IMPACT OF PRE- AND POST- PLANTING HERBICIDES ON GROWTH PERFORMANCE AND YIELD OF ORYZA GENOTYPES IN SRI LANKA

Herbicide application is one of the most effective methods of weed control in agricultural crops. However, herbicides can cause adverse effects on crops including rice (Oryza species). A preliminary greenhouse study was conducted to evaluate the herbicide tolerance in rice using five improved (BG-360, BG-352, BG-359, AT-306, AT-308), three traditional (“Machel”, “Kuruluthuda”, “Madathawaru”) varieties of O. sativa and five wild rice spp. (O. nivara, O. rufipogon, O. eichingeri, O. rhizomatis, O. granulata). Broad spectrum pre-planting (glyphosate; 360g/l Count-up®) and post-planting (Fenoxaprop-p-ethyl; 69g/l RiceStar®) herbicides were used in single (0.5 g/l, 5.0 g/l) and double dose (1.0 g/l, 10.0 g/l) concentrations respectively with control and eight treatment combinations. Seedling emergence time, plant height after two weeks and one month, whole plant biomass at maturity and productive yield were measured. Results indicated that herbicide treatments have caused a significant (p≥0.05) impact on the growth and yield of all rice genotypes at single and double doses. After treating with herbicides, traditional and wild genotypes showed comparatively a shorter germination time and better growth compared to improved varieties. Single and double doses of both herbicides indicated a significant yield loss as well as reduced biomass. Compared to AT- and BG-varieties, traditional varieties showed significantly a higher tolerance to both herbicides. The tolerance was even higher in wild genotypes. There were no comprehensive studies carried out so far on effects of pre- and post-planting herbicides on rice genotypes available in Sri Lanka. The results revealed the significance of evaluating herbicide tolerance in terms of their concentrations among cultivated rice varieties to minimize the crop and yield damage due to herbicide application.