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.