Fusarium Blight, more commonly known as Necrotic Ring Spot, is a soil borne lawn fungus, which is identified by circular to irregular sunken straw colored or gray patches approximately 4-16 inches in diameter. Necrotic ring spot fungus is caused by severe over watering of a lawn for a long period of time and is cured by stopping these poor cultural practices caused by humans.
Necrotic ring spot (NRS) in lawns is a symptom of a problem and if we stop the cause of the problem, we should expect the symptoms to go away. Therefore, the first step in fixing the Necrotic Ring Spot problem is to stop the severe over watering of the lawn. Necrotic ring spot is a common lawn fungus worldwide, but it is most common in states like Colorado where the majority of lawns have sprinkler systems. Mother nature typically does not over water a lawn for months on end; however, irrigation system can over water a lawn for many consecutive months.
Over watering is the cause of necrotic ring spot fungus in lawns for two reasons. First, over watering stimulates the Necrotic Ring Spot fungus spores and secondly over watering the lawn kills the beneficial microbial activity in the soil, causing a problem we call "dead soils".
Dead soils lack beneficial microbes, which stabilize the soil's microbiome, and the absence of beneficial microbes means the necrotic ring spot fungi can live without competition from other microorganisms. Without the beneficial microbes to compete with the Necrotic Ring Spot fungus, plus the over saturation of soils which stimulate the fungus spores, the necrotic ring spot fungus can spread through a lawn quickly.
When a necrotic ring spot lawn fungus outbreak does occur, the fungus in lawns can be difficult to control and will take about 9 months or longer to cure. The reason for the extended length of time for treatment is because it takes 6 months to 1 year to rebuild the soil. Until the microbial activity in the soil is fully reestablished then the necrotic ring spot fungus will continue to be a problem. Patience is a very important aspect when a lawn is recovering form necrotic ring spot.
Necrotic Ring Spot treatment is only possible if we first correct the over watering of the lawn. Colorado is one of the worst states for Necrotic Ring Spot due to the amount of lawn with irrigation.
Always avoid using a fungicide when treating Necrotic Ring Spot in a lawn. The fungicide is designed to kill microbes and it will kill both the bad microorganisms and the beneficial microorganisms that are living in the soil. The long-term cure for necrotic ring spot is to stimulate a large population of diverse microorganisms in the soil. After the soil is reestablished and the soil is teaming with microbes, the beneficial microbes will kill the necrotic ring spot fungus spores.
The reason the beneficial microbes died in the first place was because too much water replaces air in the soil and without air the microbes die.
Important Note: The Necrotic Ring Spot fungus spores are present in all soils and are not spread via core aeration, lawn mowing or other lawn equipment. The fungus spores are everywhere; the only time they become a problem is when they are stimulated by severe over watering for a long period of time.
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Treatment of necrotic ring spot fungus seems simple; however getting the watering corrected can be complicated. Our recommendation is to contact Organo-Lawn in Boulder (303) 499-2000 or Fort Collins (970) 225-9425 and schedule a disease diagnosis with one of our professional lawn care technicians. Our state licensed lawn care technician will come up with a plan to correct the problems that are causing this fungus.
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Mild necrotic ring spot in a lawn in Boulder, Colorado.
Severe necrotic ring spot in a lawn in Fort Collins, Colorado.
Necrotic ring spot is always found in areas of the lawn that are severely over watered.
Necrotic ring spot is a clear sign of a dead soil.
This is a severe case of Necrotic Ring Spot in a lawn in Longmont, CO.
This is a very severe case of necrotic ring spot fungus that was found in a lawn in Lafayette, Colorado.
This is a very common photo of what necrotic ring spot looks like in a lawn in Loveland, Colorado.
This severe case of NRS in Fort Collins took 2 years to repair.
Necrotic ring spot takes anywhere from 1-2 years to cure.
To cure Necrotic Ring Spot we must stop what is causing the problem and not just treat the symptoms. Necrotic Ring Spot Fungus infestations in a lawn indicate that the lawn has been severely over watered for many months. Typically the most damaging lawn fungus problems like Necrotic Ring Spot are caused by severe over watering of a lawn. Water replaces air in the soil which creates an anaerobic environment where only certain types of soil microbes can survive. The most important step in curing the fungus problem is watering deeply and infrequently according to the 1-2-3-2-1 lawn watering technique.
The key to curing a Necrotic Ring Spot Lawn fungus problem is to create a living soil that is teeming with microbial activity. The more diverse and competitive the microbial population is in the soil the healthier the lawn will be. Important lawn care services to help cure Necrotic Ring Spot fungus without chemicals include Humate soil conditioner, lawn aeration, and proper lawn mowing. Never apply a lawn fungicide to a lawn that is infested with Necrotic Ring Spot because fungicides will kill both the damaging microbes and the beneficial microbes in the soil and this is the opposite approach to curing the lawn fungus problem.