BIFS rice project leads to new approach with weeds
Beginning in 1999, a three-year Sacramento Valley Biologically Integrated Farming Systems (BIFS) project partnered rice growers and UC researchers to manage herbicide resistant weeds and reduce the use of chemical inputs. Project leaders Randall "Cass" Mutters, a UC Cooperative Extension farm advisor in Butte County, and Jim Eckert, a UC researcher in Butte County, worked with a team of cooperators to explore alternative practices.
Farm advisor Cass Mutters shows growers how weed populations were manipulated using alternative management practices at the Rice Experiment Station in Butte County. (photo by Bev Ransom)
Weeds are a "monumental challenge" to rice growers, the researchers noted in their final report. "Unlike insects, there is no threshold of economic injury. A single escaped weed in a field can produce thousands of seeds that remain viable in the soil for years. Consequently, the weed seed bank perpetually builds," the report states.
Collaborations that began with the BIFS rice project led to continued research partnerships. Mutters and Albert Fischer, a UC Davis plant sciences weed scientist, continued their work on weed problems with funds from the CALFED Bay-Delta Program; the Regional Water Quality Control Board; USDA Cooperative State Research, Education and Extension Service (CREES); and the statewide UC Integrated Pest Management program. Many rice growers who participated in the BIFS project became part of a grower advisory group that guided the continuing research.
Increased farming costs contributed to rice growers' interest in Mutters' and Fischer's alternative rice weed management strategies research, which was presented at a summer field tour at the Rice Experiment Station in Butte County. Growers have told researchers they are concerned about weed control costs that are often higher because of herbicide-resistant weeds. Severe weed problems can also involve increased tillage, which is more expensive because of higher diesel fuel costs. At the field tour, researchers described how growers could manipulate weed populations to encourage weeds that are easier and less costly to control.
In the replicated trials conducted at the Rice Experiment Station, five different farming systems were compared. Researchers tested the difference between water-seeded and drill-seeded planting regimes, and the difference between traditional spring tillage (which encourages germination and emergence of new weeds from the top soil layers) and no tillage (which does not encourage emergence of new seedlings from the soil, only those lying on the soil surface). When there was no tillage on a field, most of the weed population was eradicated with one treatment of glyphosate (Roundup®) prior to seed planting following a flush of irrigation to promote weed emergence, a practice known as "stale seedbed." Even with spring tillage or dry-seeded rice, the practice of the "stale seedbed" using glyphosate substantially reduced the weed populations emerging with rice. This technique can reduce the herbicide applications from two or three to just one. In addition, glyphosate is effective against all the weed biotypes that have evolved resistance to other herbicides.
As growers walked through the demonstration sites, it was evident that different stand establishment practices had resulted in different weeds. These alternative practices reduced the bank of weed seeds in the soil, and may also delay the further development of herbicide-resistant weeds. When water-seeding was alternated with dry drill-seeding, the emergence of aquatic weeds was strongly prevented; some aquatic weeds are serious rice weeds that have also evolved resistance to herbicides (ALS inhibitors).
In order to maintain sufficient yields in alternative systems, researchers are also exploring the impact of these alternative cultural systems on the nitrogen dynamics and plant needs.
"Even if some of these alternative systems result in reduced yields, it may well be worth it to save money on herbicides while at the same time changing the weed population of a given field," Mutters said.
By looking at weeds as part of an integrated farming system that can be tweaked, farmers may find that a periodic shift to a different weed management approach on particular fields could be an effective tool. For more information, contact Mutters at rgmutters@ucdavis.edu.
