CO-Horts

CO-Horts

Thursday, July 2, 2015

A Pain in the Ascochyta!

Tony Koski, Extension Turf Specialist

Ascochyta leaf blight has blown up across the state – on home lawns, sports turf and even golf courses. This disease occurs most frequently and severely when we abruptly transition from a cool, wet spring to hot, dry summer conditions. Perfectly healthy green grass develops random straw-colored blotchy patches and streaks. Brown wheel tracks from the operation of mowers and other maintenance equipment often appear, leading some to believe (incorrectly) that
equipment is tracking the fungus onto the turf. The wheel-marking occurs when wilted, drought/heat-stressed grass leaves are crushed by the wheels of heavy mowers as they move across the turf. The browning in the wheel tracks is caused by a combination of direct leaf injury (crushing) and Ascochyta occurring in the stressed turf. The wheel-marking is NOT the result of the disease organism being tracked onto the lawn from somewhere else.

The good news with this disease is that, while the turf appears dead, it will recover within a few weeks. The fungus attacks leaves (through the mowed leaf tip), but rarely kills the crown or roots. Affected grass plants must produce new leaves to replace the dead ones, a process that may take 10 days to 3 weeks depending on severity of the outbreak and species of grass affected. More rapidly growing grasses like tall fescue and perennial ryegrass will recover more quickly than will the slower-growing bluegrasses and fine fescues.

The most spectacular outbreaks occur where the turf manager or homeowner has delayed firing up the irrigation system (perhaps with the thought that “it has rained all spring, so I don’t need to begin watering yet”) or where irrigation coverage is poor due to a broken head or other system malfunction. While death by Ascochyta is uncommon, failure to repair the coverage issue or provide adequate irrigation may cause turf death that will be attributed to the disease.

Fungicides are not recommended for this disease. In fact, few fungicides will have Ascochyta on their label. Repairing the irrigation coverage problem – or beginning appropriate irrigation – will begin the recovery process. Avoid the temptation to irrigate recovering turf excessively, as saturated soil may result in other problems (weeds, other disease activity). 

Happily, once turf has recovered from an Ascochyta outbreak, the disease will generally not reappear again in the same season. While a true turf disease, an outbreak of Ascochyta almost always arises because of poor water management by the homeowner or turf manager.

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