Many timothy fields in the vicinity of Gettysburg, PA (Adams County) are heavily infested with aphids. Initial infestations were found because fields looked as though they were starting to brown.
If you grow timothy, or work with growers that do, you would be wise to scout that acreage for aphid populations. Most plants appear to have around 20 aphids per plant, but populations tend to be variable across fields. Estimates that I received put the acres infested around 2,000 - 3,000 acres, across perhaps a dozen farms. At this point we are not certain of the aphid species responsible for the infestation, but individuals are being sent to Penn State for species determination. Of course species identification is valuable for treating with approved materials, but treatment should occur soon in many of these fields to salvage productivity.
Infestations of aphids in grass hay or small grains tend to be more common in cooler parts of the year, possibly because natural enemies are not as active. Some aphids that commonly infest grasses can be particularly damaging because they inject toxins into plants as they feed, causing yellowing. In some cases, the injury looks brown, reddish, or purple. When scouting for low aphid start by looking low on the plant because some species tends to feed toward the base of plants, but move upward as populations increase.
We know that this is a serious issue around Gettysburg, but do not know how widespread the problem is beyond Adams County. We would appreciate being notified of other timothy fields in other parts of Pennsylvania with these symptoms. It would be helpful to have as many details on the history of the management of these fields as possible.