Winterkill 2014: What to do now

Dr. J.M. Vargas, Jr., Dr Kevin W. Frank, and Dr. Trey Rogers
Michigan State University

Winterkill 2014

In the last week as additional snowmelt has revealed the turf, it is now obvious that injury has occurred to annual bluegrass (Poa annua) in Michigan.  Most of the damage appears to be from ice cover that trapped toxic gases under the ice, which covered the greens for more than 45 days.  Many putting greens were under ice for 70 or more days.  In addition to ice cover, damage may also have been caused by crown hydration freeze injury, desiccation, and low temperature kill.  The questions now are primarily related to reestablishment.  Decisions would be easier if we could accurately predict the weather, but forecasts tend to lack accuracy and reliability.  If a warm spring occurs, interseeding the damaged areas with creeping bentgrass will work well. However, if a cold spring occurs, which many are predicting, it will take the interseeded areas considerable time to fill in with dense turf.  Sodding completely dead areas especially if you have an annual bluegrass nursery green may be a better option.  If you purchase sod, make sure your putting green root zone is compatible with the purchased sod root zone. However, if a nursery green is not available then seeding with creeping bentgrass is the only realistic option.   

Winterkill damage on a Poa annua putting green.

Interseeding Greens

The areas to be seeded on greens should be vertically mowed and if possible aerified, then seeded and lightly top dressed. The seed should be applied to the greens following aerification and then vertically mowed in an attempt to move the seed into the verticut slits. Another option would be to apply the seed to the greens and then run a spiker over the greens to push the seed into the soil. The aerification, verticuting and spiking should also stimulate some of the annual bluegrass seed reservoir in the soil to germinate as well.  A fertilizer with phosphorus should be applied at the time of seeding to encourage germination followed by light sand topdressing and rolling.  Research conducted on turfgrass reestablishment following winterkill at MSU indicates regular applications of fertilizer containing phosphorus results in faster establishment than nitrogen applications alone.  Foliar feeding is the preferred method of fertilizing since the cool soil temperatures and the limited root systems of the newly germinated seedling are not conducive to nutrient up take.  On ”warm” windy days, frequent light irrigation cycles will be necessary to keep the surface of the greens moist during the germination process and the earlier seedling stage.  Mowing heights should be raised to .150 in. and then gradually brought down to more normal mowing heights.  Based on our research mowing can begin 8-10 days after germination (covers will speed this up).  Do not be afraid to mow frequently in the beginning, as it helps the new seedlings establish.

Prepping a seedbed in a dead green.

Covers and diseases

If covers are available, they should be used on severely damaged greens. This will increase temperatures, especially on warm sunny days, and speed up the recovery process. Cotton grow covers can be cut into smaller pieces and used on greens that have small damaged areas allowing the green to remain in play. If covers are used on greens with major damage, temporary greens will have to be established.  Once sufficient establishment has occurred, the covers can be removed during the day to allow play to occur on the greens. At night the greens should be covered to retain the heat of the day and to further encourage as much growth as possible.  Microdochium patch fungicides should be applied to prevent this disease from developing, especially if covers are used. The QoI or dicarboximide fungicides would be good choices for management of this disease.

Covering greens may be critical for speeding reestablishment.