Weed Thresholds in Southern U.S. Rice,Oryza sativa

Abstract

Knowledge of interference thresholds, biology, and growth habits of weeds of rice is essential to implement timely, effective, economical weed control technology for profitable rice production. Regression analyses were used to determine threshold levels for weed densities and durations of interference for major weeds of rice. Weed threshold information for individual species or combinations of species can be used to develop models for initiating control inputs and determining their costs and returns. Among the grass weeds in density experiments, red rice reduced rice grain yields the most followed by barnyardgrass, beared sprangletop, and broadleaf signalgrass. Among broadleaf/aquatic weeds in density experiments, hemp sesbania reduced rice grain yields the most followed by northern jointvetch, ducksalad, spreading dayflower, and eclipta. Barnyardgrass, broadleaf signalgrass, and ducksalad interfered with rice the most during early season, whereas eclipta, hemp sesbania, northern jointvetch, red rice, and spreading dayflower caused greater interference during mid- to late-season.

Upland Rice and Allelopathy

“…], [47] which is a major weed in the southern United States and causes a 21% reduction in the yields of direct-seeded rice. [48] In field experiments, some rice cultivars produced a weed free radius of 10 to 15 cm around an individual plant while other were densely surrounded by ducksalad. Rice cultivars with an allelopathic effect to barnyardgrass [Echinochloa crus-galli (L.) Beauv.]…”

Identification of QTL Controlling Allelopathic Effects in Rice: Genetic Approaches to Biological Control of Weeds

“…For instance, ducksalad, which is one of the main weeds in the southern part of USA, caused a 21% yield reduction in direct-seeded rice 20 . Although various kinds of chemical herbicides are applied to control weeds, recent efforts aim at decreasing the amount of herbicides applied to the rice ecosystems because of their cost and adverse effects on the environment.…”

Rice seedling and plant development as affected by increasing rates of penoxsulam under controlled environments

“…Herbicides contribute significantly to increase yield, mainly under the conventional sowing system, where herbicidal chemicals are the main method used for weed control . Without control, weeds can reduce grain yield in as much as 80% (Smith, 1988). Rice establishment, regardless of the cultivation system, is a critical component of the practices used to ensure competitive advantage of rice over weeds.…”