MSc

The study on “Physiological evaluation of herbicidal effects on rice, broadleaved weeds and sedges” was conducted during the period from July 2018 to November 2018 at Agricultural Research Station, Mannuthy, Thrissur. The objectives of the study were identification of broadleaved weeds and sedges that are selectively controlled by Almix®, penoxsulam and 2,4-D and also to evaluate the effect of these herbicides on the growth, physiology and yield of rice.

The experiment was laid out in RBD with three replications and six herbicidal treatments. The rice variety selected for the study was Jyothi. Treatments included normal and twice the normal doses of 2,4-D, Almix® and penoxsulam and two controls (hand weeded and unweeded). The herbicides were sprayed 20 DAS. Morphological parameters were observed at 20 days interval. Biochemical parameters were estimated before herbicidal application, one week after herbicidal application and at the time of flowering. Yield attributes and yield were recorded during the harvest of the crop.

Twice the normal doses of herbicides resulted in 10-12% reduction in plant height of rice while normal doses of herbicides resulted in 3-6% reduction in plant height at the time of harvest. Tiller number of rice crop was found to be affected by herbicide application.At the time of harvest, tiller number of 2,4-D (normal dose) applied plot was on par with hand weeded plot while in case of Almix® and penoxsulam the reduction was 4 and 5 % respectively. Twice the normal doses of herbicides adversely affected tiller number in all three herbicide treatments and it was significantly lower than unweeded control. Number of days taken for flowering was found to be affected by herbicide application compared to hand weeded control. Effect of herbicides on growth indices viz., crop growth rate (CGR) and net assimilation rate (NAR) indicated that only after critical period of growth, there was a significant variation among the treatments. In case of relative growth rate



(RGR) and leaf area index (LAI) there was a significant reduction in herbicide applied plots compared to hand weeded control throughout the growth stages. Twice the normal doses of herbicides showed greater reduction in the growth attributes.

Biochemical parameters such as soluble protein, total amino acid and nitrate reductase enzyme activity showed a decline in herbicide treatments compared to hand weeded control. Proline content and catalase enzyme activity showed an increase with herbicide application while physiological parameters such as IAA content, cholorophyll content, stomatal conductance and net photosynthesis showed a decline. Twice the normal doses of herbicides significantly affected these parameters compared to the recommended doses of these chemicals.

Weed count, dry weight, weed control efficiency and weed persistence index were taken one week after herbicide application and at 60 DAS. Lower weed count, dry weight, weed persistence index and higher weed control efficiency were recorded in twice the normal doses of herbicides as compared to the normal doses.

In the present study, grain yield was highest in handweeded plot which was on par with normal doses of 2,4-D and Almix®. Since disease infestation was higher in penoxsulam treatment the yield was also affected. Twice the normal doses of herbicides contributed to 22-33% reduction in grain and 19-23% reduction in straw yield respectively. Among the herbicides 2,4-D (synthetic auxin type) showed a better performance compared to Almix® and penoxsulam (ALS inhibiting type).

A net house experiment was conducted to understand the bioefficacy of the herbicides on broadleaved weeds and sedges, viz. Marsilea quadrifoliata, Ludwigia parviflora, Cyperus iria, Fimbristylis miliacea and Sphenoclea zeylanica. The study revealed that Marsilea quadrifoliata was not controlled by both the doses of 2,4-D and penoxsulam while both the doses of Almix®



could effectively control the weed. Ludwigia parviflora was controlled by both the doses of 2,4-D while only twice the normal dose of Almix® could control the weed. Penoxsulam did not have any effect on the weed. Fimbristylis miliacea was controlled by penoxsulam and 2,4-D but Almix® was not effective for this weed. Cyperus iria could be controlled only by 2,4-D while Sphenoclea zeylanica was effectively controlled by all the three herbicide formulations. The dosage of chemical influenced the time taken for complete drying of the plant. Though catalase and superoxide dismutase enzyme activity showed increase in the resistant weeds, further studies are required to elucidate the resistance mechanism.