In summer, your lawn serves as the welcome mat for pool parties, barbecues and Fourth of July celebrations.

But the seasonal heat can bring unwelcome, uninvited visitors, too: brown patch and other summer fungus lawn diseases. 

“I kind of jokingly tell people when you wake up in the morning and go out, and all you hear is the hum of you neighbor’s air conditioning, it’s already hot and humid, that’s perfect brown patch weather,” says Dennis Patton. He’s the ornamentals, turf and extension master gardeners agent for the Kansas State Extension in Johnson County, where brown patch is a common headache. 

If you’ve seen those tell-tale brown splotches or signs of other lawn diseases appearing across your yard, here’s how to stop brown patch in its tracks to get your home lawn back to its green best, and how to make fungicide a part of your lawn care arsenal so it doesn’t crop back up next year.

What Is Brown Patch 

Brown patch can invade rapidly, Patton says. You can come home at 5 in the afternoon, walk through a perfectly green front lawn and wake up to brown patch taking hold. 

That’s because while you were sleeping, a foliar disease started coloring your grass blades with brown leaf spots. 

It’s a summer disease, according to the Purdue University Extension. It survives the winter, dormant, in your lawn’s thatch. Then it turns active when dew periods exceed 10 hours and nighttime temperatures climb above 65.

Nighttime temperatures in the 70s mean perfect brown patch weather, Patton said. In the Kansas City area that usually translates to around mid to late June. 

Those temperatures are the perfect habitat for fungi like the one that causes brown patch. 

The big brown circle in your lawn is the disease spreading from grass blade to grass blade. They turn brown and brittle and create the spots that give brown patch its name.

Often, the perimeter of those spots is a gray-white band called a “smoke ring.” And sometimes the center of the circle will recover and start turning back to green. 

The effect will also depend on the type of grass you have. 

Cool-season grasses like tall fescue, perennial ryegrass, Kentucky bluegrass and bentgrass usually start showing symptoms in late spring. 

Warm-season species like St. Augustinegrass, Zoysiagrass, Bermudagrass and centipedegrass show symptoms twice during the year: early spring and late fall.

Other Common Summer Lawn Fungus Diseases

Large Patch is very similar to brown patch, caused by another strain of the Rhizoctonia solani fungus, the Clemson HGIC says. Affected grass will show the same symptoms — thinning patches of light brown grass. Symptoms will vary greatly depending on soil conditions and grass types.

Dollar spot is also caused by a fungal pathogen, presenting smaller brown spots.

Red thread
Red thread in a lawn. A largely cosmetic issue, red thread makes a lawn look ragged but rarely kills it.

Red thread thrives in cool, humid conditions such as the Pacific Northwest, mostly in nutrient-poor soils, according to a guide from manufacturer Scotts. You’ll know you’ve got it if you see thin red hairs or strands extending from the grass blades themselves.

Rust diseases appear as irregular light-green or yellow patches on the lawn, but looking closely will reveal orange-yellow rust spores on individual grass blades. Proper fertilization in the spring can help prevent it.

Summer patch usually appears between June and September, during periods of high humidity when daytime temperatures climb above 85, showing up in the form of irregular brown patches, rings and crescent shapes.

Preventing Brown Patch: Do the Basics

Good basic lawn care practices represent the best way to prevent brown patch and other lawn diseases.

“the best way to prevent brown patch or large patch in the home lawn is by following good lawn care practices,” Clemson HGIC says.

“Once you have an outbreak, you really can’t treat symptoms,” Patton says. What’s already been affected won’t be cured overnight. 

The best defense for your lawn, as with other pest and disease problems, is a good foundation, he said. “the best way to prevent brown patch or large patch in the home lawn is by following good lawn care practices,” according to Clemson’s guide.

Attention to cultural practices — taking proper care of your lawn with regular mowing, proper fertilizing, irrigation, air circulation and weed control — help prevent brown patch.

  • Avoid applying too much nitrogen fertilizer during the summer, which will both reduce disease pressure and improve fungicide performance. Excess nitrogen is the first item on the list. Avoid high rates on nitrogen fertilizer and avoid fast-release forms of nitrogen fertilizer can also keep fungus from spreading and the resulting turfgrass diseases.
  • Irrigate only when needed, and only about one inch of water per week, as the fungi spread fast when free moisture is available.
  • Remove clippings if the weather is warm and moist to avoid spreading the fungal disease to other parts of your lawn.
  • Keep lawns mowed on a regular basis to the proper height for your grass species. Lower than optimum mowing height can increase the severity of the disease
  • Provide good drainage for both surface and subsurface areas and correct soil compaction with core aeration.
  • Test your soil and make recommended adjustments. Apply lime according to test recommendations. A pH less than 6.0 may increase the severity of the disease.

