Timothy hay is a very profitable cash crop produced on an estimated170,000 acres in Pennsylvania. It is usually marketed to the horse industry at premium prices ranging from $75 to $180 per ton. Gross revenues for this crop range from $216 to $315 per acre. The prices of good quality timothy hay can exceed that of alfalfa. Production of timothy in Pennsylvania is currently not high enough to satisfy the horse industry; so considerable quantities of timothy are imported into the state to meet the demand. Thus, reductions in the yield and quality of timothy grown in Pennsylvania result directly in economic losses to growers and indirectly to horse owners who have to pay higher prices for imported hay.
Adult rust mites are very small (<1mm). They are spindle-shaped, with four legs and may be white, yellow or orange. You will need a hand lens to
see them. To check for eriophyid mites, look for off-color foliage, leaf or bud abnormalities. Use a 10X or 20X hand lens. Large mite populations often produce many elongate, white shed skins. The mites feed on bulliform cells at the base of grooves on the adaxial leaf surface. Eggs are deposited in the grooves, and both eggs and immatures become distributed higher in the canopy as leaves unfold. Adult mites move downward in the plant crown, where they prefer to feed on the youngest tissues of the plant. The mite undergoes numerous generations per year (a generation time of 16-18 days at 20o C) and there is no known diapause stage. Although development is reduced, mite stages are active during the winter in the crowns of its host plants.
The feeding of A. hystrix causes direct injury to timothy, which results in retarded growth, stunting, and discoloration. No other pest species or agronomic factor is more important as a constraint in timothy production than the cereal rust mite. The feeding of A. hystrix causes direct injury to timothy, which results in retarded growth, stunting, and discoloration. Severe mite infestations have two negative impacts on local growers. Feeding injury causes substantial yield losses, as much as 50%, and also reduces hay quality by the brown discoloration. Horse producers are reluctant to buy hay that is not the normal color of quality timothy. As a side note, A. hystrix is also known to vector ryegrass mosaic virus (RMV), a serious disease of temperate grasslands, and may be a vector of agronpyron mosaic virus (AMV), a minor disease of wheat and other grasses. These diseases cause substantial losses to pasture production in other parts of the world, especially in Europe. However, the presence of RMV and AMV in the USA has not been detected. The symptoms of feeding injury on timothy resemble the typical symptoms of a viral infection; however, disease infections have never been confirmed by ELISA determinations. Nonetheless, if these foriegn viruses enter the US, there exists the potential for their virulence on forage grasses and wheat due to the abundance and wide distribution of the mite vector.
Time of Attack:
Adults and eggs are present overwinter and the adult hatch begins in March with the peak adult population peaking in April. Damage is most evident in April and will continue into May.
Growers should observe fields in early to mid March and look for the presence of small round eggs in the grooves of the timothy leaf surface.