How To Prevent & Treat Brown Patch in Lawns

You survived another long winter. You jumped into your early spring lawn care plan and began the much anticipated hard work of clean-up, applied your first application of crabgrass control and prevention, fertilizer, and are starting to see the lawn quickly green-up and grow like crazy. 

But soon both the outside temperature and humidity levels begin to rise and invites lawn diseases and funguses like brown patch.

Don’t ruin your hard spring lawn work and visions for summer and fall domination by allowing brown patch to ruin your plans. Follow this guide to help prevent and treat brown patch in your cool season lawn.

What is Brown Patch

Brown patch is a very common cool season turf disease cause by the Rhizoctonia species fungus. The cool season grass type most affected by brown patch fungus is Tall Fescue.

Images below can help identify brown patch. You will see roughly circular brown/yellowish patches in your lawn that can range from a few inches to several feet in diameter. The individual grass blades will start with circular lesions on the grass, and ultimately turn completely brown. Brown patch kills leaf blade of the grass itself, but not the crown or the roots. 

Extended days of high heat, high humidity, and overnight temperatures of 65 degrees Fahrenheit or warmer. Another rule of thumb is to add the outside degree temperature and the outside humidity. If those two numbers are approaching 150 or higher, you’re in prime fungus and disease conditions, and it’s time to take action. Example, June, July and August are prime conditions for brown patch in areas like Zone 6. Brown patch will thrive on an 80 degree day in June with 70% humidity (80 degrees + 70 percent = 150). 

Basic Fungicide Application Rates

  1. Preventative Rate
  2. Curative Rate

Types of Lawn Fungicides

  1. Systemic Fungicides
    Fungicides that are taken up and absorbed by the plant. Foliar applications which are absorbed by the grass blade – or drenching which is applying fungicide and watering it in to be absorbed by the plant roots.
  2. Contact Fungicides
    Fungicides that are not absorbed by the plant. These types of fungicides stay on the grass blade to protect the plant.

How to Prevent Brown Patch

The best mode of action against brown patch in cool season lawns is of course prevention. Apply fungicides in the early spring – May 1st – alternately at preventative rates 21-30 days apart – or according to the product label – will help prevent brown patch. More on alternative applications below. 

Cultural Practices 

  • Use a sharp mower blade. Dull blades can tear and rip the grass, leaving is more susceptible to diseases
  • Avoid overwatering – fungus thrives in damp conditions. Twice per week at 1-1 1/2 inches of total water per week
  • Avoid watering overnight – extended periods of wet grass blades will increase likelihood of fungus
  • Water in early mornings – this will allow the water enough time to penetrate the soil, and excess water on the grass blades to evaporate in the later morning/early afternoon sun
  • When fungus is present, bag clippings and clean undercarriage of mower after each use

Fungus can become resistant to fungicides if the same fungicide is used too frequently, which is why we want to “apply fungicides alternately”. For example, if you only apply Scott’s DiseasEx which main active ingredient is Azoxystrobin (FRAC Group 11) then the brown patch can essentially become immune to this fungicide. Buy multiple products with different fungicides in different FRAC Groups to prevent fungicide resistance. 

The FRAC code is a simply a combination of a number and/or letter which was assigned by the fungicide resistance action committee (FRAC). Active fungicide ingredients that target specific funguses and enzymes are grouped together to avoid the potential of resistance. And as previously mentioned, fungicides with the same FRAC code are at risk for disease and fungus resistance if used exclusively and continuously without rotation – example Azoxystrobin and Fluoxastrobin in FRAC Group 11.

An example schedule of fungicide applications to avoid resistance. You may use all three, or a combination of any two:

  • First application: Scott’s DiseaseEx (Azoxystrobin, Group 11)
  • Second application: Quali-Pro 14.3 (Propiconazole, Group 3)
  • Third application: Clearys 3336F (Thiophanate Methyl, Group 1)
  • Repeat

Most of the fungicides are considered broad-spectrum fungicides, which means they are designed to manage a wide variety of diseases. Note that fungicides do not “kill” the fungus, but arrests the fungus. The fungicides will stop the growth and spreading of the disease, and help mitigate further damage, but will not repair what was done.

Fungicides to Prevent & Treat Brown Patch

While most fungicides below are broad-spectrum, these fungicides are particularly good at treating brown patch. The table below contains a list on fungicides types and popular fungicide products to help treat and prevent brown patch in your lawn. It is best to rotate the FRAC Groups in every other application, or no more than twice in a row. 

Bolded are recommended products after haven been used by Lawn Phix and proven effective.

