How to diagnose grass ailments

By tom Dominguez, Extension Service

Winter kill is a general term used to describe the loss of turfgrass plants during winter months. It 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 New Mexico, including winter months, loss of turfgrass from desiccation is potentially going to be a major problem.

If turfgrass plants were not watered during the winter months, you could experience loss of plant material.

Grasses such as St. Augustine and Centipede are especially susceptible to winter kill from desiccation.

While it is a little early to tell how extensive the damage will be, I would expect there to be a significant loss of St. Augustine grass in lawns that were not watered during the past winter months.

It is also possible to loose turfgrasses such as bermudagrass and zoysia grass, especially if they were not watered at all in late summer and winter months. Trying to diagnose what killed the turfgrass 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 in the winter months.

l 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.

l Grub damage

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.

The white grub, larval stage of the May/June beetle will feed on the turfgrass plants in late summer to early fall months, destroying the root system.

Again, the easy way to distinguish between grub damage from environmental damage is to pull on the turfgrass plants. If it pulls up very easily, then the damage is likely from grubs.

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.

l Diseases
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, Centipede and zoysia grasses 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. Augustine grass 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.

The short, dark brown to black roots is a very key characteristic for identifying TARR activity.
In some cases, due to the extensively damaged root system, the St. Augustine grass can be pulled up similar to grub damage. However, with grub damage, the roots have been completely chewed off the plant, while with TARR you will still find the short, dark brown to black roots on the stolons.

Tom Dominguez is an agent with the Quay County Extension, NMSU Extension Service. He can be reached by emailing tdomingu@nmsu.edu or calling 461-0562.