Ph.D

The study entitled ‘Integrated management of purple nutsedge (Cyperus rotundus L.) in grain legumes’ was conducted at the College of Agriculture, Vellayani, Thiruvananthapuram, Kerala, during 2020-2025. The objectives of the study were to standardize land preparation methods to deplete the tuber reserves of nutsedge, formulate an integrated management strategy for Cyperus rotundus in grain cowpea, assess the residual effect of the herbicides on successive crop, and evaluate the in vitro sensitivity of beneficial organisms to these herbicides. The investigation comprised of five experiments. The first experiment was conducted was conducted at Instructional Farm, College of Agriculture, Vellayani to evaluate the efficacy of land preparation methods to exhaust tuber reserve and nutsedge regeneration. The experiment was laid out in randomized complete block design (RCBD) with eight treatments replicated thrice. The treatments were: T1 [stale seed bed method (SSB) with halosulfuron methyl at 60 g ha-1], T2 [SSB with halosulfuron methyl at 67.5 g ha-1], T3 [SSB with halosulfuron methyl at 75 g ha-1], T4 [SSB with chlorimuron ethyl at 9 g ha-1], T5 [SSB with chlorimuron ethyl at 12 g ha-1], T6 [SSB with glyphosate at 1.5 kg ha-1], T7 [SSB with mechanical destruction] and T8 [SSB alone]. The herbicides were applied when the nutsedge plants were at three to four leaf stage. Results revealed that T6 resulted in lower final population, shoot dry weight, tuber dry weight and tuber viability of nutsedge at 6 weeks after spraying of herbicide (WASP) and comparable with T3 and T2. The treatments, T6, T3 and T2 resulted in higher weed control efficiency (88.52, 82.28 and 82.27 %, respectively) and lower regeneration count at 6 WASP (11.11, 13.33 and 15.56 m-2). The study confirmed that halosulfuron methyl at 67.5 g ha-1 was equally effective as glyphosate at 1.5 kg ha-1 in depleting the tuber reserves and regeneration count of C. rotundus under SSB and hence, this treatment was selected as the most effective land preparation method for raising grain cowpea. The second experiment ‘Integrated management of purple nutsedge’ was conducted in the locations having severe nutsedge infestation at Instructional Farm, College of Agriculture, Vellayani during first (kharif) and second crop (rabi) seasons of 2022-23. The experiment was laid out in RCBD with nine treatments replicated thrice. The treatments comprised of T1 (pre-emergence diclosulam at 12.5g ha-1), T2 (post directed application of chlorimuron ethyl at 9 g ha-1 at 20 DAS), T3 (post emergence haloxyfop R methyl at 100 g ha-1 at 20 DAS), T4 (T1 followed by (fb) wheel hoe weeding (WH) at 25 DAS), T5 (T2 fb WH at 40 DAS), T6 (T3 fb WH at 40 DAS), T7 (pre-emergence pretilachlor at 0.75 kg ha-1), T8 (hand weeding twice at 20 and 40 DAS) and T9 (weedy check). The grain cowpea variety DC-15 was raised as per KAU POP recommendations. The growth parameters of grain cowpea were significantly influenced by the weed management practices. The treatment T4 resulted in taller plants, higher branches per plant, green leaves per plant, leaf area index and dry matter production per plant at harvest and was comparable with T8 and T1 during both the seasons. The yield attributes viz., number of pods per plant, pod weight per plant, seed yield and haulm yield per plant were found to be higher in T4 during both the seasons. Pooled analysis over both seasons revealed that the highest seed yield was recorded in T4 (1717 kg ha-1) while the lowest in T9 (871 kg ha-1). The yield reduction due to weeds in cowpea was estimated to be 46.66 per cent during kharif and 50.56 per cent during rabi. The treatment T4 resulted in lower total weed population and dry weight resulting in higher weed control efficiency at 15 and 30 DAS during both kharif (90.96 and 84.50 %, respectively) and rabi seasons (78.84 and 82.67 %, respectively). Lower regeneration counts of C. rotundus at 45 DAS was noted in T4 (13.33 and 11.10 m-2) during both seasons, respectively. The N, P and K removal by weeds was found to be lower at 15 and 30 DAS in T4 during both seasons. Further, at just before spraying, T6 showed higher microbial and enzyme activity, while T8 noted the highest microbial and enzyme activity at 15 and 30 days after spraying, across both the seasons. Pre emergence diclosulam (12.5 g ha-1) fb WH at 25 DAS turned out to be the most economic nutsedge management strategy in cowpea with higher net income (₹ 41,894 and ₹ 19,081 ha-1) and B: C ratio (1.69 and 1.32) during kharif and rabi seasons, respectively and was comparable with T1. The third experiment ‘Screening of indicator plants’ was conducted in a net house with two test crops (finger millet and cucumber) and three herbicides (diclosulam, halosulfuron methyl and haloxyfop R methyl) to identify the most sensitive indicator plant for each herbicide. The experiment was laid out in completely randomised design (CRD) with eight treatments replicated thrice. Treatments comprised of different concentrations of the test herbicides (ppm) viz., T1 (0.01), T2 (0.05), T3 (0.1), T4 (0.5), T5 (1.0), T6 (10), T7 (100) and T8 (control). Results revealed that all the three tested herbicides had a significant impact on the growth of both the crops tested. As herbicide concentration increased, there was a corresponding decline in shoot length, root length, shoot and root dry weights of both test crops. Finger millet exhibited greater sensitivity to diclosulam and halosulfuron methyl than cucumber, with the highest R² values recorded for all parameters using cubic polynomial regression equations and hence selected as the successive crop for assessing residual herbicide effects. The fourth experiment ‘Assessing the residual effect of herbicides on succeeding crop’ was carried out after the harvest of cowpea using the finger millet variety VR-847. Hundred per cent seedling emergence without significant grain yield reduction was observed indicating no residual impact of the herbicides on successive crop. The fifth experiment ‘in vitro sensitivity of beneficial organisms’ was conducted to assess in vitro sensitivity of Trichodermaasperellum and Rhizobium sp. (RH-15) to three herbicides (diclosulam, halosulfuron methyl and haloxyfop R methyl). The experiment was laid out in CRD with eight treatments replicated thrice. The treatments comprised of different concentrations (ppm) of diclosulam (T1-20, T2- 25, T3- 30, T4- 35, T5- 40, T6- 45, T7- 50 and T8-control); halosulfuron methyl (T1-100, T2 120, T3- 140, T4- 160, T5- 180, T6- 200, T7- 220 and T8-control) and haloxyfop R methyl (T1-180, T2-200, T3- 220, T4- 240, T5- 260, T6- 280, T7- 300 and T8-control). Results revealed that diclosulam and haloxyfop R methyl had no significant effect on the radial growth of Trichodermaasperellum, with all concentrations showing uniform colony diameter of 9 cm and zero inhibition. In contrast, halosulfuron methyl significantly inhibited T. asperellum growth, ranging from 38.55 to 76.67 per cent. Further, Rhizobium sp. showed no zone of inhibition for any of the three herbicides, indicating no adverse effect on its growth. The study identified stale seedbed with halosulfuron methyl (67.5 g ha-1) followed by pre-emergence diclosulam (12.5 g ha-1) along with wheel hoe weeding at 25 DAS as the most effective and economical integrated management strategy for purple nutsedge in grain cowpea. The tested herbicides (diclosulam, halosulfuron methyl, and haloxyfop R methyl) had no adverse effects on soil health, enzyme activity, or residual impact and were compatible with Rhizobium sp. However, Trichodermaasperellum showed sensitivity to halosulfuron methyl.





The study entitled ‘Integrated management of purple nutsedge (Cyperus rotundus L.) in grain legumes’ was conducted at the College of Agriculture, Vellayani, Thiruvananthapuram, Kerala, during 2020-2025. The objectives of the study were to standardize land preparation methods to deplete the tuber reserves of nutsedge, formulate an integrated management strategy for Cyperus rotundus in grain cowpea, assess the residual effect of the herbicides on successive crop, and evaluate the in vitro sensitivity of beneficial organisms to these herbicides. The investigation comprised of five experiments. The first experiment was conducted was conducted at Instructional Farm, College of Agriculture, Vellayani to evaluate the efficacy of land preparation methods to exhaust tuber reserve and nutsedge regeneration. The experiment was laid out in randomized complete block design (RCBD) with eight treatments replicated thrice. The treatments were: T1 [stale seed bed method (SSB) with halosulfuron methyl at 60 g ha-1], T2 [SSB with halosulfuron methyl at 67.5 g ha-1], T3 [SSB with halosulfuron methyl at 75 g ha-1], T4 [SSB with chlorimuron ethyl at 9 g ha-1], T5 [SSB with chlorimuron ethyl at 12 g ha-1], T6 [SSB with glyphosate at 1.5 kg ha-1], T7 [SSB with mechanical destruction] and T8 [SSB alone]. The herbicides were applied when the nutsedge plants were at three to four leaf stage. Results revealed that T6 resulted in lower final population, shoot dry weight, tuber dry weight and tuber viability of nutsedge at 6 weeks after spraying of herbicide (WASP) and comparable with T3 and T2. The treatments, T6, T3 and T2 resulted in higher weed control efficiency (88.52, 82.28 and 82.27 %, respectively) and lower regeneration count at 6 WASP (11.11, 13.33 and 15.56 m-2). The study confirmed that halosulfuron methyl at 67.5 g ha-1 was equally effective as glyphosate at 1.5 kg ha-1 in depleting the tuber reserves and regeneration count of C. rotundus under SSB and hence, this treatment was selected as the most effective land preparation method for raising grain cowpea. The second experiment ‘Integrated management of purple nutsedge’ was conducted in the locations having severe nutsedge infestation at Instructional Farm, College of Agriculture, Vellayani during first (kharif) and second crop (rabi) seasons of 2022-23. The experiment was laid out in RCBD with nine treatments replicated thrice. The treatments comprised of T1 (pre-emergence diclosulam at 12.5g ha-1), T2 (post directed application of chlorimuron ethyl at 9 g ha-1 at 20 DAS), T3 (post