Native Grass Establishment following Application of Pyridine Herbicides

Invasive species management is often more successful if desirable species are seeded after the target weed is controlled. However, control of invasive plants must be maintained following reseeding or the seeded species may fail to establish. A regional study conducted in Minnesota, North Dakota, and South Dakota evaluated the effect of aminopyralid, clopyralid, or picloram applied in the fall prior to fall-dormant seeding or seeding the following spring on cool- and warm-season native grass species establishment. Herbicides were applied at standard rates used to control invasive broadleaf weeds in the upper midwestern tallgrass prairie region of the United States. Cool-season species included Canada wildrye, green needlegrass, and intermediate wheatgrass. Warm-season species included big bluestem, little bluestem, sideoats grama, switchgrass, and Indiangrass. Aminopyralid did not reduce seedling establishment in either fall or spring seeding. Grasses generally were not affected by a pretreatment of the pyridine standards clopyralid or picloram either, with the exception of a slight reduction in fall-seeded establishment of intermediate wheatgrass. Picloram also slightly reduced fall-seeded establishment of Canada wildrye. Application of aminopyralid can safely be used to control susceptible invasive species preceding grass species establishment, with a safety margin similar to or slightly better than that with the pyridine standards clopyralid or picloram.