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The study on “Mitigating the phytotoxic effect of ALS inhibiting herbicides in rice (Oryza sativa L.).” was conducted during 2015-2016 at Agricultural research station, Mannuthy, with the prime objective of mitigating the growth inhibition due to the application of post emergent ALS (Aceto Lactate Synthase) inhibitors, bispyribac sodium azimsulfuron and to improve the productivity of rice.
The experiment was laid out in RBD with three replications and there were eleven treatments comprising of two Aceto Lactate Synthase inhibitors viz., bispyribac sodium (30 g ai/ha) , azimsulfiiron (35g ai/ha) and five mitigating treatments viz., Urea spray (0.1%), Micronutrient spray (1 gm each of zinc sulphate and borax, 0.01 gm of molybdic acid/litre), NAA spray (100ppm), Tank mix and water spray (1000 ml) with hand weeded as control. Herbicides were sprayed on 15 DAS whereas mitigating treatments were sprayed on 35 DAS. Observations on morphological, physiological, biochemical, yield and yield attributes of rice were recorded. Morphological characters were studied at 15 days interval and biochemical estimations were done 7 days after herbicide application and at the time of flowering.
Mitigation treatments resulted in a 10- 13 % increase in height and 4-8 % improvement in tiller number of rice plant at harvest compared to plants in the hand weeded plot. Effect of mitigating treatments on growth attributes viz., relative growth rate, crop growth rate , net assimilation rate, and leaf area index indicated that at the final stages of growth there was no significant difference between the treatments. However during the critical stages of growth i.e.,45-75 DAS significant variation was observed. Among the mitigation treatments, bispyribac sodium followed by tank mix applied plots had higher values as compared to the other treatments whereas azimsulfuron applied plots had the lowest value for these parameters.
The biochemical parameters such as nitrate reductase enzyme activity and total soluble protein content showed an initial decline when estimated one week after application of herbicide. At the time of flowering, recovery was higher in the plants where foliar spray of mitigating treatments were given as compared to water spray. Tank mix applied plots

recorded more value for the above biochemical parameters in both bispyribac sodium and azimsulfuron applied plots.
Proline content and catalase enzyme activity showed increase with herbicide application when compared to hand weeded control indicating that application of these chemicals may be imparting stress to the plant, however by flowering time in most of the treatments there was recovery.
The physiological parameters such as chlorophyll content, and IAA content showed decline but there was no significant variation in photosynthetic rate and stomatal conductance between treatments when estimated one week after herbicide application. In the case of chlorophyll content the recovery of the plant was comparatively less as compared to all other chemical constituents. Treatments in azimsufuron applied plots showed maximum reduction in these constituents.
In the present study, among the ALS inhibiting herbicides azimsulfuron contributed to higher inhibition in growth and yield of rice when compared with bispyribac sodium. Mitigating treatments contributed to 20 to 24 % increase in grain yield and 20 to 27 % increase in straw yield of rice. Tank mix applied plots recorded highest grain yield and urea applied plots recorded highest straw yield.