Efficacy of New Brands of Clethodium in Control of Weeds of Onion (Allium cepa) in South Kerman

Introduction: Onion (Allium cepa L.) is a monocot and bulbous perennial plant belongs to the Amaryllidaceae family. It is one of the most important crops in Iran and Southern Kerman. The total area cultivation of this crop is about 63 thousand hectares in Iran and 7.5 thousand hectares in Southern Kerman. Weeds are one of the greatest limiting factors in crop production. Onion is more susceptibility to weed competition in compared to many crops due to its inherent characteristics such as slow germination, extremely slow growth in the early stage, non-branching habit, sparse foliage and shallow root system. Weed competition can reduce average onion yield by 46- 86% compared to weed-free control. The most important weeds of onion fields in Iran are Alopecurus spp, Avena fatua L., Bromus spp., Dactyloctenium aegypticum (L.) P.Beauv, Echinochloa colonum. (L.) Link, Cyperus esculentus L., Cynodon dactylon L. Pers., Hordeum spp., Lolium spp., Setaria viridis L. Application of herbicides is the most prevalent method of weed control in onion fields. Oxyfluorfen, oxadiazon, ioxynil, clethodium, haloxyfop-r-methyl ester, sethoxydim, and cycloxydim are the commonly used herbicides for weed control in onion fields in Iran.Materials and Methods: In order to study the efficacy of herbicides to control narrow leaf weeds of onion fields, an experiment was conducted at South Kerman Agricultural and Natural Resources Research and Education Center, Jiroft, during 2016- 2017 growing season. Plots were located on a sandy loam soil with pH 7.4. Experiment was carried out in randomized complete block design with 4 replications. Treatments included clethodium (Elective 24% EC) at 1.2 lit ha-1 equivalent 288 g a.i. ha-1, clethodium (Superpower 12% EC), at 1.2 lit ha-1 equivalent 144 g a.i. ha-1, clethodium (Select 24% EC), at 1.2 lit ha-1 equivalent 288 g a.i. ha-1, haloxyfop-r-methyl ester (Gallant-Super 10.8% EC) at 750 ml ha-1 equivalent 81 g a.i. ha-1, sethoxydim (Nabu-S 12.5% EC) at 2 lit ha-1 equivalent 375 g a.i. ha-1, cycloxydim (Focus 10% EC) at 2 lit ha-1 equivalent 200 g a.i. ha-1 ,and hand weeded as control treatment. Broadleaf weeds were hand removed during the season. The herbicides were applied 30 days after planting of onion transplants when onion plants were at the 3–4 leaf stage and weeds were at 5–10 cm in height. The herbicides were applied using a Matabi sprayer equipped with an 8002 flat fan nozzle tip delivering 350 L ha-1 at 2 bar spray pressure. Weed density and dry weight were determined in a 0.70-m2 quadrate per each plot randomly. Fresh weight of onion bulbs was recorded for a 2.5-m2 quadrate per each plot. Statistical analysis of data were done by SAS ver.9 and comparison of means were tested using the LSD test at 95% level of significant.Results and Discussion: Dominated narrow-leaf weeds were Polypogon monspeliensis L., B. tectorum L., Phalaris brachystachys L., L. perenne L., Lophochloa phleoides (Vill.) Reichb, E. colonum (L.) Link, H. murinum L., A. fatua L. Visual observation confirmed that the most of the weeds were effectively controlled by herbicide treatments. The statistical analysis of the data on the weed density and biomass indicated that herbicides in onion significantly decreased the weed density and biomass. Results also showed that application of Focus, Select and Gallant-super provided excellent control of the dominant weeds. These treatments reduced biomass of P. monspeliensis, B. tectorum, P. brachystachy, L. perenne and total weeds more than 94%. Application of Superpower and Elective reduced weed biomass in B. tectorum about 75% and 68%, respectively. The results also showed that the weed biomass of P. monspeliensis were decreased about 80% and 79% using Superpower and Elective, respectively. The decreasing effect for Superpower and Elective on weed biomass of L. perenne and P. brachystachy were about 79 and 75%, respectively. The effect of Superpower and Elective on total weed biomass were approximately 80 and 71%, respectively. Onion yield in the plots treated by Focus, Select and Gallant-super increased about 250%. Onion yield for Superpower and Elective treatments was 55 and 46 ton ha-1, respectively, that showed an increasing in yield approximately 201% and 162%, respectively.Conclusion: Results showed that the best herbicide treatments were Focus, Select and Gallant-super. These treatments decreased density and biomass of weeds and increased onion yield. In general, Superpower was superior to Elective in control of the dominant weeds and increased onion yield.