Weed management in drip irrigated rice

A study was carried out in 2015 in northern Italy to assess the efficacy of weed control strategies in rice watered by drip irrigation. Two conventional and one Clearfield varieties were included. Six plots (20m x 18 m each) were randomly selected within each field: three were subjected to the planned weed control strategy, and three were maintained untreated (check). Water was supplied by means of superficial drip irrigation lines 90 cm spaced. All fields were treated in pre-emergence with pendimethalin (687.5 gai/ha) and clomazone (137.5 gai/ha). Post-emergence treatments were carried out with cyhalofop-butyl (240 gai/ha) + profoxydim (80 gai/ha) followed by MCPA (310 gai/ha) + byspiribac-sodium (33.6 gai/ha), in conventional varieties, and with imazamox (33 gai/ha) + byspiribac-sodium (33.6 gai/ha) followed by imazamox (37 gai/ha) + MCPA (266.4 gai/ha) in Clearfield variety. In each plot weed density and weed cover on the ground were assessed three times during the season. Yield and yield components were assessed at harvest. Weed infestation was mostly represented by Digitaria sanguinalis, Chenopodium album, Portulaca olearacea and Sorghum halepense. In check plots weed infestation was particularly high at the first assessment with, on average, 329 plants/m2, without statistical differences between varieties and with a ground cover above 77%. In treated plots weed infestation was not higher than 17.04 plants/m2 in conventional varieties, and 17.31 plants/m2 in Clearfield variety. At the last assessment, weed density in treated plots was on average 43.55 plants/m2 in conventional varieties, and 64 plants/m2 in Clearfield variety. In these plots weed infestation was mainly represented by Digitaria sanguinalis and, in a less extent, by Chenopodium album and Portulaca oleracea. In treated plots the highest number of culms (428 culms/m2) and the highest yield (3.5 t/ha) was observed in the Clearfield variety