Manipulating weed management practices can reduce herbicide dependency in rice
A University of California, Davis research team has found that different
rice establishment methods can keep weeds from developing, reduce herbicide
dependency, lower fuel use, and help reduce herbicide-resistant weeds in
Weed scientist Al Fischer and Jim Hill, UC Cooperative Extension specialist, coordinated the project. “As California rice growers find their herbicide options dwindling because of widespread herbicide resistance in the major weeds of rice, the need for nonchemical means of manipulating weed management practices is imperative,” says Fischer. “Both molinate and thiobencarb had been for years the most relevant herbicides for grass control in rice, but due to resistance they no longer control watergrass. Molinate registration will expire by 2008. In addition, rice straw burning restrictions and subsequent increased straw incorporation has increased soil weed seed banks by protecting the seeds from scavengers like birds and rodents."
Continued >> With funding from the UC IPM Program, CalFed, and USDA, Fischer and his research team conducted field studies to find diverse weed management options in rice cropping systems to reduce dependency on herbicides.
Fischer experimented with rice establishment treatments including water- or drill-seeded rice, fall or spring tillage, no-till, and stale-seedbed techniques to assess their effects on weed recruitment and control.
During the three-year study, the lowest weed infestation occurred where rice was water-seeded after a stale seedbed without spring tillage. In the stale seedbed technique, growers use irrigation flushes to promote weed emergence, followed by pre-plant burn-down application of glyphosate (Roundup) for which resistance has not evolved in weeds of rice. This method depletes weed populations from the upper soil layer and markedly diminishes the amount of weeds emerging with the crop. Glyphosate is also considered an environmentally benign herbicide.
“Success with the stale-seedbed technique depends on keeping seedbeds moist and allowing sufficient time for most weeds to emerge prior to glyphosate application,” says Fischer. “If the stale-seedbed technique is followed by limited or no soil disturbance prior to seeding rice, very little weed control is needed thereafter.”
In addition, experiments show eliminating spring tillage (preparing land for crop planting by plowing or disking) reduced weeds by 75 percent in the water-seeded treatments, suggesting that this may be an effective cultural technique to further reduce weed populations in rice. Less tillage also means lowering the costs for fuel—a very real concern in the face of ever increasing energy prices.
Dry-seeded and water-seeded rice can drastically alter the species composition of weed populations that emerge with the crop. Aquatic weeds are strongly disfavored in drill-seeded rice, while grasses like barnyardgrass or sprangletop are suppressed by water seeding.
“By alternating stand establishment systems, we can break weed life cycles to reduce weed infestations and weed seed input to the soil seed-bank,” says Fischer. “Also, drill-seeded systems and the stale-seedbed technique allow using herbicides with new modes of action to control weeds that have evolved resistance to herbicides currently used with water-seeded rice. A crop established without weed interference rapidly develops a competitive canopy that suppresses further weed establishment.”
Modeling of weed recruitment and growth is being evaluated for this experiment to identify stand establishment sequences that may reduce seed-banks of problematic weed species. Results from this research will be used to develop integrated weed management programs by breaking weed life cycles through rotation of stand establishment methods, alternating herbicide modes of action, as well as effective crop interference.
“In many rice-growing areas, the crop is grown in heavy-textured, rice-only soils where no other crops are economically viable, and it is these cases that we are trying to address in this work,” says Hill. ”A viable and practical solution to manage herbicide-resistant weeds in these rice-only rotations is to alternate conventional water seeding with new rice establishment methods.”
Members of Fischer and Hill’s research team are:
From Plant Sciences at UC Davis:
From UC Cooperative Extension: Farm Advisors Randall “Cass” Mutters, Butte County, and Christopher Greer, Colusa County.
Tom Barcellos of T-Bar Dairy/Barcellos Farms in Porterville is a believer in conservation tillage, and it wasn’t a hard sell. Barcellos has been named the 2006 Conservation Tillage Farmer Innovator by the University of California Agriculture and Natural Resources Conservation Tillage (CT) Workgroup at its annual conference Oct. 19 in Five Points.
