I have been receiving calls from concerned hay producers in Colquitt County. We are seeing bermudagrass fields dying off or having a brown or bronze appearance. Bermuda grass leaf rust has been observed in these fields. We have observed symptoms such as those shown in the pictures below:
The causal fungus of leaf rust, Puccinia cynodontis, appears late in the summer when the humidity is high. Heavy infestations can decrease both hay yields and quality. Another disease called Helminthosporium leaf spot can look similar to rust to the naked eye and can cause similar damage.
So what can I do about it? Disease management for Helminthosporium and leaf rust is similar. Below are some points:
Variety Selection: Resistant varieties are the best way to control this issue. When preparing to establish new plantings of bermuda grass, select hybrid varieties such as Tifton 85, Russell, or Coastal, that exhibit some level of disease resistance. Alicia bermuda grass is extremely susceptible to this complex.
Soil Fertility: Soil potassium is critical for leaf spot resistance. Most reported leaf spot cases are directly related to low soil potash. Nutrients are removed from Bermuda grass hay fields in approximately a 4-1-3 ratio of N, P2O5, and K2O with hay harvest. Split applications are particularly helpful in sandy soils such as Colquitt County. Please note that soil tests can be misleading. There have been cases where adequate soil levels were present, but plant tissue samples indicate a nutrient deficiency. If leaf spot/rust has become a problem and soil tests do not recommend potassium, submit a clipped sample of hay for plant tissue analysis. If the sample analysis indicates a potassium level less than 1.8 percent on a dry matter basis, then apply additional potash.
Irrigation Management: If you are an irrigated bermuda grass producer then turn off irrigation water from mid-afternoon until the following morning. This allows bermuda grass leaves to dry and prevents plants from staying wet through mid-morning the following day.
Manage Thatch: Some leaf spot/rust infections appear to be associated with the amount of thatch present in hay fields, with heavy thatch loads producing higher incidences of this issue. Thatch ties up nutrients and contains abundant decaying material, which may serve as a “spore reservoir.” In addition, thatch retains water and reduces air circulation, creating humid conditions and promoting leaf spot/rust incidence. The only practical way to reduce thatch is to burn in spring months just prior to bermuda grass green-up.
MAINTAIN A FREQUENT CUTTING INTERVAL: Maintaining a proper cutting interval does more than keep nutrient quality of hay high. Timely cutting may improve disease resistance, at least indirectly. The potassium necessary for disease resistance is mobile in plants and typically moves from older to younger tissue when there is a nutrient deficiency. This predisposes older tissue to infection leaf spot diseases.
For more information about managing these disease problems in bermudagrass, go to the UGA Cooperative Extension publication entitled “Leaf Spot Diagnosis and Management in Bermudagrass Forages” (C 887) at https://www.caes.uga.edu/Publications/pubDetail.cfm?pk_id=7386