Herbicide Resistant Horseweed in New York and Possible Implications
Mike Basedow, Tree Fruit Specialist
Eastern New York Commercial Horticulture
Horseweed (also called marestail) is a frequently occurring species in New York. It can be found growing in a variety of habitats, including along roadsides, in field crop and vegetable operations, and in berries, grapes, and tree fruit. Often considered a winter annual, horseweed has a wide germination window and seedlings can emerge in the spring, summer, and fall. Herbicide resistance, particularly to glyphosate, is widespread in the US and has recently been identified in New York (see the 2022 summer issue of Fruit Quarterly https://nyshs.org/fruit-quarterly/). Many of these populations were collected from soybean systems where glyphosate is frequently used for managing unwanted vegetation. Two New York populations, collected from a vineyard and an apple orchard in the Finger Lakes Region, were found to be susceptible to glyphosate but resistant to labeled rates of paraquat. Paraquat resistance in horseweed has been formally confirmed previously in Belgium (nurseries), Canada (peaches), Japan (orchards, grapes, roadsides, railways), California (almonds), Delaware (soybeans) and Mississippi (soybeans) (https://weedscience.org/Home.a... ).
Herbicide Resistant Horseweed in New York and Possible Implications (pdf; 1849KB)

Upcoming Events
2026 Champlain Valley Summer Orchard Field Tour
July 15, 2026 : 2026 Champlain Valley Summer Orchard Field Tour
Keeseville, NY
Join the ENYCHP and Cornell scientists on July 15 for our annual Champlain Valley Summer Orchard Meeting! This year we will be meeting at Hart Apple Farm to learn about the varieties they are growing in one of their newer plantings, hear updates from faculty and extension agents on their current research projects, and view a few of Mike's local thinning projects firsthand.
DEC credits in categories 22, 1A, and 10 will be available. Refreshments will be provided.
Free to attend, however we do ask that you register ahead so we know how many people to expect. Rain date is July 16.
