Bermuda Lawn Spring Dead Spot

Spring Dead Spot affects Bermuda lawns

Bill Sevier: Ask a Master Gardener

Monday, June 6, 2016

Q: There are some dead spots in my Bermuda lawn. What might cause this and what can I do? Troy, Tulsa

A: While there are several factors that may kill areas of Bermuda lawns that are noticed in spring, winter-kill and a fungal disease called “Spring Dead Spot” (SDS) are the chief causes in Bermuda lawns in our area.

To sort this out after you have eliminated such things as chemical spills, animal urine and soil compaction, you should address the questions of whether it was there last year.

Almost without exception, winter kill spots were not there last year and are found only after a wet and cold winter with snow cover for an extended period of time.

SDS once started tends to enlarge and shrink in the same area from year to year. This disease is due to one of two fungi that infect and damage Bermuda grass in the fall, but the consequences are not seen until the following spring due to the lack of greening of the dead grass, hence the name.

SDS patches may be a few inches to several feet wide. When the roots and rhizomes are inspected, they are usually black as opposed to a cream color of healthy plants. The open patches may harbor weed invasions in the summer. The fungus does not usually affect weeds or other plants.

After a decision is reached about the presence of SDS, how to prevent and cure it is the next challenge. This is not something for which one can run down to the garden center and obtain an effective fungicide to eliminate it.

Most of the control is cultural, that is to say, altering the way you grow and manage your grass. It also depends on the variety of Bermuda; some are more disease resistant than others.

The timing of fertilizer applications is important for disease susceptibility. Studies have revealed that fertilizing Bermuda lawns late in the growing season — after Sept. 1 — is associated with an increased incidence of this disease. Late fertilization delays winter dormancy, which reduces tolerance to disease.

Raking out all the diseased Bermuda will help the healthy grass spread into the bare spot during summer. Core aerification and dethatching may help by improving the health of the grass; however, it should be done in winter, to avoid spreading the disease.

Fungicides are available for treatment of SDS. Some of these are restricted-use chemicals available only to licensed applicators. Some are expensive, as well.

If a fungicide is used, it should be sprayed in September after the temperature is below 70 degrees and repeated in 30 days. Some suggest using two different types of fungicides for these applications.

Oklahoma State Extension information lists fungicides to use in SDS, but the head of the turfgrass department has concluded the organism that causes the disease in Oklahoma is so poorly responsive that he does not recommend them.

Garden tips

§  Insect Alert: Now is the time to be on the lookout for bagworms on juniper and arborvitae and lace bugs on sycamore, pyracantha and azaleas. Contact Tulsa Master Gardeners at 918-746-3701 for control suggestions.

§  Thatch is a layer of dead and living stems, shoots and roots that pile up on top of the soil at the base of lawn grasses. If it is more than ½-inch thick it should be removed with either a core-aerator or power-rake. Now is the time to de-thatch Bermuda and zoysia, if needed. Dethatch fescue in the fall.

§  Bermuda lawns will benefit from up to 2-5 pounds of nitrogen fertilizer per 1000 square foot in divided applications from now until the end of August. Apply the first application now. Fertilize tall fescue lawns now if you have not fertilized this spring. Do not fertilize these lawns in summer, it will make them susceptible to heat and disease damage.