Sugars on cotton lint are colorless but a typical sign sugars are or were present is the sooty mold growth that often but not always follows Photo by Peter Ellsworth

Sugars on cotton lint are colorless but a typical sign sugars are or were present is the sooty mold growth that often, but not always, follows. Photo by Peter Ellsworth.

Season-long whitefly management essential in cotton

Excess sugars from insects are nothing new to the cotton industry. While it rarely occurs, the impact can threaten economic viability and product reliability across the fiber chain. If fallowed ground is located near cotton fields, it tends to have more weeds, including morning glory which is an excellent whitefly host.

Excess sugars from insects are nothing new to the cotton industry. While it rarely occurs, the impact can threaten economic viability and product reliability across the fiber chain.

Most cotton growers and pest managers perform yeoman’s work to prevent high sugar levels. Yet, it can take just one or two people not quite thorough enough in cotton management to result in a problem issue and possibly create problems for many people across a cotton-growing region.

A key source of excess sugar is the whitefly – specifically the B biotype, Bemisia tabaci, in the West. The insect excretes sugar which, after boll opening, can move to the open fiber causing the fiber to become sticky.

 

While excess sugar may not be 100 percent preventable, there is a misconception by some who believe that whitefly prevention efforts should start at boll opening.

Two western entomologists agree the best way to help avoid sugar buildup is begin whitefly monitoring and population management efforts at least two months prior to boll opening. This can help prevent whitefly buildup early and reduce any excessive sugar later.

Pete Goodell perspective

In California, Pete Goodell says whitefly management is job one on the pest side of farming cotton.

“This is always an issue we take seriously in the San Joaquin Valley,” says Goodell, IPM advisor with the University of California Cooperative Extension (UCCE).

“Excess sugar is the number one threat to our cotton quality reputation,” Goodell said. “The growers and others which I work with are very aggressive in successfully managing this issue.

“But it requires everyone doing a good job.”

Over the last several years, the whitefly population in California has increased and become more widespread. Some cotton industry folks have not seen such high levels in 10-15 years.

Drought-whitefly connection

One reason for the higher numbers may be tied to California’s extreme drought now entering its fourth consecutive year. More on this later.

Along with more whiteflies comes the higher risk for excess sugars in cotton. A special meeting of cotton brokers, growers, ginners, and others held in January 2014 addressed this issue. UCCE and the California Cotton Growers Association held area-wide meetings last summer to discuss the threat and ways to control the issue.

Looking back at last year’s cotton crop, Goodell said, “People really got on top of the issue and were very aggressive. In many cases, they treated cotton when whitefly populations were under the recommended threshold.”

With most of the 2015 California crop now planted, he says, “The most important thing we need to do this year is to inspect the leaves for whitefly starting in early July even though it may be another month or so before boll opening.”

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Goodell says the key to whitefly management is early monitoring.

“It’s a proven system,” he emphasized. “You need to get in the field early and some people may not be doing that. You have to catch the whitefly populations when they first come in and not allow the population to build up.”

Spray approach

Goodell recommends the following targeted whitefly spray approach.

1 - Start with insect growth regulators using the most selective, non-disruptive products available to manage population and generational numbers to prevent whitefly buildup.

2 – If a large adult migration begins to move in, more broad-spectrum insecticides are recommended.

“The approach is to start first with selective products, then semi-selective products, and then non-selective products toward the end of the season to knock down any remaining whitefly adults,” Goodell said.

Fallowed ground

The drought was noted earlier as a reason for increased whitefly numbers. If fallowed ground is located near cotton fields, growers should be aware that fallowed acres tend to have more weeds, including morning glory, which Goodell says is an excellent whitefly host.

This is especially true in western Fresno County where many fallowed fields exist.

In addition to the drought, temperatures over the last two years have been well above normal during the winter and summer. This allows whitefly populations to develop larger population densities earlier and additional generations during the year.

To learn more about whitefly management in California cotton, Goodell suggests watching an online webinar he recorded last summer.

Ellsworth perspective 

In neighboring Arizona, University of Arizona IPM Specialist Peter Ellsworth has worked with the cotton industry for about 25 years on whitefly management. At cotton meetings, he often starts his PowerPoint presentations with a startling photo taken outside the front doors of the Maricopa Agricultural Center (MAC) in Maricopa where Ellsworth is based.

