Although they do not infect grasses, blue-green algae are a significant pest problem in the turfgrass industry. These organisms contain chlorophyll just like plants, but they grow by producing chains of thread-like cells similar to fungi. Symptoms of algae appear in areas where the turf canopy has been thinned by poor growing conditions or other pest activity. In these areas, a green or black mat of fuzzy growth is evident in the turf canopy or on the surface of the thatch. During periods of dry weather, this algal growth forms a dry, cracking crust on the thatch surface that repels water and impedes turf recovery.
Algae may develop whenever thinning of the turf canopy permits sufficient air, light, and water to reach the thatch surface. Algal growth is most aggressive during the late spring, summer, and early fall when warm, humid conditions are conducive to algae growth and turf thinning. Low mowing heights, shady conditions, poor soil drainage, and frequent irrigation also encourage algal growth in the turf canopy. Repeat applications of plant growth regulators and/or DMI fungicides may cause thinning of the turf canopy in close-cut turf such as a golf course putting green and lead to algae invasion.
Algae have historically been thought of as secondary colonizers, meaning that they only fill-in areas where turf density has been reduced by some other problem. However, mounting evidence indicates that high levels of algae activity can directly cause thinning of putting green turf, possibly by production of toxins or competition for air, water, and nutrients. An aggressive algae management program can greatly increase the density and overall quality of putting greens during periods of warm and humid weather.
Maintenance of dense, healthy turf is the most effective way to prevent algae invasions. Avoid establishing turf in areas that are heavily shaded or poorly drained, or take steps to correct these problems in established turf. Mow at the recommended height for each turfgrass species, and increase mowing heights in shady areas to compensate for the reduced light levels. Irrigation should be applied deeply and infrequently; apply sufficient water to wet the entire root zone, and then reapply as needed when the turf shows signs of wilt. Putting greens and other high traffic areas must be cultivated regularly to maintain soil drainage and aeration.
Ammonium sulfate, hydrated lime, or other materials can be applied to “burn” the algae in infested areas. Extreme caution is needed when doing this, especially on golf course putting greens, as these materials can also burn the turf or cause nutritional imbalances in the soil.
The fungicides chlorothalonil and mancozeb are effective algaecides. These products will control algae on a preventative or curative basis, but preventative applications are much more effective. Repeat applications on a 10 to 14 day interval during warm, humid weather provides excellent algae control and significantly increases the density of putting green turfgrasses. Note that chlorothalonil and mancozeb are not approved for application to residential lawns.
Fungicides containing copper hydroxide should be used with caution, as copper can accumulate in the soil to toxic levels after repeated applications. For this reason, copper hydroxide should only be used under extreme circumstances to bring severe algae infestations under control.
Once a severe algae infestation has occurred, fungicide applications alone will not provide acceptable control. Additional steps must be taken to physically break-up the mat of algal growth so that the turf can recover. Spiking, aerification, verticutting, topdressing, or combinations thereof are effective ways to accomplish this.
2 Apply fungicides in 2 to 5 gallons of water per 1,000 square feet according to label directions. Use lower rates for preventive and higher rates for curative applications.
3 Use shorter intervals when conditions are very favorable for disease.
* Products marked with an asterisk are not labeled for home lawn use.
++++ = excellent control when conditions are highly favorable for disease development
+++ = good control when disease pressure is high, excellent control when disease pressure is moderate
++ = good control when disease pressure is moderate, excellent control when disease pressure is low
+ = good control when disease pressure is low
? = not rated due to insufficient data
Low = Rotate to different chemical class after 3-4 applications; tank mixing not necessary
Medium = Rotate to different chemical class after 1-2 applications; tank-mixing with low or medium risk product recommended
High = Rotate to different chemical class after EVERY application; tank-mix with low or medium risk product for EVERY application
? = not rated due to insufficient data