Dollar Spot Fungus in Missouri Lawns: Identification, Treatment, and Prevention

If your St. Charles County lawn has small, straw-colored patches showing up this July — especially after warm days and humid nights — you are likely looking at dollar spot fungus. It is one of the most common lawn diseases in Missouri, and it shows up from April all the way through November here. The good news: it rarely kills the grass outright, and a few simple changes to how you water and fertilize can usually stop it from spreading.

What Is Dollar Spot Fungus?

Dollar spot is caused by the fungus Clarireedia jacksonii (formerly classified as Sclerotinia homoeocarpa). It attacks the leaves of the grass rather than the roots or crown, which means the grass can recover if you catch it early.

In Missouri, dollar spot primarily affects tall fescue, Kentucky bluegrass, and perennial ryegrass — which covers most lawns in St. Charles County. It is most active when daytime temperatures sit between 60 and 90 degrees, nights are cool enough for heavy dew, and the grass is already under some kind of stress.

According to University of Missouri Extension, dollar spot can appear from mid-spring through late fall here, with the worst outbreaks happening during stretches of warm, humid weather followed by cool, dewy nights. That describes a lot of late July and August in this part of Missouri.

How to Identify Dollar Spot

Dollar spot gets its name from the size of the patches — roughly the size of a silver dollar. But on a home lawn with taller grass, the spots can range anywhere from an inch to six inches across.

Here is what to look for:

• Small, round, straw-colored patches. They look bleached or tan, not dark brown. The patches may grow together into larger irregular areas if the fungus spreads.
• Lesions on individual grass blades. This is the telltale sign. Look closely at the green grass around the edges of a patch. You will see tan or bleached spots on the leaves, often with a reddish-brown border. Some lesions look like an hourglass — narrow in the middle, wider at both ends.
• White, cobweb-like growth early in the morning. If you check the lawn at sunrise when the dew is still on it, you might see fine white fungal threads on the affected grass blades. This disappears as the grass dries.
• The leaf tip may stay green. Unlike some other diseases that kill the whole blade, dollar spot often leaves the tip of the leaf green while the lesion runs across the middle.

Dollar Spot vs Brown Patch

This is the most common confusion. Brown patch also shows up in summer and creates circular brown areas. The main differences:

Sign	Dollar Spot	Brown Patch
Patch size	1–6 inches (silver-dollar sized)	Several inches to several feet
Lesion shape	Hourglass pattern with reddish border	Dark, water-soaked edges
Active temperature	60–90°F	75–95°F
Time of year	April–November	Mid-summer peak
Grasses most affected	Fescue, bluegrass, ryegrass, bentgrass	All cool-season grasses

If the patches in your yard are the size of a dinner plate or larger, you are more likely dealing with brown patch. We have a full guide on brown patch identification and treatment that covers that separately.

Why St. Charles County Lawns Get Dollar Spot in July

Several factors make our area a prime spot for dollar spot during mid-to-late summer:

Clay soil. Most of St. Charles County sits on clay. Clay holds moisture longer than loamy or sandy soil, which means the grass stays damp longer after rain or watering. Dollar spot needs leaf moisture to infect the grass.

Tall fescue. The most common lawn grass in our area is tall fescue, and while it handles heat better than some other cool-season grasses, it is still susceptible to dollar spot — especially when it is stressed.

Low nitrogen. Dollar spot thrives when the grass is nitrogen-deficient. If you skipped a summer fertilization or went too light, the slow-growing grass gives the fungus an opening. At the same time, too much nitrogen can cause other problems. It is a balancing act.

Heavy dew. July nights in St. Charles County cool down just enough for heavy dew formation. That overnight moisture sitting on the grass blades for 10–12 hours creates ideal conditions for the fungus to spread.

How to Treat Dollar Spot Without Chemicals

For mild to moderate cases, you can often stop dollar spot from spreading with better lawn care practices alone. Here is what works:

Water in the Morning

This is the single most effective change you can make. Watering in the evening keeps the grass wet all night — perfect conditions for dollar spot to spread. Water early in the morning instead, so the sun can dry the grass during the day. Deep, infrequent watering (about one inch per week) is better than light daily sprinkling.

Our Missouri lawn watering schedule guide has more detail on how much and how often.

Keep Nitrogen Levels Right

Dollar spot is more severe when the lawn is low on nitrogen. A light application of a balanced fertilizer can help the grass outgrow the infection. But do not overdo it — excessive nitrogen in summer can make the grass lush and vulnerable to other diseases.

If you have not done a soil test lately, it is worth knowing exactly what your lawn needs. We have a guide on soil testing for Missouri lawns that walks through the process.

Mow at the Right Height

Mowing too short stresses tall fescue, and stressed grass is more vulnerable to dollar spot. Keep your mower blades at 3–4 inches during summer. That taller grass develops deeper roots and handles disease pressure better.

For the full breakdown by grass type, see our lawn mowing height guide.

Remove Excess Thatch

Thatch thicker than half an inch traps moisture near the grass blades and gives fungus a place to live. If you have not dethatched or aerated in a while, fall is a good time to tackle it. Aeration also helps with drainage and root health, both of which reduce disease pressure.

When to Use Fungicides

If the patches keep spreading despite better watering and fertilization, or if the outbreak is severe enough that large areas of the lawn look thin, fungicides may be needed.

Dollar spot can develop resistance to certain fungicides over time, especially if the same product is used repeatedly. Products containing chlorothalonil, propiconazole, or myclobutanil are commonly used for dollar spot control. But timing matters — fungicides work best when applied preventively or at the very first sign of infection.

For most homeowners, the practical choice comes down to this: if cultural fixes (watering, mowing, fertilizing) are not stopping it within a couple of weeks, bring in someone who has commercial-grade products and knows how to rotate them to avoid resistance.

Can Dollar Spot Kill Your Lawn?

In most cases, no. Dollar spot attacks the leaves, not the roots. The grass usually recovers once the weather changes or you correct the underlying issue. But if it goes untreated for weeks and the outbreak is severe, the thinning grass can open the lawn up to weeds and other problems.

Fall is the natural recovery period for cool-season grass in Missouri. If you keep the lawn healthy through the rest of summer — proper watering, correct mowing height, balanced nutrition — the grass will fill back in when cooler weather arrives.

When to Call a Professional

If you have tried adjusting your watering and mowing and the patches are still spreading, or if you are not sure whether you are looking at dollar spot, brown patch, or something else entirely, it is worth having someone look at it in person. Lawn diseases are easy to misidentify, and treating the wrong thing wastes time and money.

The providers on our network know St. Charles County lawns — the clay soil, the tall fescue, the summer humidity patterns. They can identify dollar spot quickly and apply the right treatment if it is needed.

Get connected with a local lawn care provider who can take a look and put together a plan for your yard.

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Jerry Bennes is the founder of Midwest Lawn Care, a referral platform connecting St. Charles County homeowners with trusted local lawn care providers. Last updated: July 25, 2026.