Control of barnyard grass in rice in the Murrumbidgee Irrigation Area using 3,4,dichloropropinionanilide

Barnyard grass (Echinochloa spp.) is an extremely effective competitor with rice. In two experiments at the Yanco Agricultural Research Station, rice severely infested with barnyard grass produced approximately' 50 per cent less tillers per sq. ft. 90 days after sowing, approximately 50 per cent less panicles at harvest, and 33-55 per cent less yield than rice treated with 3,4-dichloropropionanilide ( DPA ) to control barnyard grass. In untreated plots, barnyard grass absorbed over 60 per cent of the total nitrogen taken up from the s oil by both the weed and rice during the first 90 days of growth. DPA applied at a rate of 4 lb an acre gave excellent control of barnyard grass. In the first experiment, when the grass was in the 1-3 leaf stage, application two or ,four days before irrigation resulted in much less weed surviving than when applied three hours before irrigation. This irrigation was followed by permanent flooding six day later. In the second experiment the grass was in the 4-7 leaf stage. There was no significant difference in kill of weeds between DPA applied at different times and rates. Survival of weeds in all treated plots in both experiments was significantly less than in the untreated plots. Treatment with DPA increased the yield significantly in all cases. Although the amount of grass surviving 90 days after sowing varied somewhat with different times of DPA application, the total yield, number of panicles per sq. ft., and panicle weight of rice, for any of these treatments were not significantly different.