The Effects of Nitrogen Source and Spray Volume on the Colonization of Silvery-Thread Moss.

Turf managers often spray soluble nitrogen sources as tank-mix partners with fungicides and plant growth regulators, however, it has been observed that soluble nitrogen increases the severity of silvery-thread moss (STM) in golf course putting greens. The effects of differing soluble N sources on STM colonization when applied at various spray volumes is unknown. Two N sources, urea and ammonium sulfate (AMS), were applied weekly at 4.89 kg N ha^-1 at three spray volumes. Dibasic potassium phosphate was used to supply all treatments with 0.42 kg P ha^-1 and 1.058 kg K ha^-1, including a water control. Treatments were completely randomized with four replications, and the study was repeated. Applications were made using a CO₂ powered backpack sprayer, and the three spray volumes were produced using TeeJet 8001EVS, 8004EVS, 8008EVS nozzles to apply 93, 411, and 1019 L H₂O ha^-1, respectively.  Silvery-thread moss was propagated from plugs collected in the field and grown in the greenhouse. The plugs were dried, ground, and 0.7 g of plant material were evenly placed in each pot. The pots were 10.16 cm diameter lysimeters filled with sand meeting USGA specifications for putting green root zones.  Pots were photographed weekly within a custom-made light box. Digital images were analyzed to determine percent STM cover. At experiment completion (7 WAT), plants were harvested, dried, and weighed. Fertility was significant in both runs, on every rating date. Spray volume was significant on several rating dates in run 1, with the lowest spray volume resulting in less moss coverage. At 6 WAT, AMS resulted in 70.9 and 55.6% moss coverage in run 1 and 2, respectively, which was significantly higher than urea. Moss treated with AMS produced three times as much dry matter compared to plants treated with urea in both runs of the study.