Smith detailed results of his 1999 and 2000 trials during the recent Salinas Valley Weed School at Spreckles.
Stressing that prevention is the first defense, he recommended that growers treat small infestations before they get out of control. Frequent tillage is another way to hold the weed at bay.
He said the best time to treat for yellow nutsedge is before the fifth-leaf stage when the weed sets nutlets.
The first of the treatments was applied at the end of cutting and the second one month later.
Smith’s trial in 2001 compared in-season treatments of Sandea, Dual Magnum, and Lorox with cultivation. The best was the Sandea plot where nutsedge plant counts as of May 4 showed about 29 plants per five cubic feet of soil. The cultivated portion showed 37 plants, and the untreated check was 116 plants.
He also observed a smaller biomass of nutsedge tops, also indicating improved control of the Sandea applications.
In another asparagus trial, Smith evaluated Sandea and Roundup Ultra for control of perennial peppergrass. However, the trial was cut short and results indicated only the short-term results. Roundup gave excellent burndown of peppergrass, and Sandea stunted and yellowed it. He hopes to resume trials to evaluate long-term strategies against perennial peppergrass with the two herbicides.
Kerb on lettuce
Another speaker, Yuma, Ariz., County Agent Barry Tickes, recounted his trials with Kerb on lettuce. He said some Low Desert growers complained that its performance was lower after the manufacturing was changed from Rohm and Haas to Dow Chemical.
"Actually, its formulation changed little in the mid-1980s and performance is identical with the earlier product. But because of some problems with it in the last 10 years or so, people thought it had changed," he said.
Using a bag of Kerb dating from 1980 and some "new" Kerb, Tickes compared the two with incorporated furrow and sprinkler irrigation. He found that 1.5 pounds of either under furrow gave better control of shepherdspurse than the same rate under sprinklers.
"In Yuma over the past 20 years, we have slowly gone from furrows to sprinklers for the entire season for lettuce as well as cotton and other crops. We knew from trial with dead-level, basin-irrigated alfalfa that Kerb will move with a lot of water."
He concluded after studies on lettuce about three years ago that Kerb was being leached by sprinkler irrigation before the weeds germinated. The subbing of furrow water held the material in place. "We know now we have to concentrate the herbicide in the top half-inch of soil."
The most common practice in the Yuma area now is to apply Kerb by air and incorporate the herbicide after about three or four days. It will also give some post emergence control of mustard and some other sensitive weeds.
But he also pointed to some trade-offs: there is greater sensitivity with leaf lettuce than head lettuce and aerial application is less precise than banding over beds. In general, he added, better weed control often results in more crop injury.
Tickes said another herbicide long-used in Yuma, Prefar, whose ownership has changed, works in an opposite fashion from Kerb. Prefar works better when banded after planting and incorporated with sprinklers.
He said a third herbicide, preplant Balan, has long been used significantly in the Yuma area in combination with Kerb and Prefar. Kerb is used on about 50 percent to 70 percent of the acreage, Prefar is used on about 30 percent, and Balan is used on about 50 percent.