What are the most common lawn diseases and how can you treat them? Here’s what to know

Picture of Paul Cappiello Ph.D.

Paul Cappiello Ph.D.

Yew Dell Botanical Gardens Executive Director

Lawns are interesting things. Not commonplace until the middle part of the 20th century – at least not commonplace in the way we know them today – what seems from a distance as a pretty mundane and uniform thing, can take many different forms. 

Viewed from a distance (both literally and figuratively) many people know a lawn as the flat, green space over which one pushes a mower once a week between tee time and halftime. Of course, to some the lawn is a form of religion with multiple commandments that, if followed precisely, yield that emerald-colored land of milk and honey. To others, the lawn is more of an expression of botanical bacchanalia that resides just this side of anarchy. To each their own. . .

Regardless of your preferred lawn style, we all have a vision in our heads of how we expect the lawn to look by mid-summer. And so it is concerning when you pull in the driveway one afternoon and notice that something looks amiss. You might not be able to identify it right away but there’s definitely something not as it should be. So, following are a few mid-summer lawn problems to look for and how to deal with them.

Lawn Diseases

Yellow spots, sudden die-off of isolated patches of the lawn . . . there’s a long list of potential disease-causing culprits that can plague the summer lawn. The good news is that most of them can be managed with a change of cultural practices – water deeply, not frequently, raise your mowing height (4” is my preferred mark), rake out thatch (that layer of accumulated dead grass that hugs the ground) and don’t overfertilize, particularly with nitrogen. And here’s a good pro tip – turn over that mower and clean out all the built-up debris. The cleaner the underside of the mower deck, the more efficient it will be at cutting cleanly – leading to less potential for disease trouble.

If you do suspect a disease and are considering a chemical treatment, it’s best to have a professional make a diagnosis. Your county cooperative extension office is a great place to start and depending on pathogen and/or extent of the impact, can recommend cultural or chemical control.


Broadleaf Bonanza

If you’re one of those folks who wants that perfect, barefoot walkin’ lawn, it can be concerning when you go for your evening stroll in the grass and find yourself trodding over a hodgepodge of plantains and thistles. Most pre-emergent herbicides have a maximum of about 90 days of control so even if you did your spring thing, this time of year you might find some of those broadleaf weeds moving back in.

The easiest fix to the mid-summer broadleaf invasion is not to reach for the spray bottle, but to set your mower higher. Mowing at  a 4-inch height can shift the competitive advantage in the direction of the grass and allow it to outcompete the broadleaf weeds without having you resort to chemical sprays. And don’t fret over a little clover in the lawn. Sure, it’s not grass. It’s a broadleaf plant. But it stays short, it stays green, and it can actually help provide a bit of nitrogen to the soil.


The Nasty Nut Sedge

I receive tons of phone calls and emails this time of year from people worried about a “yellowish-green, grassy looking thing” that seems to be invading the lawn. The usual culprit . . . yellow nutsedge (Cyperus esculentus). 

This beast of an invader seems to grow twice the rate of lawn grasses, yielding a shaggy looking lawn just a few days after mowing. And unfortunately, it’s a bit of a bear to control. 

Yellow nutsedge is a plant that loves damp soils. So if you have it showing up in your lawn, the best path is figuring out how to reduce water build up in that area. This might mean redirecting gutter downspouts, putting in subsurface drain lines to move the water away from the area or even some regrading. Unfortunately, not all those things are easy to accomplish. Selective herbicides are available, but I’ve found this approach to have limited success. Not many good options with this one . . .


Thinning Grass in Shade

Some places are just hard to grow quality turf. Trying to grow a perfect lawn under the dense shade of trees with aggressive roots – maples, for instance – can be maddening. The heavy shade reduces turf plant vigor, and the aggressive roots make it hard to keep sufficient moisture in the soil. 

One solution for these tough shady spots is to have an arborist thin the canopy of the shade tree to let in more sunlight and give the grass a fighting chance. Of course the other option is to simply remove the grass (or what’s left of it) from that spot and plant a shade-loving groundcover like pachysandra (Pachysandra terminalis) or native ginger (Asarum canadense).

The White Striped Lawn

Most lawns show patterns left by both mower wheels and the various directions the mower travels. The pattern shows up as alternating bands of darker and lighter green. But when those lighter green bits start to look white, you’ve got a problem. 

The whitish looking bands in the lawn result from having a dull mower blade. A sharp blade slices cleanly through the grass while a dull blade tears and leaves a jagged edge that goes off color quickly after mowing. This leaves the lawn with a white cast. 

Fortunately, this one’s a quick fix. Simply give the blade a quick sharpening (or have someone do it for you if that’s more your style) and you’ll be back in business in no time. Not sure if you need your blade sharpened? Here’s a simple rule of thumb. If you can’t remember the last time your blade was sharpened . . . it’s been way, way too long!

This article was originally submitted to the Courier Journal on July 18, 2023.

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