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Rice was introduced into Louisiana in the late 1800’s and is currently grown on 162,000–243,000 hectares annually. Production is centered in two diverse areas: the southwestern coastal prairie and the Mississippi River floodplain of northeast Louisiana. Economic losses due to weeds, including weed control costs and direct losses are estimated to be $172 (US) per hectare annually. Red rice, barnyardgrass, and junglerice are common and troublesome weeds from the family Gramineae. Alligatorweed, dayflower, ducksalad, purple ammania, and eclipta are major aquatic or wetland broadleaf weeds. Problem terrestrial broadleaf weeds include hemp sesbania, Indian jointvetch, texasweed, and palmleaf morningglory. Crop rotation, cultural management, and chemical control each play significant roles in current weed control strategies. A rotation of one year in rice and two years in soybean is most common. Early planting and establishing a permanent flood as soon as possible in both dry- and water-seeded systems are cultural practices that are used to suppress terrestrial weeds. Herbicides are used on essentially all rice produced in Louisiana. Where red rice is the major weed of concern, molinate (4.5 kg/ha) is most often used preplant incorporated prior to early water-seeding with brief drainage. Where barnyardgrass and junglerice are most troublesome, foliar applications of propanil at rates of 3.4–4.5 kg/ha are used when weeds reach the 2–3-leaf stage. Thiobencarb or molinate (3.4 kg/ha) are increasingly used to enhance the performance of propanil and provide residual weed control, which tends to reduce the need for successive propanil treatments. Broadleaf weeds that are not controlled by molinate or propanil treatments are generally controlled by mid-season application of 2,4-D (0.6–1.7 kg/ha) in southwest Louisiana. In northeast Louisiana where 2,4-D use is restricted, aquatic and wetland broadleaf weeds are most often controlled with bentazon (1.1 kg/ha). Terrestrial broadleaf escapes can be controlled with triclopyr or bromoxynil (0.28–0.42 kg/ha). Rice flatsedge and yellow nutsedge escapes are controlled with bentazon (1.1 kg/ha). |
