Screening of post-emergence herbicides to control weeds in Vicia villosa fields in orchards

Abstract: 【Objective】Vicia villosa, an annual leguminous plant, is usually used as high-quality forage,green fertilizer or cover crop, and widely distributed in Europe, Central Asia, Iran and the eastern Unit-ed States. In China, V. villosa is being widely grown as cover or companion crop in orchards, which can greatly improve pollination rate by attracting insects. At the same time, it can reduce soil water evapora-tion, increase soil organic matter content and porosity, and improve pH value in soil surface and micro-bial activity in soil. In addition, compared with weeds, V. villosa has stronger competitiveness to living factors such as light, living space, water and nutrients, which can effectively inhibit the germination,emergence and growth of other harmful weeds. However, it was found that V. villosa is not easy to estab-lish population due to the competition of other harmful weeds in the early stage of cover crop growing,and the weed chemical control in the early stage of cover crop growing is particularly important. Thus,this study aimed to finding out appropriate post-emergence (POST) herbicides against harmful weeds in V. villosa fields in orchads.【Methods】Whole-plant dose response experiments were conducted in green-house to evaluate the safty to V. Villosa and efficacy against weeds of eight POST herbicides that are safe for legumes and screen out herbicides for mixing. The joint effect type, the safety to V. Villosa and the selectivity indexs (SIs) of the mixtures were futher evaluated in greenhouse. Weed control efficacy and response of V. Villosa to the mixtures were also investigated in field experiments.【Results】The re-sults of greenhouse study showed that flumetsulam, fluoroglycofen- ethyl, fomesafen and clopyralid caused serious damage to V. Villosa, with fresh weight inhibition higher than 90% at 1×filed recommended rates, while bentazone, imazethapyr and quizalofop-P-ethyl were safe to V. villosa, with fresh weight inhibiton lower than 30% at 2×filed recommended rates. In weed control spectrum tests, ima-zethapyr POST application at 75 g active ingredient (a.i.) per hm ² caused more than 80% of fresh weight reduction against eight weed species including Amaranthus retroflexus, Cyperus iria, Digitaria sanguinalis, Eleusine indica, Setaria viridis, Portulaca oleracea, Capsella bursa-pastoris, Descurainia sophia and Myosoton aquaticum; bentazone POST application at 576 g a.i. per hm² caused more than 70% of fresh weight reduction against Abutilon theophrasti, C. iria, E. indica, Calystegia hederacea, C. bursa-pastoris and D. sophia; quizalofop-P-ethyl POST application at 37.5 g a.i. per hm ² caused more than 70% of fresh weight reduction against D. sanguinalis, E. indica and S. viridis. The SIs of imazetha-pyr between V. villosa and C. iria, D. sanguinalis, E. indica, S. viridis, D. sophia as well as M. aquati-cum were all above 2.0; the SIs of bentazone between V. villosa and C. bursa-pastoris, D. sophia as well as M. aquaticum were below 0.7, with poor safety; the SIs of quizalofop-P-ethyl between V. villosa and D. sanguinalis, E. indica, S. viridis were above 8.8. Imazethapyr showed high selectivity between V. villosa and broad-leaved weed (D sophia and M. aquaticum), but its selectivity between V. villosa and gramineous weeds is lower than that of quizalofop-p-ethyl. Therefore, the combination of imazethapyr and quizalofop-P-ethyl was conducted to complement the their weed control spectrums.The joint effect type was additive when imazethapyr was mixed with quizalofop-P-ethyl for the control of D. sanguina- lis, E. indica, Alopecurus aequalis, M. aquaticum, D. sophia, C. bursa-pastoris, with fresh weight inhi-bition higher than 80%, and when the mass ratio was 2 : 1 (imazethapyr : quizalofop-P-ethyl), the SIs of mixtures between V. villosa and the six weeds above ranged from 2.4-8.9. The results of the field experi- ments showed that the POST application of the mixtures of imazethapyr and quizalofop-P-ethyl at 125-150 g a.i. per hm² showed at least 86% of reduction in total fresh weight, against C. bursa-pastoris, D.sophia and A. aequalis, and high safety to V. Villosa, while imazethapyr at 90g·hm^-2 and quizalofop-P-ethyl at 60 g a.i. per hm² possessed poor control efficacy to A. aequalis and broadleaf weeds, respective-ly.【Conclusion】The POST application of imazethapyr and quizalofop-P-ethyl can effectively control the main weeds in orchards and their weed control spectrums were complementary, and was safe for V. villosa. When the mass ratio was (1-4)∶1(imazethapyr∶quizalofop-P-ethyl), it improved weed control efficacy and the safety to V. villosa of imazethapyr when controlling gramineous weeds. When the mass ratio was (1-4)∶1 (imazethapyr∶quizalofop-P-ethyl) and the application rates were 125-150 g a.i. per hm²,the mixtures possessed high control efficacy against on D. sophia, C. bursa-pastoris and A. aequalis in V. villosa fields in peach orchards. At the same time, it was safe for V. villosa and had the potential to be applied for weed control V. villosa cover crop field in orchards. This study provides a theoretical ba-sis for the chemical control of weeds in the early stage of V. villosa fields in orchards and has important practical value for the rapid establishment of stable community of V. villosa in orchards.