Originally created 08/07/03

Wet summer brings out moss, algae

The wet summer continues, and so do problems with moss and algae in lawns.

Mosses are branched, threadlike plants that form a tangled, thick mat over the soil. Algae are threadlike plants that form a dense, green scum over the soil surface. Neither moss nor algae is considered parasitic, and both are spread by wind-blown spores.

Once algae dries out, it forms a tough black crust. Moss also can form a crust on the soil surface, which reduces air and water movement into the soil.

Factors that favor their development include wet and humid conditions and compacted soil with thin turf. Moss is more common in shady areas with infertile, acidic soils and excessive thatch, while algae is found in full-sun conditions and fertile soil. Many golf-course superintendents are fighting algae problems on golf greens.

The only permanent control of moss and algae is to correct the conditions reducing the grass growth. The following practices will help you overcome your problem:

Maintain good soil fertility and pH. Have the soil tested to determine proper lime and fertilizer needs.

For most turfgrasses, the pH should be 6.0 to 6.5. Centipede tolerates a lower pH better than other grasses.

Improve drainage. Soils that stay moist because of poor drainage should be contoured so that water will drain off. In some cases, tile drainage (French drains) may be necessary to correct wet conditions.

Increase light penetration and air circulation. Pruning tree limbs below 10 feet and selected limbs in the crown will improve light penetration and air movement.

Removing some of the least-desirable trees and thinning or removing shrubs also will help. Areas around buildings and vegetation with limbs close to the ground may require considerable work to provide adequate air circulation and light penetration. But if you love your shrubs and trees more than the grass, you sometimes have to decide what is more important to you.

Use a shade-tolerant grass. If there is too much shade for centipede or Bermuda, try St. Augustine or zoysia.

In areas with no direct light or little filtered light during the day, an ornamental ground cover or mulch may be better.

Cultivate compacted soils. Aeration with a machine that removes plugs of soil will help reduce compaction. Core aerators can be rented, purchased or contracted through lawn-care companies.

Cultivation and adding large amounts or organic matter can improve drainage in fine-textured soils (clay).

Irrigate deeply and infrequently (if we do have to water). Avoid light, frequent watering. Wait for signs of moisture stress, such as the development of a bluish-gray, dull color, before irrigating. Then irrigate to wet the soil to at least 6 inches.

Most healthy turfgrasses need about 1 inch of water per week during active growth. If puddling occurs, stop irrigating and wait two to three hours for the water to soak into the soil before irrigating again. Repeat the cycle as needed until the soil is wet to the desired depth.

Renovate. Generally, turf can be renovated if at least 50 percent of the area has the desired turf. If grass cover is less than 50 percent, then re-establishment will be necessary.

Chemical control of moss and algae is temporary and the problem will recur unless the growing conditions are changed. Some of the products for this use contain zinc, copper, and ferrous sulfate.

A couple of brand names are Moss Master and Moss Control. Algae also can be controlled with copper sulfate at the rate of 2 to 3 ounces per 1,000 square feet.

A nonselective herbicide such as Roundup will kill moss, but it also will kill your grass. However, Roundup could be used in limited spots completely covered by moss. Then, in 10 to 14 days, you could proceed with renovation.

Sid Mullis is director of the University of Georgia Extension Service office for Richmond County. Call 821-2349, or send e-mail to smullis@uga.edu.


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