Microdochium patch (Microdochium nivale) (sometimes referred to as Fusarium patch in older references) is problematic from fall through early-summer in areas west of the Cascade Mountains.
The Pacific Northwest can be the ideal climate for Microdochium patch given the long dew periods, frequent rainfall, and cool, wet weather that persists for much of the growing season. Without snow cover, Microdochium patch occurs as reddish-brown to copper-coloured spots in the turf. The spots range in diameter from less than 2.5 cm to about 20 cm, but larger spots are sometimes found. The pathogen is a prolific spore producer and can spread quite readily via mechanical traffic, surface water, and even wind. Mycelium and spores survive in the thatch and debris of the turf stand and re-infect when conditions are favourable and turf growth is slow. This disease is favoured in shaded or poorly-drained locations and in areas that receive excessive nitrogen fertility.
Symptoms and signs: Fusarium patch appears as reddish-brown spots 2 to 3 inches in diameter, but spots may enlarge to 6 or more inches. Foliar mycelium may be evident during early morning hours in the margins of large patches. Streaks of blighted turf, reminescent of Pythium blight, can occur when spores and mycelium are moved by wheels or water. Pink snow mold develops under snow or at snow melt. The leaves of infected plants initially are water-soaked and patches range from 3 to 8 inches in diameter. Large patches can be associated with snow cover. As snow recedes, patch size increases and the centers become bleached-white, but the peripheries display a distinctive pinkish color. As plants collapse and die, the leaves become matted and develop a tan color. On closer inspection, you may notice that these leaves have a pale-pinkish cast.