Author(s): B. DUARY AND N. T. YADURAJU

Abstract: Experiments were conducted in soil typic Ustochrepts (Inceptisol) during winter season of 1997-99 to detennine the effects of varying densities of little seed canary grass (Phalaris minor Retz.) on the grain yield of wheat. As the density of weed incre11Sed from 0 to 200/m2 the yield of wheat was reduced by 23.9 and 32.6% in the first and second year respectively. To predict the yield of wheat, the yield data was fitted to an empirical model based on hyperbolic relationships over P. minor densities. The obsetved and predicted yield losses were close. The relationship between wheat and little seed canary grass was also shown by a non-linear regression model based on relative leaf area of woods estimated in earlier stage. This single parameter model also gave good fit to the data on yield loss calculated frpm the observed weed free crop yields. From the yield loss-weed density model the economic threshold of this weed for the herbicide isoproturon was calculated as 13.0 to 19.7 /m2 for the single season.

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