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Measuring localized movement of lygus into SJV cotton

Peter Goodell’s business card could read “Mr. Lygus.” The respected insect researcher in Western agriculture, who is interim director of the University of California Statewide Integrated Pest Management Program, is widely known as a top point man for the insect Lygus Hesperus, including the insect’s movement and impact on crops in California’s San Joaquin Valley.

Lygus Hesperus populations develop externally and internally in California’s San Joaquin Valley,” he says. “In certain years, weed hosts are favored by precipitation patterns that can provide extended habitat where lygus populations can build.”

Goodell, based at the Kearney Ag Center in Parlier, Calif., painted a picture of local lygus movement into SJV cotton during the recent Second International Lygus Symposium at Pacific Grove, Calif.

He summarized years of lygus research, including a 2005 study where tarweed (Hemizonia kelloggii) was found in high density bordering cotton fields.

The results showed that, even with a large lygus population in surrounding vegetation, the main lygus problem didn’t come from rangeland or wild uncultivated areas. Rather, surrounding fields were the lygus’ host.

“Instead of an outside-the-valley problem, it was an inside-the-valley problem. It was what your neighbors were doing, not what nature was doing to you,” Goodell said. “Everybody always talks about the large movement from the foothills. That’s a possibility, but the odds are your cotton field will get infested from a neighboring crop as opposed to something that’s external to the cultivated area.”

He pointed to tarweed, where lygus typically stay put during physical development until a neighboring crop is disked. Then the bugs move into cotton.

“As long as an area has a host that is sustaining lygus and it’s undisturbed, the lygus will remain in the host as long as possible. If you mow or disk the weeds, then you’ll force them over into cotton.”

An example of man’s spreading lygus is new almond orchards. When almonds are first planted, the trees don’t produce for the first three years, cotton or beans might be grown between the rows. But usually the native vegetation comes up, and when the weeds are mowed, lygus move into the cotton.

“What can cause lygus movement is more the manipulation of the environment than the eventual decline of their hosts,” Goodell explained. “Both are involved, but year-in and year-out you don’t find a large buildup in native areas (uncultivated areas). You’ll always find a population in appropriate cultivated areas that, year-in and year-outm would be potentially there if not managed appropriately.”

Another study involved using land satellite remote sensing equipment to estimate large lygus populations on 200,000 acres of tarweed. But spring rain and clouds kept researchers from seeing the ground, limiting the value of the satellite imagery.

Lygus outlook for 2007

With the 2007 SJV cotton crop in the ground, Goodell was asked about possible lygus numbers in this year’s SJV cotton crop.

“From the weather pattern we’ve had so far (late April), it doesn’t appear that lygus infestation in the western foothills will be a major factor in 2007. But this is very preliminary.”

Some cold temperatures in the spring may have reduced the possibility for lygus moving into some hosts, he said. “Lygus should not be a factor this year as an outside west hills component; there should be little impact based on the hillside effect.”

He said farmers should be fully aware of which crops will border cotton inside the valley away from the foothills.

Wild card

The wild card this year will be an increased amount of safflower and corn in the area because of the biofuels movement and how those crops will host lygus, Goodell said.

“If you live near a safflower field, you’re going to have more lygus problems. That’s a historic fact.”

He urged growers to work together to manage safflower by preempting lygus from moving, such as timing an insecticide spray to knock out the immature population to prevent them from becoming adults.

“We’re not sure how corn will act as a host, so we’ll have to play it by ear.”

Goodell said the University of California is teaming up with Arizona State University and the University of Texas to study 50 different cotton fields, sampling the cotton and surrounding fields for a mile around to understand which crops are acting as primary lygus hosts to the local cotton. Some results are expected by the end of 2007.

He offered suggestions to assist cotton growers in managing lygus in ’07.

“Take notice of what’s in bordering fields, what’s two fields away, and what’s a mile around, to get an idea of what your sources might be.

“If you have alfalfa and have any management authority, let the fields work as a sponge for the surrounding area, so the lygus will move into the alfalfa and stay there. When cutting alfalfa, leave a strip here and there — it will pay for itself by keeping lygus out of your cotton”

And if a cotton grower is in an area that will provide abundant lygus numbers, have a pest control advisor watch the field closely and monitor square retention, Goodell said..

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