Necrotic Ring Spot: The Zombie Apocalypse on Your Lawn


It’s September!  Fall has begun to unveil itself, and the crisp cooler temps have come to the Wonderful World of Weed Man.  Welcome back!  We appreciate you joining us for the next installment of “Your Lawn May Have the Sniffles!” series.  We will be discussing the various lawn diseases we find in the Treasure Valley at this time of the year.

We will begin with Necrotic Ring Spot.  Walmart has the Halloween gear out already, so it seems appropriate to start with this lawn fungus.  It sounds like something you would associate with a zombie.  After all, Necrotic Ring Spot is a parasitic form of plant life: fungus.  It is fitting.  If you see Necrotic Ring Spot on your lawn, the lawn zombie apocalypse has occurred.


Necrotic Ring Spot, or NRS, is a fungus that attacks cool-season grasses, particularly Kentucky bluegrass.  The fungus in question is a soil-borne fungus called Ophiosphaerella korrea.  That was a mouthful – we will just stick to NRS.  NRS is a pathogen that will infect and kill the crowns and roots of the grass.  Essentially the disease spreads throughout the lawn in the form of spores.  Wind, air, water, and animals (even humans) can spread these spores.  The spores, once transferred to the soil may lie dormant for years until the perfect storm of conditions appear for it to thrive.

So what are the ‘perfect storm’ of conditions needed to produce this parasitic lawn disease?  I’m glad you asked!  NRS can be caused by improper mowing and watering.  Because Necrotic Ring Spot is a root disease, it is important to have a healthy and thriving root system for your lawn.  When you continually mow below a recommended mowing height your grass roots will become stunted and unhealthy.  NRS finds it easier to attack the root system.

Fungi happen to like water as well.  At a certain point, if you are watering too much, you stop watering the way the lawn needs watered, and start watering the way a fungus needs watered.   Are you using cultural practices that create favorable conditions for your lawn and unfavorable conditions for lawn disease?  Or is your lawn seeing the opposite?  If you are unsure on recommended practices, you can check out our articles on mowing and watering.

NRS can also be a brought on by compact, high nitrogen soils as well.  This is one of the myriad of reasons we choose to use a slow release granular fertilizer, and recommend annual aeration.

Warning:  Rabbit Trail! – Slow release granular fertilizers will slowly meter out small amounts of nitrogen over a long necrotic-ringspotsperiod of time.  They generally are not real heavy in nitrogen either.  Some fertilizer products might be as high as 48% nitrogen, and a quick release fertilizer as well.  That is a lot of nitrogen released in a short period of time.  Will every lawn treated with a quick release fertilizer with heavy levels of nitrogen all get NRS?  No, however, they can be more susceptible to the disease if the other conditions needed are met as well.

During cool, wet weather circular patches of infected turf will develop.  Though the disease develops in cool weather, the summer heat and drought stress can make the symptoms much more noticeable.  You will start to see the ‘rings’ stand out more and even spread in diameter up to 2-3 ft.  The rings start out light green, then turn yellow.  Over time, if the underlying causes are not addressed, the disease will progress.  The yellowing rings will turn brown or black and leave a sunken bare spot eventually.  The interior green area most times is the lawns attempt at recolonizing the infected areas, but sometimes the internal area will die off as well.

It can get pretty gnarly, and not in a good way. 


If you happen to get NRS in your lawn, here are some great management practices to try:

  • First and foremost, fix the underlying cause of the disease, not the symptoms.  NRS is only found in moist or wet areas with poor drainage.
  • Prevent your lawn from becoming droughty. A lawn requires 1 to 11/2 inches (3-4 cm) of water weekly. Traditionally you should water deep and infrequently – but if your soil is very compact, your lawn will not drain very well.  According to recent theories a lawn should receive light, frequent watering to control Necrotic Ring. Do this until you can aerate your soil which will improve the drainage.  WATER SHOULD NOT BE APPLIED AT NIGHT. Water laying on grass plants overnight encourages disease to spread in the water droplets.
  • Mow your lawn frequently to a desirable height of 3 to 4 inches with a razor sharp blade.  This will help strengthen the root system to help fight off the infection.
  • When the disease first occurs rings may be dug out with a shovel to rid the soil of the disease spores. Remove the grass and soil to a depth of 6 to 8 inches (15-20 cm). Wash the shovel before using it again.
  • Rake the area open; fill in the hole with some potting soil to create a seed bed.
  • Over-seed the area with a perennial rye grass seed mixture and rake the area lightly. Step on the area lightly to ensure good seed-soil contact. Keep the seed bed moist for at least 21 days.
  • If the area becomes so infected that removing the rings becomes unreasonable, correct maintenance practices must be used to control the problem.
  • Use fertilizers with moderate to high amounts of phosphorous and potash
  • Maintain adequate nitrogen levels using a balanced fertility program
  • Reduce soil compaction with an aeration

If you think you are having disease issues in your lawn, give us a call!

Promoting a healthy lawn is the key to preventing Necrotic Ring from appearing. Have your Weed Man fertilize your lawn and advise you on correct maintenance practices to ensure a healthy disease free lawn. Fungicides are not an economical form of control. They are regarded only as a temporary control.

Fungicides only control Necrotic Ring until heavy rains wash the fungicide off the grass blade. Fungicide applications would have to be done every 10-14 days all season long and are very expensive. The Weed Man strongly advises against the use of fungicides. Cultural control is superior and more effective, and cheaper!

If you think you are having disease issues in your lawn, give us a call!  208-888-9911 #wecareforyourlawn





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