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Options for Chemical Control of Moss in Putting Greens

Silvery thread moss (Bryum argenteum) in putting greens is becoming an all-too-common occurrence on Pennsylvania golf courses. It can creep into a green virtually unnoticed, until suddenly it seems as though it is taking over the entire playing surface. Once established, moss is extremely difficult to control and almost impossible to eradicate. Chemical control measures are often tough on turf, and slow in killing the moss. However, a few new products and strategies for moss control are providing some relief for Pennsylvania superintendents.

Silvery thread moss on a putting green

Although chemical control strategies can suppress or kill moss, they must be coupled with changes in the cultural conditions that allowed moss to encroach into the greens in the first place. The most obvious culprits, low nitrogen levels, aggressive mowing practices, and liberal irrigation, can usually be adjusted to some degree. Other causes of moss encroachment, poor drainage, disease problems, shade, traffic, and poor air circulation, represent greater challenges. If the major causes of moss encroachment are not dealt with, even the best chemical control program will not prevent it from coming back.

A flurry of moss control research at Oregon State, Cornell, North Carolina State, and Penn State have revealed that several products (some labeled for moss control and some not labeled) have provided good control of silvery thread moss when used at proper rates and application timings. The following is a product-by-product summary of these products and their effects on moss.

Summary of Chemical Moss Control Options

Chemical controls for moss include products containing metals, soaps, salts, or herbicides. All of these products can damage turf, so be sure to thoroughly test each product on a practice area or nursery before large-scale use. Realize that results of moss control programs can be much more variable than those for diseases and weeds. Factors such as climate, pH of soil and spray tank water, rate of product and dilution rate of water, time of year, and grass type can all influence efficacy and the potential to injure turf. Therefore, results obtained at your course may differ somewhat from those described for the products listed below.

Metals:

Iron sulfate - Iron sulfate has been used to control moss in putting greens for decades. Studies at Penn State showed that iron sulfate applied at 0.15 to 0.2 lb iron in 2 gallons water/1000 ft² on 14 day intervals (four to seven applications) provides good moss control. The pH of tank water may influence efficacy, with slightly acidic water (pH = 5.8 to 6.5) providing better control that alkaline water (pH > 7.5). Iron sulfate can be applied at any time during the growing season, but moss control and turf recovery is better during periods of moderate temperatures (50 to 80°F). Some application difficulties may occur due to clogging of nozzles and tracking of spray residue on turf. Iron sulfate produces a noticeable, but temporary black color on moss and turf. When the black color dissipates, a pleasing green up of the turf occurs. Iron sulfate is not labeled for moss control in turf.

Blackening of moss following application of iron sulfate

Junction® (copper hydroxide) - Junction is a turfgrass fungicide that contains 15% mancozeb and 46% copper hydroxide. Recently, the manufacturer of Junction released a FIFRA Section 2(ee) recommendation for moss control on turf (greens, tees, and fairways). The recommendation lists a preventative and a curative program for moss control. We don’t see a lot of value in the preventative program if you don’t already have a moss problem. It calls for 1 to 2 oz of product applied on 7-day intervals beginning in early spring and continuing to early fall. This is an intensive, costly spray schedule that is difficult to evaluate if you don’t have a moss problem. The curative program of 4 oz product in 2 gallons water/1000 ft² applied every 7 to 14 days (the 2 (ee) recommendation states that seven or more applications may be required) in the fall has shown promise in the northeast and mid-Atlantic regions. However, we have some concerns about the open ended statement "seven or more applications" which appears on the 2 (ee) recommendation. There is probably a limit as to how much of this product can be safely applied during a season before serious copper-related injury occurs. Our research has shown noticeable, but minor injury following only five, 5 oz/1000 ft² applications of Junction in fall.

Research at Oregon State, Cornell, and Penn State revealed that Junction applied at 5.0 oz product/1000 ft² every 14 days beginning in mid-October for a total of five applications provides good to excellent control of silvery thread moss the following spring. In our tests, we did not observe any noticeable effects on moss during the fall application period. It is possible that as copper concentrations accumulate in moss during fall, the plants become weaker, eventually succumbing to the copper during the winter months. Studies at Penn State showed poor moss control with Junction when applied in warm weather during the summer months. We also found that fall applications are much more effective in controlling moss than spring applications.

