Necrotic Ring Spot

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What is Necrotic Ring Spot?

  • A troublesome disease that infects lawns across CA
  • This disease is a parasitic form of plant life called fungi. Fungi live in the soil, thatch and dead leaves all year round. These fungi feed off the grass by drawing nutrients from it.
  • The disease spreads throughout the lawn in the form of spores. Wind, air, water and humans spread these spores. (spores are minute reproductive cells) The disease may occur from year to year depending on environmental and cultural conditions.
  • The disease may be caused by improper mowing and watering (refer to Weed Man  mowing and watering Fact Sheets for proper maintenance procedures). Discuss maintenance procedures with your Merced, CA Weed Man. If the lawn is put under stress the disease may occur.
  • The disease takes the form of perfectly shaped rings of yellowed out grass with healthy grass growing within the ring.
  • The grass blades appear straw yellow and die from the tip down.
  • As a result of its appearance, the disease is also referred to as "frog-eye".
  • The disease first attacks very early in the season and becomes especially visible during warm weather.
  • Necrotic Ring usually attacks sodded lawns but may also attack seeded lawns in both sun and shade.


Control

  • Necrotic Ring is a very difficult disease to control.
  • 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.
  • Overseed the area with a perennial ryegrass 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.
  • First and foremost, prevent your lawn from becoming droughty. A lawn requires 1 to 11/2 inches (3-4 cm) of water weekly. According to recent theories a lawn should receive light, frequent watering to control Necrotic Ring. 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 2 to 21/2 inches (5-6 cm) with a razor sharp blade.
Promoting a healthy lawn is the key to preventing Necrotic Ring from appearing. Have your Merced, CA 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. Weed Man Merced, CA strongly advises against the use of fungicides. Cultural control is superior and more effective.
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