By John Tooker
As timothy fields start to green up, it is time to scout for cereal rust mite, which is also called timothy mite when it feeds on timothy. Timothy mite is a cool-season pest that 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. With early season warmth this year, it seems that populations are likely to be active earlier than normal.
Source : psu.edu
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. The mites are very small so to see them you will need a good hand lens or other magnifying device. 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.