IDENTIFYING CANDIDATE HERBICIDES FOR MOSS CONTROL. A. Post*, S. Askew, and D. McCall, Virginia Tech, Blacksburg, VA (23)


   Since the loss of organometallic herbicides, prevalence of silvery threadmoss (Bryum argenteum) in golf course putting greens has increased. Demands for faster playing surfaces have led to reduced putting green mowing heights and fertility, creating perfect conditions for competitive displacement of creeping bentgrass by silvery threadmoss. Currently only one professional herbicide, carfentrazone (Quicksilver) and two fungicides, chlorothalonil (Daconil) and mancozeb (Manzeb) are labeled for moss control on putting greens. With a limited number of products available, the golf industry has experimented with off-label products with moderate success, including baking soda, lime, iron-containing fertilizers, and Ultra Dawn dish detergent. Research to date has not provided a solid understanding of which chemistries work and which do not. The goal of this research is to more thoroughly screen available crop protection chemicals for effects on silvery threadmoss and ultimately discover new options for its control. 

   A preliminary herbicide screen on silvery threadmoss was established as a randomized complete block design with ten replications. It included 49 herbicides applied at one and two times the labeled use rate and a non-treated control. Over 1200 actively growing moss plugs approximately 1cm in diameter were collected from a bentgrass putting green and separated into groups of 99 plugs for each of the ten replicates. For each of 98 herbicide treatments, ten moss plugs were treated in a spray chamber calibrated at 814 L/ha. After treatment, plugs were randomly placed into 24-well cell culture plates. Photos were taken at 0, 3, 7, 10, 14, 21, and 28 days after treatment (DAT) and data were captured in Sigma Scan Pro 5. Sigma Scan counted green pixels in the range of hue=38 to 100 and saturation=0 to 100. When compared to the 0 DAT pixel counts, % reduction in green color was calculated for each moss plug which we equate to a measure of control. Data were subject to ANOVA and means separated by Fishers protected LSD (p=0.05). At 3 DAT, carfentrazone reduced green color 55% and pelargonic acid reduced green color by 89% and more than all other treatments.  Other herbicides which significantly reduced green color included: flumioxazin, MSMA, glufosinate, sulfentrazone, and an experimental. By 10 DAT, several herbicides reduced green color by more than 90% including flumioxazin, carfentrazone, fosamine, diquat, and sulfentrazone. However, by this time fungal growth over the moss plugs was significantly limiting ability to attribute reduction in green color to herbicide activity versus fungal growth; the nontreated control plugs had 70% reduction in green color where no herbicide was applied.  

The study was completed despite the fungal problem and this preliminary screening supported previous literature reports that carfentrazone, flumioxazin, and pelargonic acid effectively control silvery threadmoss. We were not able to support findings that oxadiazon and oxyfluorofen are effective but several chemicals were added to the list of potential candidates for moss control, including: an experimental product, MSMA, sulfentrazone, and fosamine. Fungicide and surface sterilization screens are in progress to develop a procedure to prevent fungal growth in future chemical screens.  Herbicides, fungicides, plant growth regulators, adjuvants, and biocontrol organisms are slated for future evaluation.