Description: Initially, infected lawns show scattered light-green patches, 2-6 inches in diameter in roughly circular or crescent-shaped patterns. As the disease progresses these patches enlarge, the colour changes from a light-green to dull brown then fades to tan; the pattern becomes more distinctly circular or crescent-shaped with tufts of apparently unaffected grass in the center of each patch, producing what is generally referred to as a 'frog-eye" effect. Individual patches may enlarge up to 3 feet in diameter and these overlap to result in large areas of blighted grass. Plants die as the crowns and roots are destroyed.
Control: Once in your lawn, necrotic ring spot is hard to eradicate. The key to control is to keep the grass growing vigorously using sound management practices. Fungicides are generally not very effective against necrotic ring spot. Fungicides are generally not inexpensive and not always effective.
- Remove thatch when it accumulates in excess of 1 cm. Thatch provides an ideal medium for the fungi to multiply and also interferes with proper movement of water and nutrients. Remove heavy clippings to prevent thatch accumulation. Core-Aeration is the best method to reduce thatch. Aeration increases the rate of organic matter decomposition.
- Necrotic Ring Spot affects the roots. The roots are not able to function at 100%. The effects of the disease are thus more noticeable in hot, dry weather. During dry periods, water thoroughly, wetting the soil to a depth of at least 6 inches every 7 days or so. Severe damage occurs when weather is hot and humid but dry(no rain). Avoid watering at times when the grass will remain moist all night.
- Kentucky bluegrasses in general are more susceptible to necrotic ring spot. Overseed with resistant species. We recommend grass seed mixes with at least 20-30% turf-type perennial ryegrass seed. Re-sodding only delays the re-occurrence of this disease.
- Balanced nutrition is important. Regular feeding is important but not to be overdone. Avoid soluble or fast-releasing nitrogen during the summer.
- Increase the beneficial microbial population by using organic based fertilizers. The more beneficial microbes in the soil, the less moisture and oxygen available for unwanted organisms. Our regular Turf King fertilizer is high in organic matter.
- In severe situations, we recommend a regimen of "Sustane" natural fertilizer. Sustane is an organic, composted poultry fertilizer. Increased organic matter increases the population of good microorganisms in the soil. Sustane should be used 3-4 times throughout the season for about 2 seasons.
In some cases, there are so many spots of the disease that there may be a large patch of infected lawn. Call your lawn care expert for advice