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 Plant stress and unbalanced fertility in soil normally trigger the anthracnose on grass and leaves. Photo: Charles Averre, N.c State University, Bugwood.orgIf your lawn is going to be hit with a disease, anthracnose might be the one you want.
That’s according to Alfredo Martinez, associate professor and extension plant pathologist in the plant pathology department at the University of Georgia.
“While you don’t want this scenario to happen, if I could choose any disease to have, I’d probably choose a foliar disease and within these, I would probably select anthracnose,” he says, because the disease is a plant stress disease. “Without trivializing the disease, there are several cultural factors and practices that you can implement. Usually in anthracnose, fertility is important. Nitrogen and potassium levels should be optimal.”
Anthracnose is produced by a pathogen called Colletotrichum cereale (formely C. graminicola). Plant stress and unbalanced fertility in soil normally trigger the disease.
Stresses such as high temperature, root zone compaction, thatch accumulation, low fertility, drought, low mowing height and insect infestation make turfgrass susceptible to Colletotrichum cereale.
Cultural practices that reduce these and other stresses often help to limit anthracnose incidence and severity. These practices include core aerification, growing locally adapted, disease resistant grasses; correcting and/or avoiding low fertility or unbalanced fertility according to a soil test and local recommendations; and relieving soil compaction by reducing traffic.
“Whenever I see some anthracnose, the first thing is to do a soil or plant tissue test to see the fertility levels – what is actually going on in there,” he says.
An improper water pattern can also cause anthracnose.
“Fungi love water or humidity,” he says. “Especially on the leaves. Sometimes we wet the grass only, but it is not getting to the root. Anthracnose takes advantage of that.
Watering properly means to water deeply and infrequently instead of just frequent and light irrigation. Frequent and light irrigation will just bring you problems with diseases. It is better to water one time and deep, than many times and just wet the canopy of the turf.”
Anthracnose can be mistaken for drought stress, or other overall stresses, or with diseases that produce overall off-color, yellowing on the foliage.
“There are several diseases that can cause some similar symptoms. So, it requires some knowledge of what’s going on in that area,” he says.
You can identify anthracnose by the production of setae – black, hair-like structures on the grass or a leaf – which are unique to the disease.
On cool weather grass, you will see lesions on the affected area. On warm weather grasses, you won’t see those lesions, but you will see an overall yellowing to the area.
Setae can usually be observed with a 10X magnification lens and are often abundant on dead or dying leaves, leaf sheaths or stolons. Setae denotes the presence of acervuli – fruiting bodies which produce asexual spores contained in a mucilaginous matrix.
Martinez says if you suspect anthracnose, but have doubts, you can take it to a specialist who can look at a sampling under a microscope. Extension services or outreach in many universities have county agents, who are trained to help at the local level.
A quick online search for, example, “university extension service” will bring up available options in your area.
The author is associate editor for Lawn & Landscape. He can reach him at bhorn@gie.net.
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