Our research showed that yellowing of Poa annua may occur during spring following fall applications of Junction, and this year we observed some yellowing immediately after our early fall applications. In all of our tests, this yellowing was minor and no turf thinning occurred. We have spoken with one superintendent in Pennsylvania who experienced strong and objectionable yellowing following an application of Junction, so be sure to put out a test strip on a nursery or practice green before making broadcast applications on your greens.

Yellowing of Poa annua following fall applications of Junction

We frequently get questions regarding excess copper build up in soils following multiple application of Junction. This is probably not a big concern on most greens if the program is limited to about seven applications and is only carried out for one or two years. However, more research is needed to determine the number of applications that can be safely applied over consecutive (three or more) years.

Another question involving Junction is how the pH of tank water influences efficacy. Generally, the solubility of copper increases as pH of the tank solution decreases. It follows that slightly acidic tank water will probably help to increase moss control. The pH of the tank water in our study was between 6.5 and 7.0 and appeared to be adequate for obtaining good moss control. Keep in mind that copper hydroxide is a base, and pH of the tank water will likely increase after Junction is added. Using very acidic tank water can also increase the chance of copper-related turf injury.

Soaps and Salts:

Dawn Ultra - Dawn Ultra dishwashing detergent applied at 2 to 8 oz product/1000 ft² during cool or warm weather on 14 day intervals (4 to 6 applications) can control moss in some cases. You may need to apply Dawn Ultra as a drench (in 6 to 12 gal water/1000 ft²) if applications in 2 gallons of water/1000 ft² are not effective. Trials with Dawn Ultra at Penn State during summer and fall using different rates, timings, and water dilution rates yielded poor moss control. Inconsistent results and burning of turf may be a concern when using Dawn Ultra. This product is not labeled for moss control in turf and probably never will be.

Baking soda (sodium bicarbonate) - Baking soda is useful for spot treatments only. Our studies revealed that drenching individual moss patches with a solution of 2 to 3 tablespoons baking soda/quart of water on warm, sunny days provided very good control. In most cases, only one or two applications were required for complete control. If you want to try baking soda, be very careful when spraying the moss patches as some burning of surrounding turf may occur. As with all moss treatments, be sure to test baking soda on a practice area before using on a green. As you may have guessed, baking soda is not labeled for moss control in turf.

TerraCyte(sodium carbonate peroxyhydrate) - TerraCyte is a granular product labeled for moss and algae control in established greens, tees, and fairways. According to label directions, the product should be applied with a drop spreader at 8 lb/1000 ft² in spring or fall when temperatures are 50°F or above. Because TerraCyte is a fine granular product, coverage of moss is incomplete and repeat applications are usually required. The label allows for subsequent applications on consecutive days at rates of 2 to 4 lb/1000 ft². TerraCyte should be watered-in immediately following application.

Terracyte is a fine granular product that should be applied with a drop spreader.

At Penn State, we found that TerraCyte applied at 8 lb/1000 ft² every 14 days for a total of four to five applications in warm and cool weather provides excellent moss control. We observed some burning of turf following applications during high humidity conditions. Consecutive day applications of 4 lb/1000 ft² increased efficacy, but also increased burning of turf. Burning of turf is more pronounced on dew-covered turf, so be sure to mow prior to application of TerraCyte.

Herbicides:

Quicksilver(carfentrazone) - Researchers at North Carolina State University recently found that Quicksilver herbicide controls moss in putting greens without serious turf injury. Researchers report that Quicksilver applied at 7 oz product/acre in 100 gallons water on 14 day intervals for two to three applications provides excellent control of moss. Quicksilver appears to work under warm (mid 80’s) and cool conditions. This product is not labeled for moss control. Although we have no first hand experience with this product, we will initiate studies this summer.

Dr. Peter Landschoot and Mr. Joshua Cook, Dept. of Crop and Soil Sciences, Penn State  June 9, 2005

Moss control research at Penn State is funded by the Pennsylvania Turfgrass Council. Products were donated by Harrell’s Turf Specialty and BioSafe Systems.