Common mistakes

Some common mistakes that Patton sees are homeowners waiting too late to start getting a handle on their fungicide regimen. 

Homeowners may want to go ahead and get a preventative schedule of fungicide applications in place before the weather turns, he said, because it just takes one change in the weather and it’s too late. 

This is especially important with summer patch, Patton explained, a disease that attacks bluegrass more than fescue, but one that takes hold around May though doesn’t show symptoms until the hot weather stress kicks in around July.

Normal fungicide only lasts about three to four weeks, he added, depending on the product, so your fungicide application schedule could stretch into July or even August. It won’t be just a one-and-done.

Chemical control

“Unfortunately, a lot of times cultural practices fail,” Patton said. So if you have a history of brown patch, you’ll want to take some preventative measures.

A good strategy is to not wait for those weather conditions that favor brown patch, but to go ahead and treat your lawn with fungicide starting in the spring. 

And to start that regimen, you’ll need to know which chemical to pick, as not all fungicides are created equal. Some treat only certain pathogens, so make sure you’ve identified the fungus affecting your lawn before you head to the store. 

Patton warns that fungicides can be expensive, too, so expect a little sticker shock. 

And always be sure to read the labels to know it treats brown patch, and to see how it’s best applied. 

Fungicides won’t solve all your problems if you’re already seeing brown spots in your grass.

Regular application, though, will definitely improve how your lawn looks, Clemson says.

Which fungicides to pick? 

Clemson’s HGIC guide also provides a table of fungicide active ingredients and their effectiveness on brown patch fungus:

Some that the table lists as excellent are:

  • Pyraclostrobin in Pillar G Intrinsic Fungicide.
  • Fluoxastrobin in Disarm 0.25.
  • Azoxystrobin, both with and without Propicanazol.

It’s a good idea to go ahead and pick up two different fungicides. Alternating which ones you use can help prevent a buildup of resistance to any certain fungicide. 

Fungicide application

Make sure you read and follow all label instructions, Patton said. Pay particular attention to whether to apply them when grass blades are wet so the product will stick, or whether to apply a granular fungicide when dry and water it in. 

Many people don’t read the label, they just pour it in the hopper and away they go, he said, listing another of the mistakes he sees homeowners make. 

Fungicides, like fertilizers, can come in liquid and granular forms, but for amounts needed to cover your lawn, application intervals and other product-specific information, always read the packaging carefully. 

When in doubt, consult a local extension agent or other experts who can help point you in the right direction. 

The first step is to gauge the size of your lawn to see how much you’ll need.

Granular fungicides can be spread with a regular lawn spreader that’s also used for seeding and fertilizing. 

Check the back of the package to see how much to use and what you should set your spreader’s dial to for best results. 

Once the spreader is filled, Scotts recommends first spreading the fungicide around the perimeter of the lawn and then using rows to completely fill in the interior of the lawn the same way you would if you were walking behind your mower.

Apply regularly

Regular applications every 14-28 days will make sure your lawn is free of fungus and stays looking healthy and green through the summer. 

For liquid fungicides, it’s important to have the appropriate type of sprayer and to calibrate it for the product you’re using, explains the Michigan State University Extension.

Adjust the sprayer nozzle for best coverage and apply the fungicide in a sufficient volume of water to obtain thorough coverage, but not produce runoff. 

Spray at a sufficient height from the grass and in appropriate weather conditions to avoid drift, or the product flowing out to plants you’re not trying to treat. 

Spraying fungicides with a light breeze, between 2 and 6 mph, is better than spraying during completely still conditions, though, the MSU Extension explains. That’s because even without wind, there can be updrafts and eddies that cause the fungicide to fall off target. A little wind will give consistent movement to allow you to adjust accordingly. 

For safety, be sure to follow instructions on the label for that particular product when it comes to mixing, spraying and personal protective equipment. 

When you have a spot of brown patch, there’s also the question when applying fungicide of whether to spot-treat or spray the whole lawn. That depends on several factors, including the size of the lawn and if the homeowner is working to reduce chemical usage, Patton said. He recommends homeowners look at places in their yard where brown patch has historically been a problem and start there. 

Look at some of those locations and how you target your sprays and applications, and decide whether you need to treat the entire lawn. 

In any case, the best way to deal with brown patch is to get ahead of it. 

“The idea is to prevent the outbreak,” Patton said. Once you already see the damage, you’re working to prevent new outbreaks.

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