7 Summer Lawn Diseases to Watch For

A beautiful green lawn is one of the greatest joys of summer gardening. And nothing ruins a beautiful summer lawn faster than disease. Brown patches or strange spots seem to appear overnight and become such an eyesore that they’re hard to ignore.

Many lawn diseases thrive with the combination of heat, humidity, and moisture stress that defines most summer growing conditions. Catching diseases in their initial stages makes treatment far more effective and prevents widespread damage. Unfortunately, some are incredibly difficult to deal with once they spread.

Many lawn diseases look similar at first glance, but each has distinctive characteristics that help with proper diagnosis. Here are the seven most common summer lawn diseases and what to do about them to keep your lawn looking fresh.

Dollar Spot

Up first and incredibly common, this disease gets its name from the dollar-sized spots it creates on lawns. Individual spots start a few inches across, making them harder to see. But these spots can merge into larger irregular patches over time if left untreated.

Dollar spot loves stressed lawns, particularly those lacking nitrogen or suffering from drought conditions. The disease typically appears during warm, humid weather when nighttime temperatures are slightly cooler.

Look for circular spots with bleached centers in a straw color. Individual grass blades show distinctive lesions that look bleached with red borders. You might notice white, cobweb-like fungal growth on affected areas if your area has high humidity. Cool-season grasses are susceptible, though Bermuda can also be affected.

Although fungicides can be used in extreme cases, management mostly involves adjusting your growing conditions to prevent spread. Increase nitrogen fertility, improve drainage, and ensure adequate watering without keeping grass wet overnight. This disease is quite aggressive, so keep up with management even if signs are limited.

Brown Patch

Brown patch creates the large, irregular dead areas that panic most homeowners. This is another aggressive disease that can destroy entire lawns in just a few days when conditions are right.

The disease thrives when daytime temperatures exceed 80°F (29°C) and nighttime temperatures stay above 70°F (21°C) with high humidity. Overwatering and excessive nitrogen from incorrect feeding also make lawns more susceptible.

Like other summer lawn diseases, brown patch starts as small circular spots that expand into large, irregular patches. The centers become lighter while the outer edges continue spreading, creating a distinctive border pattern.

Tall fescue and perennial ryegrass are particularly vulnerable. The disease can spread in so many ways (lawn care equipment, foot traffic, or water) that it’s easy to accidentally become a spreading vector yourself.  Avoid walking on infected areas when the grass is wet if you spot any of these signs.

As it is so aggressive and difficult to tackle, prevention works better than treatment for this summer lawn disease. Don’t overwater, avoid late watering, improve air circulation, and never overfeed, especially in summer. Fungicides can slow and manage active infections, but won’t repair existing damage, so prevention is your best option.

Leaf Spot

A common issue in the garden, leaf spot diseases create (you guessed it) spots on individual grass blades that eventually weaken the entire lawn. It’s not caused by one species but rather several related fungi that cause similar symptoms.

Initial symptoms appear as small, dark spots on grass blades that gradually enlarge and develop light brown centers. Eventually, blades turn yellow and die, creating an overall thinning effect rather than distinct dead patches like the previous two entries.

Leaf spot problems often develop when there are warm temperatures with extended moisture from rain, overwatering, or heavy dew. The disease is particularly problematic on Kentucky bluegrass and tall fescue.

Keeping your grass healthy with correct watering and feeding is the best defence against this summer lawn disease. Remove dense areas of growth that hold moisture and create favorable disease conditions.

Red Thread

Red thread creates pinkish-red threads visible on affected grass that make this summer lawn disease one of the easiest to identify. It typically occurs during cool, moist conditions in late spring and early summer.

To identify this disease, look for circular patches of straw-colored grass with pink or red thread-like structures extending from dead leaf tips. These threads are actually fungal structures that give the disease its name and distinctive appearance.

Red thread primarily affects areas with low nitrogen fertility. The disease rarely kills grass but creates weak areas that invite weed invasion. Cooler summer temperatures combined with high humidity create ideal conditions for the development of this summer lawn disease.

Since nitrogen is one of the major concerns, improving nitrogen fertility often resolves red thread problems without additional treatment. It does take a few weeks, so don’t be surprised if it doesn’t disappear immediately. But over time, the patches will slowly subside.

Rust

Gardeners will be familiar with rust, which causes grass blades to develop orange or reddish spores that are incredibly easy to spot. Since it looks nothing like other summer lawn diseases, you should have no trouble diagnosing this issue.

Individual blades develop reddish-brown spots that eventually rupture to release orange spores. Heavily infected grass takes on an overall orange appearance, quite an alarming sight. Rust typically develops during warm, humid conditions on slow-growing, stressed grass. Kentucky bluegrass and perennial ryegrass are most commonly affected, particularly during late summer when growth slows.

The disease spreads through airborne spores and by mechanical transfer on equipment or foot traffic. Morning dew and extended moisture periods also promote spore production and infection. Keep this in mind during management to avoid spreading the issue further.

Increasing nitrogen fertility and proper watering promote vigorous growth. This often competes with disease development, slowing the spread and preventing further problems. Mowing regularly also removes infected leaf tips and reduces spore production, although you’ll need to clean your tools often to avoid spreading the issue.

Summer Patch

Summer patch, like brown patch, creates distinctive dead areas that start small but can expand to several feet across. The disease gets its name from timing, as symptoms typically appear during the hottest part of summer. This isn’t as common in home gardens compared to larger areas like golf courses, but it’s still a summer lawn disease to keep an eye out for.

The disease primarily affects Kentucky bluegrass and fescue, particularly in compacted soils or areas with poor drainage. The patches can become sunken, easier to see if you haven’t mowed for a while.

Summer patch is actually a root disease that develops during cool, moist spring conditions but doesn’t show symptoms until summer heat stresses the already-damaged root systems. This delayed symptom development creates problems in prevention and management, so it’s a little tougher to control.

Improve drainage, reduce thatch, lower soil pH if necessary, and avoid overwatering. The disease often indicates underlying soil problems that need correction.

Fairy Ring

Fairy rings create distinctive circular patterns of dark green grass, mushrooms, or dead zones that expand outward each year. It’s common in cooler weather but can also pop up as a summer lawn disease, depending on your climate and the type.

Three types of fairy rings occur in lawns. Type 1 produces dead grass in circular patterns, Type 2 creates rings of dark green, rapidly growing grass, and Type 3 produces mushroom rings without affecting grass growth. Types 1 and 2 are the ones to watch for in summer.