Some Factors Affecting Herbicide Selectivity in Upland Rice

Several methods were used to overcome herbicide phytotoxicity to upland rice (Oryza sativa L., 'IR8'). Seed pelleting with activated carbon and band application of acti- vated carbon slurry over the rice seed were ineffective in re- ducing the toxicity of chloramben (3-amino-2,5-dichloroben- zoic acid) and atrazine (2-chloro-4-(ethylamino)-6-(isopropyl- amino)-s-triazine) to upland rice. In contrast, a 2.5-cm layer of activated carbon and vermiculite mixture (1: 1) placed over the rice seed was effective in overcoming the toxicity of these herbicides. Deep sowing (3.0 to 4.5 cm) of rice seed was ade- quate in protecting upland rice from herbicides which are tox- ic to direct seeded, flooded rice but are not toxic to trans- planted rice. The degree of protection from deep sowing, however, was determined by site of uptake, herbicide adsorp- tion by soil, leaching, and inherent toxicity of the herbicides to rice seedlings.