Integrated weed management in blackgram [Vigna mungo (L.) Hepper] with pre-mix herbicides.

Abstract

An investigation entitled ‘Integrated weed management in blackgram [Vigna mungo (L.) Hepper] with pre-mix herbicides’ was conducted at College of Agriculture, Vellayani during 2022-2024. The major objective was to formulate an integrated weed management strategy using pre-mix herbicides for black gram intercropped in coconut garden. The field experiment was conducted at the Instructional Farm, Vellayani during the summer season from February to April 2024 in a coconut garden with palms above 40 years of age. The experiment was laid out in randomized block design with nine treatments replicated thrice. The weed management practices tested were: T1- pre emergence (PE) pendimethalin + imazethapyr (premix 1) 800 g ha-1; T2 - T1 followed by (fb) hand weeding (HW) at 30 days after sowing (DAS); T3- post emergence (PoE) propaquizafop + imazethapyr (premix 2) 125 g ha-1; T4- T3 fb HW at 40 DAS; T5- PE pendimethalin 1kg ha-1 fb HW at 30 DAS; T6- PE pendimethalin 1kg ha-1fb PoE imazethapyr 50g ha-1; T7- PE pendimethalin 1kg ha-1 fb PoE propaquizafop 100g ha- 1; T8- HW at 15 and 30 DAS; T9- weedy check. The blackgram variety DBGV-5 treated with Bradyrhizobium inoculant BMBS 47 was dibbled in the interspaces of coconut and managed as per the KAU Package of Practices. Pre emergence herbicide was applied on the next day of sowing and post emergence applied at 15 DAS. Symptoms of phytotoxicity were observed in crop as mild stunting in plots sprayed with premix combination, pendimethalin + imazethapyr which persisted upto 10 days after herbicide application. The results of the study revealed that weed management practices had no significant influence on the growth attributes of blackgram. However, the yield and yield attributes were significantly influenced by the weed management practices. Higher pods per plant was recorded in T4 (36.00) and was comparable with T7 (35.83) while weedy check recorded the lowest number of pods (14.24). Hundred seed weight was recorded higher in T2 (5.33 g) and was on par with T4 (5.17 g) and T1 (5.13 g). The highest seed yield per plant was recorded in T4 (9.60 g) followed by T7 (9.23g), T6 (8.3g) and T5 (8.23g). Post emergence application of premix 2 fb HW at 40 DAS resulted in higher seed yield per ha (1793 kg) and was comparable with T7 (1731 kg). Higher haulm yield per ha was recorded in T5 (3658 kg) and was comparable with T4 (3616 kg), T6 (3581 kg) and T7 (3485 kg). The study observed that absence of weeding led to the highest yield reduction in blackgram, with a weed index of 54.44 per cent while yield reduction was lower in T4 (2.45%) and on par with T7 (5.35%). The predominant weed flora in the experimental field was grasses. However, more diversity was observed in the flora of broad leaf weeds. Pre emergence application of premix 1 fb HW at 30 DAS resulted in significantly lower weed density and weed dry weight and higher weed control efficiency at all stages of observation and was comparable with T7, T4 and T6. At 30 and 45 DAS, T1, T2, T5, T6 and T7 resulted in lower relative biomass of grasses that was comparable with T4 and the highest relative biomass of grasses was recorded in weedy check (85.92 %). Treatments involving both pre- and post-emergence herbicide applications (T7 and T6) resulted in higher dehydrogenase enzyme activity at 30 DAS, while their combination with hand weeding (T4, T5) showed increased activity at 45 DAS. Weed management practices significantly influenced nutrient uptake, with T7 and T1 exhibiting higher N, P and K uptake. The integration of premix herbicides with hand weeding and use of pre and post-emergence herbicides, significantly reduced N, P, and K removal by weeds throughout the growth period. The BC ratio varied significantly among the weed management practices with the highest in T4 (1.95), followed by T7 (1.94), with the lowest ratios in hand weeding twice (1.05) and weedy check (0.82). Weed management practices significantly influenced the population of Bradyrhizobium, fungi and actinomycetes in rhizospheric soil at 30 DAS with T2 showing higher count and on par with T1. However, no significant differences were noted in the population of phosphorus solubilising bacteria across all time points. The in vitro sensitivity test of Bradyrhizobium to premix 1 and 2 at concentrations of 800 to 2000 ppm and 175 to 325 ppm respectively showed positive growth with no inhibition zones around the sterile disc containing herbicide mixture placed on a lawn of Bradyrhizobium in the medium. The study identified application of propaquizafop + imazethapyr 125 g ha-1 at 15 DAS fb HW at 40 DAS; and application of pendimethalin 1kg ha-1 on the next day of sowing fb propaquizafop 100g ha-1 at 15 DAS as the most effective weed management strategies in terms of yield, weed control efficiency and gross return in blackgram. Considering economics, application of propaquizafop + imazethapyr at 15 DAS fb HW at 40 DAS could be adjudged as the most effective integrated weed management strategy for achieving higher seed yield in blackgram intercropped in coconut garden.