Effect of Phosphite Rate and Source on Cyanobacteria Colonization of Putting Green Turf

Cyanobacteria compete with putting green turf, resulting in algal surface crusts that can reduce turf density and quality. The objectives of this study were to assess preventive control of surface cyanobacteria colonization of putting green turf with various phosphite salt sources and formulations. An optimal rate of phosphorous acid to suppress cyanobacteria while minimizing phytotoxicity was also examined. Two field studies were conducted concurrently on an ‘L‐93’ creeping bentgrass (Agrostis stolonifera L.) putting green in Storrs, CT, during 2010 and 2011. Study 1 assessed various commercial formulations and sources of phosphite salts, potassium phosphate, and non‐phosphonate fungicides on percent plot area infested by algae. Study 2 identified rates of phosphorous or phosphoric acid applied as commercial formulations of potassium phosphite or technical preparations of potassium phosphite and phosphate, which reduce or enhance algae development and turf quality. Potassium phosphite reduced percent plot area infested by 90 to 100% and 52 to 86% compared with potassium phosphate in study 1 during 2010 and 2011, respectively. Few differences in plot area infested were observed among six commercial phosphite formulations and sources or non‐phosphonate fungicides throughout study 1. Area under the algae development curve decreased by 52 to 78% as phosphorous acid increased from 2.9 to 5.4 or 8.1 kg ha−1 throughout the 2‐yr study. Turf quality was reduced in phosphorous acid‐treated plots at rates greater than 10.8 kg ha−1. Phosphite products applied at 5.4 to 8.1 kg ha−1 every 14 d can be used to suppress cyanobacteria with reduced risk of phytotoxicity for putting green turf.