A drought-stressed look in timothy hayfields and pastures this time of year could be a sign that cereal rust mite is present, says John Tooker, entomologist with Penn State University Extension.

The cool-season pest first showed up in fields in south-central Pennsylvania about 10 years ago. Since then, the mite has spread to other parts of the state and region, causing headaches – including reduced growth and crop quality – for many growers.

In scouting for signs of damage, Tooker advises using a good magnifying glass, since the mites are microscopic and challenging to see. Look for leaf blades that are rolled up tightly, rather than blades that are flat and normally expanded.

“The feeding of the mites causes leaves to roll up, presumably to provide the mites with better protection and microclimate.”

Treatment is recommended if 25% of tillers show leaf curling within several weeks of green-up. Chemical options are limited, but Sevin XLR has a supplemental label allowing its use against mites on timothy in Pennsylvania. Applicators need to use high pressure to force the material into the leaf rolls.

See a fact sheet from Penn State for more on cereal rust mite.