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Pythium Blight: Should You Be Concerned?

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Grass growing from seed stage Roger Grose, Franchise Owner in Marietta, Ohio sent me this picture of Pythium Blight that developed on newly seeded Tall Fescue turf. According to the homeowner, many of these spots appeared overnight on the lawn.

Pythium Blight Marietta, Ohio

There are several different strains of Pythium Blight that can occur on turfgrass. It grows mostly on golf course greens and tees and is not a disease we see in most home lawns. It can be a common problem on newly seeded turf, especially when too much seed is planted in too small of an area. If all the seed germinates at the same time, competition for space and resources weakens the plants. This allows seedling blights like Pythium, to infect and damage or even kill the new seedlings. Pythium Blight is a member of the “water molds,” it is sometimes referred to as “cottony blight.” This disease is most abundant when there is a lot of moisture on the plants for more than 12 hours, especially after a night of rain or heavy dew in the morning. Air temperature has a lot to do with its development as well. It is especially severe when day time temperatures exceed 82 degrees and evening temperatures stay above 68 degrees.

Two primary causes of seedling failure:

  1. Lack of moisture to the seed bed
  2. Spreading too much seed in too small of an area
If you are reseeding with Tall Fescue, the average amount of seed you need to sow in an existing lawn is 5 pounds per 1,000 square feet. If you are seeding a small area, such as a 2 foot by 3 foot area, you only need a tiny amount, about 2 to 3 ounces of seed. There are about 230,000 seeds in a pound of Tall Fescue, so 2 ounces is still close to 29,000 individual seeds. Fall is the time that many people are overseeding cool-season turf. If you are seeding small spots, don’t use too much seed. In the case of the homeowner in Ohio, if the conditions are right, diseases can and will develop. There are disease control treatments available to control Pythium Blight to keep it from getting any worse.  If you plan to seed your lawn this fall, I encourage you to contact your neighborhood lawn care professional at Spring-Green and inquire about our seeding services.