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How to Treat Gray Leaf Spot

If your lawn has suddenly lost its vibrancy, it’s likely because your turf is under attack by a fungal disease. Among the many lawn diseases that homeowners should be aware of is gray leaf spot (Pyricularia grisea). This condition is known for the oblong spots it creates on the leaves of grass. 

When not attended to, this disease can kill entire lawns, particularly newly-established turfgrasses. In order to effectively get rid of gray leaf spot, it’s important to understand the symptoms of this fungal disease. Today, we’ll explain how to identify gray leaf spot and properly treat it with fungicide.

What does gray leaf spot look like?

The first and most diagnostic disease symptom is a round or oval spot that appears on the surface of a grass blade. This spot is typically tan in color with a dark brown border. 

When exposed to high humidity or wet conditions, the oblong leaf spots will become gray and fuzzy with increased sporulation growth. This disease will soon expand across the entire grass leaf, resulting in plant death.

What causes gray leaf spot?

Gray leaf spot is caused by Pyricularia grisea, which readily infects and kills the leaf blades in turf. 

A factor that influences the occurrence of gray leaf spot is temperature. Generally, this disease requires temperatures between 70 degrees Fahrenheit and 95 degrees Fahrenheit in order to infect plants. 

Additionally, the fungus requires a minimum of 14 hours of continuous leaf wetness. When leaf wetness is increased by improper irrigation, cloud cover, shade or excessive rainfall, the condition worsens.

When does gray leaf spot appear in lawns?

Gray leaf spot is commonly found in newly-established lawns, typically during their first year of establishment. The disease is most severe during this period and can damage entire lawns.

 As the turf matures, the disease will gradually become less damaging but may still present certain issues. For this reason, it is important to properly manage gray leaf spot with cultural or chemical control.

Depending on the type of turf you have, gray leaf spot may occur anytime in late spring through early fall. In St. Augustine turfs, gray leaf spot is most active from June through August. 

As for perennial ryegrass and tall fescue, gray leaf spot is mainly active from late July through September.

What types of grass does gray leaf spot affect?

Although gray leaf spot generally occurs on St. Augustine grass, it may also be occasionally spotted on tall fescue, perennial ryegrass, bermuda grass and centipede grass.

The severity of this disease often depends on the type of grass it affects. For instance, St. Augustine grass is more resistant to gray leaf spot fungus, while perennial ryegrass is rapidly affected by the disease. In fact, gray leaf spot on St. Augustine grass rarely results in significant damage when given proper treatment. 

Perennial ryegrass, however, quickly suffers from this disease and may die in only a few days. Other grass types, such as tall fescue have an intermediate level of resistance to the disease.

How do I treat gray leaf spot?

Cultural Control of Gray Leaf Spot

There are many preventive measures homeowners may take to hinder the development of gray leaf spot. Reducing the thatch layer, using correct fertilizer and mowing at the proper height can greatly reduce the chance of gray leaf spot occurring. 

Additionally, irrigating the lawn deeply but infrequently can prevent continuous leaf wetness, the ideal environment for gray leaf spot. 

If gray leaf spot is already present in your lawn, these cultural control techniques may successfully get rid of the disease. In most cases, however, fungicide is the best option for controlling gray leaf spot in lawns.

Generally speaking, most big box fertilization programs prescribe too much nitrogen, which can lead to fungus outbreaks. There are two problems with this strategy:

  1. Lawns need nitrogen—but not in copious amounts. Slow-release nitrogen fertilizers keep too much nitrogen from entering your soil and plants at once. They’ll also feed your lawn over an extended amount of time so that you don’t have to apply fertilizer repetitively.
  2. It is better to feed your lawn incrementally throughout the growing season (March—November); not just two times a year.

Sod Solutions recommends the Lawnifi® Fertilization Program. Lawnifi gives your lawn what it needs in the form of nano-sized nutrients, exactly when it needs it in the form of easy-to-apply monthly applications from March to November. For these reasons, Lawnifi is less likely to cause fungus outbreaks.

It’s important to note that even with the use of an improved fertilizer program, the timely applications of fungicide is still necessary for overall lawn health. If you fertilize your lawn with nitrogen before applying a fungicide and presently have a fungus, that fungus will expand exponentially, which can be disastrous for your lawn.

Chemical Control of Gray Leaf Spot

When searching for the best fungicide, there are many gray leaf spot control products to consider.

What is the Best Gray Leaf Spot Fungicide?

Azoxystrobin, chlorothalonil, fluoxastrobin and propiconazole gray spot products are just a few fungicides that control this disease. They are available in a variety of brands, including Heritage G and Fame, as well as many others.

How do I prevent gray leaf spot?

While disease control products are generally used for fixing gray leaf spot in your lawn, it may also be used to prevent the disease from occurring in the first place. Apply one of the products above at a preventive rate.

When applying these products to your lawn, be sure to carefully follow the label’s instructions. Depending on the type of fungicide you’re using, you may consider rotating to a different chemical class after application. Consider rotating group 3 (propiconazole) and group 11 (azoxystrobin) fungicides to keep this from happening. This will prevent fungicide resistance that occurs with certain brands of chemical products on gray leaf spot. Learn more here.

Whether you’re trying to prevent gray leaf spot fungus or you’re treating it with fungicide, closely monitoring your turf is extremely important. By properly maintaining your lawn, you can encourage healthy growth throughout the season, thus resulting in a beautiful, flourishing lawn.

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