Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 31, 2013
Publication Date: January 6, 2014
Citation: Gealy, D.R., Anders, M., Watkins, B., Duke, S.E. 2014. Crop performance and weed suppression by weed-suppressive rice cultivars in furrow- and flood-irrigated systems under reduced herbicide inputs. Weed Science. 62(2):303-320. Interpretive Summary: Weeds are a major problem on rice farms throughout the world. On top of this, weeds are becoming an even trickier problem because some of them have developed "resistance" to the herbicides used to kill them. Rice production is also becoming potentially less sustainable because the abundant quantities of flood-irrigation water necessary for healthy crop growth are more and more difficult to obtain and less and less affordable. We are attempting to counter both of these undesirable trends by indentifying special rice varieties that can produce high yields with less water, and also control weeds naturally. In a three-year experiment, we compared the rice yields and weed control potential of seven varieties supplied with traditional "flood" irrigation, which consumes very large amounts of water, to an alternative "furrow" irrigation system, which consumes much less water. In these fields, "traditional" rates of herbicide were also compared to "reduced" rates. A commercial hybrid rice variety and a variety known to release weed-fighting chemicals called "allelochemicals" produced the highest rice yields and the best weed control in both irrigation systems. However, rice yields with furrow irrigation were only about one-fourth as high as with traditional flooding, which indicated weeds and other sources of "stress" can severely limit production in the absence of a flood. When treated with "reduced" rates of herbicide, the high-yielding, weed-suppressive varieties controlled weeds just as well as the lowest-yielding, non-suppressive varieties did when they were treated with "high" rates of herbicide. Our findings indicate that some weed-suppressive varieties have a natural ability to recover from situations in which herbicides fail to control weeds as expected. This work is important because it demonstrated that these high-yielding, weed-suppressive varieties might be able to thrive better than most of our existing varieties in rice fields managed with reduced amounts of irrigation water or herbicides, or on organic production farms which limit the use of weed control chemicals.
Technical Abstract: Weed control in rice is challenging, particularly in light of increased resistance to herbicides in weed populations and diminishing availability of irrigation water. Certain indica rice cultivars can produce high yields and suppress weeds in conventional flood-irrigated, drill-seeded systems in the southern U.S. under reduced herbicide inputs, but their response to reduced irrigation inputs in these systems in not known. Rice productivity and weed control by weed-suppressive cultivars and conventional non-suppressive cultivars were evaluated in a non-flooded furrow-irrigated (FU) system and a conventionally flooded (FL) system under three levels of weed management (herbicide inputs) in a three-year field study. Rice yields across all weed management levels yielded approx. 76% less in the FU system than in the FL system. The allelopathic indica cultivar PI 312777 and commercial hybrid rice CLXL729 generally produced the highest grain yields and greatest suppression of barnyardgrass in both irrigation systems. Bengal and Wells were the top yielding conventional cultivars, while Lemont and CL171AR yielded the least. Weed suppression by PI 312777 and CLXL729 under "medium" weed management was equivalent to that of Lemont and CL171AR at the "high" management level, suggesting that the weed-suppressive cultivars may be able to compensate for suboptimal herbicide inputs or incomplete weed control.