San Antonio Express News
Sunday, April 16, 2006
Winter kill is a general term used to describe the loss of turfgrass plants during winter months. Loss of turfgrass plants during winter months can be caused by factors such as: low temperature kill (freeze damage), desiccation (drying out of plant material), disease activity and insect damage such as grubs. In most years, desiccation is the number one reason for loss of turfgrass in home lawns, commercial properties, sports fields and golf courses. With the extensive drought conditions throughout South Texas in 2005, including winter months, loss of turfgrass from desiccation is potentially going to be a continued major problem throughout the spring of 2006.
Individuals who did not water their turfgrass plants during the 2005-2006 winter months could experience loss of plant material. Grasses such as St. Augustinegrass are especially susceptible to winter kill from desiccation during winter months. In fact, numerous St. Augustinegrass lawns in the area appear to have lost some grass. While it is a little early to tell how extensive the damage will be, expect there to be a significant loss of St. Augustinegrass in lawns that were not watered during the past winter months. While St. Augustinegrass is hardest hit by the dry conditions, it is also possible to loose turfgrasses such as bermudagrass and zoysiagrass, especially if they were not watered at all in late summer and winter months.
Trying to diagnose what killed the turfgrass plant during the dormant winter period can sometimes be difficult. Listed below are symptoms to look for when trying to determine the actual cause for loss of turfgrass areas from the winter months.
A. Low Temperature/Desiccation
The symptoms for both of these causes are very similar and it is often impossible to determine which one actually killed the grass. In some situations, loss of grass can be attributed to both dry soil conditions and low temperature injury. With both of these factors, the entire turfgrass plant will be a brown to tan color, eventually turning a gray color in late winter to early spring. Even though the root system is dead, the turfgrass plant will still be firmly attached to the ground. However, this past winter, we did not have any significant cold spells. In comparison, if the loss is due to grub injury, the dead grass can be easily lifted from the soil because all the roots have been chewed off by the grubs.
B. Grub Damage
The white grub, larval stage of the May/June beetle will feed on the turfgrass plants in late summer to early fall months, thus destroying the root system of the grass plants. Without any root system, the grass plant cannot take up the necessary nutrients and water required for survival. Again, the easy way to distinguish between grub damage from environmental damage is to pull on the turfgrass plants, and if the grass pulls up very easily, then the damage is likely to have been caused by grubs feeding on the root system the previous summer and fall months. Also, in late winter to early spring months you should be able to find the white C-shaped larvae in the soil below the damaged turfgrass. Generally, it takes at least 4 to 5 grubs per square foot to cause loss of turfgrass.
There are two main disease problems that can cause serious damage and/or loss of turfgrass plants in the winter months. These are brown patch and Take-All Root Rot (TARR). While brown patch will attack all major turfgrass plants, it is primarily a problem on St. Augustine-grass and zoysiagrass in the fall months when night time temperatures drop below 70° F and excess water is available. Usually, the brown patch fungus does not kill the plants, but will kill all the leaf blades in the affected areas, thus weakening the plants and making them more susceptible to low temperature injury. Also, affected sites in the lawn will be slower to green up in the following spring and may appear to be dead areas as the lawn starts to green up. The easiest method to identify old brown patch injury is to pull on the leaf blades in the affected area and if they pull away from the stolons without any resistance, then the damage was caused by brown patch. Also, if brown patch is the only problem, then the stolons and roots will still be white to light green in color.
Take-All Root Rot is caused by a soil borne fungi that attacks the root system of the plant in the fall and spring months when soil temperatures are in the 60 to 65° F range. This fungus has also been shown to attack all turfgrasses, but has primarily been a major problem on St. Augustine-grass. Symptoms of TARR in the spring include thin, yellow stands of St. Augustinegrass to large patches of totally dead grass. Due to the drought conditions in the fall and winter months in 2005 – 2006, there is probably going to be a lot of TARR problems showing up in lawns this spring. TARR and brown patch are often confused with each other and in some cases, it is possible that both diseases were active in the lawn. Outlined below is a chart to help distinguish the difference in damage from TARR and brown patch.
Take-All Root Rot
|Leaves from stolons||brown color, firmly attached||brown color, easily pulled|
|Stolons||brown color||white to light green color|
|Roots||short, dark brown to black color*||white color|
|* The short, dark brown to black roots is a key characteristic for identifying TARR activity. In some cases, due to the extensively damaged root system, St. Augustinegrass can be pulled up similar to grub damage. However, with grub damage, roots have been completely chewed off the plant, while with TARR you will still find short, dark brown to black roots on stolons.|
Next week’s article, will list some best management practices for managing turfgrasses in a lawn during drought conditions.
Special Thanks: To the Turfgrass Specialists of Texas A&M University-Dr. James McAfee, Dr. David Chalmers, and Mr. Roger Havlak all with the Department of Soil and Crop Sciences, for their inputs and contributions with this article.
Remember, Learn and Have Fun!
David Rodriguez is the County Extension Agent-Horticulture for Bexar County. He represents the Texas Cooperative Extension with the Texas A&M University System. For any landscape or gardening information, call the Bexar County Master Gardeners AHotline@ at (210) 467-6575, email questions to firstname.lastname@example.org, or visit our County Extension website at http:bexar-tx.tamu.edu