1/12/2024 - By Mike Hess

Turfgrass diseases can return with a vengeance during the spring. There are many different turfgrass diseases you may encounter, and it is important to understand how to identify and treat each one. Continue reading for an overview of the most important turfgrass diseases you may see during the spring.

Let’s start with Pythium Root Rot:

Pythium Root Rot

Pythium root rot develops in poorly drained areas where standing water and soil saturation is a consistent problem. Some species of Pythium that can cause root rot can be active in the cooler weather of the winter and can specifically cause issues on warm-season turfgrasses. But, these issues are slow-growing through the harsh winter months and during spring rains and snow melts. Pythium root rot attacks the roots and rots from the ground up, appearing as patches of brown/tan and spreading outward.

A few products you can use to counter this disease are Harrell’s ProtectMAX® Cyazo, Title Phyte® Systemic Fungicide and Fluoxastrobin SC.

Pythium Blight

Pythium blight comes from an overabundance of water on turfgrass without proper drainage, causing the pathogen to grow, spread, and kill turf. The main difference between blight and root rot is where the disease occurs in the plant. Blight affects the foliar tissues and tends to move with surface water or mechanical traffic on the green during wet, rainy periods of weather that can be frequent in the winter months. Pythium blight can often be distinguished by a cottony, white aerial mycelium growth that can be evident during the morning dew or moisture.

Prevention of Pythium blight is largely similar to root rot – ProtectMAX® Cyazo is a top option for this disease both curatively and preventively. Title Phyte® Systemic Fungicide is also a great preventive solution for Pythium blight when used in a regular turf health and nutritional program and has been shown to perform as good or better than other Pythium standards.

Dollar Spot

This disease is primarily a monster on cool-season grasses but does cause some significant headaches during fall, winter, and spring on warm-season turf – especially seashore paspalum. The causal pathogen thrives in the humid, wet conditions that winter brings and really takes hold when soil conditions dry down.

Dollar spot is one of several diseases that thrive in low-nitrogen environments and can be especially devastating on turf that is malnourished and growing slowly. The disease starts as straw-colored lesions across the leaf blade and can lead to tip dieback and foliar collapse.

Spots are typically silver dollar-sized hence the name, and individual infection centers can often coalesce or merge together to form more irregular areas of dead turf. Dollar spot is spread not by spores but by cobweb-like mycelia and hyphal cells that can often be seen in early morning dew when conditions are right.

Many different fungicides can be used effectively to manage dollar spot. Preventive applications to manage populations and keep inoculum low throughout peak disease season are recommended. Curative applications can be effective, but turf recovery may be slow during winter months. The top options in the ProtectMAX® portfolio for dollar spot are Fluazinam, Chlorothalonil 6L, Propiconazole, Tebuconazole, and T-methyl.

Snow Mold

Snow mold is a cool-weather complex of diseases that develops primarily on cool-season grasses throughout the winter. However, most damage may not be noticed until snow melts in the early spring. The causal fungi mainly begin growing in the fall with the onset of cooler temperatures, but when the ground hasn’t completely frozen yet. Ample moisture, leaf debris, and slow-growing turfgrass create a breeding ground for snow molds.

The two types of snow mold are gray and pink, both caused by different fungal pathogens or complexes of pathogens. Snow mold will appear as gray or straw-colored, circular patches that vary in size. Gray snow mold appears as more of a gray/white color while pink snow mold appears as a white/pink color and can be significantly more deadly than gray when it appears.

Snow mold is best controlled preventatively in the late fall/early winter before permanent snowfall in the northern U.S. Applications of product mixtures that incorporate both systemic and contact fungicides have proven to be the most effective strategy at keeping snow mold at bay throughout the often long winters of rain and snow events.

Microdochium (Fusarium or Pink Snow Mold) Patch

In case it isn’t clear yet, an overabundance of water on turf without proper drainage or dispersal is the leading cause for disease coming out of winter, and Microdochium patch is no different. Michrodochium patch is a fungal pathogen blights leave and causes foliar blemishes and in severe cases, this disease can damage crowns and lead to complete death.

You can spot Microdochium patch by the copper/red circular spots that usually appear sporadically. Pink tones can sometimes be seen on the outer edges of the patches and a tan center is usually evident as the disease progresses.

Preventing and controlling Michrodochium patch patch can be done with numerous different fungicides. Harrell’s ProtectMAX® has several great solutions that offer different modes of action for controlling Microdochium patch and other key winter diseases. ProtectMAX® Fluoxastrobin SC, Azoxy, Propiconazole, and Chlorothalonil are all excellent choices.

It’s worth noting that ProtectMAX® Title Phyte® Systemic Fungicide is also now labeled (2EE) for the control of Microdochium patch, making it one of the only potassium phosphite fungicides labeled for this disease!