Quali-Pro 14.3 On Amazon

FRAC GROUP Fungicide Amazon DoMyOwn Rates Duration
Group 1 Thiophanate Methyl Clearys 3336F On Amazon Clearys 3336F 2-4  fl. oz. per 1,000 ft² 14 days
Group 3 Propiconazole 14.3 on Amazon Quali-Pro 14.3 1-2  fl. oz. per 1,000 ft² 14-21 days
Group 3 Propiconazole Bio Advanced On Amazon Bio Advanced Fungus Control 32 fl. oz. treats up to 5,000 ft² 14 days curative
30 day preventative
Group 3 Propiconazole Prime Source 14.3 On Amazon Prime Source 14.3 1-2 fl. oz. per 1,000 ft² 14-21 days
Group 3 Myclobutanil Eagle 20Ew On Amazon  Eagle 20EW 1.2 fl. oz. per 1,000 ft² 14 days
Group 11 Azoxystrobin Scott’S Disease-Ex On Amazon Scotts Disease-Ex 10 lbs. covers up to 5,000 ft² 14-28 days
Group 11 Azoxystrobin Azoxy 2SC On Amazon Azoxy 2SC 0.38-0.77 ounces per 1,000 ft² 14-28 days
Group 11 Azoxystrobin Heritage G On Amazon Heritage G 2-4 lbs.per 1,000 ft² 14-28 days

Note: This list is not exhaustive. There are more fungicides in some FRAC Groups that are not listed in the table above. Also note that some products such as Headway G contains active ingredients in multiple FRAC Groups (Axozystrobin in Group 11, and Propiconazole in Group 3). I provided product links to both Amazon and DoMyOwn.

However, you can find a lot of these fungicides at your local hardware store and big box stores, too. Products like Bayer Bio Advanced (Group 3) and Scott’s DiseaseEx (Group 11) are usually readily available. The main takeaway is reading the labels and ensuring you’re buying fungicides in more than one FRAC Group to prevent resistance. 

How To Treat & Get Rid of Brown Patch Fungus

Without proper action, brown patch will move and spread quickly. In just a matter couple days, brown patch can decimate several hundreds – even a couple of thousand – square feet of lawn. 

  • Continue to bag your clippings when mowing. And ensure the mower is cleaned before using again, and before moving to a new area
  • Increase airflow. If needed, lightly rake the area to ‘fluff’ the grass and allow more oxygen to pass through
  • Apply three applications of fungicides, about two weeks apart. Rotate FRAC groups and follow the labels, as two weeks is a general guideline
  • Use a liquid fungicide. The plant will be able to uptake a liquid application quicker than a drenching through the roots
  • Keep lawn as dry as possible. This means eliminating watering unless watering in granular fungicides 
  • Lower the fertilization rates, and switch to a slow release organic nitrogen fertilizer until the fungus has cleared. Spoon feed at lower rates
  • Late summer and early fall, repair the turf with dethatching, core aeration and overseeding your lawn
  • In a full Tall Fescue lawn, consider overseeding with Perennial Ryegrass and Kentucky Bluegrass (KBG). These two grass types pose a lower risk to brown patch. Species diversity can aid in limiting the risk and damage from brown patch fungus

If you’ve every experienced lawn diseases such as brown patch, it’s not a pretty site. This fungus can grow rapidly and decimate a lawn without the proper precautions. Follow these steps to prevent and treat brown patch for a green lawn and successful growing season!


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When should I first apply fungicide on my lawn?

The best action against lawn fungus and diseases is prevention. Your first preventive application of fungicide should be early Spring – around May 1.

What are the best fungicides for brown patch?

Products that contain Propiconazole (FRAC 3) and Azoxystrobin (FRAC 11) are two very effective fungicides for preventing and curing brown patch lawn disease. Quali-Pro Propiconazole 14.3, Heritage G, Azoxy 2SC, and Eagle 20EW (Myclobutanil) are several great products to choose from when dealing with brown patch.

How often should I apply fungicide to treat brown patch?

Always read the label of the products you’re applying. Generally for brown patch prevention, re-apply every 21-30 days at preventative rates. For curing brown patch, generally curative rates every 14-21 days apart.

What grass types are susceptible to brown patch fungus?

While most all cool season grass types (KBG, perennial Ryegrass) and many warm season grasses can become affected by brown patch, Tall Fescue that is the most common cool season grass species that is most greatly susceptible and impacted by brown patch. Overseeding, particularly with a cool season grass species diversity, can help heal and prevent brown patch disease. Common warm season grass types that are affected by brown patch disease are Bermuda, Centipede, St. Augustine, and Zoysia.


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