Pythium Blight on New Grass

robieusa(5)August 3, 2014

Hi. I planted an area of new seed this year, and it was doing very well. Until this weekend.

It is classic pythium blight (grease spot). It is my fault for over-seeding and over-watering during rainy/humid season. I noticed it yesterday, and it spread like wildfire.

I treated today with chlorothalonil, Daconil, a fungicide purported to kill pythium.

Wondering how long it takes for the fungicide to take effect? That is, when should I expect to see the grass stop dying and know it worked?

And... I am not going to over water that patch any more this year. Lesson learned.

Thanks for any experienced info.

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dchall_san_antonio(8 San Antonio)

Where do you live?
What kind of grass do you have?
When did you plant it?
Did you read the label on the fungicide where it says not to apply when temps are going to be 90 degrees or above? What they meant to say was 85 degrees or above.

I would give this a week or so to see if you're going to have any grass left at all. Then evaluate for any remaining disease.

I would have used ordinary corn meal on it, especially in the summer. Corn meal works biologically by attracting a different fungus which is predatory on the disease fungus.

    Bookmark   August 6, 2014 at 1:41PM
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In order of your questions / comments:

- I live in Lexington, KY
- I planted a blend of ryes, fescue. bluegrass
- Planted maybe a month ago, or slightly more
- It has been unseasonably cool here for the past several weeks. Many days with highs in the 70s.
- Today is the hottest it has been for weeks, hitting 84F. So, I do not worry about the efficacy of the fungicide at those temps.

The Daconil had an immediate effect. The pythium stopped charging across the grass within a day or two. We are expecting wet weather for several days; I will see how it hold under days of rain. I will likely re-apply to be safe after the rain leaves us.

I like the suggestion of corn meal, and would use that as a preventative in the future. I was just a bit panicked that my lush new grass was succombing to slimey death and pulled out the big gun.

Thanks for your questions and your suggestion.

    Bookmark   August 6, 2014 at 5:35PM
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dchall_san_antonio(8 San Antonio)

You may be the luckiest accidental gardener in Kentucky. You planted at the worst time of year to plant new seed; however, you got lucky with the weather.

Your mix of three grasses might be your salvation. My preference of the three is KBG because it will repair itself. In this case it might repair the entire lawn for you.

Since you have applied Daconil this year, corn meal would not have any anti-fungal effect. Next year it should, though. I would not reapply a chemical fungicide. Once should do it. The health of your soil absolutely relies on tens of thousands of beneficial fungi species that live in the soil. When you spray fungicide, many of those species must find their way back into your environment. When you respray, it just sets the health of your soil back that much further. That's why I always look for an organic approach first.

    Bookmark   August 6, 2014 at 10:19PM
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In my own tepid defence... it was not as accidental as a known risk-taking venture that I lucked out on. I saw the long term weather forecast and decided I had a good window to plant, and jumped on it. If not for the polar vortex, I would not have any new grass to write about.

The patch I planted is a relatively small area that was destroyed during some recent construction. Maybe 300 SF total. I needed to get something growing quick before a big upcoming fundraiser. The rest of the yard -- and old mix of this and that, with plenty of clover -- is doing just fine. I will mix clover into the new area this fall for consistency and preference.

Organic cures are definitely preferred. But, I am glad I shot only the small area with fungicide and had such immediate results.

The big lesson for me was about watering. If I had shown more restraint with the water, I likely would have avoided the blight altogether. I have not watered since Saturday, and the grass is doing just fine. Rain is forecast for later today. Nature will take care of the rest.

It's all about balance.

    Bookmark   August 7, 2014 at 6:36AM
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