In the photo, the outside doors are difficult to see due to a snowy, blizzard-look in front. A hint – it’s likely never snowed at the MAC.

The snow-like entrance is actually millions of whiteflies. Ellsworth snapped the photo in 1992; the first year the B-biotype whitefly was found at outbreak levels in central Arizona.

Excess sugar causes

The entomologist notes that three components are required for excess sugar to occur: the insect which produces the sugar, exposed lint where the sugar is deposited, plus an interaction between the fiber, sugar on the fiber, and sensitive equipment in gins and mills.

Ellsworth points out that the excess sugar is not always attributed to the whitefly. All plants naturally have carbohydrate sugars critical to plant development. Other insect sugar sources include aphids and mealybugs.

In Arizona, aphids can be found in cotton fields at about 3,000 feet above sea level in eastern and southeastern counties. The same is true at lower elevations along the Colorado River including the Blythe, Calif. area.

Buildups in aphid numbers, Ellsworth says, can be tied to very mild winters, continuous cropping, areas near riparian habitat, and migratory routes for aphids.

5 ways to prevent whitefly buildup

Ellsworth offers these “Top 5” ways to prevent heavy whitefly buildups.

1- Variety - Be aware that the hairy leaf characteristic in some cotton varieties is a risk factor for whitefly. Ellsworth does not suggest avoiding hairy leaf varieties for this reason, but growers should be more vigilant as the buildup of whitefly on hairy varieties can occur much faster compared to smooth leaf cultivars.

“Be hyper cautious under these conditions,” he advised. “Sample for whiteflies sooner than usual and be prepared for faster growing populations.”

2 - Water relations - Maintain good water relations which ties into inadequate water supplies. Growers should ask themselves – is there enough water to grow a cotton crop? If there is, maintain good plant-water relations at all times as inadequate water levels can cause plant stress.

“The whitefly is a stress-loving insect and anything which causes stress in a crop creates an environment where whiteflies can thrive,” Ellsworth said.

3 - Sampling – Routinely measure whitefly numbers in the field. The findings can help pest managers know when to respond and how.

Ellsworth says reducing sticky cotton comes down to integrated pest management and implementing methods developed through research and validated on hundreds of thousands acres of commercial cotton.

“They work,” he stated.

“I’ve worked with whitefly for more a long time and still can’t walk to a side of the field, brush my hand across the top of the plant or my net across the top of the plant, and watch the whitefly fly up and make a good, informed decision.”

He says about seven minutes are needed to properly sample an average-size cotton field.

Whitefly threshold

4 - Threshold – There are two essential measurements needed to determine insect levels relative to threshold guidelines. First, separately count the adults only through a leaf turn per leaf disk. Second, count large nymphs using a separate leaf turn.

“Every grower or field man or woman should do this,” said Ellsworth.

He encourages cotton growers and PCAs to check out his whitefly management webcast, including specific sampling and threshold guidelines, plus other management information.

“A sampling program at least 1-2 weeks before threshold numbers are expected is best – even sooner if risk factors are operational in the field, including hairy cultivars, poor water relations, or the earlier use of broad-spectrum insecticides.”

Whitefly sprays are all about timing. While some people may think it’s best to spray a product early before the threshold guideline is reached, Ellsworth warns against this since it can reduce the effectiveness of the active ingredient as the crop matures.

5 - Chemistry – Use an effective product chemistry known to effectively take down whiteflies and preserve the natural enemy population in the field.

“Good options are the insect growth regulators Knack and Courier, plus the lipid biosynthesis inhibitor Oberon,” Ellsworth said. “One of these products should be used as the first spray against whitefly in most situations.”

Spray favorite product early 

He says some growers prefer to delay using a ‘favorite product’ until later in the season, and instead use a product with broader spectrum characteristics earlier. This can compromise natural enemies up front, Ellsworth says. The preferred compound may not work as well later due to fewer natural enemies.

In summary, technological advancements may one day eliminate the excess sugar on cotton issue. In the meantime, every cotton grower and pest manager should follow proven pest management guidelines to minimize the issue.

http://ag.arizona.edu/crop/cotton/insects/wf/stickycss.pdf

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