Rice (Oryza sativa L.) response to clomazone as influenced by rate, soil type, and planting date

Clomazone is an effective herbicide widely used for preemergence grass control in rice. However, use of clomazone on sandy textured soils of the western Texas rice belt may cause serious rice injury. When labeled for rice in 2001, sandy textured soils were excluded. Laboratory experiments were conducted to determine the effect of soil characteristics and water potential on plant-available clomazone and rice injury. A centrifugal double-tube technique was used to determine plant-available concentration in soil solution (ACSS), total amount available in soil solution (TASS), and K_d values for clomazone on four soils at four water potentials. A rice bioassay was conducted parallel to the plant-available study to correlate biological availability to ACSS, TASS, and K_d. TASS was significantly different in all soils at the 1% level of significance. The order of increasing TASS for the soils studied was Morey-1 clomazone, respectively, provided optimum weed control with minimal rice injury. Data suggests that clomazone is safe to use on rice on sandy textured soils. Injury may occur, but, rates suggested from this research will minimize injury and achieve excellent weed control. As a result, amendments to the herbicide label will allow clomazone use on sandy textured soils giving rice producers more flexibility and access to another effective herbicide.