Spotted Knapweed, Ohio’s New Pasture Invader

Clif Little, Extension Educator, AgNR, OSU Extension, Guernsey & Noble Counties

Spotted knapweed, a noxious weed was first detected in our area two years ago. The weed seed was most likely purchased in a pasture seed mix. Since that time this noxious weed has expanded more rapidly than could be imagined. Heavy infestations of this weed can now be found concentrated in the Quaker City area. The plant seed is easily distributed with the movements of equipment and hay. Observations along the roadways confirm pockets of these weeds extending into Noble, Guernsey, Belmont and Monroe counties.

Spotted knapweed is the most aggressive perennial weed to impact hay and pasture fields in Ohio. This plant can produce as much as 1000 seeds per plant. The western United States has struggled with the weed for many years and it has only recently become a problem for us. The plant is attractive and resembles the bloom of red clover. Currently, the plant is 1-3 feet tall. The problem with this weed is that it can completely take over hay fields and pasture land as indicated by the picture (a hay field near Quaker City). Livestock avoid eating the plant while it crowds out desirable grasses and legumes.

Plant seeds are inadvertently spread through the actions of hay hauling and mowing. It is also likely vehicles venturing into infested areas have contributed to plant distribution. My recommendations are to control the plant as soon as you see it. In small areas around the house you can pull it up and burn it. It may also be spot sprayed utilizing a glyphosate product such as Roundup or one of the many other products containing this active ingredient. For pasture and grass hay fields there are several broadleaf herbicides options depending on knapweed state of maturity and use of the forage. At the current state of knapweed development and according to University studies Milestone at 5-7 oz/Acre or ForeFront at 2-2.6 pt/Acre can provide effective control. Refer to product labels for herbicide use restrictions regarding grazing, hay harvest and replanting. The application of broadleaf herbicides will injure legumes such as clover and alfalfa.


The best knapweed control program is early detection and eradication. Avoid spreading this weed seed on farm machinery. Don’t purchase hay containing knapweeds and utilize only certified seed when planting. Manage hayfields and pastures to promote dense grass growth and this will help to reduce knapweed invasion. For more information contact your local OSU Extension office.