|Weed Control in Rice-97
Project Leader and Principal UC Investigators
James E. Hill - Extension Agronomist and Chair Department of Agronomy and Range Science, UC Davis
W. Mick Canevari - UC Farm Advisor, San Joaquin County
Barney P. Caton - Postgraduate Researcher, Department of Agronomy and Range Science, UC Davis
Randall G. "Cass" Muitters - UC Farm Advisor, Butte County
Stacey R. Roberts - Postgraduate Researcher, Department of Agronomy and Range Science, UC Davis
Steven C. Seardaci - UC Farm Advisor, Colusa, Glenn and Yolo counties
John F. "Jack" Williams - UC Farm Advisor, Sutter and Yuba counties
research continues to be one of the most challenging areas of scientific inquiry funded by
the California Rice Research Board. Much of the work in the last few years has been driven
by the need to find alternative methods of dealing with Londax®-resistant weeds.
Encouraging developments have taken place in this area, as well as in the brave new world
of transgenic rice. This past years weed control research was driven by four primary
The following summarizes principal accomplishments from this research.
Promising New Herbicides
Researchers are optimistic about FMC's new herbicide carfentrazone (Shark®). In growers field studies during 1996, the first year of testing, carfentrazone provided excellent control of the four Londax®-resistant weeds - smallflower umbrella sedge, ricefield bulrush, California arrow- head and redstem. In 1997 carfentrazone provided "good but not excellent" control of these species in grower field studies. This was attributed to lower rates, high weed infestations and poorer rice stands in test areas. Carfentrazone also provided satisfactory control of Gregg's arrowhead at one site. In studies at the Rice Experiment Station, carfentrazone proved injurious to rice at the three-leaf stage and did not completely control ricefield bulrush. Future studies will need to more thoroughly evaluate the use of surfactants and whether carfentrazone should be applied into the water or with the water drained.
As it had in previous tests, another experimental herbicide (V-10029) completely controlled watergrass and can be expected to provide partial control of ricefield bulrush. Because both carfentrazone and V-10029 may be available for use within a few years, researchers examined rate and timing combinations for the first time. Combinations of both herbicides controlled both grass and broadleaf weeds (except Sprangletop) at very low rates of application. Although weeds were controlled with an early (three-leaf) application, rice was severely injured. However, very low rates may provide rice safety and good weed control. Injury was much lower at the six-leaf stage. Studies on rate and timing will continue.
Researchers also examined other experimental herbicides in early field studies. Further testing will be necessary to determine whether any of them fit in California's water-seeded system. .
Due to regulatory changes, researchers were also able to evaluate new formulations of propanil for the first time in many years. In tests at the Rice Experiment Station early treatments of propanil alone and in combination with Abolish (thiobencarb) to drained rice gave good control of both broadleaf and grass weeds. This combination works well, allowing propanil to control emerged weeds while Abolish® added both foliar and residual activity. Furthermore, these studies indicated that the rates of both herbicides in the combination may be lowered significantly from rates normally used for each alone.
The use of transgenic rice cultivars with "built in" resistance to broad spectrum herbicides is a technology for weed control still in its infancy. California- adapted cultivars are only in the early stages of development and thus seed was not available in 1997 for large-scale field testing. However, researchers were able to examine a transgenic rice variety provided by Louisiana State University to evaluate timing and split applications of the herbicide Liberty (glufosinate). Control ratings and yields were quite variable in this experiment, perhaps because the cultivar was not well adapted to California conditions. Nonetheless, these tests "clearly" showed that split applications may be necessary for good weed control if foliar-active herbicides are to be used alone. The benefit of a split application or tank mixes with residual herbicides will be investigated further..
In related greenhouse studies at UC Davis, researchers also tested Roundup" (glyphosate) against the most important rice weeds in preparation for the possibility of Roundup"-Ready rice. Roundup® gave excellent control of grass weeds but only moderate control of smallflower umbrella sedge. These trials suggest that Roundup® may control grasses and broadleaf weeds readily but might need to be mixed with a separate product for adequate sedge control.
Competitiveness Of Rice
Four experiments at the Rice Experiment Station sought to examine the relative competitive ability of commercial rice cultivars against weeds. The idea behind this study, supported largely by the University of California Statewide Integrated Pest Management Project, is to see if the use of more competitive cultivars might enable lower herbicide rates to be used.