Necrotic Ring Spot is one of the worst fungal lawn diseases which can attack our Cool Season lawns, and it's treatment and removal is never easily achieved. In fact, killing Necrotic Ring Spot will consist of several management techniques which will need to be combined together for an effective result to be achieved.
Necrotic Ring Spot will attack many Cool Season grass types including Fescues and Annual Bluegrass, but it creates the most devastating damage to Kentucky Bluegrass. Perennial Ryegrass turf is immune to NRS, and while it affects Kentucky Bluegrass the worst, there are some strains of this lawn type which is proving to have some resistance to the disease, so it is recommended to research each turf type before purchase to find these more resistant types.
Necrotic Ring Spot is a perennial turf disease, meaning it can live indefinitely and continue damaging lawns unless it is killed. The disease is most easily noticeable by it's brown ring of dead grass it creates which can measure between 3 inches to many feet in diameter. The inside of the circle is often green which gives an appearance of a "frogs eye".
The disease feeds on the roots and crowns of the turf, and first becomes noticeable in Cool Season grasses in Spring and progressively gets worse and spreads right through until the Fall. The infestation of the lawn disease can be localized to a small patch of the lawn, or it can spread over vast areas of turf if left untreated for too long.
Lawn mowers will unlikely spread NRS as the disease mainly lives in the soil and very low thatch layer. Over watering the lawn will increase the severity of the disease, as will poorly drained turf areas.
Treatment is difficult because fungicide treatments have proven unreliable in their results, so the best course of action in killing Necrotic Dead Spot will be several practices combined together.
Treatment of Necrotic Ring Spot
Reduce watering: while it may seem like a good idea to water the dead patches in the lawn more often, this will only make the disease worse.
Water only in the morning: this allows the turf to use the water in the day, which is the only time it can absorb it, whereas watering at night leaves massive amounts of moisture on the lawn at night which creates a perfect feeding ground for all lawn diseases.
Repair dead patches: for small patches, dig out the soil and sod of an affected area to several inches around the affected area and up to a foot in depth. Fill the hole with clean soil from elsewhere on the property and re-seed the affected area.
Mow regularly: regular lawn mowing at correct mowing heights creates a stronger, healthier lawn which can then better fight off all lawn diseases, so mow regularly enough so as to never remove more than 1/3 of the leaf material at any one time.
Use less nitrogen fertilizers: reduce the usage of high nitrogen fertilizers, while they may help make the lawn healthier to help fight off diseases in general, they also feed the Necrotic Ring Spot and make it stronger than the turf itself. So some fertilizer is OK, but reduce normal usage under these disease conditions.
Fungicide: Fungicide treatment for NRS should begin in mid Spring, and should be repeated 1 month later, and then 1 month later after that again. The local gardening store should stock these fungicides, and we recommend following manufacturers guidelines exactly.
If in any doubt about treating Necrotic Ring Spot, please contact a lawn care professional in your area.