Fungi from the Pythium genus are soil borne plant pathogens capable of causing different diseases on a range of turfgrasses. Pythium spp. can be a disease to both seedling and mature turfgrass swards. Pythium aphanidermatum and Pythium ultimum are the two most predominant turf infecting species.
The first symptoms of Pythium blight are circular reddish brown spots in turf, ranging in size from 2.5 - 15cm. In the morning dew, infected leaf blades appear water soaked and dark, may feel slimy and often mat together. As they dry, the leaf blades shrivel and turn reddish brown. On humid nights when dew form, you may see mycelium on the outer margins of the spots the next morning. The mycelium may remain active and visible far into the day, as long as there is plentiful moisture on the plant.
The infected grass plants collapses quickly. If temperature and relative humidity remain high, the spots may coalesce, and large areas of turf can be lost.
Both species of Pythium survive as a saprophyte in the thatch, soil or both. When conditions are favourable, the disease invades roots as well as plant tissue and spreads from plant to plant via active mycelial growth. Pythium is a 'water mould' and survives well in waterlogged soils or on debris in ponds. Pythium can occur year round, however the disease is most severe when temperatures and relative humidity is high. Nutter et al found in 1983 that Pythium infection was likely to occur when 1) a maximum daily temperature was higher than 30 degrees Celcius, 2) followed by at least 14 hr of relative humidity greater than 90%, provided the minimum temperature was higher than 20 degrees celcius. More recent work undertaken by Shane in 1994 modified Nutter et al findings to the following infection requirements; 1) a maximum daily temperature was higher than 27.7 degrees Celcius, 2) followed by at least 9 hr of relative humidity greater than 90%, provided the minimum temperature was higher than 20 degrees celcius.
Cultural Control Practices
Good soil drainage will reduce Pythium activity. Hence, in areas where drainage is poor soil amendment maybe required. Thatch control and avoidance of over fertilisation are recommended for limiting the possibility for disease incidence. Good au circulation also helps minimise disease activity.
Chemical Control Options
Chemical control options are highlighted below;
Propamocarb – eg. Banol.
Fosetyl al – eg. Signature.
Thiram – eg. TMTD 600.
Azoxystrobin – eg. Heritage Maxx, Headway Maxx.
Metalaxyl M – eg. Subdue Maxx.