Red rice (Oryza sativa L.) control in herbicide tolerant rice (Oryza sativa L.)

Abstract

Red rice has interfered with production of commercial rice in the United States for over 150 years. Because of the genetic and physiological similarities between red rice and commercial rice, herbicides have been unsuccessful in adequately controlling this weed. More recently, advances in plant breeding and genetic engineering have led to commercial rice tolerant of several herbicides that control red rice. Two recent advances include glufosinate and imazethapyr tolerant rice. This technology may provide a means of chemically controlling red rice in commercial rice fields. Field experiments were conducted in 1998 and 1999 at several locations in the Texas rice belt. Glufosinate studies were located at the Texas Agricultural Experiment Station (TAES) Research and Extension Center near Beaumont, and at the Coastal Ag Research Farm, near East Bernard, TX. Experiments involving imazethapyr tolerant rice were conducted near Beaumont and at the TAES site near Eagle Lake, TX. At the Beaumont location, red rice control was adequate with imazethapyr rates of 0.011 kg/ha and higher, applied preplant incorporated or postemergence. However, postemergence treatments resulted in crop stunting and chlorosis as high as 29% at 21 days after treatment. Preplant incorporated and preemergence applications of imazethapyr at all rates followed by 0.04 to 0.07 kg/ha postemergence resulted in excellent red rice control with minimal crop injury. Near Beaumont in 1998, single applications of glufosinate at 0.29, 0.45, or 0.60 kg/ha provided similar levels of red rice control, whether applied at the 1 to 2-leaf stage, or the 4-leaf, 2-tiller stage. However, the following year early postemergence applications were more efficacious than single late postemergence treatments. When applied sequentially at each timing, rates of glufosinate above 0.29 kg/ha controlled red rice better than most single applications. Each herbicide tolerant system is an effective tool for chemically controlling red rice. Proper rate and application timing is essential for effective and efficient weed control. With imazethapyr, a postemergence application, following a soil-applied treatment, is necessary to provide season-long red rice control. Sequential applications of glufosinate, made at the 1 to 2-leaf stage and 4-leaf, 2-tiller stage are also needed for acceptable control of red rice.