Weed control through allelopathic crop water extracts and S-metolachlor in cotton

Weeds are one of the most important biological constraint to cotton production, and resulting in a yield losses of up to 90%. The evolution of hundreds of resistant weed species, the lack of new herbicide chemistries, and the increase in weed management costs are all making weed management more arduous for the growers. Hence, a field experiment was conducted to investigate the efficacy of allelopathic crop water extracts (ACWEs) alone and in combination with one third rate of S-metolachlor (717 g a.i. ha−1) for effective weed management in cotton. The treatments investigated were; weedy check, sorghum + brassica water extract (WE) at 1.5 L ha−1, sorghum + sunflower WE at 1.5 L ha−1, sorghum + brassica + sunflower WE at 1.5 L ha−1, sorghum + brassica WE at 1.5 L ha−1 + S-metolachlor at 717 g a.i.ha−1, sorghum + sunflower WE at 1.5 L ha−1 + S-metolachlor at 717 g a.i.ha−1, sorghum + brassica WE + sunflower WE at 1.5 L ha−1 + S-metolachlor at 717 g a.i.ha−1, and S-metolachlor at recommended rate of 2.15 kg a.i. ha−1. Results revealed that pre-emergent application of sorghum + brassica water extract (WE) at 1.5 L ha−1 was the best treatment in terms of effective dry biomass reduction (40%) of Trianthema portulacastrum and Cyperus rotundus, and increase in seed cotton yield (12%). The second best treatment was sorghum + sunflower WE at 1.5 L ha−1 + S-metolachlor at 717 g a.i. ha−1 with yield increase of 11% over the weedy control. In comparison, S-metolachlor at recommended rate 2.15 kg a.i. ha−1 recorded only 4% decrease in weeds dry biomass reduction and 8% increase in seed cotton yield. Hence, it can be predicted that binary combination of sorghum and brassica WE at 1.5 L ha−1 or binary combination of sorghum + sunflower WE at 1.5 L ha−1 with one third dose of S-metolachlor (717 g a.i. ha−1) can be used for effective weed management and increase in seed cotton yield. Furthermore, adoption of this technique will also reduce the herbicide application, which is not only beneficial for the ecosystem but, also minimize the evolution of herbicide-resistant weed species.