In this section, I will be discussing turfgrass diseases. I understand your average turfgrass warrior may not have the training or experience to successfully diagnose and treat turfgrass diseases. But, my intent here is to perhaps make you warriors aware of the various diseases. And, perhaps, you will be able to understand more if you think your turf area has a disease. At that point, you can call in a guy like me for some fire support.
As I say all the time, the best way to fight disease, drought, weeds and other stresses to your stand of turfgrass is to have a thick, healthy stand. Once you get your stand going, if one of these diseases does strike, then you may need to do some analysis, some soul searching and perhaps take some other courses of action.
Diseases for most plants can be caused by forces of the physical and biological environment surrounding the plant. These diseases can be divided into two categories: noninfectious and infectious.
Noninfectious diseases are usually caused by nonliving agents like a surplus or deficit of fertilizer, a chemical spill or environmental stresses like high or low temperatures, drought or salinity. Mowing improperly or heavy traffic can also be considered a noninfectious disease injury.
The pathogens associated with infectious diseases are: fungi, viruses, bacteria and nematodes. Most of the turfgrass infectious diseases are caused by fungi. Before modern methods for analysis, scientists thought fungi were part of the plant kingdom. But, fungi do not have chlorophyll and are unable to produce their own food through photosynthesis. Some fungi feed on the dead leaves, stems, and roots of our beloved turf.
A fungus (the singular form, the plural form is fungi or funguses) begins when a spore or sclerotium (plural is sclerotia) germinates. The germinating spore or sclerotium produces microscopic threads called a hyphae. A mass of hyphae is called a mycelium (plural is mycelia). These mycelia are sometimes seen as “cotton like” or “cob web like” growths in the turfgrass.
Disease causing hyphae can enter the turfgrass through “wounds” in the tissue (caused by improper mowing, for example). Or, they can enter through the natural openings on the surface of the turf tissue called stomates. The hyphae can grow inside the plant and take plant nutrients, denying the nutrients for your turfgrass. And, the hyphae can reproduce outside the tissue and spread to other plants. Thousands of spores can be found in just 0.25 inches of tissue. During peak discharge times, a fungus may release more than 100,000 spores an hour. Moist tissue aids hyphae in spreading more easily.
For the sake of brevity, I will list some of the more common diseases.
These are foliar diseases:
Brown Patch or Rhizoctonia Blight (Rhizocatonia Solani)
Gray Leaf Spot (Pyricularia Grisea)
Dollar Spot (Sclerotonia Homoeocarpa)
Gray Snow Mold or Typhula Blight (Typhula Incarnata)
Pink Snow Mold and Fusarium Patch (Microdochium Nivale)
Leaf Smuts (Stripe Smut, Ustilago Striiformis, and Flag Smut, Urocystis Agropyri)
Red Thread (Laetisaria Fuciformis, formerly Corticium Fuciforme)
Powdery Mildew (Erysiphe Graminis)
Pink Patch (Limonomyces Roseipellis)
Rust (Puccinia & Uromyces)
White Patch (Melanotus Phillipsii)
Southern Blight or Sclerotium Blight (Sclerotium Rolfsii)
Yellow Patch (Rhizoctonia Cerealis)
These are foliage and/or root diseases:
Curvularia Blight (spp.)
Anthracnose (Colletotrichum Graminicolaand Glomerella Gramincola)
Downy Mildew or Yellow Tuft (Sclerophthora Macrospora)
Drechslera Leaf (spp. formerly known as Helminthosporium)
Fusarium Diseases (Crown and Root Rot)
Necrotic Ring Spot (Leptoshaerea Korrae, formerly known as Fusarium Blight)
Spring Dead Spot (Leptoshaeria Narmari)
Pythium Blight, Cottony Blight, GreasySpot (spp.)
Take All Patch (Gaeumannomyces Gramminis, formerly known as Ophiobolus Patch)
These are some other diseases and disorders:
White Leaf of Bermudagrass (Spiroplasma Citri)
Fairy Ring (Several Soil Inhabiting Fungi)
St. Augustinegrass Decline Virus (SADV– Panicum Mosaic Virus)
Slime Mold (Mucilago Crustacea, Physarum& Fuligo)
I don’t want to get into the various hosts, symptoms, favorable conditions and control strategies for each of these diseases. That will take forever. You’ll have to wait for the book. In fact, there have been many books written just on these diseases. But, before I move on, I’d like to say a few words about NEMATODES. These are basically roundworms. Depending on the species, a nematode may be beneficial or detrimental to plant health. From agriculture and horticulture perspectives, the two categories of nematodes are the predatory ones, which will kill garden pests like cutworms, and the pest nematodes, like the root-knot nematode, which attacks plants, and includes those nematodes that act as a vector, spreading viruses between plants.
Disease control and diagnosis:
In order for a disease to take hold in your turfgrass, three crucial factors must be present. These three conditions are commonly referred to as the “Disease Triangle”. Before you can attack and hopefully control diseases, turfgrass warriors must have an understanding of the disease triangle.
