Turf - Plan Now for Annual Bluegrass Control

By now, turf areas that had annual bluegrass will have died out. Note these areas and plan for late summer control measures.

Annual bluegrass, Poa annua var. annua can be a very difficult weed in turf and landscape beds. To make matters worse, a perennial form Poa annua var. reptans is also found, primarily on golf greens. Annual bluegrass tolerates low mowing and compaction. It is a prolific seeder and can quickly infest an area. Annual bluegrass starts to germinate in late summer as soil temperatures drop below 70°F and continues to germinate throughout the winter. Annual bluegrass is a problem in turf because it forms a weak sod, provides poor footing on athletic fields, produces unsightly seed heads, and dies out in late spring. In ornamental plantings it can compete with perennial landscape plants and groundcovers in the cool season.

Control starts with reducing spread by equipment. Maintain grass or groundcover vigor to shade it out, reduce compaction with aeration, increase mowing height, and avoid overwatering that encourages annual bluegrass growth. Withholding water can help to stress and kill out annual bluegrass in some cases. Preemergence herbicides such as dithiopyr, pendimethalin, or prodiamine can be used to limit seedling germination on established cool season turf. Make the application before seed germinates in late August when soil temperatures go below 70°F. Use benefin if fall seeding is planned (wait 6 weeks). Ethofumesate (Prograss) is the only selective herbicide for postemergence annual bluegrass control in cool-season turfgrass. Apply ethofumesate during the peak of annual bluegrass germination and again just before winter. Do not use on turf containing fine fescues (cannot be used on lawns with shade mixtures for example). In landscape beds, preemergence grass herbicides will give some control late August applied, non-selective herbicides can be used spot sprayed, and clethodim (Envoy plus) can be used as a selective post-emergence control. Mesotrione (Tenacity), a new herbicide registered for golf courses and sod farms, will good annual bluegrass control pre and post.

Gordon Johnson, Extension Horticulture Agent, UD, Kent County