Maintaining turf throughout the winter can be expensive in terms of labor, water, fertility, the seed itself, and other costs. 

A number of sports field managers have moved away from the overseeding practice because of budgetary restraints. Some facilities utilized throughout winter, however, will still require overseeding, like those in areas where baseball starts early in the spring.

Overseeding fields for winter activity can also be beneficial because it can help reduce injury and improve playability. From a sports turf health perspective, seeding with cool season grasses also helps protect dormant bermudagrass from traffic damage. 

Controlling weeds through the winter can help reduce injury as well and enhance the turf canopy for the year to come. The downside is that watering and fertility practices for overseeded fields can greatly enhance weed growth. There are two reasons why weeds may appear:

• Late season traffic on both cool season and warm season fields creates wear. 
• Areas devoid of turf cover allows patches of weeds to freely invade. 

Research shows that areas of thin and worn turf can be a great environment for weeds, yielding exponentially more weedy plants per square yard. Below are tips for weed control as you make decisions about overseeding for your athletic fields this winter.

Weed Control on Non-overseeded Sports Turf

Those fields that are not overseeded with cool season grasses tend to be easier to manage from a weed perspective because there are many more options for pre- and post-emergent herbicides. Often pre-emergent herbicides are used to prevent winter annual weeds including Poa annua, henbit, and common chickweed, which are particularly problematic. 

There are many such products including prodiamine, pendimethalin, and dithiopyr. Materials including simazine and indaziflam can be applied later in the fall to combat early Poa while providing residual pre-emergent control. Oxadiazon is an excellent option for pre-emergent control of Poa where concern exists over herbicide resistance, as it is of a different mode of action than those mentioned above. 

Weed Control after Overseeding Sports Turf

Some sports turf managers will opt to avoid the use of pre-emergent herbicides due largely to the concern over spring recovery from heavy traffic. Depending on rates and product selection, control can last into the spring, discouraging the natural progression of bermudagrass from filling in thinned areas.

Often times ALS inhibiting (sulfonylurea - SU) herbicides are used in the spring following bermudagrass green up for weed control. These include chemistries like:

• Trifloxysulfuron 
• Combinations of metsulfuron and rimsulfuron, which can be used at low application rates
• Flazasulfuron, which is particularly effective in the spring if following an application of over 0.5Lbs/1000 square feet of readily available nitrogen

This same class of chemistry is also used to chemically transition from cool season back to warm season grasses. In other words, control the cool season ryegrass to accelerate and improve the bermudagrass spring green up. 

For best results with ALS inhibitors in the spring, follow these tips:

• Make sure that soil temperatures are above 60 F.
• They are tank-mixed with a non-ionic surfactant.
• Try Glufosinate as another option for dormant weed control.
• Non-selectives like Glyphosate (Roundup and others) can be used for less expensive options in the war on weeds.

All of these applications should be made below the 50 F air temperature threshold. If burn down products such as diquat are selected, be sure to note that it may take multiple applications for adequate control. 

Additionally, it is imperative that the bermudagrass is completely dormant before applying any non-selective herbicides as major damage can occur if there are any green leaves or stolons left. 

Weed Control after Overseeding Cool Season Turfgrass

Many of those who opted for ryegrass fields for the winter have already completed the project or will be soon. With the first frost, bermudagrass will begin going into winter dormancy, reducing its competitive nature on emerging weeds. 

Winter annual weeds prove to be a greater problem as they have recently or will be soon germinating and emerging with less crowding from actively growing bermuda. Of those weeds, annual bluegrass (Poa annua) can be the most problematic, primarily because selectively controlling annual bluegrass in perennial and annual ryegrass, or any other cool season turfgrass for that matter, can be extremely difficult if not impossible without incurring some damage to the desirable species. 

Broadleaf weeds, on the other hand, tend to be far less challenging to handle. There are several chemistries that are safe for use on ryegrasses including 2,4-D, MCPP, and dicamba. Across the market there are dozens of products with these three components in combination with one another. These 2-, 3-, and 4-way types of products are effective on hundreds of broadleaf weeds and are normally a tool in most sports turf managers’ arsenal. 

Use caution in regard to timing relative to the ryegrass establishment. As a rule of thumb, no applications should be made to seedling cool season grasses until after their second mowing as damage may become an issue. Common products include Speedzone and Trimec Southern. Remember to read the label as some of these products will have triclopyr in them. Err on the side of caution, and stay away as that active ingredient can be damaging to bermudagrass. 

As a side note, careful consideration should be given to pre-emergent selection, timing, and rates in the spring for those that plan to overseed. Later applications and higher rates can persist into the fall, interfering with good cool season turf cover. Be sure to check with your local extension agent for specific recommendations for your area.  

For more information on the subject, check out the article Poa Annua Control in Turf from the University of Arizona.