The bottom line with regard to the disease triangle (I know this is a Venn diagram, but, work with me here.) concept is that if any one of the three factors or conditions are missing, disease development will not happen. Please see below:
Here are some simple examples. If you have Tall Fescue grass, you will probably NOT be susceptible to Spring Dead Spot – since Spring Dead Spot only occurs in Bermudagrass. Therefore, you do not have a susceptible host. If there are no pathogens present because you only use disease free soil or sprigs, one of these conditions, the pathogen piece, would be missing. Finally, if you are aware of, or are able to manage some of, your environmental circumstances (including cultural practices), like being aware of the weather, or managing your watering (e.g. most turfgrass diseases need at least 12 hours of moisture before the turfgrass can be penetrated), you are eliminating the conducive environment piece.
The primary method of attacking turf diseases is using fungicides. Much like herbicides, there are two types of fungicides: contact and systemic. Contact fungicides are sprayed on the fungus and inhibit its growth. Contact fungicides will not kill the fungus already in a plant. Systemic fungicides are taken up by the fungus and are effective against fungi that are already in the plant.
If you really want to attempt a proper identification and diagnosis of a turfgrass disease, you must consider these four basic steps: 1. You must correctly identify the turfgrass you have, 2. You must be able to identify the symptoms of the disease, 3. You must be able to have a handle of the environmental conditions (to the extent you can), and 4. You must be able to recognize the signs of the particular pathogen. This is much more difficult than it sounds; trust me.
Ensuring you know what species of grass you have can be tough, especially since there are about 9,000 varieties. Many pathogens are specific to certain species of turfgrass. Similar to the example I gave above, regarding Tall Fescue and Bermudagrass, knowing exactly what kind of grass you have can eliminate many types of diseases and be a big help in the diagnosis process. NC State has excellent online resources for disease identification.
Steps 2 and 4 are very closely related. You must know the difference between SYMPTOMS and SIGNS. I’m serious. SYMPTOMS are changes in the normal appearance of the grass. Larger symptoms may be brown spots, patches or rings. Smaller symptoms may be lesions on the grass leaves. SIGNS are visual evidence that there is a particular pathogen present. Is there “cotton like” mycelia? Smut, Rust, Powdery Mildew each have a different look. The best time to look for signs is in the morning with dew on the grass. Dry turf often does not easily reveal signs of disease.
And, of course, step 3 is all the stuff I’ve been talking about throughout this blog – climatic conditions and cultural practices. Certain diseases are more aggressive in certain temperatures. Most diseases favor conditions of high moisture, high humidity, overcast skies, low light/shade; in addition to improper mowing, watering and excessive thatch.
Just like our other battle streamers for fighting weeds or pests, this may require some special forces. There are some fungicides that can be obtained over the counter. As always, I urge my troops to use caution, read the label and follow directions. Fertilizers, pesticides, herbicides and FUNGICIDES are nothing to take lightly, or try to make in your basement.
Don’t guess. If you need help, give me a shout; or, I can refer you to an expert closer to you. Don’t mess around with this.
Here's an addendum to my post (above) regarding turfgrass diseases. I got a call from Jack. Jack is a customer in the Del Ray area of Alexandria, Virginia. I did his lawn last year. You can see pictures of his lawn in my blog post "Lawns we are working on..." Jack calls me and says, "My Lawn is dying and you gotta come see it!" So I screeched out of my driveway with the turf-mobile and went over to Jack's house. (Maybe I should get some sort of flashing light for the roof of my truck.) Here's some pictures:
Jack's lawn was not doing well. Immediately, I was able to make a diagnosis. Jack's lawn had Brown Patch or Rhizoctonia Blight (Rhizocatonia Solani).
Jack didn't believe me. So, I took a sod sample. This is different from a soil sample. A sod sample is basically an inverted circular and cone shaped cut into the turf, about 8 inches in diameter and 8 inches down.
I shipped that sample to the lab at NC State University. I mentioned above that NC State has some pretty good resources for online turf disease diagnosis. Well, they also have the nation's foremost lab for turfgrass disease diagnosis. But you got to send them sod from the infected area, not just soil.
The lab verified my initial diagnosis - brown patch. How did this happen? Well, I started asking Jack alot of questions. Most of the questions centered around Jack's management practices. Especially his management practices AFTER he was provided my report on what needed to be done to his lawn. My investigation revealed that Jack had been watering too much and he had made an unauthorized application of fertilizer. In fact, Jack had no idea about the fertilizer he put down. Apparently he mixed together a few bags of remnant, old fertilizer he had sitting around his garage. Jack was sufficiently counseled and sent on his way. The good news is, I was able to "prescribe" a good fungicide that could correct the situation. Jack, go forth and sin no more.
I saw Jack after this last post. He and his wife are getting ready to retire to Arizona. He sent me a picture of his future lawn.....well, yard, really.
This is one way to ensure you never have another turfgrass disease!