Although treatments of Telone C35 followed by Eptam can initially reduce nutsedge in lettuce, the tuberous weed returns by the following season, according to results of California Lettuce Research Board (CLRB) trials in the Coachella Valley.

Steve Fennimore, University of California weed specialist based at Salinas, detailed his fumigation trials during the board's recent annual reports near Coalinga.

After some favorable indications in 2003, Fennimore said, his 2004 trials with fallow applications of Telone C35 followed by Eptam gave good control of nutsedge in the Coachella Valley, where the weed has been a tough problem for generations of growers.

In 2005 he continued the trials with applications of metam potassium (Kpam) and Telone C35 at Coachella in June and metam sodium and Telone C35 at Thermal in August. The plots were then treated with Eptam, lettuce was planted in September, and several weeks later nutsedge density counts were recorded.

“We found that initially the Telone C35 and Eptam treatment was very good, but it has a limited lifetime,” Fennimore said. “Shank injected Kpam provided some good control but not as good as Telone C35. The water-run metam sodium did not work because it did not penetrate deeply enough.”

Consider rotation

Since the treatments cost $700 to $800 per acre, he said, rather than using Telone C35, lettuce growers might want to consider rotation with pepper or melon ground fumigated with Inline for weed control.

Use of impermeable films for preplant fumigation of peppers might also be worthy of additional research, based on their success in strawberries, he added.

Fennimore also investigated the application of Kerb through sprinklers, an established practice on lettuce in desert production areas. He said none of his work points to it being superior to ground applications in the Salinas Valley, although it might be cheaper.

Recent field studies in Fresno County, however, suggest the chemigation method has some promise, provided precise timing to intercept weed emergence is followed.

Fennimore said the key to using Kerb is to hold it near the soil surface where weeds germinate. That's why he taking another look at various soils to learn more about its mobility.

Soil types study

Although herbicides generally adhere to clay soils, Kerb behaves differently and can leach out in some heavier soils, depending on their clay and organic content. In lighter soils, Kerb tends to bind to soil particles.

He is using columns of soil and a gas chromatograph in a laboratory to trace movement of the herbicide and learn which soil types perform best with the chemigation practice.

His research during 2005 indicated that IDBR1, an experimental, butterhead lettuce germplasm from Idaho, is tolerant of sulfonylurea herbicides. In the trials, the germplasm tolerated pre-emergence treatments of Envoke, Londax, Maverick, Python, and Regiment, and postemergence applications of Express and Harmony.

PAM in drip

In another 2005 project for the board, Fennimore concluded that Stinger and the experimental herbicide V-10142 are not safe for lettuce.

Michael Cahn, Monterey County farm advisor, reported that his CLRB-supported research at Salinas with polyacrylamide (PAM) in drip irrigation of germinating lettuce did not demonstrate significant improvement in moving moisture from drip lines to seed.

The object of the project was to find a way to use drip lines in lettuce for both germination and later irrigation of the crop. Drip has been used for several years by many growers after crop emergence, but it has not measured up to overhead sprinklers for stand establishment.

Drip has been often unreliable because of difficulties in moving moisture from the tape to the seed line, Cahn explained. On the other hand, he added, if practices can be developed to combine the use of PAM successfully with drip, the run-off problems of sprinkler use on some soils might be reduced.

Other potential benefits of using drip exclusively would be elimination of the need for sprinkler equipment for germination only, more efficient use of water, and avoiding splashing of contaminating sediment onto the crop.

For the 2006 season, Cahn said, he hopes to experiment further with PAM and drip with various emitter spacings and bed preparation practices to compare them with sprinklers.

Water viscosity

PAM is an inert, chemical polymer that increases the viscosity of water. In higher concentrations, he found that it actually reduced lateral movement in the trials.

He said although higher discharge rates through the drip system increased lateral water movement and crop germination, nitrate leaching in the soil profile also occurred.

Cahn also wants to evaluate the use of Kerb treatments combined with drip to establish lettuce stands.

The research report event also saw the introduction of Mary Zischke, who succeeds Ed Kurtz as chief executive officer of the CLRB.

Zischke, who took over the post in January, was formerly vice president of lettuce operations with Dole Fresh Vegetables in Salinas. A graduate of Michigan State University with a Bachelor of Science degree in horticulture, she began with Dole as a researcher in 1984. She has also served as a CLRB director.

Kurtz, a veteran consultant in crop production research and pesticide-related regulatory affairs, retired from the position after 15 years. He held long-time appointments with FMC Corp. and Basic Vegetable Products before coming to the board.

In addition to lettuce, his specialties have been onions, garlic, strawberries, parsley, and other minor crops. Kurtz holds a Bachelor of Science degree in entomology from the University of California, Davis.

The CLRB serves the California industry producing each year some 90 million carton-equivalents of iceberg and 68 million carton-equivalents of leaf lettuce. The industry provides 70 to 75 percent of the U.S. lettuce output.

A research-only state marketing order board, it evolved from the Iceberg Lettuce Advisory Board established in 1973. Leaf lettuce crops were added in 1998. Its handler-funded programs deal with production, processing, and distribution of lettuce, and its annual budgets are in the range of $550,000 to $600,000.

The CLRB has provided more than $12 million in research funds since its inception. About 60 percent of that has gone to development of improved cultivars with the balance going to research in pest management, fertility, food safety, and postharvest shipping and handling. Much of the research is done by USDA and University of California scientists.