Evaluation of Chemical Control of Purple Nutsedge (Cyperus rotundus L.) in Onion (Allium cepa L.) Fields in South Kerman

Onion (Allium cepa L.) is one of the most important vegetables (with 2.305 million tons production) in Iran. Onion cultivation area of southern Kerman is 5732 hectares and this region is ranked first for onion production (307 thousand tons of production) in Iran. Onion growth and yield are significantly reduced by weed competition. Among the dominant weeds in onion fields at southern Kerman, Cyperus rotundus is one of the most important and problematic weeds. The slow growth of onion in the early stage, causes a significant yield loss due to the competition. C. rotundus is a perennial weed of the Cyperaceae family spreading quickly throughout the extensive underground system and tuber, with high ability to compete. This weed can decrease the average onions yield by 23 – 84%. Application of herbicides is the most prevalent weed control method in onion fields. Oxyfluorfen, and haloxyfop-r-methyl ester, are the commonly used herbicides for C. rotundus control in onion fields at southern Kerman. Therefore, the objective of this study was to investigate the effects of different herbicides on this weed.

This experiment was conducted in Agricultural and Natural Resources research and Education Center, Jiroft, southern Kerman, during 2017-2018 and 2018-19. The experiment was carried out in randomized complete block design with three replications. The experiment treatments included: T1- Metribuzin (Sencor) 80% WP 500 gr.ha-1, T2- Oxyfluorfen(goal) EC24%, 2 lit.ha-1, T3- Oxadiazon (ronstar) EC 12% 3 lit.ha-1 + Oxyfluorfen(goal) EC24%, 2 lit.ha-1, T4- Pendimethalin (stomp) EC33% ,3 lit.ha-1, T5 Oxadiazon (ronstar) EC 12% 3 lit.ha-1, T6- Oxadiazon (ronstar) EC 12% 3 lit.ha-1 + Bentazon (bazageran) SL48% 3 lit.ha-1, T7- Oxyfluorfen(goal) EC24% at 1/5 lit.ha-1 two stages by 0.75 lit.ha-1, (one week after transplanting and three weeks afterwards), T8- Pendimethalin (prowl) CS 45.5% 3 lit.ha-1, T9- hand weeding and T10- control (no control). Other weeds except C. rotundus were hand-removed during the season. The herbicides were applied using a Matabi sprayer with delivering 354 L ha-1 at 2 bar spray pressure. C. rotundus shoot and underground organs dry weight, density, average of bulb weight and onion yield were measured. Statistical analysis was carried out using SAS ver.9.1 software and the comparison of means was undertaken based on the LSD test.

The combined analysis of variance showed that the effect of treatment was significant on shoot and underground organs dry weight and density of C. rotundus, mean onion weight of bulb and yield, and reduced dry weight and density of C. rotundus and increased the onion yield. Among the chemical treatments, the combined application of Oxadiazon (Ronstar) as pre emergence followed by application of Bentazon (Bazageran) as post emergence (Treatment 6), decreased the density, underground and shoot dry weight of C. rotundus by 96.89 and 93% relative to the control, respectively. The highest onion yield was obtained from the mentioned treatment and increased the onion yield by 87% with respect to the control.Indeed, the combined application of these two herbicides in different growth stages of weeds and onion, was able to resolve the limitations of separate application of these herbicides leading to the most effective control of C. rotundus.

The results of this experiment show that the combination of herbicides can be an effective strategy to increase their effectiveness. The combined application of Oxadiazon (Ronstar) EC 12% at 3 lit.ha-1 as pre emergence + Bentazon (Bazageran) SL48% at 3 lit.ha-1  as post emergence was the most effective treatment after hand-weeding on purple nutsedge management and increasing  the onion yield. Therefore, the mentioned treatment is recommended to control of C. rotundus in transplanting cultivation of onion in autumn farming in south of Kerman Provence.