Evaluation of Herbicidal properties of Horticultural crop products and by-products in Organic Farming of Okra [Abelmoschus esculentus (L..) Moench]

Abstract

The study entitled “Evaluation of herbicidal properties of horticultural crop products and by-products in organic farming of okra [Abelmoschus esculentus (L.) Moench]” was conducted in the Department of Vegetable Science, College of Agriculture, Vellayani during 2018-19. The study aims to evaluate the herbicidal properties of different horticultural crop products and by-products such as coconut vinegar, cashew nut shell liquid, lemon extract, clove leaf oil and eucalyptus oil and to study their herbicidal efficacy in organic farming of okra. The study was conducted in two parts: 1) Preliminary evaluation of horticultural crop products and by-products as herbicides and 2) Evaluation of herbicides in organic farming of okra. For preliminary evaluation of herbicides, seed beds were prepared by tilling with rotavator and weeds were allowed to grow for 45 days. The emerged weeds were smothered by herbicide preparations in randomly selected mini plots in separate experiments for each horticultural product and by product in Completely Randomised Design replicated five times. For preliminary evaluation as herbicides, acetic acid content of coconut vinegar was enhanced from 4 to 5, 7.5,10 and 12.5 percent by freeze distillation (CVH), cashew nut shell liquid was emulsified to 5, 10, 15 and 20 percent (CNSLH), citric acid in lemon extract was enhanced to 2.5, 5, 7.5 and 10 percent by evaporation (LEH) and sprayed on weeds @ 50mlm-2. CVH at 12.5 percent consistently reduced absolute density of grasses, sedges and broad leaved weeds at 15 and 45 days after spraying as well as lower root biomass, shoot biomass and higher weed control efficiency (70.37 and 56.3% at 15 and 45 DAS). Among CNSL emulsions 20 percent CNSLH consistently reduced absolute density of grasses, sedges and broad leaved weeds as well as recorded lower root biomass, shoot biomass and higher weed control efficiency. Among LEH though, absolute density of grasses and sedges were not significantly reduced by any of the concentrations. 10 percent lemon extract significantly reduced absolute density of broad leaved weeds at 15 DAS (32.97) at 15 and 45 DAS as well as recorded lower root biomass and shoot biomass and weed control efficiency. Enhanced weed growth at 45 days compared to 15 days after spraying warrant repeated application of herbicides for adequate control. CVH with 12.5percent acetic acid along with 1, 2, 3 and 4 percent clove leaf oil (CLOH) was sprayed on weeds @ 50mlm-2. CLOH consisting 4 percent clove leaf oil consistently reduced absolute density of grasses, sedges and broad leaved weeds at 15 and 45 DAS as well as recorded lower root biomass, shoot biomass and weed control efficiency. CVH with 12.5 percent acetic acid along with 1, 2, 3, 4 percent eucalyptus oil (EOH) was sprayed on weeds @ 50mlm-2. EOH consisting 4 percent eucalyptus oil consistently reduced absolute density of grasses, sedges and broad leaved weeds at 15 and 45 DAS as well as recorded lower root biomass, shoot biomass and weed control efficiency (96.96 and 67.46% at 15 and 45 DAS). In part II of the study 12.5 percent CVH, 20 percent CNSLH, 10 percent LEH, 4 percent CLOH and 4 percent EOH were sprayed on the 45 day old weeds on stale seed bed, repeated application thirty days after sowing of okra variety Anjitha seeds in comparison to organic mulching with mango leaves, hand weeding till 7th week and weedy check. All treatments controlled weeds compared to weedy check with regard to growth parameters and CLOH spray at 15 days before and 30 days after sowing, performed on par with hand weeded plot for higher germination of okra (90.97%), plant height (114.20cm), branches (2.87), number of leaves (20) and lower duration for 50 percent flowering (49.20 days). All treatments improved yield parameters compared to weedy check except number of flowers per plant wherein lemon extract did not differ. CLOH performed on par to hand weeding for more harvests (17), flowers per plant (10.18), fruit set (87.42%), number of fruits per plant (8.90) yield (9.89tha-1) and extended crop duration (105 days). All treatments reduced absolute density of grasses, sedges and broad leaved weeds except LEH on entire crop duration. Hand weeding reduced absolute density of grasses and sedges up to 30 days after sowing but CLOH and EOH were on par for control of broad leaved weeds only. After the second spraying at 30 days after sowing, CLOH and EOH performed on par with hand weeding for controlling grasses, sedges and broad leaved weeds. Hand weeding reduced root and shoot biomass up to 60 days after sowing but CLOH performed on par after second spray at 30 days after sowing. Hand weeding and CLOH were on par for weed control efficiency, weed index, lower nutrient uptake by weeds and higher nutrient uptake by okra. CLOH reduced pH, but on par for organic carbon content and EC of soil compared to hand weeding. CVH improved microbial population of soil, but on par with CLOH for fungi. Herbicide application did not change population of earthworms but improved dehydrogenase activity over weedy check. Single spray of CLOH 15 days before sowing recorded highest B:C ratio (1.54) In conclusion, Clove Leaf Oil Herbicide (mixture of coconut vinegar with 12.5% acetic acid and 4% clove leaf oil) performed on par with hand weeding for improving major growth and yield parameters, control of grasses, sedges and broad leaved weeds with similar weed control efficiency, weed index without adversely affecting the organic carbon content, EC, nutrient and microbial composition of soil when sprayed on stale seed bed 15 days before and 30 days after sowing but highest B:C ratio was obtained for single spray at 15 days before sowing in organic okra. Hence, strategies to flush out maximum weeds out of weed seed bank for smothering in the stale seed bed itself and technologies for reducing cost of herbicidal components are essential. Moreover, long term impact on ecosystem need to be assessed.