Those bare spots in your yard could be take-all root rot. Here's how to spot it and fix it
- Take-all root rot is a warm-season turf disease affecting zoysia, Bermuda, and St. Augustine grasses.
- Symptoms include yellowing, thinning turf, and black, rotten roots.
- Proper irrigation, fertilization, weed control, and mowing height are crucial for prevention.
- Micronutrient fertilization and fungicides can help manage existing disease, but prevention is more effective.
When spring and summer rains combine with heat and humidity, we can expect the resurgence of warm-season turf diseases. One disease that is always present but really makes itself known in our landscapes during the summer is take-all root rot, (Gauemannomyces graminis var. graminis). Take-all root rot occurs in all warm-season grasses including zoysia, Bermuda and St. Augustine.
You may have already noticed the symptoms of take-all root rot but didn’t know what they were. Many folks have complained about spots in their turf that they have had to re-sod multiple times and the same patch of sod continues to struggle. In the spring, these bare spots don’t fill in with new growth and appear dried up.
Take-all root rot symptoms
The first symptom of take-all root rot that we notice is the turf starts yellowing in irregular patterns. These yellow patches soon start to thin out and become bare. The bare patches get larger. In a short time, the turf goes from thick and green to thin and patchy.
Once the above-ground symptoms become noticeable, significant damage to the turf root system has already occurred. If you pull up one of the remaining patches of turf you will notice that the roots have become short, black, and rotten and the outer layer sloughs off between your fingertips.
Diagnosing take-all root rot
As the above-ground turf symptoms may get confused with other pests or problems, inspecting the parts of the turf that grow underground with a microscope is the best way to diagnose this disease. If you inspect the parts of the turf that grow under the soil surface (roots, rhizomes and stolons) with the naked eye they may appear dirty.
However, under a microscope, you will see the telltale signs of take-all: masses of dark strands emerging from these below-ground parts. The dark strands are parts of the fungus called mycelium that have colonized the turf roots. If you suspect take-all root rot, you can send a sample to the University of Florida Plant Disease Clinic. For more information go to: https://plantpath.ifas.ufl.edu/extension/plant-diagnostic-center/.
What causes take-all root rot?
Like any plant disease, prevention of take-all root rot in turf is always easier than trying to control the disease after symptoms are observed. Take-all root rot takes advantage of stressed turf. Putting in place cultural practices that promote healthy turf will go a long way in preventing take-all root rot. Those practices include proper irrigation, proper fertilization, proper weed control, and mowing at the correct height.
Poor irrigation practices are one of the most common causes of lawn disease that we see. To avoid overwatering or underwatering, calibrate your irrigation system, ensure your rain sensor is functioning and make sure you’re watering only when needed; no more than ½ inch to ¾ inch twice a week. The longer the turf blades are wet greatly increases the conditions that are favorable to take-all root rot; if you need to irrigate, always water in the early morning.
The use of high-nitrogen fertilizers can also create conditions favorable for the disease. Slow-release nitrogen and slow-release potassium sources should be used. Additionally, fertilizers that have equal amounts of potassium and nitrogen such as 16-0-16 are preferable. Don’t forget to monitor your soil pH, keep it between 5.5 and 6.5 (target 6.0). A pH over 6.5 has been shown to contribute somewhat to take-all root rot disease.
Even when turf herbicides are used properly, they can stress the turf slightly. Proper weed control includes spot treating when possible and applying according to the label instructions.
Preventing take-all root rot
Mowing turf at the correct height allows the leaf blades to capture the sunlight that it needs to perform photosynthesis, the process in which plants make their own food. Mowing turf too low can interfere with that process and stress the turf. Different turf species require different mowing heights. St. Augustine should be mowed between 2.5 inches for dwarf varieties to 4 inches for standard varieties. Bermudagrass should be mowed to .5-1.5 inches and Zoysiagrass should be mowed to a height of 2-2.5 inches.
If you had issues with take-all root rot last year, go ahead and start applying preventative fungicide applications in addition to practicing proper turf management. Keep applying fungicides once a month until the weather is no longer conducive to disease development. For a list of fungicides recommended for take-all root rot, go to https://edis.ifas.ufl.edu/publication/LH079.
If you have already seen signs of take-all root rot in your turf this year, try fertilizing with liquid micronutrients. Small, frequent applications may be necessary if the roots are severely damaged. While fungicide applications are also recommended, they are much less effective in controlling the disease as they are in preventing the disease.
By practicing proper cultural practices on your turf such as proper irrigation, proper fertilization, proper weed control, and mowing at the correct height, you can get ahead of the game in preventing this serious turf disease.
Larry Figart is an urban forestry extension agent with the University of Florida/IFAS.