September Turf Tips - Homeowners

Jeffrey Derr and Adam Nichols

Turf Management for Homeowners

As our temperatures decrease as we move into fall, there are several items to consider for  lawn maintenance.  Winter weed control, fertilization, and overseeding are topics to consider this time of year.

Once temperatures cool in September, coupled with rainfall to trigger germination, winter annual weeds will start to emerge.  Most germination of winter annuals occurs in September to November. One weed of concern is annual bluegrass, often called poa due to its scientific name Poa annua.  Annual bluegrass will be most noticeable in spring when it produces whitish seedheads. For homeowners there is little available for selective control of emerged annual bluegrass.  One way to address control of annual bluegrass would be to apply a crabgrass preventer, such as prodiamine (Barricade, others), dithiopyr (Dimension, others) or pendimethalin (Scotts® Halts® Crabgrass & Grassy Weed Preventer, others), prior to annual bluegrass germination.  Ideally this should be done sometime between mid-August and early September. In most cases, though, one would not be able to overseed the lawn as the crabgrass preventers will also prevent successful germination of tall fescue and other turf species. 

So one needs to decide what is more important, overseeding or applying a preemergence to stop annual bluegrass germination.  If the turf is thin, it probably would be better to put the money towards purchasing and sowing turf seed.  In one study we conducted, the annual bluegrass population decreased as the overseeding rate increased due to crop competition.

Another advantage of applying a crabgrass preventer in late summer or early fall is that they will also control certain winter annual broadleaf weeds like common chickweed and henbit.  Although these broadleaf weeds can be controlled postemergence, one has to live with dead or dying broadleaf weeds as the product works.  A weed like henbit can take a while to die after a postemergence treatment, while with use of a preemergence product the weed never appears in the lawn. For broader spectrum preemergence broadleaf control, products such as Crew, a granular product that contains both isoxaben and dithiopyr, can be applied. 

 One winter annual broadleaf weed that has increased in the area is lawn burweed (Soliva sessilis).  We receive calls in spring about this weed as it forms sharp spines on the seed, which form in the center of the rosette.    The spines  prevent walking barefoot in the lawn.  Isoxaben will control this weed if applied before emergence. Emerged plants of lawn burweed  can be controlled with common three-way postemergence herbicides containing dicamba or triclopyr, but the weed ideally needs to be treated in fall or winter before it has produced spines.  Bermudagrass can be suppressed in tall fescue using products such as BioAdvanced Bermudagrass Control for Lawns but treatments need to be done before bermudagrass goes dormant.