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Changing crop mosaic creates complications in lygus control

Lygus was a significant problem in cotton last year, particularly on the West Side of Fresno County. However it wasn’t consistent from one area to the next.

“Usually when you have a problem, you have it up and down the state,” said Pete Goodell, University of California’s IPM specialist at the 2008 Central Coast Cotton Conference.

Lygus didn’t appear to “play by the rules” last season, and researchers are trying pinpoint why. One factor is the changing mosaic of the state’s cropping patterns. As cotton acres have plummeted in recent years, growers are replacing that acreage with permanent crops or row crops that have different susceptibilities to lygus.

In the past, growers and researchers kept an eye on weeds in the adjacent foothills. If late winter and early spring rains kept weeds green well into the season, it was anticipated lygus would move into cotton during the critical fruiting period.

“In reality, those years are rare,” Goodell said. “Our threat is mostly internal. We produce our own lygus in the Valley. They develop in an adjacent crop and then move over to cotton or something else as early planted crops are harvested.”

That’s a compounded problem for cotton growers. “Critical fruit set is occurring at a time when there’s an increasing lygus population and a declining crop so they’re being concentrated in the number of crops we have left,” Goodell said. “It’s a double whammy.”

The dynamics of lygus movement have changed in ways that researchers and growers are still trying to understand.

Safflower acreage, in particular, has grown substantially in the last two years. An estimated 30,586 acres of safflower was grown last year in an area that UC researchers surveyed from San Joaquin south to Stratford. Cotton plantings in that same area dropped to an estimated 30,722 acres.

With a near 1:1 ratio of safflower to cotton, the potential for lygus to move into cotton is overwhelming. Additionally, the timing of safflower plantings last season changed the lygus dynamic from what has been seen in the past.

“Safflower was planted over a long period of time last year — anywhere from Thanksgiving to March,” Goodell said.

That staggered planting meant different crop maturities throughout the season, providing an excellent area-wide habitat for an extended period of time. The constant waves of lygus just kept coming.

“Some fields lost three or four weeks of fruiting where estimated losses of 50 percent to 60 percent were common,” Goodell said. “Whole fruiting branches were destroyed. They were so bad last year we had alfalfa fields that couldn’t hold them all. There were alfalfa fields with 150 counts.”

As the cropping mosaic has changed dramatically, researchers are warning growers not to rely entirely on historical patterns when coming up with a management plan. It’s more important than ever to consider an entire area.

One option is to spray safflower after 660 degree days have accumulated after April 1. This UC-tested strategy is effective because it targets the third instars before they develop wings. “The problem is how are you going to spray all that safflower?” Goodell asked.

Even being near or adjacent to alfalfa is not the key in every situation. “It’s my understanding growers here were practicing deficit irrigation the way they do it in Arizona,” he said. “They put on minimal irrigation in the summer and let it go, so the lygus all move out. So if this alfalfa is now acting as a source of lygus, the whole system in California is really undergoing a change.”

The best solution to manage the problem is unclear at this point, but it’s clear to Goodell it will take cooperation from the grower community to limit the impact of lygus.

“We need to start looking at the situation on an area-wide basis,” he said. Possibilities include trying to obtain financial support to put in small strips of alfalfa interspersed throughout an area, and trying to get more growers to leave checks in their alfalfa instead of drying the entire field out at once.

“This is not going to be easy,” Goodell said. “It’s going to require commitment and shared values, but I think the alternative is just too expensive. These two-bale, three-bale crops on the West Side aren’t going to make it, and it’s going to be one more pressure on this industry.”

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