Golf Course Management

MAR 2018

Golf Course Management magazine is dedicated to advancing the golf course superintendent profession and helping GCSAA members achieve career success.

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03.18 GOLF COURSE MANAGEMENT 67 Cyanobacteria, or blue-green algae, are a common problem on putting greens. Several genera of cyanobacteria (for example, Lyng - bya, Nostoc, Oscillatoria, P ormidium, etc.) are known to reduce putting green quality. Typi - cally, cyanobacteria affecting putting greens are filamentous organisms that produce food through photosynthesis. They proliferate on putting greens under various conditions: where thin turf offers opportunities for colonization, where sunlight passes through the turf canopy to the soil surface, where frequent irrigation maintains surface moisture, and where nitro - gen and phosphorous are readily available (1). Turf managers who use reclaimed water to irri - gate putting greens have also reported increases in algae. Both increased use of reclaimed water and aggressive cultural practices that reduce the turf 's competitive ability promote opportu - nities for cyanobacteria to be a persistent chal- lenge to the quality of putting greens. Impacts of cyanobacteria on putting greens Detrimental impacts of cyanobacteria on putting greens include the formation of algal surface crusts (1) and subsurface anaerobic con - ditions, both of which contribute, in part, to black layer. Surface crusts begin as films of ac - tively growing algal colonies near the crown of turfgrass plants (Figure 1). During prolonged wet conditions, filaments grow upward along stem bases, extending vertically and horizon - tally to form a layer of cyanobacteria in the upper turf canopy that can smother small or weak tillers. Once dry, algae and matted til - lers are reduced to a thin, impermeable crust in affected areas. As turf cover is reduced, water movement and growth of the turf through algal crusts is inhibited. Several species of cyanobac - teria and green algae have been associated with the formation of algal crusts. More recently, yellow spot, a malady purportedly induced by cyanobacteria species, has been reported on putting greens in various regions of the United States (8). Symptoms are associated with ag - gregates of filamentous P ormidium species or Oscillatoria species, which are suspected of ex - uding compounds toxic to foliage. Existing control options Control of algae on putting greens is accom- plished primarily through cultural practices that promote rapid surface drying and favor vigorous turf growth (1). However, chemical control of cyanobacteria and/or green algae is often required on sites with shade and/or poor drainage where turfgrass growth is reduced. Fungicides containing chlorothalonil, manco - zeb, and copper hydroxide + mancozeb reduce surface algae symptoms. However, efficacy of these active ingredients in controlling algae has been variable. Label restrictions limit the total number of applications and/or the amount of chlorothalonil and copper hydroxide + man - cozeb applied to putting surfaces each year, and some state and local restrictions prohibit chlorothalonil applications in environmentally sensitive areas. These restrictions can reduce the ability of turf managers to control algae when conditions favorable for algal growth are prolonged. Applications of copper hydroxide + mancozeb applied during elevated tempera - tures can also be phytotoxic to putting green turf, thus limiting its use during the summer. Phosphites Phosphite (H 2 PO 3 – ) is a form of phospho- rous that differs from phosphate (HPO 4 – ) by the substitution of an oxygen atom for a hy - drogen. Both forms, as well as the fungicide fosetyl-Al, are generally referred to as phospho - nates. Phosphate is used by plants in various bioenergetic reactions and for structural cellu - lar components. However, the hydrogen substi- tution in phosphite prevents the use of this ion as a phosphorous source for cellular activities and components in plants and other organisms (7). Phosphite fungicides and fertilizers are gen - erally derived from a solution of phosphorous acid and water that has been pH-neutralized with a base, ester or alcohol (for example, po - tassium hydroxide or sodium hydroxide). The resulting products are commercially available formulations of potassium phosphite, ammo - nium phosphite or sodium phosphite. Phos- phites have been demonstrated to suppress the severity of Pythium blight (caused by Pyt ium ap anidermatum) (2), anthracnose (caused by Colletotri um cereale) (3), and Microdochium patch (caused by Microdoc ium nivale) (4). Phosphites have also been observed to sup - press algae. However, determination of the in- fluence of phosphite source, application rate and efficacy relative to current chemical algae control products is needed. Therefore, the ob - jectives of this study were to assess whether various phosphite sources could preventively suppress surface cyanobacteria colonization of putting green turf, and to determine optimal application rates of various phosphites for sup - pressing surface colonization by cyanobacteria. Materials and methods Site description Field studies were conducted during 2010 and 2011 on an L-93 creeping bentgrass (Agrostis stolonifera) putting green established on a native sandy loam soil with a pH of 6.2 at the University of Connecticut Plant Sci - ence Research and Education Facility in Storrs, Conn. During the study, the field was mowed twice daily, five days per week, with a triplex mower adjusted to a bench setting of 0.125 inch (3.2 mm). Nitrogen was applied at moder - ate to low annual rates to reduce turf vigor and encourage algae infestation. Phosphorous and potassium levels were within the optimal range based on soil tests. Irrigation was applied at ap - proximately 0.1 inch (2.5 mm), two to three times daily, and black-knit, 60% shade cloth was placed on the turf surface periodically to promote uniform colonization of the turf sur - face by cyanobacteria. Experimental design and treatments Two independent studies were conducted over two years within the same field, and were arranged as randomized complete block de - signs with four blocks. Study 1: P os ite sources. Study 1 consisted of 12 treatments: three commercial phosphite fungicides; three commercial phosphite fer - tilizers; potassium phosphite and potassium phosphate laboratory-prepared analytical stan - dards; three non-phosphonate-based fungicides labeled for algae control; and a non-treated con - trol. Rates of commercial products were gener- ally selected based on the intermediate rate listed on product labels. Specific products and the active ingredient, phosphite source, formu - lation and application rate for each evaluated in Study 1 are listed in Table 1. The phosphite fertilizer Magnum was evaluated only dur - ing 2011. Study 2: P os onate formulation and rate. Treatments in Study 2 contained two main fac - tors: phosphonate formulation and rate. Phos- phonate formulations included a potassium phosphite fungicide (Alude, Cleary Chemical Corp.), potassium phosphite fertilizer (Phos - phite 30, Plant Food Co.), potassium phosphite analytical standard, and potassium phosphate analytical standard. Each phosphonate formu - lation was applied at equivalent rates of phos- phorous or phosphoric acid including: 0.06, 0.11, 0.17, 0.22, 0.28 and 0.32 pound/1,000 square feet (0.29, 0.54, 0.83, 1.07, 1.37 and 1.56 grams/square meter).

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