DOLLAR SPOT

         Dollar spot is a common and persistent disease that occurs on most turf grass species throughout the world. 

Symptoms:  On closely mowed grasses (as on golf greens) the overall symptom of dollar spot is small, circular patches that rarely exceed 6 cm in diameter.  These patches coalesce into larger, irregular patches if the disease becomes severe.  Residential lawns and other taller turfs may exhibit irregularly shaped, bleached patches of blighted grass 2-15 cm or more across.  Patches may coalesce to cover large areas.   Individual infected leaves develop a lesion that is first chlorotic, then water-soaked, and finally a bleached color.  Dollar spot lesions are characteristically bounded by a tan to reddish brown margin and they generally enlarge to extend across the entire leaf, except on grasses with coarse leaves (such as Paspalaum).  Lesions often appear hourglass shaped.  Dieback from leaf tips is also common.  Individual leaf blades may have a single lesion, have many small lesions, or be entirely blighted.  Leaf symptoms may be confused with those caused by red thread, copper spot, brown patch and Pythium blight. When dew is present on grass blades and the pathogen is active, a white, cottony or cobwebby growth of fungal mycelium may be seen on diseased turf.  The mycelium disappears as the leaves dry.  This aerial mycelium can be confused with that produced by species of Pythium, Nigrospora and Rhizoctonia.

Time & Weather Conditions:  Prolonged high humidity in the turf grass canopy is required for fungal growth.  The dollar spot fungus may commence activity from late spring through late autumn.  Favorable environmental conditions for disease include warm, humid weather and cool nights that result in heavy dews.  A temperature range of 15°C to nearly 30°C appears favorable.  Disease becomes more severe in dry soils, even though high moisture in the aerial turf canopy is also required.  Turf grasses grown under low nitrogen fertility are most susceptible.  Soil pH and phosphorus fertility levels apparently have no influence on disease severity. 

Control:  Maintain adequate to high nitrogen fertility during the period of dollar spot activity.  Water thoroughly (deeply) and as infrequently as possible without causing moisture stress between waterings.  Do not water in the late afternoon or evening, for this prolongs the period of leaf wetness during cool nights when dew is likely to form.  Promote good air circulation over the turf by pruning or removing trees or shrubs and removing other barriers.  Mow the grass regularly at recommended heights.  Before seeding a new lawn, consult a local extension specialist for recommended cultivars that are resistant to dollar spot.  

            Many fungicides are available for dollar spot control, but aside from centipede (which you really don’t want to over fertilize) you can mostly control this fungus with a good fertilization program. In extreme cases were it has gotten out of hand a fungicide program may be called for