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.