Evaluating the efficacy of herbicide options in controlling purple nutsedge (Cyperus rotundus L.) in onion (Allium cepa L.) fields

Purple nutsedge (Cyperus rotundus L.) is a major weed problem worldwide, particularly in onion (Allium cepa L.) fields in Iran. No specific herbicide has been registered or reported for controlling purple nutsedge in onion fields in the country. To address this, two field experiments were conducted over two years (2021 and 2022) at the Jiroft Culture and Industry Company in Jiroft, Kerman, Iran, using a randomized complete block design (RCBD) with 13 treatments and three replications. The experiments aimed to evaluate the effectiveness of various chemical control methods on onion and purple nutsedge growth.The results indicated that all herbicides significantly reduced the stem number, tuber number, and both aboveground and belowground dry weight of purple nutsedge. The highest level of weed control (100%) was achieved with a combination of Florasulam + Fluazifop P butyl + Pretilachlor and Allyl isothiocyanate, with no phytotoxic effects on onions. The highest onion yields were observed in plots treated with Florasulam + Fluazifop P butyl + Pretilachlor (ranging from 75.047 to 71.856 t ha-1) and Allyl isothiocyanate (ranging from 73.618 to 71.323 t ha-1). Furthermore, purple nutsedge competition reduced onion yield by 88.97% and 90.80% compared to the weed-free control over the two years of the experiment.While Council and Krismat herbicides effectively suppressed purple nutsedge growth, they caused damage to the onion plants. Based on the results, the application of Florasulam + Fluazifop P butyl + Pretilachlor (800 g per hectare) and Allyl isothiocyanate (280 L per hectare) is recommended for controlling purple nutsedge in onion fields. Although Allyl isothiocyanate, as a bio-herbicide, showed promising results similar to the chemical herbicide, Florasulam + Fluazifop P butyl + Pretilachlor is more cost-effective, easier to apply, and safer for users.