Controlling Moss and Algae in Turf
Edited from a publication by Gil Landry and Tim Murphy, Extension Crop & Soil Sciences
Occasionally turfgrass begins to thin and moss and algae begin to grow. These primitive plants develop because conditions for growing dense, healthy turf have declined. Neither moss nor algae are thought to be parasitic and both are spread by wind blown spores. Moss and algae can both form crusts on the soil surface which reduces air and water movement into the soil. Factors that favor the development of moss and algae include wet and humid conditions and compacted soils with thin turf.
Mosses are branched, threadlike green plants which form a tangled, thick mat over the soil. Moss is more common in shady areas with infertile, acidic soils and excessive thatch.
Algae are thread-like green plants which form a dense, green scum over the soil surface. Algae is common in full sun conditions and fertile soils.
Cultural practices that favor growth of turfgrasses will reduce the competition from moss and algae:
Maintain good soil fertility and pH - Have the soil tested to determine proper lime and fertilizer needs. For most turfgrasses, the soil pH should be between 5.5 and 6.5.
Improve drainage - Soils which stay moist because of poor drainage should be contoured so that water will drain off the area. In some cases, underground drainage may be necessary to correct wet conditions.
Increase light penetration and air circulation - Pruning tree limbs below 10 feet and removing selected limbs in the crown will improve light penetration and air movement. Also removing some of the least desirable trees and thinning and/or removing shrubs will help. Areas surrounded by buildings and vegetation with limbs close to the ground may require considerable work to provide adequate air circulation and light penetration.
Use a shade tolerant grass - Use St. Augustinegrass, zoysiagrass or tall fescue. If direct sunlight does not reach the ground during the day, an ornamental ground cover or mulch may be better for the site.
Cultivate compacted soils - Aerify with a machine that removes plugs of soil to reduce compaction. Drainage in fine textured soils (clay) can be improved by cultivation and adding organic matter.
Irrigate deeply and infrequently - Avoid light frequent irrigations. Wait for signs of moisture stress such as the development of a bluish-gray, dull color before irrigating. Then irrigate to wet the soil at least 6 inches deep. 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 may be renovated if at least 50 percent of the area has the desired turf. If turf cover is less than 50 percent, then reestablishment will be necessary. Refer to information on lawn renovation found on page 14 of Lawns in Georgia - http://pubs.caes.uga.edu/caespubs/pubs/PDF/b773.pdf. Under heavily shaded conditions, sodding is the recommended means of reestablishing turf.
Chemical suppression of moss and algae is temporary unless the growing conditions are improved. For both mosses and algae, raking or vertical mowing to break up the layer prior to and after chemical treatment and topdressing after will be helpful.
The key to algae control is to allow it to dry then break-up, or disturb, the algal mat allowing turf stolons to root into the soil. Typically the algae is associated with over irrigation or high rainfall and low mowing heights, so turning off the irrigation and raising the mowing height can reduce algal growth.
For Algae control see page 9 of this publication - http://www.ent.uga.edu/pmh/Com_Turf.pdf
For Moss control:
Hydrated lime -Apply 2 to 3 pounds of hydrated lime in 3 gallons of water per 1,000 sq. ft.
Ferrous sulfate -Apply 4 to 7 ounces or 10 ounces of ferrous ammonium sulfate in 3 to 5 gallons of water per 1,000 sq. ft. Other forms of iron are available alone (Scotts Moss Control Granules) or in combination with fertilizer for moss control (Scotts Lawn Fertilizer Plus Moss Control and Fertilome Classic Lawn Food Plus Moss Control).
Certain herbicides can be used to control moss and algae. However, as with the chemicals previously discussed, control is temporary unless growing conditions are improved.
Quicksilver (carfentrazone) selectively controls moss. It is labeled for most major warm season grasses. Follow labeled rates and directions closely.
Nonselective herbicides, such as glyphosate (Roundup, other trade names) will kill moss, but will also kill, or severely injure turfgrasses. The use of glyphosate should be limited to spots completely covered by moss when renovation of the site is planned. Allow 10 to 14 days following the application of glyphosate before seeding or sodding the site.
Research shows that oxadiazon, the active ingredient in Ronstar, reduced moss infestations on golf course putting greens. This research was not conducted in Georgia so it is not known if oxadiazon containing herbicides would control the various moss species here. Also, herbicides that contain oxadiazon are registered for use only on turfgrasses located on commercial properties (golf courses, commercial buildings, athletic fields, etc.). Oxadiazon containing herbicides are not registered for use on home lawns; therefore, their use is not recommended for lawn care companies that maintain home lawns.
Various products that contain potassium salts of fatty acids (Lesco Moss and Algae Eraser, Safer Demoss and Algaecide, Safer Moss Killer for Lawns) may be used to control moss and algae in turfgrasses. These products kill moss or algae through a contact mode of action. Use varies according to the specific product. Unless directions on the label are carefully followed, these products can injure desirable turfgrasses.
Acknowledgement: The authors acknowledge the University of Tennessee publication entitled Algae and Mosses in Turfgrasses by T. Samples and A. Windham from which the original circular was patterned.
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