Drier conditions this spring have helped to keep some turf diseases at bay, but interestingly enough two separate, impressive occurrences of powdery mildew were recently observed on lawn turf.
Most recognize powdery mildew as a quirky disease that causes susceptible plants to appear if they have been dusted with flour or limestone. The fungus may be bright white, as in turf (see photo at right), while other strains can exhibit a grayish color. Vigorous turf can often support the presence of the disease without significant injury, but more advanced cases occasionally lead to yellowing and even thinning of the stand. Shaded turf areas with poor air circulation are prime targets for powdery mildew development. The disease affects bluegrass and fescue species, but is especially common on Kentucky bluegrass.
Unlike other fungal diseases that plague turf, powdery mildew fungi are unique in that they do not require leaf wetness to cause infection. In fact, leaf wetness can actually inhibit the process. Cool, humid weather favors disease development. However it is not uncommon for powdery mildew to appear in the midst of dry spells like we have experienced this spring, as higher humidity during nighttime hours is sufficient to initiate infection. Once infection occurs, powdery mildew diseases continue to develop regardless of moisture.
Powdery mildew typically resolves on its own when conditions improve, the growth rate of the turf increases, and as infected blades are removed by mowing. When the disease re-occurs regularly, cultural steps can be taken to significantly lessen or eliminate infection. In shaded areas, reduce nitrogen fertility and take advantage of any available means to reduce shade and improve air circulation. Kentucky bluegrass cultivars with improved shade tolerance and powdery mildew resistance are also available. Fungicides are not indicated or necessary in the vast majority of situations. For troublesome cases in intensively-managed turf, several commercially available fungicides are labeled for powdery mildew.
Submitted by: Jason Lanier and M. Bess Dicklow