Ferrous sulfate or ferrous ammonium sulfate are two products usually used for suppressing or temporarily eliminating moss problems in field crops and turf. These products, however, are not registered for pasture use in Washington State. Permanent control of moss in pastures will require a change of management practices applied to the problem area.
Moss grows in poorly drained or damp, shaded, poorly fertilized areas or where over-grazing occurs. Major improvements in these individual management practices or combinations of these management practices will control the problem. If the area is wet, improve the drainage. If the vegetation vigor is low, improve the fertility of the area by applying adequate quantities of fertilizer and/or lime. If noncompetitive vegetation is present, reseed with improved species such as tall fescue, perennial ryegrass, timothy and white clover or, on well drained soils, orchardgrass.
Once the vegetation is established and growing well, do not overgraze. Graze in a rotational manner (graze only one section of the pasture a time) to a height of 4-6 inches. Allow the pasture to regrow to 10-14 inches before grazing again. Vegetative competition is the best answer to moss control.
Information is available on pasture renovation, reseeding, soil testing, fertilizing and liming. If permanent forage management practices are not instituted to prevent moss development, moss suppressant chemicals generally will give only temporary relief.
For more information contact your local WSU Extension Office.