Remember, mold-free hay is an important sign of quality, especially for horse customers. Development of mold-causing microorganisms is directly related to the curing process and the percentage of moisture in the hay at harvest. Also, the current demands for leafiness and high-density bales increase the chances for mold.
It is more difficult to get moisture out of stems than out of leaves. The most efficient way to increase the drying of stems is to use a conditioner (which splits or cracks the stems) in combination with the mower. Hay that has been mowed with a mower-conditioner dries more quickly by releasing moisture more rapidly than unconditioned hay.
Small square bales that are baled after the hay dries to a moisture of 20 percent or less (18 percent for large round bales) usually are considered safe for storage with minimum mold development.
In addition, the use of acid preservatives on hay in the 20- to 30-percent moisture range should help reduce mold development. Chemical preservatives that prohibit mold growth are applied to the hay as it is lifted from the windrow and before it enters the baler.
Research and farm experience report that propionic acid is one of the most effective preservatives that has been approved for this use. Other effective preservatives are either not approved for farm use or application methods have not been fully developed.
Few producers use preservatives on hay with moisture above 30 percent
because of the cost for higher chemical rates, problems in handling heavy
bales, and the tendency of bales to shrink and become loosely tied or light
in weight.