Summer Lawn Woes: Reasons Why Tall Fescue Grass Declines at This Time of Year

It seems like a while ago, but it was only 5 weeks ago that we were experiencing a fairly gentle start to summer. We even had a few days in June with highs in the 60’s and it made for pretty easy lawn growing weather.

Flip the calendar to mid-July and it has been a different story. All of us knew summer would arrive eventually, and now we are dealing with high temperature and high humidity conditions very typical of mid-summer in Maryland.

For those with warm-season grass lawns, like zoysiagrass, the lawn should be thriving, as these grasses enjoy the heat. For most homeowners who have tall fescue, summer is always a challenge to minimize the heat stress and disease pressure on the lawn. Tall fescue is best adapted to growth when low temperatures are in the 50’s and highs are in the 70’s to around 80. Through July, we have had many days near or above 90 and many nights where the temperature didn’t drop below 70.

drought stress symptoms on tall fescue lawn
Drought stress symptoms appearing in tall fescue lawn. Drought-stressed plants exhibit a purple to grayish hue. Photo: Geoff Rinehart

There are a few different reasons your tall fescue lawn may be going brown or declining this time of year—the most common are related to drought stress, soils that are too wet, or brown patch disease. Typically, growth slows down a bit in mid-summer anyway as part of a grass’s natural growth cycle as it uses more carbohydrates (food reserves) than it makes. So when the grass does experience stress or disease it is slower to recover. Drought-stressed plants exhibit a purple to grayish hue, a narrower or “curled up” leaf blade, and footprints are visible for several minutes after walking across a drought-stressed area.

Brown patch has been in full force on a lot of lawns throughout the region. Typically this fungus will cause medium-large, tan-brown patches, and sometimes you might even see some “cobwebby” fungal strands in the morning dew. Individual leaves infected with brown patch will have tan lesions with a dark brown border when the fungus is active, fading to just brown after the damage is done.

brown patch symptoms in lawn
Brown patch symptoms in a lawn. Photo: Geoff Rinehart

There are homeowner-available fungicides that can be applied to treat this disease; the most common active ingredients are chlorothalonil, propiconazole, and azoxystrobin. While best applied preventatively (before the weather conditions for the disease occurs), they can be applied curatively to “arrest” the disease progression. Keep in mind that applying a fungicide will not lead to “automatic” recovery. Properly applied, it will arrest the fungus, but if it is hot and the damage is already done, it will take some time for the affected area to produce new disease-free leaves to replace the old damaged ones. Always follow label directions for any pesticide product.

Thinking ahead now is a great time to plan a strategy for lawn rejuvenation around early September. You can read my previous blog post from about September lawn renovation here.

By Geoff Rinehart, Lecturer, Turfgrass Management, Institute of Applied Agriculture, University of Maryland

One thought on “Summer Lawn Woes: Reasons Why Tall Fescue Grass Declines at This Time of Year

  1. Landscaper August 2, 2019 / 4:39 am

    Summer certainly can be a difficult time for some plants in the garden. I am based up in Connecticut and it can sometimes be difficult to manage customers’ expectations when plants are struggling in the heat, particularly as many don’t want to use a fungicide on their lawns if possible. Summer can be an amazing time for plants to thrive in the garden, but for others it is definitely a relief when fall comes. I love your site, thanks for the work you put into it.

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