Bermudagrass decline is a term that broadly describes the gradual thinning and sometimes the outright loss of pasture grass stands over time. The term is broad because the problem is often linked to several different causes. These primary causes are often exacerbated by extreme environmental stresses like drought, heavy rainfalls, harsh winters, and late spring freezes. Let’s look at some of the primary causes.
Probably the number one cause of bermudagrass stand decline is the lack of an appropriate fertility program. Although nitrogen (N) is an important nutrient in forage production, it is often the only nutrient applied. Potassium (K) and Phosphorus (P) are essential for forage production and persistence. Grass requires phosphorus for photosynthesis, energy, cell division, carbohydrate production, protein synthesis, root development and early growth, winterhardiness, and nitrogen fixation. Potassium plays an equally, if not more important role in improving the crop's tolerance to drought, minimizing susceptibility to disease, and promoting rhizome and stolon production. In most cases potassium is the limiting factor in a forage fertility program.
Low soil pH causes a problem by creating the opportunity for toxic levels of certain nutrients, such as aluminum, to be absorbed by the plant. This can burn back fine root hairs and prevent root growth. Low soil pH also reduced the availability of other important nutrients, such as phosphorus, potassium, magnesium, calcium, and others. Essentially, low soil pH staves the plant of water and other nutrients.
When pastures are overgrazed, it places excessive pressure on forage resources. Heavy, continuous grazing can decrease plant vigor, just as mowing hayfields too closely can. Grass plants must be given adequate rest times between grazing / cuttings and be left with enough green leaf material to replenish depleted nutrient stores.
With frequent use of heavy machinery in hayfields and excessive animal foot traffic in pastures, soil compaction can become an issue. Georgia soil types, particularly in the Piedmont, can be low in organic matter and are predisposed to compaction. Compacted soil particles create a barrier holding air and water from passing through. It results in soil layers that are difficult for roots to penetrate and thus reduces grass productivity.
Many bermudagrass production systems utilize cool-season annual forages, like ryegrass to supplement nutrition programs in the fall and winter. In years where the ryegrass is extremely productive well into the time when bermudagrass begins to emerge from winter dormancy, it can compete with the bermuda for sunlight, moisture and nutrients. Particularly, a heavy growth of ryegrass during the spring can remove a large amount of potassium from the soil, thus reducing the amount available for the newly emerging bermudagrass.
Invasive weeds can dominate pastures, compete with grasses, and reduce the productive capability of bermudagrass. Insect infestations, like fall armyworms, grasshoppers, and grubs, can have a devastating effect on grass production and cause severe damage. Most often these pest pressures combines with other stressors, like drought and poor fertility, can lead to decline.
It is important to understand that the loss of bermudagrass stands is often a combination of numerous stressors that ultimately lead to grass death. Proper management and a good fertility program and help keep bermudagrass decline from becoming an issue. For more information on how to properly manage pastures and hayfields go to georigaforages.com or contact our office at 706-795-2281 / firstname.lastname@example.org.
Carole Knight is Madison County’s Agriculture and Natural Resources Agent.