Controlling Ascochyta lawn blight

//Controlling Ascochyta lawn blight

Controlling Ascochyta lawn blight

Question: I have noticed a few spots in the grass on one side of my house? Could it be something in the fertilizer that will go away or might it be a fungus? 

Answer: We are seeing a whole lot of Ascochyta leaf blight all over Denver this year. The fungus is a leaf blight meaning it usually affects only the above ground growth, that being the visible grass blade or leaf. Its main point of entry is through injury from mowing with a dull blade along with the right weather patterns. This year,  our weather has paved the way for this fungus and anybody who has a dull mower blade or is over-watering is getting this fungus.

Good news is, it usually subsides on its own over time, so be patient while it is active. You can  read more about Ascochyta leaf blight at the Colorado State agricultural extension website. 

What to do about Ascochyta leaf blight

  1. Water no more than three days per week with two back-to-back cycles each watering day. This is called soak and cycle.  Fixed spray heads should be set to 18-20 minutes each day split into two 9-10 minute cycles. Rotary heads set to 38-40 minutes total per watering day split into two 18-19 min cycles.  Heavy shade areas may require these times to be reduced by 30%.
  2. Keep your mower blade sharp and wash mower wheels after each mowing. This prevents spread to other parts of lawn.
  3. Bag, do not mulch during active growth of fungus.
  4.  Aerate every spring.

We’d be glad to do a quote if you think there is something else going on with your lawn.


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Tree care updates and news items as well as best practices for canopy management to keep your trees and lawn sustainably growing. These posts represent a synthesis of our best practices and knowledge from serving thousands of customers.