Category Archives: Turf

We’ve been looking at lawn problems with commercial landscape folks this past week, and I thought I’d put a little piece about what we’re seeing. Brown patch (Rhizoctonia solani) is the most common disease I find, and most common disease the diagnostic lab in Athens sees as well. Down here, we see it in centipede, and also St. Augustine. Brown patch is generally a disease of spring and fall. However, temperatures from October through January have been ideal for this pathogen.

Just after Christmas, I was asked to look at lots of centipede yards from homeowners where symptoms looked like brown patch. On the microscope, I never was able to confirm the pathogen. UGA Extension Pathologist Dr. Elizabeth Little confirmed that too much rain – environmental conditions – was to blame for these problems across the state. Once January freezes began, I had no more calls about lawn issues. Grass finally went dormant where lawns were open. We still have green turf under trees – mostly St. Augustine.

Last week, we looked at some St. Augustine affected with brown patch. Much of it is not dormant. It had been treated three weeks ago. Before this, it was treated in November. This inquired lots of questions like is it active? Should we spray again now?

Upon looking at the yard, the symptoms represented old disease. The disease infected during the warm period sometime between December and January. The recent cold weather is too cold for the pathogen to be active.

Should we treat now?

There are some spots that appear to show some activity. Conditions that favor brown patch pathogen night temperature above 60 degrees and daytime temperature above 80 degrees. Our days have become warmer, though nights are still cool. A pathogen in infected grass could become active during these temperatures. However, does a small chance at pathogen activity warrant a spray? According to UGA Extension Turf Pathologist Dr. Alfredo Martinez, we need consistent days of 65 degree soil temperatures for the right conditions for Brown Patch to exist. Any fungicide sprays now will likely not be effective.

Fungicide treatments in dormant turf?

When turf is dormant, it is not recommended to apply fungicides. Strobilurins (Heritage) and DMI’s (propiconazole) are systemic in the plant. When turf is dormant, these fungicides – which are our heavy hitters for soil pathogens – are not effective. On the other hand, contact fungicides, like chlorothanonil, may be effective on a pathogen in dormant grass. However, with cold temperatures, the pathogen is less or completely inactive.

Keep in mind that managing disease is more cultural than chemical. With brown patch, we need to limit our nitrogen when disease is active. We may also increase our potash. Fertilizers with K only can be used at the end of the season to increase vigor through winter. We also need to watch irrigation. The most common cultural issue I find is lawns watered 2 and 3 times a week. This makes disease almost certain. We need to irrigate between 9pm and 9am and apply enough to give the turf 1 inch of water per week, once per week. Deep, infrequent water events help increase rooting depth and lessen disease conditions. To see more on brown patch, visit Turf Diseases In Georgia: Identification & Control.

“When it rains, it pours.” And it has brought lots of issues with our yards other than slime mold. Even growers are asking about these issues they are seeing. Why is the grass is turning yellow and dying in irregular shapes? In between our commercial ag calls, us county agents answer residential calls about landscape issues also. I’ve learned a lot about centipede and St. Augustinegrass in 3 1/2 years, but some of the things I’m seeing for the first time this week.

Rain and humidity provide the environment for disease. Usually, Large Patch (Rhizoctonia solani) will show up in centipedegrass during this time. You will see brown spots in the lawn with a nearly perfect expanding circle. St. Augustine generally gets Take-All Patch (Gaeumannomyces graminis) with significant damage. Another common issue during periods of rain is yellowing of the grass blades. This is result of nitrogen and potassium leaching out with rain (below).

Centipede nutrient deficiency from rain

The reason I wrote this post is because I visited a centipede lawn earlier this week with dead grass in irregular shapes. The symptoms did not look at all biotic (disease, insect damage) but abiotic (environmental, cultural). The lawn held lots of water and you could clearly see where water sat for long periods, and roots went without oxygen and died. However, I saw a few small circles, but not typical sign of Rhizoctonia. I took some samples and looked under the microscope. Under the dissecting scope, when you see these black dots…. they are usually hyphopodia (puzzle pieces) from Take-All Patch…

Mycelium on base of centipedegrass blade

……however, we always look under the compound scope to confirm it. In this case, the “hyphopodia” turned out to be clumps of mycelia. The issue was that these mycelia did not have all the key ID features of Rhizoctonia (Brown color, crosswalls, 90 degree branch angle, and taper at the branch).