The Harrell's ProtectMAX® lineup has several excellent choices for controlling snow mold including Tebuconazole, Propiconazole, Chlorothalonil 6L, Fluoxastrobin SC, ProtectMAX® T-methyl, Fluazinam, and Azoxy. Our 1, 2, 3 snow mold program is a simple and affordable approach that has been tested and proven under some of the worst snow mold conditions at various university trials over the last several years.

Large Patch

This disease is one of the more unsightly in the turf world and it can affect many different species of warm-season turfgrass including Seashore Paspalum, centipedegrass, zoysia, St. Augustine, and even bermudagrass. Large patch starts to develop when things are a bit warmer in the spring and fall but can remain problematic throughout the winter, especially in more southern areas where soil temperatures may stay in the optimal zone for extended periods of time.

While symptoms may not appear until springtime when warm season turf may start to green up, the infection of this pathogen is most severe during cool, wet stretches of weather, which can be several months of winter in many areas. One thing we know about large patch is that it can be favored or made worse by excessive nitrogen fertility as well as in areas where soil moisture is excessive, and drainage is poor. You can spot large patch by the size of the patches which can often be up to 20 ft in diameter.

Symptoms will start as light brown, sunken areas which are often noticeably slow to recover when coming out of winter. Bright, sometimes even beautiful orange borders are often associated with this disease. In many cases, especially on highly susceptible species and cultivars, chemical intervention with fungicides is necessary. This is best done preventively in the early fall when soil temperatures drop consistently below 75 degrees F. Curative or winter treatments can be effective at halting the spread of the disease and aiding in spring green-up and recovery.

A couple of top fungicide options for large patch management are Tebuconazole, Fluoxastrobin SC, and Azoxy. These all do well on rhizoctonia disease, like large patch, and are all labeled for broad use on golf courses and in the case of Azoxy and Fluoxastrobin SC, home lawns as well.

Take-All Root Rot

Take-all root rot (TARR) poses a significant threat to warm-season turfgrass, causing widespread damage in regions with high temperatures. This soil-borne disease, caused by the fungus Gaeumannomyces graminis var. graminis, targets the roots, leading to a decline in turf health. Bermudagrass and St. Augustine are particularly susceptible to TARR.

Symptoms include yellowing, thinning, and wilting of the grass, often mistaken for other stress-related issues. Effective management involves promoting proper drainage, avoiding excessive thatch buildup, and employing preventive fungicide applications when soil temperatures are between 75 and 85 F. Regular monitoring and early intervention are crucial to mitigate the impact of take-all root rot and healthy stands of turf.

The top options for chemical intervention on TARR are the DMI and QoI chemistries. Products like ProtectMAX® Tebuconazole, ProtectMAX® Propiconazole, Fluoxastrobin SC, and Azoxy are all excellent options within the Harrell's portfolio. Pre-mix products that include multiple active ingredients within these classes have also been shown to be highly effective in programs. Because this is a root-associated disease, it’s important that fungicide applications get watered into the root zone with at least 1/8” post-application irrigation for optimal efficacy.

Leaf Spot – Warm and Cool Season

Leaf spot primarily affects bermudagrass during the winter months but the bipolaris, dreschslera, and other leaf spot pathogens tend to be widespread and indiscriminate to different turf species if conditions are right. This disease, like many of the others, prefers the cool, wet periods of fall and winter – especially long stretches of prolonged cloud cover and low sunlight. Leaf spot is most severe on slow-growing bermudagrass and starts primarily as a foliar infection. However, if left unchecked, the disease can move to the crowns and roots of the plant and cause much more significant damage.

Leaf spot spreads by spores or conidia and can spread with equipment or traffic. Symptoms start as water-soaked lesions on leaves but then progress to a more red/purple spotting of the turfgrass, sometimes in irregularly shaped patterns.

Management of leaf spot is very similar to dollar spot – minimize the time the leaves of the plant stay wet and improve air movement and sunlight if possible. Fungicides can often be necessary to manage outbreaks during cloudy/rainy periods – the top options include the QoI or strobilurins like ProtectMAX® Fluoxastrobin SC and ProtectMAX® Azoxy. ProtectMAX® Fluazinam is also a great multisite fungicide for leaf spot control and so is ProtectMAX® Chlorothalonil. Iprodione fungicides like 26GT or Interface® Stressgard®. Finally, mancozeb, such as the new ProtectMAX® Mancozeb, is another contact fungicide option that is great for leaf spot control.

Reach Out to Your Harrell’s Rep

Though there are many diseases to consider and prepare for, and there will always be some surprises, your Harrell's Rep and our team of agronomists are always here to help you prevent and control even the toughest turfgrass diseases. Reach out for more information or to get started.