that drops dramatically after bolls begin to crack.

“At that point, we're recommending a threshold of only 10-15 aphids per leaf.”

Whitefly threshold

For whiteflies, a count of five adults per leaf when lint is exposed constitutes an action threshold. Pyrethroids or other products that provide a quick knockdown should be used to regain control of the situation.

Finally, there is the question of defoliation strategy and how that plays into the entire late season pest management scheme. While it is often tempting for growers to extend the season and make a little extra lint, that strategy can backfire rather quickly.

“When you try to extend the season in an attempt to make a few extra bolls, you run the risk of complicating not only defoliation, but also late season pest control,” says Steve Wright, Tulare County farm advisor.

Reducing the period of lint exposure is a key consideration in minimizing problems with late season aphid and whitefly problems. “Using a product that defoliates the leaves and opens bolls quickly can be a real advantage in avoiding potential problems,” Wright says. “Harvest aids such as Finish or anything else with ethephon can significantly reduce the time it takes to open bolls and get the crop ready for picking. Ultimately, that just reduces the chance of experiencing problems with late season whitefly and aphid because there is simply less time for the problem to develop.”

Defoliation trials have shown that Finish, either by itself or in a tank mix, opens mature bolls faster than other products and enables growers to complete harvest at least three to five days sooner.

As growers prepare to get the crop to the gin in the next few weeks, industry leaders are urging vigilance.

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