Fungistatic activity of herbicides against Rhizoctonia solani, the incitant of sheath blight of rice

Among the rice diseases, known to reduce production, sheath blight caused by Rhizoctonia solani Kuhn (AG-1 IA) is a major biotic constraint causing substantial losses in grain yield of rice. The present studies were undertaken to evaluate the efficacy of five pre-emergence soil applied herbicides viz. butachlor 50 EC, pretilachlor 50 EC, pendimethalin 30 EC, anilophos 30 EC and oxadiargyl 80 WP at CCS HAU Rice Research Station, Kaul for their fungistatic effect on R. solani in vitro and on sheath blight of rice under field conditions during Kharif 2016 and 2017. Analysis of data revealed that all the herbicides significantly reduced the mycelial growth and sclerotia formation of R.solani. Pretilachlor was found to be the most effective herbicide in suppressing the mycelial growth and sclerotial formation followed by butachlor while pendimethalin and anilophos were most promising in curtailing the sclerotial germination of the fungus. The increasing concentrations of the herbicides significantly increased the inhibition of sclerotial germination at all the concentrations except 50 & 100 ppm, 1000 & 1500 ppm and 1500 and 2000 ppm. The suppression of sclerotial germination was more pronounced at higher concentrations (1000 ppm and above) of all the herbicides except oxadiargyl in which there was no significant decrease in germination beyond 100 ppm. Almost complete sclerotial germination inhibition was recorded at the concentrations of 1000 ppm and above of pendimethalin and anilophos and at 1500 ppm and above in butachlor. A significant reduction in sheath blight was recorded in all the herbicidal treatments except oxadiargyl. On mean basis, pendimethalin suppressed the disease severity by 35.30% along with 9.74% increase in grain yield of rice followed by pretilachlor and butachlor. The present information would aid in selection of herbicides for formulating integrated disease management strategy against sheath blight of rice.