ARS | Publication request: ALLELOPATHY IN RICE AS A WEED CONTROL STRATEGY

Submitted to: International Weed Control Congress Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: June 6, 2000
Publication Date: N/A

Technical Abstract: More than 50 weed species infest direct-seeded rice (Oryza sativa L.) and cause major losses in U.S. rice production. Annual losses due to weeds in rice have been estimated at about 17% of the total production. Barnyardgrass [Echinochloa crus-galli (L.) Beauv.], a weed that is found primarily in dry-seeded rice fields can cause almost total loss of field yields and is the most frequently reported weed in rice. Ducksalad [Heterantheia limosa (Sw.) Willd.], an aquatic weed that can reduce rice yields by 30% when competing with rice in a water-seeded culture, is second to barnyardgrass as the most frequently reported weed in rice. Allelopathic activity is believed to be the joint action of several secondary metabolites that may act synergistically. Cultivars of rice with allelopathic activity to major weed species could reduce the loss of field yields due to weeds and reduce herbicide costs. We evaluated the USDA-ARS rice collection and identified accessions or varieties with apparent allelopathic properties to weed species, prevalent in either water-seeded or dry-seeded culture, that can be used in variety development programs. A total of 412 rice accessions were identified in field tests in 1988, 1989 and 1990 that had a radius of activity >10 cm to ducksalad and 145 accessions that had the same radius of activity to redstem (Ammannia sp.). In 1994, a total of 94 accessions demonstrated apparent allelopathic activity to barnyardgrass in field test. In barnyardgrass infested plots, the grain yield reduction of rice accessions that demonstrated apparent allelopathic activity was 37% as compared to a 68% reduction in grain yield of non-allelopathic accessions. Field and green house trials have shown a reduced number and size of both ducksalad and barnyardgrass plants when