Once established on a putting green, silver-threaded moss (Byrum argenteum) can be very difficult to eradicate. This is true for several reasons:  

• Moss is a non-vascular plant. It does not have xylem or phloem and, therefore, cannot translocate herbicides.  

• Moss can survive extended periods of drought by going dormant and then resume growth when rehydrated.  

• The same practices that contribute to firm, fast greens (low cutting heights, low fertility, minimal water applications) contribute to the establishment and persistence of moss.  

Here are the two keys to eradicating moss on putting greens:  

1. Place the priority on growing healthy turf and not having lightning-fast green speeds. This is not what golfers want to hear, but moss gets established where the turf is weak due to scalping and low fertility – precisely the practices superintendents use to produce fast greens. Slightly increasing the cutting height and switching to solid front rollers on the mowers will help desirable grasses compete against moss. Increasing nutrient applications and maintaining balanced soil moisture are other important practices that shift the advantage to the turf.  
   
2. Be persistent with treatments to kill the moss. Since moss is not a vascular plant, it does not translocate herbicides or control products. It is necessary to burn it back layer by layer, hopefully without damaging desirable turfgrasses. There are many labeled and non-labeled treatments that have been tried for moss control, including Dawn Ultra dishwashing detergent (non-labeled), oregano oil (Moss Buster), hydrated lime, and others. In my experience, repeat applications of the herbicide carfentrazone (Quick Silver) or high rates of iron sulfate are the most effective. The Quick Silver label states that applications should be made at the rate of 2.0 to 6.7 fluid oz. per acre and mixed with a non-ionic surfactant, with a follow-up application in 14 days. Note: consult the herbicide label for tolerant turfgrass species and application details. The other product that is very effective for moss control is high rates of iron sulfate. An effective rate is 10 oz. to 12 oz. per 1000 sq. ft. As many have found out the hard way, high rates of iron sulfate can cause burning and turn the turf black, especially Poa annua. The burning and discoloration can be reduced by mixing and applying the iron sulfate in 6 gallons of water per 1000 sq. ft. Applications should be made at 10-day intervals to gradually burn back the moss.  

The article “Managing Silver-threaded Moss in Golf Course Greens” from Golf Course Management Magazine offers additional information and perspective on this difficult pest problem.  

If you have any questions about turfgrass management, irrigation, or water use efficiency, feel free to email them to me at pgross@ewingos.com.