I get a lot of calls from PCOs, golf courses and homeowners about patch diseases in turf. These diseases tend to happen suddenly, seemingly overnight, where normal looking turf suddenly browns out and becomes quite ugly. The pest control company may have done something innocuous, such as a chinch bug spray. Then the patch disease happens, and of course the pest control company gets blamed, when the true cause of the problem has nothing to do with the application! There are two main fungal pathogens that cause these diseases in Florida, and I will discuss them here in detail.
Take- all Root Rot
This disease attacks pretty much all turfgrass varieties grown in Florida. It is most prevalent in the summer months, though in some areas it can happen in winter too. The pathogen, Gaeumannomyces graminis graminis is often present in the turf. Any type of stress can bring on the symptoms. It may start out as an odd yellowing of the foliage on some of the runners, especially in cooler months. These weaker areas may turn into fairly large dead patches very quickly. It will often happen in the same area year after year. Not all of the lawn is affected, just large brown areas. All St. Augustine varieties appear to be susceptible.
With Take–all, the roots turn black and the runners pull up easily. Stolons may show lesions as well. The disease does not directly attack foliage, though with loss of roots, leaves may die. With a good hand lens, you can see fungal bodies on the black roots that look like pieces of a puzzle. Stress factors that can bring on Take- all include shade, thatch, soil compaction, poor drainage, excess irrigation, or improper fertilizer or herbicide applications. Notice that most of these are not under the control of the pest control operator.
I see this disease frequently in my pathology lab, but I don’t tend to see it in bunches. While weather is always a factor, weather changes don’t seem to immediately make Take-all happen. I wondered for a long time what DOES bring it on. I started reading the wheat research. Wheat is a grass, in the family graminae. Take- all is also a major pathogen of wheat. The wheat research says that Take- all is triggered by high soil pH and low manganese availability, with iron being a factor as well. Much of coastal Florida from Tampa and Daytona south have, guess what, high soil pH and low manganese availability!
With most turf diseases, you diagnose the cause and apply the appropriate fungicides and cultural measures, and the problem goes away. Take- all is different. Fungicides can help preventatively, but they are usually not your best control option. Don’t lime soil when fighting Take- all, and don’t use calcium nitrate or ammonium nitrate. Acidifying the soil will definitely help. I often recommend adding ammonium sulfate and manganese sulfate to fungicide applications. Broadcasting 10 pounds of granular sulfur per thousand square feet may help as well. For those preferring an organic approach, broadcasting a bale of sphagnum peat moss per thousand will help. The pH of sphagnum peat is usually between 4.0 and 4.4. Microbial inoculants containing Streptomyces can also be helpful.
This turf disease is better known than Take-all. In my experience, it is more common in central and north Florida than South Florida. Caused by the fungus Rhizoctonia, it is more common from November to May. High rainfall and humidity encourage Brown patch, which tends to become active around 73° and dormant above 90°. You don’t tend to see Brown patch in the summer, though there are some other types of Rhizoctonia, including R. zeae, that can cause leaf spot and blight in summer. Disease patches tend to be more ring – like and circular, and can be smaller than Take-all. Brown patch occurs in much of the country, whereas Take-all is more limited to the Southeast and California. Some references say that Brown patch is a warm weather disease, others a cool weather disease. I think what qualifies as warm and cool may be different to Floridians than those in say Ohio. There are always exceptions in biology, however.
Brown patch is a leaf and sheath rot. Leaves can pull away from the stem, giving you a rotten smell. You will often see rings of yellow or brown turf within the affected patches. Most all warm season turf grasses are susceptible to Brown patch. Brown patch to me looks a little more defined in terms of the sizes and shapes of the patches. Weeds will often quickly infest diseased areas if treatments are not promptly undertaken.
Culturally, be conservative with nitrogen applications when fighting Brown patch, and use slow-release sources. Low soil pH may not be your friend here. Irrigate only during the early morning hours, when the dew may already be out. Encourage your clients not to over irrigate, but instead to dry the area out to help control the fungus. Chemically, there are numerous fungicide products which are effective against Brown patch. These are of course most effective when applied preventatively in anticipation of disease – favoring conditions. There are a few fungicides that are effective against both Take- all and Brown patch. Both diseases are spread by mowers, foot traffic, pets, birds and many other things.
So, when your customer calls you, complaining of these immense terrible dead patches in the lawn and she’s paying all this money, what do you do? These diseases are not totally preventable, and they can even come in on new sod. With Take-all, the roots turn black and the stems pull up easily. Leaves will not be directly affected, though they may die out. Brown patch is not a root rot, but a leaf and sheath rot. Brown patch is more common in cooler months, Take- all in warmer months. If you are not sure, a lab test is the best way to tell.