Comparison of Phosphonate Materials and Application Rate On Algae Development In Putting Green Turf.

Algae infestations in putting green turf often require repeat fungicide applications to control.� A field study was conducted in 2009 and 2010 on �L-93' creeping bentgrass (Agrostis stolonifera) turf in Storrs, CT to identify alternative options for algae control. �Turf was maintained at 4.0 mm and lightly irrigated two to three times day^-1 between 1100 and 1600 hrs from July through September to encourage algae development.� Phosphonate materials and application rate were evaluated as a 4 by 6 factorial within a randomized complete block design with four blocks.� Phosphonate materials included a phosphite fungicide, phosphite fertilizer, and H₃PO₃/KOH each containing mono- and di-potassium salts of phosphorous acid, or H₃PO₄/KOH.� Phosphorous acid or phosphoric acid (H₃PO_x) was applied at 2.69, 5.43, 8.15, 10.86, 13.58, and 16.29 kg ha^-1 every 14 days from 16 Jun to 24 Sep 2009 and 20 May to 26 Aug 2010.� Under limited pressure, algae was least severe in phosphite fertilizer treated turf and most severe where H₃PO₄/KOH was applied throughout 2009.� Phosphite fungicide and H₃PO₃/KOH treated turf were similar to turf treated with phosphite fertilizer.� In 2010 algae development was more severe.� All phosphites reduced algae 4 � 24% compared to phosphate, but did not differ from each other.� Algae decreased linearly with increasing application rate of various phosphonates.� However, turf quality was reduced in August 2010 at phosphonate rates greater than 10.9 kg ha^-1.� These data suggest that phosphites can suppress algae development regardless of formulation, although repeat applications at high rates may reduce turf quality during the summer.