Leaf Spot and Melting-Out

Helminthosporium species

Symptoms
Leaf spot caused by Bipolaris spp is considered a warm weather disease. Melting-out caused by Drechslera spp is considered a cool weather disease. Both diseases have 2 similar stages that begin at the leaf level and finishes at the crown and root level with both diseases having similar symptoms. Small, dark purple to black spots on leaf blades with centers turning tan as spots emlarge. As the diseases moves down to the crown and roots, turf appears straw coloured and severe thinning of turfgrass stand can occur. 

Turfgrass Affected
Annual bluegrass, Kentucky bluegrass

Occurrence
Leaf spot is confined to the leaf blade level during cool weather <21C, but will infect crowns and roots during hot, humid weather over 30C.
Both stages of Melting-Out occur early in the spring and turf recovers when temperature reaches 21C.

Control Options
- Water deeply but infrequently
- Minimize thatch buildup
- Avoid high levels of nitrogen
- Raise mowing heights to 3.8cm (1.5 inches) or above


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