We rely heavily on our Bermuda grass pastures and hay meadows during the summer in some parts of Texas. Often times we are disappointed with production, see a thinning of our stand and/or see disease-like symptoms. This is often referred to as “Bermuda grass decline” and we quickly blame weather. Granted, weather can have an impact on each of those issues, however, there’s often a deeper problem that we need to assess.
Primary causes of Bermuda grass decline
Low Potassium Fertility: A deficiency in potassium will result in poor stress tolerance, reduced winter hardiness, decreased disease resistance and reduced rhizome and stolon production. To determine if potassium deficiency is causing the problem, a soil analysis will be imperative. Collect representative soil samples from the affected areas and another from areas nearby that are unaffected or less affected. More soil testing information can be located at http://soiltesting.tamu.edu. Potassium deficiency may occur during periods of water stress. The plant absorbs potassium from the soil by drawing in water that contains potassium. Therefore, even if the soil test indicates an adequate level of potassium, a drought can reduce the amount available to the plant.
Low Soil pH: There are several ways that soil pH causes a problem. First, toxic levels of soluble aluminum can occur in soils where the soil pH has dropped too low. This burns back the fine root hairs and prevents root growth. Low soil pH also reduces the availability of other nutrients such as phosphorus, potassium, magnesium, calcium and others. Ultimately, low soil pH starves the plant of water and nutrients. Soil pH, as evaluated by soil test, showed not to be less than 5.5 for Coastal Bermuda grass and 5.8 for Tifton 85 Bermuda grass. Overseeded forages such as clover and ryegrass need a pH of 6.0 or higher for optimum growth.
Leaf Spot: Helminthosporium leaf spot is commonly associated with Bermuda grass decline. Helminthosporium leaf spot commonly attacks Bermuda grass stands where potassium levels are low.
Ryegrass: The past two springs have been abundant with rainfall and ryegrass — volunteer or otherwise. In the spring when Bermuda grass is breaking dormancy, an abundance of ryegrass can out-compete Bermuda grass for water, nutrients and light. Heavy growth of ryegrass and removal as hay can deplete large amounts of potassium from the soil, thus effectively reducing the amount of potassium available to the Bermuda grass. To avoid this problem, be sure to avoid late applications of nitrogen to ryegrass stands and utilize as much ryegrass forage as possible by grazing.
Drought: Bermuda grass is quite drought tolerant. However, if drought is combined with other stressors such as potassium and pH stress, drought can be challenging for Bermuda grass to handle. Remember to maintain soil fertility during good growing conditions and periods of rainfall, so if drought does become an issue, Bermuda grass will be better prepared, so to speak.
Poor Nutrient Management in Hay Production: Bermuda grass can be an excellent hay crop if properly managed. High rates of nitrogen fertilization with no attention to depletion of other plant nutrients, especially potassium, can lead to low soil potassium and the associated problems as listed above. Annual soil testing and special attention to potassium levels will help alleviate these problems.
— by Vanessa Olson, associate professor, Texas A&M College of Agriculture and Life Sciences Department of Soil and Crop Sciences, and Texas A&M AgriLife Extension Service state forage specialist, Overton