Thirty populations of marestail (horseweed) were collected in the fall of 2020 and are being screened for resistance to commonly used herbicides. Of the 30 collected, 27 appear to be resistant to glyphosate (Roundup) and 28 populations appear to be resistant to cloransulam herbicide, an ALS-inhibitor. This indicates that we have multiple-resistance in NY. It is also suspected that 4 of these 30 samples may be resistant to paraquat (Gramoxone) herbicide. The screening efforts will continue to evaluate the effect of products like 2,4-D and dicamba, Liberty, and PPO-inhibiting herbicides like Reflex and Sharpen.