Southwest Environment

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Department of Soil, Water and Environmental Science
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Technology helps keep pests out of Arizona’s cotton fields

By Ben Beal
cotton crop Photo by Brian Dunnette. Some rights reserved
A look across an Arizona cotton crop. Cotton is one of Arizona’s major industries.

The tractor lurched steadily forward as it pulled a trailer full of southern Arizona cotton farmers, leading them out into experimental crops of cotton. The trailer serves as a mobile classroom with tiered seating so a couple dozen people can tour the University of Arizona’s Maricopa Agricultural Center, and learn about the scientific research of farming firsthand.

“The work we do has a greater impact when the farmers see the fields and compare side-by-side what works and what does not,” commented UA Cooperative Extension’s Peter Ellsworth, a specialist in integrated pest management who works with farmers to improve and maximize crop production.

In a late September event designed for Central Arizona farmers, Ellsworth showcased the experimental crops he has been working with as director of the Arizona Pest Management Center. He has been focused on managing insect pests in cotton crops –
the most notorious being the lygus bug.

“Lygus are the number one yield-limiting pest of cotton. They are (also) very hard to kill with insecticides,” said Peter Asiimwe, a doctoral candidate who is working with Ellsworth.  

Lygus (Lygus hesperus), also known as the western tarnished plant bug, use their long straw-like beaks to pierce cotton bolls. A boll develops from a flower and is the part of the plant that produces the cotton. Once a developing flower is damaged by the lygus it does not develop correctly. This reduces the amount of cotton that the plant produces, which already lose about 50 percent of its bolls naturally, explained Asiimwe, and when lygus have infested a crop, the farmer’s losses are significant.

Since these bugs can be so difficult to control, Ellsworth has also employed resources beyond the traditional to help farmers with decision making.

As part of a project funded by the U.S. Department of Agriculture, Ellsworth and a team of 12 other scientists have worked to bring together the benefits of video game technology and generations of inherited knowledge from farmers.

A room of farmers all sitting at computers playing a video game may seem a bit unusual at first, but this  technology is being used to help cotton growers manage pests in their southern Arizona crops. The farmers also considered playing video games a bit uncharacteristic, so since the first demonstration, Ellsworth has referred to the games as simulations.

The simulation immerses farmers in a virtual planting season with a plot of land and a list of potential crops to plant, such as cotton, alfalfa and safflower. Farmers lay out the farms to their liking and then check through the computer-generated modeling how the decisions they make in crop location can adversely or positively affect their cotton yield. Later in the simulation they also see how their choices can affect their virtual neighbors and vice versa.

A key concept of the simulation is the idea of “source” and “sink” crops. A source is any crop that is known to produce a pest, and a sink crop is one that tends to attract the pests from the source crop.

This isn’t a new concept to farmers. What is new is that a source crop, when maintained properly, can potentially act as an effective sink crop, Ellsworth indicated.

Lygus bug populations are typically higher in alfalfa than in cotton when both crops are present. Traditionally, farmers see alfalfa as a source and cotton as a sink for lygus. The computer simulations are designed to highlight how farmers can utilize alfalfa as a sink crop in order to protect their cotton.

Lygus Bug Photo by Ken-ichi Ueda. Some rights reserved
The western tarnished plant bug (Lygus hesperus) can cause problems for many a cotton farmer.

Lygus have no adverse affects on alfalfa when it’s used for feed rather than seed, or on safflower, a crop used to produce seed oil. By timing the harvesting of safflower and alfalfa and the strategic use of insecticides, the farmers can produce and utilize both sink and source crops more efficiently together.

The effects of source and sink crops are not restricted to one farmer’s crops. Entire communities can be affected by the management decisions of a single farmer. Ellsworth uses this concept to local farmers’ advantage in the Maricopa experimental cotton plots.

“I purposely plant late in the season to attract everyone else’s problems,” he said. The summer’s accumulated pests are drawn to his crops as other farmers harvest theirs.

A method once used commonly by farmers in the control of pests was to spray insecticides unsparingly until the insects were killed or controlled, Ellsworth noted. This was done without regard for the beneficial insects or the environment as a whole. By understanding that they will get the maximum efficiency from the insecticides if they wait until the lygus lay eggs and then spray to kill the vulnerable nymphs, farmers can use fewer insecticides and save money.  

Ellsworth has spent many years and funding to support his work and to improve farmers’ ability to wisely manage the lygus bug, whitefly and other pests that feed on cotton, while encouraging the presence of beneficial insects.

Working specifically to maintain beneficial insects in the crop that prey on the pest insects “is something others have not done in the past,” Ellsworth said. Spraying fewer insecticides can help protect non-target insects, such as the lygus-eating assassin bug. Assanin Bug Photo by Alan Moore. Some rights reserved.
The assassin bug (Zelus renardii) presents a great threat to other insects with its fold-out sucking beak and relatively imposing size

“It’s much like the medical field, where you study how the drug helps, but also what side effects it may have. We developed life tables – well, they should really be called death tables,” said Ellsworth, referring to his detailed studies on how pests live and die in the fields. Use of the tables could minimize the negative side effects of insecticides while still helping growers manage their crops.

The tables show that the target pest is most vulnerable to the insecticides in its nymph stage, roughly the first weeks after emerging from their eggs. With an ample dose of patience and vigilance, farmers can wait and watch for the best time to spray insecticides, rather than spray at the first signs of infestation.

Spreading new ideas and strategies based on scientific research is not as easy as publishing an article.
It involves more than holding a single Cooperative Extension event. It takes time, resources and events to change past practices and foster new ideas. But Ellsworth and others believe the effort is worthwhile for its potential benefits to society.

Ellsworth hopes that after the farmers complete the computer simulation, they are better aware of how their decisions affect their neighbors. The hope is that as a result they will communicate with their real-life neighbors to more effectively manage pests and to jointly benefit. Coupled with the wise and conservative use of insecticides, farmers will not only sustain cotton production but also protect the environment and the beneficial insects it contains and save money.

Ben Beal is a sophomore at the University of Arizona. He was born in Idaho and moved to Arizona as a child. He has been married for six years and has two children. He plans to focus his studies on entomology. Ben is interested in everything from cars, machines and buildings to animals and plants.


Related story: The assassin bug preys on lygus

Integrated Lygus Management in Arizona

Background on Peter Ellsworth and his program

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