– Mark Loux, OSU Extension Weed Specialist
Some hay producers have been unpleasantly surprised in the past when cressleaf groundsel infestations became evident in their hay fields in May prior to first cutting. Cressleaf groundsel in hay or silage is toxic to animals, and infested areas of the field should not be harvested and fed. Groundsel is a winter annual, emerging in late summer into fall, when it develops into a rosette that overwinters. Growth restarts in spring, with stem elongation and an eventual height of up to several feet tall. The weed becomes evident in hay fields when in becomes taller than the alfalfa/grass and develops bright yellow flowers in May. The problem with passively waiting until this point to discover that the hay is infested with groundsel is that: 1) it’s too late to control it with herbicides; and 2) hay from infested areas has to be discarded instead of sold or fed, and large plant skeletons are still toxic even if herbicides were effective on them. Groundsel plants finish their life cycle in late spring, once they flower and go to seed, so it should not be problem in subsequent cuttings.
The solution to this is scouting of hay fields in fall and early spring to determine the presence of cressleaf groundsel, when it is small and still susceptible to the few herbicides that can be used. We expect groundsel to be more of a problem in new August seedings, since it would be emerging with the new stand of alfalfa/grass. A well-managed established and . . .