Thursday, October 01, 2009

Water-logged lawns

As flood waters across the state recede after record rainfall, homeowners are left with a messy aftermath to deal with. This includes water-logged lawns that could suffer from the effect of too much of a good thing.

“Excessive rainfall creates an unfavorable soil environment for root growth,” said Alfredo Martinez, a University of Georgia Cooperative Extension plant pathologist. “The oxygen is displaced in the soil pores by water.”

Roots need oxygen

Without oxygen, root growth is restricted. In extreme cases, toxic gases such as hydrogen sulfides and metallic sulfides can accumulate, he said.

The result is weak or dead plants. Water-logged soil stays warmer longer and can increase turfgrass damage.

“Turfgrass injury due to flooding appears as dead brown areas,” Martinez said.

Symptoms will appear a few days after the flood water recedes, and the injured areas will follow the outline of low flooded areas. The first sign of trouble is raw sewage-like odor, which indicates a lack of oxygen in the soil.

After long periods of flooding, turfgrass can partially rot, he said.

“As with diagnosis of many turfgrass problems, history of the area is critical to correctly identify the problem,” Martinez said.

Watch for signs of damage

Additional problems associated with excess water are the diseases that thrive in extremely moist conditions and take advantage of the stressed plants.

The extent of damage depends on the length of flooding, said UGA Extension turfgrass specialist Clint Waltz.

Bermuda grass and bahia grass are most tolerant of flooding. Centipede is least tolerant. Zoysia and St. Augustine are intermediate.

To assess damage, look for white roots, green leaves or green or white runners above and below the soil surface. Green and white indicate a healthy plant while soft, milky white or brown stems and roots suggest the plant is dead.

Lend a helping hand

Lightly rake brown turf areas to determine if some grass has survived.

To help your lawn recovery from the flood:

* Improve surface and subsurface drainage. Keep drains clean. Dig temporary surface drains or put in subsurface drains.

* Remove any sediment like soil and organic debris on the surface by raking or shoveling to help surviving turf recover. Mow off dead leaves.

* Apply one-half pound of nitrogen per 1,000 square feet to encourage grass recovery. Follow normal maintenance practices the rest of the year.

If 40 percent to 50 percent of the area has healthy grass, there’s probably enough left to ‘grow in’ the rest, Waltz said.

Replacement an option

If more than 60 percent is lost, consider using sod, seed, plugs or planting a cover to restore the lawn. Sod produces an instant lawn with less long-term mess.
You can seed tall fescue now until early-November. Plugs should be installed later in the growing season.

You can establish a temporary cover with ryegrass or tall fescue. This should be done from mid-September through early-November. Turf-type tall fescue seeded at five pounds to six pounds per 1,000 square feet may survive if seeded in September. Higher seedling rates will lead to disease and other stress problems and should be avoided.

If tall fescue is used and bermuda, centipede or zoysia is wanted, the tall fescue will survive until next summer when centipede can be seeded or sodded into the tall fescue providing a gradual transition.

“In conditions like these, keeping things simple and being patient are the best strategies,” Waltz said.

For more information on caring for your turfgrass and landscape, contact your local UGA Extension agent at 1-800-ASK-UGA1. Or, visit the Web site www.GeorgiaTurf.com.

By Sharon Dowdy
University of Georgia

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