Smith-Lever (3b&c) Funding | Agricultural Systems
New York | Cornell Cooperative Extension | Northeast Region
On-farm research and practice demonstrate cost-saving alternative to hand weeding perennial sow thistle in onions grown in muck.
Perennial sow thistle has emerged as a devastating weed problem in certain muck land areas where onions are grown in New York, especially in the Elba area of Western NY where 500 acres are already severely infested. Perennial sow thistle aggressively competes with the onion crop and when not controlled, losses to yield and bulb size can be severe, to the extent that the crop is not worth harvesting. There are already reports of perennial sow thistle infestations in muck pockets in Oswego and Linwood; approximately 10,500 acres of onion-growing muck land is at risk for perennial sow thistle in New York alone. Onions are the third most important vegetable crop grown in New York with an average value of $55 million. A management strategy to effectively control perennial sow thistle during the growing season within an onion crop was urgently needed.
The Cornell Cooperative Extension Vegetable Program's Onion Specialist, Christy Hoepting and Program Aid, Elizabeth Buck focused their efforts on the herbicide Stinger, because of its known activity against this weed. The active ingredient in Stinger is a systemic growth regulator type of herbicide that has the ability to move downward into the perennial sow thistle plant and kill its rhizomes, destroying its abilities to regenerate and persist over winter. In 2013 and 2014, the Vegetable Program conducted four extensive on-farm field studies that determined the optimal use of Stinger in order to achieve the highest weed control while providing the lowest risk of injury to the onion crop. To ensure Stinger could be labeled on onions, they worked closely with the privately owned company that manufactures and sells Stinger, and with IR-4, which is a federally funded program that provides pest management tools to specialty crop growers by developing research data to support new product uses.
This research identified the stage of perennial sow thistle that is the most susceptible to the herbicide Stinger and the stages when Stinger is not a productive treatment option. Research results identified the mid- to late-rosette stage of perennial sow thistle to be the most susceptible stage, with earlier and older stages more challenging to control with Stinger. Determining whether the necessary rate of Stinger for controlling perennial sow thistle was safe on onions was critical to ensure its feasibility. The best time to apply Stinger was when the onions had between four and six leaves, which resulted in more than 95% marketable bulbs. The team requested that Stinger be labeled on onions in the way that it proved most effective and safe in their research studies. With the support of the manufacturer, the request was accepted. As a result of this on farm study, New York onion growers who face severe infestation with perennial Sow thistle will have options other than costly hand weeding or having to divert valuable muck land out of onion production. There is an estimated $110,000 in savings in hand weeding expenses per year for every 500 acres of severely infested muck land.