Necrotic Ring Spot in Denver
Because of the very wet spring and a strong summer warm-up, the Front Range is seeing heavier than normal NRS this year.
Necrotic Ring Spot (NRS) is a fungus affecting Kentucky bluegrass and annual bluegrass in Colorado. Other diseases can be confused with necrotic ring spot; therefore, an accurate assessment by a trained diagnostician is crucial to identifying the pathogen to properly address management of the disease. Management of this disease is difficult and requires an integrated approach utilizing cultural, chemical, and varietal control measures.
Necrotic Ring Spot forms a circle of dead grass. In larger rings, the center will be green. In smaller circles, the grass will all be dead. The dieback results in a sunken depression. Grass can also be yellow or brown and appear in scattered patterns; however, where lots of rings are present, the lawn can appear to have a serpentine appearance of dead/sunken areas. No leaf lesions are present on foliage infected with Necrotic Ring Spot. As the disease advances, roots, crowns, and lower stems will develop a black or brown discoloration.
In many cases, dandelions find the dead ring an easy place to get established, but they often appear weak or small when they do grow inside an NRS ring.
The following information comes from the University of Utah website:
Necrotic ring spot is a disease that infects cool-season grasses, primarily Kentucky bluegrass. The disease is damaging to bluegrass because the pathogen will infect and kill the crowns and roots, resulting in a slow recovery. This pathogen belongs to a larger group of pathogens that cause “patch” diseases in turfgrass, although taxonomically they are not related. A patch is characterized by the blighted appearance of turf in a section of otherwise green turf. Patch diseases are difficult to diagnose in the field because some of the symptoms associated with this pathogen can also be caused by a variety of other stresses. For example, stress caused by poor or extreme soil moisture, or improper mowing will result in brown turfgrass in irregular shaped patches. Diagnosis can also be difficult because of the similarity of individual symptoms between different pathogens.
The first symptoms are small, light green areas of turf. These areas will get larger and under drought conditions can go beyond 2-3 feet. Symptoms may also increase in size and severity with successive years. As the leaves are infected, they will turn a reddish brown to bronze color then weaken to a light straw color.
As you can see from the above excerpt, NRS is not easy to identify at early stages. In addition to the University of Utah information, many yards are hit with other fungi before NRS appear. It is not uncommon for a yard with Ascochyta or Melting Out to get rings weeks after the first disease is successfully treated.
First and foremost, the first thing to understand when fighting NRS is there is no quick fix and no “cure”. However, there are a variety of treatment options.
To property combat NRS, a combination of chemical and cultural practices needs to be maintained.
1) Slow release fertilizer program: Mountain High offers an Extended Release fertilizer program. This fertilizer breaks down slowly enough to feed the lawn without feeding the fungus.
2) Two aerations per year: the Front Range has heavy soil compaction issues. Relieving this compaction not only strengthens the lawn, it also helps keep the NRS fungus in the soil and out of the crowns of the plants. Mountain High offers aeration services in the spring and fall (we do not recommend any aeration during the heat of the summer).
3) Proper watering: proper watering prevents stress to lawn which in turn makes the lawn more resistant to NRS and other diseases. Watering deeply (but less often) is much better than watering more often with less water. This gives the lawn a reason to develop deeper roots.
Overwatering can cause water damage to the roots while also bringing the NRS into the crowns of the plants. Under watering puts the grass under a great deal of stress and makes it vulnerable to insects and diseases like NRS.
Mountain High recommends about 2.5 inches of water per week, spread out over three or four watering days. During really hot weather more water is needed.
4) Fungicides: NRS cannot be cured, but there are a few fungicide combinations available to ‘knock back’ the disease. Mountain High offers NRS fungicide treatments, but we recommend them only after fertilizer and cultural practices do not show enough improvement to the lawn.
As with any lawn problem, the lawn care professionals at Mountain High have the knowledge and expertise to provide the proper programs and treatment recommendations for NRS. Call us at 303.232.0666 or send us an estimate request below: