Pest Thresholds In Cotton

Use an integrated pest management plan to control whiteflies in the West.

Monitoring cotton pest thresholds has proven to be one of the more successful tools for keeping insect pressures in check. In the West, established research-based thresholds aid in determining treatment of cotton pests. Adherence to those standards can be the difference between making or breaking the crop.

“These work in the majority of situations, provided producers stay within the guidelines,” says Dr. Peter Ellsworth, director of the Arizona Pest Management Center at the University of Arizona.

By determining how many pests are present, and their stage of development, treatments can be managed for optimum effect and cost. Over the past 21 years, integrated pest management (IPM) and the use of thresholds to determine insect pressure have saved the Arizona cotton industry more than $500 million, Ellsworth says. IPM also has prevented more than 21 million pounds of pesticide active ingredients from having been applied to the crop, thus reducing the environmental impact.

Innovations Reduce Treatments
In the 1990s, producers saw the beginning of an invasion of a new whitefly, which devastated the Arizona crop. In 1996, insect growth regulators targeting whitefly were introduced along with a new IPM plan that included counting insect numbers and using stage-specific thresholds.

Around the same time, Bt cotton was reducing the need to spray broad-spectrum insecticides, helping to reduce treatments even more.

In 2006, an insect-specific Lygus feeding inhibitor was introduced that further reduced broad-spectrum chemical applications on cotton. All of these pest control innovations created a better cotton environment for natural predators and parasitoids that make the IPM plan more sustainable.

Although both whitefly and Lygus treatments are effective, they must be applied at the correct time. Insect sampling and adherence to established pest thresholds for those two pests are paramount to making sure the timing is right for each application, and in many cases to determine if any application is needed.

“Sampling and proper use of thres-holds works and creates greater certainty in management,” Ellsworth says. “Whitefly thresholds are based on samples of adults and nymphs on the fifth leaf below the cotton terminal. Lygus thresholds are based on field counts of adults and nymphs in cotton sweeps.”

He also notes in areas where there is a shorter production window outside of the West, there may be a call to incorporate the week of bloom or other crop development measures into threshold-based guidelines to better support Lygus treatment decisions.

California’s Treatment Approach
In California, concerns for maintaining San Joaquin Valley quality has led the University of California to adapt the same pest control guidelines to its treatment approach, adjusting for cropping diversity.

“Application is critically important,” says Dr. Peter Goodell, Univer-sity of California Cooperative Exten-sion farm adviser. “When control is required, effective pest control is vital to IPM.”

Goodell advises producers and crop advisers to visit fields frequently, establish good monitoring tools and manage them according to guidelines.

Following treatment guidelines is also important in California, as is selecting the best insecticide to fit the situation. Starting in mid-season, Lygus treatments can be anticipated, especially after wet winters.

“Choosing the most selective active ingredient will preserve natural enemies on which cotton growers depend for control of later-season insects, such as aphids, worms and whiteflies,” Goodell says. “Optimal treatment regimes have been established for many of the key pest insects, which is an underpinning of IPM. The goal is management of established pests, not eradication.”

More Information Resources
Producers and crop advisers can find threshold guidelines by going to their Extension cotton specialists or visiting university websites. Ellsworth and Goodell also have whitefly presentations on the Plant Management Network at these links:
More information on cotton pest issues can be obtained by going to

Brent Murphree
Brent Murphree

Brent Murphree is the Cotton Board’s Regional Communication Manager for the West. Contact him at or (602) 810-1171.

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