What is Brown Patch?
Brown Patch is a fungal turf disease that primarily affects the roots and crowns of the plant and is caused by Rhizoctonia solani.
What are the Symptoms of Brown Patch?
The symptoms of Brown Patch can vary depending on the grass cultivar, climatic and atmospheric conditions, soil and intensity of turfgrass management. Brown Patch is most severe in Spring and Autumn. Brown Patch infestation is more severe when the turf is cut shorter than the optimum height of the type of turfgrass being grown. General symptoms of Brown Patch include:
Brown discoloured circular patches that range from 5cm to 1-2m in diameter, with the grass in the centre of the ring usually remaining moderately healthy.
The outer ring of the grass turns brown and dies, usually from desiccation due to its damaged root system.
When severe infection occurs, leaf tissue can be affected, making leaves appear water-soaked, eventually drying and withering and turning brown.
When humidity is high, a 'smoke ring', of mycelium may appear as thin brown borders around the diseased patches early in the morning and disappear as the turf dries out.
On wide-bladed species, leaf lesions develop with tan centres and dark brown to black margins.
What Causes Brown Patch?
Brown Patch is caused by a pathogen known as Rhizoctonia solani. Rhizoctonia solani is a soil-borne fungus that can be found in 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.
When Does Brown Patch Occur?
In general, the conditions favouring Brown Patch are:
High relative humidity and temperatures of over 28°C during the day and over 15.5°C at night.
More than 10 hours a day of foliar wetness for several consecutive days.
Turfgrass species are most affected when night temperatures are consistently above 20°C with high humidity or moisture.
What Turfgrasses are especially susceptible to Brown Patch?
Wintergrass, Couch, Bentgrass, Fescues, Kentucky Bluegrass, Ryegrass & Buffalo Grass.
What can I do to manage Brown Patch disease?
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. Other measures to manage Brown Patch include:
Avoiding nitrogen applications when the disease is active and using low-moderate amounts of nitrogen, moderate amounts of phosphorous and moderate-to-high amount of potassium when humidity is high
Increasing the height of cut
Increasing the air circulation, reducing thatch, and minimising the amount of shade.
Irrigating turf early in the day and improving the drainage of the turf.
Removing dew from turf early in the day.