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Lygus likely to come from neighboring crops in 2008

There is no need for San Joaquin Valley cotton growers to gaze upon the foothills ringing the valley or search the ditches and abandoned fields in search of lygus bugs this season.

Better look across the road and turnrows for lygus because any square-damaging plant bugs will come from next door this season, not the native vegetation, according to University of California IPM specialist Pete Goodell.

There was no opportunity for lygus to reproduce in the foothills or on valley weeds this year because there was virtually no rainfall in March and April to spawn weeds for the insect pest to reproduce.

Goodell said damaging lygus infestations, if there are any, will be related to harvest schedules of lygus host crops this year. One of the biggest lygus hosts is safflowers.

Safflower acreage is up for the second season in a row due to good prices for the oil crop, and UC entomologists have dusted off a 40 year-old degree day model to help growers and PCAs to predict when lygus will move from the safflower to cotton. It is a tried and true degree day (DD) accumulation model that gives growers a heads up on treating lygus in safflower they move into cotton.

The degree day clock started ticking on April 1 and the alarm is going off now.

The model says when 660-degree days have been accumulated, the second generation of lygus in safflower is about to grow wings and head for the nearest cotton squares. Safflower is in many stages of development in the valley, but Goodell said the 660 DD total was reached on May 20.

Goodell did not recommend at a recent cotton meeting that growers and pest control advisers treat every safflower field for lygus at the 660 DD witching hour. Location is the key to treatment decisions.

If the lygus is next door to a susceptible cotton field, treating to control lygus in safflower at the appropriate time would likely be a good move, he said.

However, Goodell said lygus fields farther away need to be evaluated for their potential to spawn cotton-damaging lygus.

As for other crops that host lygus, Goodell has been an apostle of strip-cutting alfalfa to keep lygus in the forage crop and out of cotton. This has become a widespread practice. Lygus also are found in processing tomatoes, and Goodell suggests growers watch harvest schedules for it and other crops and compare it to the susceptibility of cotton.

“Sample cotton at least twice a week during the crop's susceptible early squaring/bloom stages,” Goodell told growers at the UC cooperative Extension at the West Side Research and Extension Center at Five Points, Calif. This critical period is generally at the end of June to the first of July in the San Joaquin.

“Lygus move slowly. They will not jump 160 acres to get to cotton,” Goodell noted.

If sampling detects damaging levels of lygus, Goodell warned PCAs not to use pyrethroids early. Use more selective materials early to preserve beneficials.

“Cotton no longer dominates in the San Joaquin, therefore if lygus becomes a problem it will likely come from adjacent crops this year,” he said.

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