Algae crusty foes for golf greens
Surface algal crusts are a long-standing problem in turfgrass management. Management practices such as reducing irrigation water, improving drainage and reducing fertilizer rates to lower the availability of nitrogen and phosphorus are helpful. However, despite these measures, algal crusts can remain a tough problem. Chemical control may be necessary during the summer months in the warmer geographical areas.
Our evolving understanding of algal crusts
Interestingly, the “algae” that cause these problems are not the typical aquatic algal species found in streams and lakes. In fact, they aren't algae at all. They are cyanobacteria — terrestrial organisms that can survive in aquatic and also in “near aquatic” habitats on land.
Cyanobacteria are considered to be the most ancient of all photosynthetic organisms. Initially classified as blue-green algae, scientists later correctly placed these organisms into a distinct group of unique photosynthetic bacteria. However, the habit of calling them “algae” still persists.
According to fossil records, the cyanobacteria have been around for about 3.5 billion years. Cyanobacteria exist in varying shapes ranging from single cells to branched or non-branched filaments. Most of the forms that cause slimy surface growth on greens are filamentous types that grow rapidly during the summer.
Cyanobacteria synthesize and secrete large quantities of polysaccharides from their cells. This protective coating enables them to withstand stress brought about by lack of water and high temperatures. Many cyanobacteria are “extremophiles” capable of surviving environmental extremes in deserts, Antarctica and even on the surface of shingle roofs.
True aquatic algae species found in freshwater sites near golf courses and streams are poorly equipped to survive in terrestrial environments. They can be likened to a “fish out of water.” By contrast, several species of cyanobacteria have adapted to moist soil surfaces with great success. They are generally opportunistic and rapidly growing species that are common in polluted lakes and streams and, unfortunately, on golf greens as well.
Cyanobacteria readily form oxygen during photosynthesis using the same chlorophyll molecule found in higher plants. After billions of years on earth, cyanobacteria may have produced most of the atmospheric oxygen we depend on today.
Why cyanobacteria thrive on greens
Cultural problems with surface algae growth can be a major concern on golf greens during the hot summer months. The conspicuous, slimy mats of surface algae are usually found on wet, compacted areas of greens that receive partial shading during the day.
While there are many cultural recommendations for reducing the retention of surface water on greens, seasonal periods of wet weather and limitations in the physical setting of many golf courses nevertheless may encourage cyanobacteria growth on greens despite your best efforts. Poorly drained areas of greens are an excellent habitat for the cyanobacteria because of available surface moisture.
When environmental conditions are favorable (adequate light, nutrients and temperatures), cyanobacteria can grow rapidly in water or on wet soils. Thus, warm summer temperatures with periods of high light intensity and ample supplies of phosphorus and nitrogen encourage prolific growth. These are the conditions you find on many golf greens, so it's not surprising that cyanobacteria can be a problem there.
Phosphorus, especially, promotes rapid growth and the formation of surface crusts by cyanobacteria. Thus, excessive use of high phosphorus in fertilizers, and phosphorous from various types of manure, play an important role in the rapid growth of cyanobacteria in ponds and lakes receiving agricultural runoff, and on golf greens as well.
How cyanobacteria affect plant growth
Growth of filamentous cyanobacteria may be so rapid that the filamentous layers of slime out-compete turfgrass growth during the hot summer months. Surface mats of cyanobacteria growth are usually noted on areas of greens with poor drainage and areas that are partially shaded. Water is a critical element favoring growth of algae and waterlogged areas under shade or areas on a low elevation of the green are preferred sites for these opportunists. Cyanobacteria species commonly observed are Oscillatoria, Phormidium and Lynbya.
The first appearance of blue-green bacteria growth on greens typically occurs during the months of June or July as a dark slime on the surface of the green. Initially these spots may be difficult to observe, but as they get larger the turf begins to yellow and thin due to a lack of oxygen and drainage under the crust (which resembles a microscopically interwoven mat 5 to 30 feet in diameter).
If water, nutrients and light are ample, the quickly developing mat forms a contiguous layer as thick as ⅛ inch. During the hot summer, algal mats are associated with areas of declining turf suffering from stagnant conditions in the root zone, reduced supplies of oxygen to roots and, possibly, the production of toxins that are released by the bacteria and then taken up by affected turfgrass plants.
Controlling outbreaks of cyanobacteria after the fact is not an easy project because their development can be so rapid during warm weather. Preventive management is the best approach.
Water management is a critical factor to consider in avoiding trouble spots on greens. Areas where dark-green to black colonies of cyanobacteria are observed must have surface moisture to support the colony. It is helpful to increase water infiltration rates on greens with poor drainage by aerating and backfilling the holes with a sand-based mix. Occasionally, irrigation frequency and duration may be the cause of excess water in these areas. If possible, avoid frequent watering that maintains high surface moisture levels on greens.
Available phosphorus appears to be a critical factor to stimulate rapid growth of cyanobacteria during the hot summer months. Organic manure products and runoff containing animal manures may contribute excess phosphorus, but also keep fertilizer rates, especially phosphorus, as low as practical.
- Chemical controls
Though preventive (cultural) measures are the first line of defense, superintendents use fungicides extensively for the control of surface algae during the summer months. The rationale for using a fungicide to reduce algae problems may seem somewhat difficult to understand because these products were designed to reduce fungal disease problems, not to control algae or blue-green bacteria. However, a few fungicides effectively reduce algae without affecting the desired turf.
It is best to employ a fungicide program before cyanobacteria have developed into an extensive mat that is difficult to penetrate. When cyanobacteria colonies are well-established, my research shows that chlorothalonil or mancozeb sprays on a 7- to 14-day schedule at the high label rates will achieve control (see graph, page Golf 7). However, preventive treatment with these fungicides requires only the low label rates to minimize algal growth. (Note: not all chlorothalonil or mancozeb products have labeling for algae. Consult labels for specific product information. Also, labels usually refer to “algae” not “cyanobacteria.”)
We have observed that spraying these fungicides on greens that are dry at the time of application is more effective at controlling cyanobacteria than similar applications to wet greens. This could be due to reduced leaching of the active ingredient into the soil. Two or three rounds of spray at 7-day intervals are usually required to establish satisfactory control.
Our experience shows that you should continue fungicide treatments at the low rates even after symptoms of colonies have disappeared. If conditions remain favorable, they are capable of returning to their original aggressiveness very quickly after treatments have ceased.
Dr. Phillip Colbaugh is a turfgrass pathologist with Texas A&M University Research Center (Dallas, Texas).
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