By John Tooker
Scouting from Schuylkill County has revealed that timothy mites are active and feeding in timothy fields. This cool-season pest, which is a form of cereal rust mite that has specialized on timothy, has caused headaches for many timothy growers, particularly in southeastern Pennsylvania where it seems to have spread to the majority of fields, reducing growth and crop quality. This year it seems that populations are active earlier than normal, which may not be surprising given how mild temperatures have been recently.
To determine whether this pest species is active in your timothy fields, scout fields for signs of damage and their presence. Mite feeding causes leaf blades to roll up, presumably to provide the mites with better protection and microclimate. Look for leaf blades that are rolled up tightly, rather than leaf blades that are flat and normally expanded. To see mites, you will need a good hand lens or other magnifying device—the mites are very small. Pick rolled leaves from around the field and inspect them carefully; mites tend to occur in grooves between the leaf veins (Figure 1). Treatment is recommended if 25% of tillers show the leaf curling within several weeks of green-up. Chemical options are very limited, but Sevin XLR has a supplemental label in PA allowing its use against mites on timothy. Treatments need to use high pressure to force the material into the leaf rolls. See
Cereal Rust Mites for more details.