Alfalfa could slow pest's movement into cotton

Geographic Information Systems (GIS) and satellite photography can help farmers and scientists trace the migration of lygus bugs in the San Joaquin Valley's mosaic of diverse crops, according to an article published in the current issue of UC Plant Protection Quarterly. This information could help farmers find ways to manage the pest with fewer insecticides.

Lygus bugs, also called western tarnished plant bugs, are native pests in California that cause an annual average yield loss in cotton of nearly $19 million, almost 2 percent of its total production value. Lygus are also pests of seed alfalfa, beans, lettuce, strawberries, and tree fruit.

In the spring, lygus can reproduce in the lush vegetation on foothills surrounding the San Joaquin Valley. As the plants dry when the weather warms and rain stops, the lygus begin looking for a new home in valley agriculture. Lygus move into various crops and weeds, and when these become unsuitable, they move into cotton. Because alfalfa is a favorite host and lygus don't damage forage alfalfa, it could play a key role in providing habitat for lygus and slowing their movement into cotton.

Haphazard strategy

This has been observed for 30 years, and scientists have worked on keeping lygus at bay by harvesting alfalfa fields in stages or leaving strips of unharvested alfalfa for lygus habitat. But the implementation of such strategies has been haphazard.

“Thirty years later, the cotton industry must rely on insecticides to manage lygus once they enter a field. Most of the insecticides can throw integrated pest management programs out of balance,” said UC integrated pest management scientist Pete Goodell, the UC Kearney Agricultural Center-based scientist who wrote the article. “By improving our understanding of lygus movement across a large area, we might be able to limit the movement and therefore some of the insecticides.”

Goodell believes the success of integrated pest management in cotton rests on the combination of satellite photography from NASA and data collected on the ground by farmers and pest control advisers (PCAs). The information can be integrated using GIS, which is software that produces maps with information gathered from a variety of sources. Two such maps are printed in color in UC Plant Protection Quarterly and are available on the publication's Web site

“We want to characterize the environment to improve lygus management,” Goodell said. “One of the key crops in the landscape is alfalfa. That is clear from the empirical observations we've made over the years. The question now becomes, how much alfalfa and exactly where?”

2001 studies

Goodell conducted three preliminary studies in 2001 with GIS and satellite photography to map possible lygus problems. Along the Interstate 5 corridor, color infrared images were able to identify large patches of healthy tarweed, a favored host plant for lygus. When the tarweed dies down, the pest can migrate into cotton or other crops.

“Knowing if lygus use this plant as a host and if the plants have built up a large population is important in pest management planning,” Goodell said.

Goodell next compared the cropping patterns in several Fresno, Kern, Madera, and Tulare county townships, which are 36-square-mile areas. When alfalfa and cotton were present, scientists analyzed the cotton-alfalfa ratio.

Finally, in the Buttonwillow area of Kern County, farmers and PCAs gathered still more data. An 8,000-acre area served by two PCAs was monitored weekly for lygus populations and the information was integrated with cropping patterns using GIS.

“These studies make an initial attempt at using the GIS tools to expand our view of the landscape in which lygus develop, move, and create pest management concerns,” Goodell said. “We demonstrated that our spring survey efforts could be improved by using satellite images and GIS to locate potential lygus hosts and track their decline.”

Eventually Goodell envisions an Internet-based program in which farmers and PCAs can input data about lygus and enable the community of growers and PCAs to visualize the population distribution of this devastating pest.

He will continue his work implementing area-wide integrated pest management using GIS and satellite photography during the 2002 growing season.

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