Necrotic ring spot and Summer patch

Fusarium blight was declared an extinct disease by J.M. Vargas Jr. in his 1994 text on turfgrass disease management, and separated into Necrotic ring spot (Leptosphaeria korrae) and Summer patch (Magnaporthe poae), both of which commonly occur on northern home lawns comprised of Kentucky bluegrass and fine fescue. It was through critical research that the disease moniker went from Fusarium to the Leptosphaeria spp. and with that, a critical integrated management program has evolved.

Cultural Approaches. With any  patch disease, basic good lawn care goes a long way. That is: balanced fertility, proper irrigation and mowing practices and core aeration to control thatch buildup.
• Fertility needs of turfgrass should be met following soil test recommendations. In most instances, turfgrass fertilizer comes with a high percentage and ratio of nitrogen when compared with the other two macroelements of phosphorus and potassium.
Many times the key to better disease management is to increase the level of these two elements with separate applications as a result of soil testing. The basic application of typical spring and fall lawn fertilizers will help to maintain a sufficient balance for healthy turfgrass growth.
•    In both instances of Necrotic ring spot and Summer patch, light daily syringing cycles from the irrigation system at mid-day to lower heat stress on the turf will reduce the symptoms of these diseases and encourage redevelopment of the damaged roots from these pathogens.
•    Mowing in the evening hours when temperatures are dropping and heat stress is minimized is better for the grass plant than early morning mowing.
Mowing should be at 3 inches or higher with cool-season grasses with the clippings returned, and should continue right through the fall as long as it is growing, with the last one at a lower mowing height with the clippings being collected.
•    Core aeration along with timely power raking when the grass is actively growing will help to correct chronic patch disease problems.
With lawns established from peat sod rather than mineral sod, a bulk density difference between the sod backing and the soil it is placed upon will contribute to patch disease development. The peat sod is preferred by both homeowners and contractors because of its generally more attractive appearance and easier handling.
Knowing that peat sod will be placed on a mineral or clay based soil should alert the homeowner that regular coring and power raking will be required for the following  three years after rooting in to keep the grass from developing this disease syndrome.

Chemical Control. For fungicide treatment, it is suggested to use either an acropetal systemic or any product that contains thiophanate-methyl as the active ingredient, or a Strobilurin class such as products that contain the active ingredient azoxystrobin or trifloxystrobi. L&L

The author is a horticulturist and turfgrass specialist at North Dakota State University.