The Causal Pathogen
The causal pothogen of Brown Patch is Rhizoctonia solani (Kuhn). Rhizoctonia solani is a soil borne fungus which can be found in the most soils and is known as a cause of disease in both established and seedling turfgrasses.
The disease does not produce spores, but instead spreads rapidly by mycelial contact. The disease is disseminated via movement of sclerotia which are produced and remain in thatch material.
Rhizoctonia solani has a characteristic mycelium over other patch diseases, whereby the mycelium branches at a 90 degree right angle, allowing for accurate diagnosis in the lab.
In Australia, Brown Patch is a disease primarily of the roots and crowns within the plant. The damage to turfgrass is in the form of a ring ranging from 5cm to 1-2m in diameter, with the grass in the centre of the ring usually remaining moderately healthy. The outer ring of grass turns brown and dies, usually from desiccation due to its damaged root system. When severe infection occurs, Rhizoctonia solani may infect leaf tissue also, making leaves appear water soaked, eventually drying and withering and turning brown. When humidity is high, a smoke ring, consisting of mycelial masses, may surround the perimeter of diseased patches in the morning. This occurrence dissapears as the turf dries out.
Rhizoctonia solani survives adverse periods as sclerotia / as mycelium on plant debris / or as a saprophyte in thatch. When soil temperatures rise to 15 - 20 Degrees Celcius, sclerotia germinate and the fungus begings to grow. Although growing at lower temperatures, Rhizoctonia solani does not infect plant tissue until air temperatures rise further and high humidity is experienced. Fidanza, Dernoedon & Grybauskus (1996) found that infection is likely to occur once minimum air temperatures rise above 16 degrees celcius and mean relative humidity increases above 75%.
Cultural Control Practices
High levels of nitrogen can increase the potential for Brown Patch infection. Hence, fertilisation with a high nitrogenous fertiliser prior to periods of high humidity should be avoided where possible.
Chemical Control Options
Chemical control options are highlighted below;
Azoxystrobin – eg. Heritage Maxx.
Tebuconazole / Trifloxystrobin – eg. Dedicate.
Propiconazole – eg. Banner Maxx.
Azoxystrobin / Propiconazole – eg. Headway Maxx.
Chlorothalonil / Fludioxynil / Propiconazole – eg. Instrata.
Mancozeb – eg. Penncozeb.
Trifloxystrobin / Iprodione – eg. Interface.