Rate Response and Comparison of Phosphonate Materials On Algae Development in Putting Green Turf.

Algae infestations in putting green turf often require repeat fungicide applications to control.  A two year field study was initiated in 2009 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 3.3 mm in 2009 and 2010, respectively.  The area was lightly irrigated two to three times day^-1 from July through September each year and periodically covered with shade cloth in 2010 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, and H₃PO₄/KOH as a phosphorous control.  Phosphorous acid and phosphoric acid (H₃PO_x/KOH) were 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 31 Aug 2010.  Algae development was limited in 2009, but turf treated with phosphite containing materials had less algae than H₃PO₄/KOH treated turf on 1 Oct.  Phosphite treated turf had 3.6 to 20.8% less algae than H₃PO₄/KOH treated turf in June and July 2010 under increased pressure.  Turf treated with 5.43 to 13.58 kg ha^-1 H₃PO_X/KOH had less algae than turf treated with 2.69 kg ha^-1 H₃PO_X/KOH regardless of source in October 2009.  However, algae development decreased with increasing H₃PO_X/KOH application rate regardless of source by July 2010.  These data suggest that preventive phosphite applications can be effectively used to manage algae on putting green turf, regardless of formulation.