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Spokane, Washington  Est. May 19, 1883
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Gardening: Control necrotic ring spot in lawn

By For The Spokesman-Review By Pat Munts

Got brown patches of grass showing up in your lawn? It may be necrotic ring spot, a fungal disease that lives in the soil and emerges when conditions are conducive to its growth. Unfortunately, those conditions are likely to be compacted soil, improper watering, overuse of synthetic fertilizers and disease prone strains of Kentucky bluegrass and turf-type fescues.

In its early stages, necrotic ring spot (NRS) appears as straw-colored, circular patches that grow wider with time. Over time the spots widen and the centers regrow grass. In a badly infested lawn, spots may grow together to create a patchy lawn. NRS takes anywhere from three to 10 years to emerge and especially common in sodded lawns.

There are preventative fungicides that can be applied in the spring and fall to treat NRS but they must be applied every year and they are expensive. The best way to prevent and treat NRS is to use good lawn management techniques that promote healthy growth.

Soil compaction and layering promotes the growth of NRS. When a lawn is installed, the base soil layer should to be worked up and 3 to 4 inches of good quality compost mixed in to create a hospitable place for roots to grow deep. When the ground is left untilled, the new roots have no way to break through the compacted layer and become deeply established. If you can’t start over with an established lawn, aerate it regularly and then apply a light layer of compost to fill in the aeration holes and build up the soil.

Overuse of synthetic fertilizers contributes to the emergence of NRS. These highly water-soluble fertilizers release a massive dose of nitrogen that in turn causes rapid growth of the grass. The lawn greens up fast but in the long run this weakens the grass plant so that it is susceptible to NRS and other diseases. Instead apply a natural fertilizer in the spring and the fall that will release its nutrients slowly at a rate the grass can use efficiently without burning itself out.

Mow your lawn properly so there is enough grass blade surface area to carry on photosynthesis to feed the grass plant. Cut the lawn to 2.5 to 3.5 inches tall and cut it often enough so you are only taking a third of the blade length at each mowing. Sharpen your lawn mower blade regularly so you don’t tear the grass blade.

Water your lawn no more than three to four times a week and water enough to get at least an inch to 1.5 inches on the lawn each week. This will water the lawn deeply but allow excess to drain away.

Lastly, overseed the damaged lawn with a Kentucky bluegrass seed that is NRS resistant or a perennial rye mix that is naturally more immune to NRS. Now is a good time to reseed lawns as we finally get some rain and the soil is still warm to sprout seed. The seed is available a better garden centers like Northwest Seed.

Pat Munts has gardened in the Spokane Valley for over 35 years. She is co-author of “Northwest Gardener’s Handbook” with Susan Mulvihill. She can be reached at pat@inlandnwgardening.com.

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