Clumps of mycelium on centipedegrass

Below is actual key ID feature of Take-All Patch…

Hyphopodia from Take-All Patch on St. Augustine

I sent to UGA Pathologist Dr. Elizabeth Little who responded saying sometimes the mycelia will clump as it enters the cell, but she and her diagnostician was not convinced this was Rhizoctonia. Below is the response from Dr. Little. To summarize, she believes the weather conditions are causing lots of issues with lawn now, and Rhizoctonia found in the samples is secondary:

I showed this to our diagnostician who sees lots of Rhizocontia and she was not convinced this is Rhizoctonia. She thought it was too erratic. However, the runner hyphae of rhizoctonia will make infection cushions of balled up hyphae where they enter the plant. That is what these look like to me. So this could be a random saprophytic fungus or possibly Rhizoctonia but you would need to look some more to confirm. When conditions are wet like this Rhizoctonia and other fungi are everywhere. I am getting many centipede samples of poor greenup but I am thinking any Rhizoctonia is probably secondary to the environmental stress, especially if there is no distinct pattern of large patch.

I’ve had two few calls today about a purple color, powdery substance showing up in circles in the yard.  Someone also brought in a few weeds with the same purple dots on the leaf. These recent rains have created the environment for slime molds to appear. It causes no problems other than being unsightly.

Slime molds belong to the Myxomycete fungi class that obtain their nutrients from dead, organic matter. They can also be seen in the flower beds and gardens where they may appear as the ‘blob’ or plasmodium. They don’t cause any direct injury to the plants, but can inhibit photosynthesis. Control does not require any chemicals. You can mow the lawn or wash off with a water hose to remove it. Here are some pictures of slime mold I have taken in centipedegrass. Here is a UGA publication on The Truth About Slime Molds, Spanish Moss, Lichens, and Mistletoe for more information.

Last week, we checked into some centipedegrass sod that was showing some odd symptoms. The patches of dying grass were shaped irregular and could see obvious wilting signs on the boarder. We checked for disease under the microscope and did find some however, with these symptoms, we decided to check nematodes. Here is the report below:

UGA Extension Pathologist, Dr. Alfredo Martinez, said centipedegrass can easily be colonized by nematodes compared to other species. The report showed both Ring and Sting nematodes being above thresholds. UGA Extension Turf Agronomist Dr. Clint Waltz says at this stage it would be best to increase irrigation and fertility. When ready, harvest this grass then consider a nematode treatment prior to reestablishment.

Also, the soil test showed pH to be 4.9. Centipedegrass can take a lower pH than bermudagrass, but below 5.5 is pushing it. Research shows a pH of closer to 6.0 is better for centipede establishment. The liming will raise the pH and take effect next year. This will help increase overall fertility. Dr. Martinez also suggested using an all purpose systemic fungicides (fungicides containing thiophanate methyl, propiconazole or an strobilurin). This might help to control any facultative pathogen/saprophyte that might be lingering.

Mr. Felix Horne, from Action Lawn Care, brought in some samples of St. Augustinegrass yesterday which appeared to have very suncken, wilted patches. It is down on a plantation where take all root rot (Gaeumannomyces graminis) has been an issue and pH has been high in areas. This is important because take-all patch typically occurs in areas with a high soil pH – most severe at pH 6.5 or above. It is also more severe on less fertile and sandy soils.

Hyphopodia seen on take all root rot with mycelium from large patch

Under the microscope, some of the roots were dark colored and looked stubby. There is actually some large patch (Rhizoctonia solani) mycelium here too. Under the compound microscope, you can see the hyphae and hypopodium referred to as “puzzle pieces.” We see more into the summer. Home lawns with this disease will really show damamge and is hard to control.

Here are some management tips for take all root rot:

• Use acidifying fertilizers.
• Apply moderate to high levels of phosphorous, potash and minor elements where these nutrients are depleted from the soil.
• Improve the drainage of the turf.
• Reduce thatch.
• Fungicides are available to control the disease. Consult the current Georgia Pest Management Handbook.

We’ve seen a number of diseases this Spring in our lawns. Large patch is the most common disease I find in Centipede and St. Augustine. Last week, Mitchell County Ag Agent, Andy Shirley, found Pythium in Bermudagrass. This week, I was asked to look at another lawn and came across another common disease we see called Fairy Rings (below).

Fairy ring symptoms follow its description well, leaving large rings in the grass. Basidiomycetes of more than 40 species can cause fairy rings. All warm season grasses are susceptible, but it particularly attacks centipede and St. Augustine grass in South Georgia. Sometimes, above ground-mushrooms and puff ball basidiocarps are present. Other casual agents have rings but no fruiting bodies.

Here are some management tips:

• Avoid using root zone mixes with high levels of undecomposed organic materials.
• Reduce thatch by vertical cutting.
• Aerate soil.
• Irrigate deeply.
• Use nitrogen fertilizer to mask symptoms on some types of fairy ring.
• Use soil wetting agents to help penetrate hydrophobic areas.
• No residential fungicides are available to control the disease, but some commercial fungicides can be found. Consult the current Georgia Pest Management Handbook.