Powdery Mildew

A fungal disease caused by Erysiphe graminis. It should not cause much concern, being more of a superficial disease which produces a white to light grey dusting of spores on infected grass leaves. These can turn yellowish where the dusting is dense as the disease obtains nutrients from the leaves, and the sward density can also be thinned, although it is more prevalent on longer rather than shorter turf.

It can often appear during dry periods, especially high humidity presence amongst the leaves, during the main growing season. It is more prevalent on grass under shaded conditions and where high applications of nitrogen have been made.
Controlling powdery mildew should involve good cultural practices of ensuring surface moisture is removed by drag brushing, removing grass clippings, reducing shade and increasing air circulation where possible, maintain good mowing practices of not removing any more than 1/3rd of the leaf per cut, scarify and verticut to keep a slightly more open sward than would be expected of a sward in full sun as this will reduce the relative humidity amongst the grass leaves, keep the area well aerated, and do not apply high levels of nitrogen, especially where the sward is shaded.

The disease is sometimes just referred to as Mildew.