Watch Out for Leaf Spot on Bermudagrass

Weeks like this when rainfall is frequent is unfortunately a good time to get leaf spot on your bermuda hayfields and pastures. Once you are able to cut hay, you may find brownish or blackish spots on bermudagrass leaves, even some discoloration on the stems.

What is leaf spot? Bermudagrass leaf spot is a disease caused by a fungus from the genus Helminthosporium. Here is a picture of leaf spot on bermuda from a University of GeorgiaCooperative Extension publication:

Why is leaf spot important? Leaf spot is important because as leaf spot progresses, it decreases yield, nutritive value and palatability. Leaf spot can be so severe as to diminish growth because it keeps leaves from maximizing sunlight for energy. Affected hayfields can become brown and thin. Other diseases can cause damage as well, such as leaf rust.

How do I identify leaf spot? Leaf spot makes circular lesions on the leaves. Spots are more plentiful near where the leaf blade joins the stem. The spots are irregularly shaped and are brownish green to black in color. Leaf rust looks similar to leaf spot but under a microscope, leaf rust appears as small, red to orange lesions. Leaf rust also starts as a small raised area or blister and the blister ruptures showing a powdery mass of orange-red spores. Rubbing a leaf infected with leaf rust will leave a rusty-colored area on your hands. Both leaf spot and leaf rust are managed similarly.

What can I do about leaf spot? Management and cultural practices are the most effective way to deal with leaf spot. According to the University of Georgia, these five practices will help reduce your risk and/or level of infection: 1) selecting a resistant bermudagrass variety, 2) maintaining soil fertility, 3) managing irrigation when applicable, 4) removing thatch, and 5) harvesting forage in a timely manner.

            In times of heavy rainfall, some of these practices will not be feasible but handle these as you are able. For variety selection, Coastal, Tifton 44, and Tifton 85 have some degree of disease resistance. As to soil fertility, addressing nutrient deficiencies is effective at managing leaf spot – soil potassium (or potash) is critical to leaf spot resistance. Split applications of potassium as with nitrogen are especially effective in the coastal plain area. Soil sample for specific soil needs.

            Irrigation management, minimizing thatch and maintaining a frequent cutting interval are all weather dependent. However, when conditions are amenable, these three items are very helpful in managing leaf spot. Since fungal diseases thrive in wet and warm environments, creating more air flow in the canopy discourages fungal growth.

What if I still have leaf spot? There are no legal, effective or economical fungicides to control leaf spot in forage bermudagrass. Remove infected forage as hay and encourage new growth to come in.