What is that White Powder on the Grass?

Powedery Mildew in Turf


There has been an outbreak of powdery mildew this spring, and it seems to be all over town. All locations are fielding calls and concerns about the silvery colored grass. The last couple weeks of cooler weather has made the conditions ideal for powdery mildew.

Symptoms of Powdery Mildew

The fungus first appears as isolated patterns of fine, gray-white, powdery growth on the upper surface of the grass leaf. This growth rapidly becomes denser and may cover the entire leaf, giving the leaf a gray-white appearance. In severe outbreaks, entire portions of turf stand may be dull white, rather than green. Individual leaves look as though they are covered with flour or powder.

Disease Cycle

The fungus organism overwinters in dead grass and infected living grass plants. Spores of the fungus spread by the wind to leaves of other turf grass plants. Conditions favorable for powdery mildew development include poor air circulating, high atmospheric humidity, low light intensity or shade, and cold air temperatures. Kentucky bluegrass, when planted in shaded areas, is particularly susceptible to this disease.

Controlling the Powdery Mildew


  • Control is easy if you do not wait too long. An application of Fungus Fighter will slow the spread. Fungus Fighter is available in a spray form or a granular application.
  • Keep your mower blade sharp. Set your mower height down a little shorter if you are mowing over 3 inches tall. A shorter cut helps the dew to dry faster, and you should be able to mow off some of the white powder.
  • Powdery Mildew typically shows up in late April or May so watch these same areas over the next 30 days. Controls work for about 14 days. If the conditions return, you could see a second infection this year.

After Effects of Powdery Mildew

The disease is not typically mortal but this year, the timing of this event can thin turf stands to a point that allow weeds to sprout in those areas. Also, a thinned turf stand allows more UV rays to contact the soil. The increase in UV rays over time will break down the effectiveness of crabgrass pre-emergence in areas usually shaded by dense turf. Uncle's Idiot Proof Lawn Care Program Step #3 Prevent crabgrass control in late May will be critical to extend crabgrass control through the summer months.

Will Powdery Mildew Go Away by Itself?

Powdery mildew doesn't just go away, it will stop growing when conditions change. It's just the gamble you take on how long that will be and how much damage will be done while you wait on Mother Nature. In addition, if the conditions should return, so will the powdery mildew. Control applications of Fungus Fighter will knock it out and give protection against its return.