Warm-season perennial grasses are the basis of pasture systems and livestock production in Texas. The most prominent warm season species are bermudagrass (seeded and hybrid) and bahiagrass. Neither of these species is native to the state of Texas but they are well adapted to Central and East Texas. Unfortunately they can be greatly impacted by cold winter temperatures. Central and East Texas have seen record temperatures in late December. Many may be concerned about whether or not their warm season forages have survived these weather conditions.
Bermudagrass and bahiagrass grow best when soil temperatures are above 70º F. These temperatures usually occur when daytime air temperature reaches approximately 80º F. Night temperatures are usually a good indicator of soil surface temperatures. Warm-season grasses will not produce roots (rhizomes and stolons) unless the soil temperature exceeds 55º F for several weeks. As day length becomes shorter and temperature drop below 50º F, bermudagrass and bahiagrass cease shoot growth, lose chlorophyll, and begin nutrient translocation (carbohydrates, nitrogen, potassium and phosphorus) for storage in the below ground tissue (rhizomes). Without proper plant nutrition, even the most winter hardy variety can succumb to winter kill or injury. Injured plants are slow to recover in the spring and after every grazing cycle or cut of hay.
As a warm-season grass, bermudagrass can be sensitive to winter damage in spite of dramatic genetic improvement to cold tolerance. Winter kill can be caused by a combination of factors. Winter kill is dependent on moisture, low temperature and the duration of low temperatures. Low temperatures can be damaging when it occurs late in the winter or early spring and last up to a week to ten days.
The most susceptible sites for winter kill include ones that are: north facing slopes; heavily shaded; poorly drained; poorly adapted cultivars; heavily trafficked during winter; substantial soil compacted, were newly sprigged or seeded last summer; and soils with deficient levels of phosphorus and potassium.
To reduce the risk of winter kill it is critical to follow best management practices during the active growing season. Those practices would include maintaining appropriate soil fertility especially potassium levels for bermudagrass. Potassium is essential in plants to combat diseases, aid in water use and for winter hardiness. Deficiencies of potassium can cause both yield losses and stand losses. Bermudagrass is especially sensitive to potassium deficiencies.
Maintaining some substantial bermudagrass stubble height (>4”) going into winter can be beneficial for the future growing season. Higher stubble height means more substantial root structure to capture deeper soil moisture and nutrients. Maintaining a higher stubble height generally results in increased loading of rhizomes reserves and increases canopy insulation of crowns during the winter.
It is important to note that winter kill in warm season perennial grasses is highly variable and difficult to estimate because it could be affected by genetics, temperature extremes, geographical location, soil drainage, nutrient management factors and endless combination of the factors that interact with each other to cause a highly variable impacted phenomenon.
Unfortunately we won’t know the true impact of this weather until bermudagrass greens up in the spring. For now we can plan ahead for improving our forage management for this coming warm season. Using best management practices that encourage healthy stands, better nutrient utilization along with grazing management and hay production practices that extend the longevity of the stand is the producer’s best line of defense.
What to look for and when to assess winter damage? While bermudagrass is still dormant, roots and rhizomes can be carefully dug up to determine if they are healthy or necrotic. Necrotic tissue will look dark and rotted while healthy roots and rhizomes will look white or tan and succulent. If they are healthy then continue to wait until green up and active growth before applying any nitrogen fertilizer. Bermudagrass and bahiagrass will break dormancy after our last frost which can occur in mid-March. Green up will usually take place from late March to mid-April depending on location. If roots and rhizomes are necrotic, wait until late-April to mid-May before making a major re-planting decision. If you decide to re-plant, select forage species and varieties that are adapted to your location as well as fit your production system goals. See Publications for forage species and variety information. Bahiagrass is a prolific seed producer so even if you have lost a portion of your stand it will fill back in as seeds germinate throughout the summer. Remember, bermudagrass is resilient and has high tolerance of cold and drought if managed appropriately.
Professor, Forage Extension Specialist
Soil & Crop Sciences Department
Texas A&M AgriLife Extension Service
Texas A&M University System