Integrated weed management in cowpea (Vigna unguiculata L.)

Abstract

An experiment entitled ‘Integrated weed management in cowpea (Vigna unguiculata L.) was conducted at Instructional farm II of College of Agriculture, Padannakkad located at Karuvacheri, from December 2020 to March 2021 with the objectives of evaluating the efficacy of different weed management practices and to find out the economics of weed management in cowpea. The experimental design was Randomized Block Design (RBD) with 11 treatments replicated thrice. The short duration cowpea variety namely PGCP 6 was used for the study. The treatments consisted of T1 (pre-emergence application of pendimethalin @ 0.75 kg ha-1 at 0-3 DAS), T2 (T1 + hand weeding at 20-25 DAS), T3 (T1 + mulching @ 7 t ha-1 ), T4 (postemergence application of imazethapyr @ 75 g ha-1 at 20 DAS), T5 (T5 + hand weeding at 35 DAS), T6 (mulching @ 7 t ha-1 + T5), T7 (mulching @ 7t ha-1 + hand weeding at 20 DAS), T8 (hand weeding alone at 15 and 30 DAS), T9 (mulching alone @ 7 t ha-1 ), T10 (weedy check/control) and T11 (weed free). Weed density, dry matter and weed control efficiency (WCE) was lowest in weed free plots throughout the observation period and weedy check (control) recorded highest density dry matter and WCE among all other treatments. At 15 DAS, pre-emergent herbicide treated plots recorded lowest density of weeds in the order T3 >T1 >T2. At 30 DAS, T2 and T7 recorded lowest density of weeds. At 45 DAS, T5, T3, T8 and T7 were recorded with lowest density of weeds and which were on par to each other. At 60 DAS, T8, T3, T7 and T6 were recorded lowest density of weeds and which were on par to each other. In the case of weed dry weight at 15 DAS, T3 recorded the lowest value for dry weight compared to all other treatments except for T11. At 30 DAS, significantly lower value for dry weight was recorded in T2, which was on par with T7 and T3. At 45 DAS, significantly lower value for weed dry weight was recorded in T8 among all the treatments which were on par with T5 and T7. At 60 DAS, dry weight recorded by the treatment T2 was significantly lower among all the weed control treatments except for T3, T5, T7 and T8 which were on par to each other. Lowest WCE was observed in control plot or weedy check (T10). At 15 DAS, the treatments T3, T2 and T1 recorded the highest WCE. At 30 DAS, T2 was recorded with significantly higher WCE. At 45 DAS, WCE was significantly higher in T8 and was on par to T5, T7 T2 and T3. At harvesting stage (60 DAS), the treatment T2 recorded significantly higher value for WCE which was on par to T3. Significantly lower value for weed index (WI) was recorded in weed free plots and T7. Plant height, number of branches per plant (harvesting stage) and leaf area index was highest in weed free plot compared to that of all other treatments. Number of nodules per plant was recorded significantly superior in T7 at flowering stage and T2 at harvesting stage. Total dry matter production was highest in T7 which was on par with T3 at flowering and harvesting stages. Number of pods per plant, pod yield and seed yield were highest in weed free plots compare to that of all other treatments. Treatment T7 recorded significantly superior results in the case of number of seeds per pod, pod weight per plant and test weight and which was on par with that of pre-emergent application of T3 and T11. Among the available soil nutrients, depletion of available N was highest in T10 and treatment T8 recorded highest soil N content. Gross returns and net returns were highest in weed free plots compare to all other treatments which was followed by T3. Similar trend was shown in the case of net return also. The highest B:C ratio of 2.45 was obtained for T7 and T3 which were on par with T11 (2.42). The overall results indicated that weed infestation significantly affected yield in cowpea and integrated weed management (IWM) especially during the critical period of crop weed competition in cowpea is inevitable for getting an economic yield and could reduce yield loss even upto 67 per cent. Even though the cost of cultivation was highest in the weed free plots, the B:C was on par with that of the best IWM practices owing to the superior yield in these plots. Pre-emergence application of pendimethalin along with mulching; and mulching along with hand weeding could effectively keep the field weed free for the critical period of crop weed competition and this treatment resulted in highest B:C ratio and highest on par yields.