Ecological Effects Of Eclipta Prostrata L. And Abutilon Theophrasti Medic. In Cotton Field And Their Chemical Control

Eclipta prostrata L. and Abutilon theophrasti Medic. are two troublesome weeds in cotton field, this study is focused on the competition, allelopathy, biology and chemical control of E. prostrate and velvetleaf. The objective of this study is to make clear the biological characteristics, damage characteristics and the harm for cotton of the two broadleaf weeds. Field experiments of density gradient were conducted during 2013-2014 to study the competitive effects of E. prostrate and velvetleaf with cotton. The allelopathic effect of aqueous extracts of E. prostrate on seed germination and seedling growth of cotton and six weed species in cotton field was investigated by using Petri dishes. The effect of different sowing date on vegetative growth and reproductive growth of velvetleaf was discussed in pot experiment. The effects of five common soil-applied herbicides and four foliar-applied herbicides in cotton field on control of velvetleaf were investigated by using petri dishes bioassay, greenhouse experiment and field plot experiment. The main results were as follows:1. Cotton height and stem diameter reduced with increasing velvetleaf density. The interference of velvetleaf resulted in a delay in cotton maturity especially at the densities of 1-8 velvetleaf plants m-1 of row. Cotton boll weight, seed numbers per boll, and lint percentage were reduced by velvetleaf interference。However Cotton height, stem diameter and boll weight et. al. were almost not affected by E. prostrate competition in this experiments. Fiber quality were not significantly influenced by both E. prostrate and velvetleaf density. The relationship between weeds density and seed cotton yield was described by the hyperbolic decay regression model, which estimated that a density of 2.6-7.9 E. prostrate and 0.44-0.48 velvetleaf m-1 of row would result in a 50% seed cotton yield loss from the maximum yield. Meanwhile, E. prostrate and velvetleaf yield per hectare tended to increase with increasing weed density, and each additional weed plant m-1 of row represented an increase in dry weed biomass of 721 kg·hm-2 and 1996-2269 kg·hm-2, respectively. Weeds seed production was indicated by logarithmic response. At a density of 1 plant m-1 of cotton row, E. prostrate and velvetleaf produced about 160000 and 20000 seeds m-2, respectively. Cotton production was reduced significantly by the critical density of 0.5-1 E. prostrate and 0.25-0.5 velvetleaf m-1 of row, they had to be controlled before they reached the critical density.2. The aqueous extracts of E. prostrate strongly inhibited the germination of weed species, but only slightly inhibited those of CRRI 49 and CRRI 79. For different grass weeds, its inhibition effects to seed germination represented as Eleusine indica(L.) Gaertn. > Digitaria sanguinalis(L.) Scop. > Echinochloa crusgalli(L.) Beauv. For different broadleaf weeds, its inhibition effects to seed germination represented as Amaranthus retroflexus L. > Portulaca oleracea L. > Abutilon theophrasti Medic. The extracts stimulated growth of cotton and weed seedlings at lower concentrations, while inhibited their growth at higher concentrations, and inhibitory effects increased with the increasing concentration of the aqueous extract, with concentrations of 0.04-0.08 g·m L-1 inhibiting radicle length and plumule length of A. retroflexus by 100%. Therefore, E. prostrate with allelopathic properties of weed control has broad application prospects in sustainable eco-agricultural development in the future.3. Different sowing date of velvetleaf showed significant difference on the growth and reproduction of velvetleaf. As the delay of sowing date, plant height, stem diameter, stem dry biomass and root dry biomass reduced, the number of days to the first flower is less, the number of fruit per plant, total seed production and thousand-seed weight reduced, the average fruit diameter and average seeds per fruit also reduced. Therefore, in order to avoid increasing seeds of the soil seed bank, velvetleaf should be controlled before flowering in July.4. Pendimethalin 33% EC(375-1500 g·hm-2), oxyfluorfen 23.5% EC(141-282 g·hm-2), oxadiazon 12% EC(360-720 g·hm-2) had the best inhibition ratios of radicle length and the best control effect on velvetleaf. The results of foliar-applied herbicides showed that excellent weed control effect could be obtained with the four herbicides in accordance with the recommended dose on velvetleaf at 1-2 leaf stage and 3-4 leaves stage. As for velvetleaf at 5-6 leaf stage, paraquat 20% AS and glufosinate-ammonium 20% AS provided good control efficacy, while fomesafen 25% AS and glyphosate 41% AS provided relatively poor control efficacy.