Effect of Nitrogen Source and Spray Volume on the Establishment and Colonization of Silvery‐Thread Moss (Bryum argenteum Hedw.) in Putting Greens

During the growing season, golf course superintendents often fertilize putting greens with low nitrogen rates on a weekly or biweekly interval, using foliar applications of soluble‐N sources such as ammonium sulfate (AMS) or urea. Silvery‐thread moss (STM) is ectohydric; consequently, we hypothesized that STM would be injured from the higher partial salt index of AMS compared to urea, and that injury would be exacerbated by low spray volumes. Therefore, the objectives of this study were to: (i) determine if STM growth is reduced by AMS compared to urea, and (ii) understand the effect of spray volume on STM growth, when using a high‐salt‐index N source. In greenhouse studies, AMS or urea were applied weekly at 4.4 lbs N acreα1 to nascent STM growing in pots. The N sources were applied at three spray volumes: 11, 44, and 110 gal H2O acre−1. Percent moss cover was determined weekly from digital images, and after 7 weeks, gametophytes were harvested, dried, and weights recorded. Contrary to our hypothesis, AMS increased STM cover and dry weight compared to urea and an untreated control. Furthermore, spray volume did not affect STM cover at any rating date. Follow‐up field studies were conducted on putting greens at Rocky Ford Turfgrass Research Center and Colbert Hills Golf Course. Although results were less consistent in the field, AMS again generally increased STM cover compared to urea and the untreated control. Superintendents managing STM infestations should limit or avoid use of AMS as an N source.