Leaf spot and melting out
Leaf spot and melting out diseases occur in lawns that are stressed from excessive nitrogen fertilizer, excessive water and a very short mowing height. The diseases are caused by two separate fungi. But, because the diseases often occur together, they're considered a single disease complex.
Leaf spot symptoms include small, purple-to-black spots on individual leaf blades. The spots become elliptical in shape and may be surrounded by a purple border. Tissue in the center of the spot may die and turn a beige or straw color. If a spot extends across the leaf, the blades wither and die.
Melting out is the more serious of the two diseases. Initially, its symptoms are similar to those of leaf spot. But as the disease progresses, the fungus works its way to a plant's base and attacks the crown and roots. Affected turf appears yellowish, thin and shabby with irregular patches of dead grass. When these areas are raked, dead grass plants are easily removed.
Both diseases occur when dry weather alternates with cloudy, wet periods and cool to moderate temperatures.
Resistant turfgrass cultivars are available, so susceptible cultivars should be avoided. Resistant Kentucky bluegrass varieties include, but are not limited to, A-20, A-34, Adelphi, Admiral, Banff, Challenger, Eclipse, Haga, Majestic, Merion, Merit, Ram II, Rugby, Touchdown and Windsor.
Chemicals rarely are needed to control the leaf spot/melting out disease complex. Proper lawn-management practices usually control the problem. If melting out attacks repeatedly, fungicide use may be warranted. Consider using fungicides that contain iprodione or mancozeb. Always follow label instructions. Remember, chemicals are most effective when they're used in conjunction with proper lawn-care practices.
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Updated Friday, April 19, 2013