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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all formulations provided equivalent algae suppression (Figure 4). However, a phosphite rate effect did show that phosphite treat - ments containing ≥ 0.11 pound phosphorous acid/1,000 square feet reduced AUADC com - pared with 0.06 pound phosphorous/1,000 square feet. Increasing the rate beyond 0.11 pound phosphorous acid/1,000 square feet did not improve control (Figure 3). There were no AUADC differences among any rates of potassium phosphate. Turf quality. Turf quality was reduced in the highest phosphite rates during 2010, but not in 2011. Potassium phosphite (for example, Alude, Phosphite 30, analytical phosphite) ap - plied at ≥ 0.28 pound phosphorous acid/1,000 square feet resulted in slight foliar tip burn and canopy chlorosis during July (Figure 5). Discussion In each year of the study, phosphites reduced the cyanobacteria epidemic 57% to 97% on putting green turf compared with non-treated turf. Phosphites applied at 0.11 pound of phos - phorous/1,000 square feet were sufficient to reduce cyanobacteria infestations regardless of source or formulation. Higher rates do not im - prove suppression of algae, and the potential for phytotoxicity to creeping bentgrass increases at rates greater than 0.22 pound phosphorous acid/1,000 square feet. Phosphite-induced algae suppression was greater during conditions that were moderately favorable for algae in 2010 compared with more conducive conditions in 2011. However, effi - cacy of conventional fungicides was also vari- able between these same periods. Interestingly, in all but one rating date during the two-year study (Study 1), commercial phosphite for - mulations provided control equivalent to the pooled effect of chlorothalonil, mancozeb, and sodium carbonate peroxyhydrate. These results suggest that phosphites may be used as a substi - tute for conventional fungicides in algae man- agement programs. Numerous phosphite products derived from various sources (for example, potassium phos - phite, sodium-ammonium-potassium phos- phite, and ammonium-potassium phosphite) and phosphorous acid are commercially avail - able. This study demonstrated that all phos- phite sources evaluated equally reduced cya- nobacterial colonization of putting green turf when applied at equivalent rates of phospho - rous acid. However, the concentration of phos- phorous acid and application rate of commer- cially formulated phosphite products differ, and can result in varying levels of algae suppression. We observed this in our Study 1, where various phosphite fungicides and fertilizers were applied at the midpoint of their label recommendation. Phosphite fungicides applied in Study 1 gener - ally received 1.7 times more active ingredient per unit area compared with phosphite fertil - izers, and resulted in greater algae control dur- ing one year of the study (Table 2). Therefore, while all phosphite products have the potential to equally suppress cyanobacteria on putting greens, label-recommended rates for specific products may limit their relative efficacy. Phosphite competes with phosphate uptake in algae and interferes with normal phosphate- starvation survival responses by preventing uti - lization of cellular phosphate reserves (5,6,9). Under these conditions, growth can be inhib - ited because available phosphate is limited, and algae cannot metabolize phosphite. In the cur - rent studies, an undetermined species of the Study 2: Phosphonate formulations on algae Figure 3. Comparisons from Study 2 of the effects of phosphonate formulations and application rates on algae epidemics, expressed as area under the algae development curve (AUADC), during 2010 and 2011 on creeping bentgrass putting green turf in Storrs, Conn. 2500 2000 1500 1000 500 0 0.06 0.11 0.17 0.22 0.28 0.33 Pound a.i. Alude Phosphite 30 Phosphite (analytical) Phosphate (analytical) AUADC Figure 4. Phosphites can reduce surface algae infestations on creeping bentgrass putting greens. Phosphate Phosphite Phosphite 30 Alude 70 GOLF COURSE MANAGEMENT 03.18

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