The Grass is Not Always Greener: Leaf Spot in Bermudagrass
Courtney Darling UF/IFAS Suwannee County Extension
Bermudagrass is a popular choice for hay production throughout the southeast, especially Florida. There are several factors that can impact forage quality and yield, including various diseases. Leaf spot or leaf blight (Bipolaris cynodontis) is one of the most common foliar diseases found in bermudagrass. This disease is caused by the fungus Helminthosporium which causes a decrease in forage nutritive value, yield, and overall palatability.
Symptoms and Identification Leaf spot typically begins to appear in late summer when the weather is hot and humid. Early symptoms start as dark brown circular lesions. Eventually the spots turn a brownish green to black color of irregular shape. As the disease progresses and starts to attack the stolons, crowns, and rhizomes of the plant, the forage stand will become thin and brown. Leaf spot looks similar to leaf rust to the naked eye and even causes similar damage to the forage stand. Leaf rust is caused by a fungus called Puccinia cynodontis. A noted difference between the two is that leaf rust has a slightly orange coloring and raised pustules that will sometimes leave an orange-brown residue on your finger when rubbed.
Management The best way to treat leaf spot in bermudagrass hayfields is by preventative measures:
▪Planting a variety that shows resistance to the disease ▪Maintaining proper soil fertility ▪Irrigation management if possible ▪Thatch removal ▪Timely harvest of forage
Coastal, Tifton 85, Russell, and Tifton 44 have shown some level of resistance to leaf spot, however, even these varieties can still fall victim to the disease, especially if not properly fertilized. Varieties that have shown higher susceptibility include Alicia and World Feeder.
Soil potassium has been noted to play a key role in leaf spot susceptibility. This can be mitigated by applying potash when soils are low. It is best to apply potash in split applications in sandy soils.
Since fungal diseases thrive in wet and warm environments, if possible, avoid turning irrigation on from mid-afternoon until morning. This will allow the forage to dry, preventing it from staying wet throughout the night into mid-morning the next day.
The presence of excess thatch has been associated with incidences of bermudagrass leaf spot. The theory is that thatch not only contributes to tying up nutrients but also it can serve as a reservoir for fungal spores because of the decaying material. Burning in the spring prior to forage green-up will help reduce thatch.
Lastly, if all other preventive measures fail, mechanical removal of the forage is an effective control method. Mowing of the infected forage will help remove the fungal inoculant, therefore limiting spread and forage damage. Since potassium is prioritized to new growth during a nutrient deficiency, mowing is both a control and a preventative method because it removes the predisposed older tissue.
If you have any questions please contact Courtney Darling at the UF/IFAS Extension Office in Suwannee County, an Equal Opportunity Institution, by calling (386) 362- 2771.