The necrotic ring spot fungus (Leptosphaeria korrae) affects several species of grasses, especially during the cool seasons. To keep a healthy lawn during this kind of weather, you need to recognize and stop this fungus before it damages your entire lawn.
Necrotic Ring Spot
The symptoms of the fungus usually appear in late spring or early autumn. The fungus starts out as light green patches ranging from 5 to 10 centimeters in diameter. They can grow to a full meter in diameter and may turn light or reddish brown in color. Streaks, semi-circular, and circular patterns show up in the affected areas of the lawn.
Necrotic ring spot lasts throughout the growing seasons but it becomes more progressed during cooler months. Although the symptoms are usually dormant during the summer, there is still a chance that the fungus will show some symptoms. When it does, the crowns and roots become very dark or blackened. Leaf lesions sometimes appear. These lesions are often yellowish, tan, or reddish brown. But you cannot identify necrotic ring spot from leaf lesions alone because other lawn diseases exhibit this symptom.
Necrotic ring spot spreads through infected lawn equipment such as lawn mowers, hoes, and rakes. It also spreads through infected turf. The fungus thrives even in the presence of other plant diseases. Should the symptoms disappear in the summer, they reappear during early autumn.
To prevent and control necrotic ring spot, avoid applying too much fertilizer on your lawn. Applying fertilizer between June and August can stimulate the growth of necrotic ring spot. Excessive thatch buildup also contributes to the growth of this fungus, so keep your thatch to minimum. Check the pH of your soil and make sure that it is above 6.2. Acidic soils promote the growth of necrotic ring spot. Lime your lawn annually to improve its pH levels. When necrotic ring spot occurs, you can treat it chemically with fungicides containing azoxystrobin, thiophanate-methyl, or triadimefon. Be sure to follow the fungicide's label when applying it on your lawn.