Conservation tillage is a process in which growers reduce plowing. In 2001, Barcellos tried conservation tillage on 70 acres of his 1,850-acre farm. This new process drew a lot of interest from neighboring farmers who debated the usefulness of the method.
But, Barcellos was enthusiastic about the results he was seeing. He decided to try 320 acres during the first trial year. “Before using conservation tillage, I had to do a lot more double cropping in the summer. I had five tractors making up to 10 passes through the field. Now, in the summer when I double crop, I use one tractor. I’m saving money on fuel and labor.”
Often farmers using conservation tillage also plant cover crops underneath the main crop or between two different crops to cover and protect the soil. Cover crops have additional benefits according to the species planted. For instance, legumes enrich the soil with nutrients, while plants with strong, deep roots break up compacted soil. In the low-rainfall regime of the San Joaquin Valley, farmers may benefit more from cover cropping in combination with conservation tillage to maintain soil fertility, as opposed to conservation tillage alone.
Continued >> Barcellos has planted up to 5,000 acres on his own farm. He also planted for neighbors who had not yet invested in the new equipment required for no-till on their farms. “Now, conservation tillage is more the standard than the exception. Even though I use Roundup, we’re actually spraying less, and I have equal or better crops. I have less dust and less exhaust because of reducing the number of tractors used. One thing I tell every farmer is that this is not a recipe. It’s a guideline. A farmer knows his own ground. You develop the mindset that you’re not running as much equipment so now you have time to look at water and spray timings.”
The availability of herbicide-tolerant crops, increased fuel prices, access to better conservation tillage, Global Positioning System technology, and environmental air quality issues are leading to an increased interest in conservation tillage systems in the San Joaquin Valley.
Some advantages of conservation tillage are that crops use water more efficiently, the water-holding capacity of the soil increases, and water losses from runoff and evaporation are reduced. However the effectiveness of conservation tillage varies considerably with crop type, agronomic practices, and growing conditions.
To encourage participation, the Natural Resources Conservation Service pays up to $30 per acre for CT production to eligible growers who apply for the Environmental Quality Incentives Program (EQIP) cost-share funds. The EQIP provides a voluntary conservation program for farmers and ranchers that promotes agricultural production and environmental quality with incentives for participants.
Conservation Management Plans, now required by the San Joaquin Valley Unified Air Pollution Control District, list Roundup Ready and the reduction of cultivations as practices acceptable in dust reduction. However, tillage has been an important weed management tool in agricultural cropping systems.
Although there are many benefits to conservation tillage, there are also concerns. “Any reduction in tillage intensity or frequency poses serious concerns for weed management that include weed species shifts (changes in the types of weeds), increased weed densities, and associated crop yield losses,” says Anil Shrestha, UC IPM weed ecologist. “These are some of the major reasons for the lack of widespread adoption of conservation tillage systems.”
Shrestha has been working with other members of the UC ANR CT Workgroup on conducting research and demonstrations, and in disseminating information on weed management issues on various CT systems in forage corn, cotton, tomato, small grains, and blackeye bean cropping systems in the San Joaquin Valley.
In some of these cropping systems, Shrestha has noticed shifts in weed species found in a field. “I fear that reliance on a single herbicide mode of action year after year could lead to the evolution of herbicide-resistant weeds, particularly in those cropping systems that use herbicide-tolerant crops,” he says.
Rotating herbicide modes of action and crops, integrating mechanical cultivation to manage certain weed species such as annual morningglory and field bindweed, and minimizing weed seed returns could be effective strategies for the success of CT systems, says Shrestha.
The CT Workgroup currently consists of more than 80 UC Cooperative Extension, Agricultural Experiment Station, USDA Agricultural Research Service, and Natural Resource Conservation Service personnel, private industry, farmers, and student members and affiliates. The group conducts a wide range of research studies, demonstration evaluations, and conferences throughout San Joaquin, Sacramento, Salinas, and Coachella Valley production regions. For more information, see The Conservation Agriculture Systems Innovation Web site.
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