emergence haloxyfop R methyl at 100 g ha-1 at 20 DAS), T4 (T1 followed by (fb) wheel hoe weeding (WH) at 25 DAS), T5 (T2 fb WH at 40 DAS), T6 (T3 fb WH at 40 DAS), T7 (pre-emergence pretilachlor at 0.75 kg ha-1), T8 (hand weeding twice at 20 and 40 DAS) and T9 (weedy check). The grain cowpea variety DC-15 was raised as per KAU POP recommendations. The growth parameters of grain cowpea were significantly influenced by the weed management practices. The treatment T4 resulted in taller plants, higher branches per plant, green leaves per plant, leaf area index and dry matter production per plant at harvest and was comparable with T8 and T1 during both the seasons. The yield attributes viz., number of pods per plant, pod weight per plant, seed yield and haulm yield per plant were found to be higher in T4 during both the seasons. Pooled analysis over both seasons revealed that the highest seed yield was recorded in T4 (1717 kg ha-1) while the lowest in T9 (871 kg ha-1). The yield reduction due to weeds in cowpea was estimated to be 46.66 per cent during kharif and 50.56 per cent during rabi. The treatment T4 resulted in lower total weed population and dry weight resulting in higher weed control efficiency at 15 and 30 DAS during both kharif (90.96 and 84.50 %, respectively) and rabi seasons (78.84 and 82.67 %, respectively). Lower regeneration counts of C. rotundus at 45 DAS was noted in T4 (13.33 and 11.10 m-2) during both seasons, respectively. The N, P and K removal by weeds was found to be lower at 15 and 30 DAS in T4 during both seasons. Further, at just before spraying, T6 showed higher microbial and enzyme activity, while T8 noted the highest microbial and enzyme activity at 15 and 30 days after spraying, across both the seasons. Pre emergence diclosulam (12.5 g ha-1) fb WH at 25 DAS turned out to be the most economic nutsedge management strategy in cowpea with higher net income (₹ 41,894 and ₹ 19,081 ha-1) and B: C ratio (1.69 and 1.32) during kharif and rabi seasons, respectively and was comparable with T1. The third experiment ‘Screening of indicator plants’ was conducted in a net house with two test crops (finger millet and cucumber) and three herbicides (diclosulam, halosulfuron methyl and haloxyfop R methyl) to identify the most sensitive indicator plant for each herbicide. The experiment was laid out in completely randomised design (CRD) with eight treatments replicated thrice. Treatments comprised of different concentrations of the test herbicides (ppm) viz., T1 (0.01), T2 (0.05), T3 (0.1), T4 (0.5), T5 (1.0), T6 (10), T7 (100) and T8 (control). Results revealed that all the three tested herbicides had a significant impact on the growth of both the crops tested. As herbicide concentration increased, there was a corresponding decline in shoot length, root length, shoot and root dry weights of both test crops. Finger millet exhibited greater sensitivity to diclosulam and halosulfuron methyl than cucumber, with the highest R² values recorded for all parameters using cubic polynomial regression equations and hence selected as the successive crop for assessing residual herbicide effects. The fourth experiment ‘Assessing the residual effect of herbicides on succeeding crop’ was carried out after the harvest of cowpea using the finger millet variety VR-847. Hundred per cent seedling emergence without significant grain yield reduction was observed indicating no residual impact of the herbicides on successive crop. The fifth experiment ‘in vitro sensitivity of beneficial organisms’ was conducted to assess in vitro sensitivity of Trichodermaasperellum and Rhizobium sp. (RH-15) to three herbicides (diclosulam, halosulfuron methyl and haloxyfop R methyl). The experiment was laid out in CRD with eight treatments replicated thrice. The treatments comprised of different concentrations (ppm) of diclosulam (T1-20, T2- 25, T3- 30, T4- 35, T5- 40, T6- 45, T7- 50 and T8-control); halosulfuron methyl (T1-100, T2 120, T3- 140, T4- 160, T5- 180, T6- 200, T7- 220 and T8-control) and haloxyfop R methyl (T1-180, T2-200, T3- 220, T4- 240, T5- 260, T6- 280, T7- 300 and T8-control). Results revealed that diclosulam and haloxyfop R methyl had no significant effect on the radial growth of Trichodermaasperellum, with all concentrations showing uniform colony diameter of 9 cm and zero inhibition. In contrast, halosulfuron methyl significantly inhibited T. asperellum growth, ranging from 38.55 to 76.67 per cent. Further, Rhizobium sp. showed no zone of inhibition for any of the three herbicides, indicating no adverse effect on its growth. The study identified stale seedbed with halosulfuron methyl (67.5 g ha-1) followed by pre-emergence diclosulam (12.5 g ha-1) along with wheel hoe weeding at 25 DAS as the most effective and economical integrated management strategy for purple nutsedge in grain cowpea. The tested herbicides (diclosulam, halosulfuron methyl, and haloxyfop R methyl) had no adverse effects on soil health, enzyme activity, or residual impact and were compatible with Rhizobium sp. However, Trichodermaasperellum showed sensitivity to halosulfuron methyl.