Brown patch
From Wikipedia, the free encyclopedia
Brown patch is a common turfgrass fungal disease that is caused by species in the genus Rhizoctonia, usually Rhizoctonia solani.[1] Brown patch can be found in all of the cool season turfgrasses found in the United States. Brown patch is most devastating to: Bentgrass (Agrostis sp.), ryegrass (Lolium sp.), Annual bluegrass (Poa annua), and Tall fescue (Festuca arundinacea).[2] Brown patch is also found in Kentucky bluegrass (Poa pratensis) and Fine fescue (Festuca sp.) but this is rare or does minimal[clarification needed] damage.[3] Brown patch is known as a foliar disease, so it does not have any effect on the crown or roots of the turf plant.[4]
Brown patch symptoms differ depending on the various maintenance practices performed on the turfgrass (mowing height, fertilizer, watering, etc.) Symptoms on turfgrasses that are wet for extended periods and are closely mowed will produce a distinctive gray-purplish bordered ring "smoke-ring" that is up to 50 cm in diameter.[3] While on taller cut grasses that are not wet for extended periods of time will begin to produce patches that can be several feet in diameter and may have a "frogeye" appearance. White mycelium can be found on dew-covered turf in the early part of the morning.[5] On a closer look at the grass leaf blades (usually on Tall Fescue) you maybe able to see tan to brown small, irregular shaped lesions.[3]
Disease cycle
The Rhizoctonia species thrives in temperatures ranging from 70 °F to 90 °F but can survive in freezing temperatures.[3] Brown patch is most common when night temperatures fail to drop below 68 °F and during extended periods of high humidity or prolonged leaf wetness.[5] The Rhizoctonia species has two specific fungi that affects the turf plant at different times of the year. In most cases Rhizoctonia solani will cause Brown patch in June throughout early July. While when temperatures begin to heat up and the air becomes more humid Rhizoctonia solani will be replaced by Rhizoctonia zeae.[3] It has been found that the Rhizoctonia species is capable of surviving in the soil for many years without affecting turfgrass.[5] During the winter months the fungus will lie dormant in the grass tissue or soil and form into resting bodies called sclerotia.[5]