St. Augustinegrass Response to the Winter of 2022-2023

Jeff Derr, Professor of Weed Science, and Adam Nichols, Research Specialist
Virginia Tech Hampton Roads Agricultural Research and Extension Center - Virginia Beach, VA

At our research station, we have been getting reports this spring of damage to St. Augustinegrass (Stenotaphrum secundatum). St. Augustinegrass (SAG) is a warm-season turfgrass that spreads  by stolons (above-ground lateral stems). It turns brown in late fall after a hard frost, and resumes growth in spring once it stays consistently warm. St. Augustinegrass is a turfgrass species strictly used in the South, as it cannot tolerate the cold winters in the Northern half of the United States. Southeastern Virginia is close to the northern limit of this warm-season turf species. A concern for those maintaining this SAG in our region is the potential for winter damage.

One situation that can lead to winter damage is sudden drops in temperature. Between December 1 and December 22, 2022, there were six days where the air temperature reached a high of 60°F or more, including 67°F on December 6 and 60°F on December 22 (weather data from the Norfolk International Airport). A cold front moved in after that point, resulting in a low temperature of 19°F on December 24. A warm-season turfgrass that is not dormant (still green and growing) is susceptible to damage from low temperatures.

Besides the rapid drop in temperatures in late December, both January 2023 and February 2023 were abnormally warm. January was, on average, 8°F warmer than a typical January, while February was 9°F warmer. There were nine days in February 2023 when the high temperature was 70°F or higher, including a high of 80°F on February 23. There were three days in early March 2023 where air temperatures were 70°F or higher. Warm temperatures such as these can trick a warm-season grass into thinking spring has arrived, resulting in the breaking of dormancy. However, between March 14 and 21, there were five days when the low temperature was 37°F or less, with the lowest temperature being 32°F on March 21.

St. Augustinegrass winter injury

Sudden drops in temperature down to freezing temperatures can damage or kill SAG stolons. St. Augustinegrass does not form rhizomes (underground lateral stems), while bermudagrass and zoysia can produce these underground stems that are more protected from cold temperatures. Thus if SAG stolons are severely damaged, there will be dead spots in a lawn. Since SAG does not form rhizomes, it will take a while for surviving stems to spread and fill in bare spots. This requires  warm temperatures but so far in 2023, we have experienced a fair of amount of cool weather in April and May, limiting the amount of growth possible in this turf species. Further exacerbating the problem in most lawns damaged this winter comes from crabgrass preemergent herbicides. While the preemergent herbicides DID NOT cause the winter injury, many homeowners are seeing, the root-inhibiting nature of these herbicides can prevent new stolons from healthy parts of the lawn to peg down and continue lateral growth. These stolon pieces can often have a chlorotic appearance due to the damaged roots. With the lack of postemergent crabgrass herbicide options labeled for SAG, however, preemergence herbicides are a more effective option to control crabgrass in SAG.

Repair of damaged areas depends upon the extent of the damage and whether a preemergence herbicide has been applied. For lawns without preemergent herbicide treatment, plugs can be pulled from unaffected areas and planted into bare spots or new plugs could be purchased and planted. If there is little overall damage, once could just allow the surviving SAG to spread and  fill in the bare spots. On lawns where preemergence applications have been made, cultivation of  the top layer of soil is required with either aeration or tilling. This will break up the herbicide  layer that would otherwise cause the root dysfunction. Activated charcoal or compost can be added to adsorb the herbicide, limiting its availability to affect SAG . Topsoil could be added to dilute the herbicide concentration at the soil surface, reducing the damage potential. Once the ground has been cultivated, plugs from either the lawn, or purchased, can be planted. Fertilization can be used to promote growth once consistently warm weather arrives.