Orchardgrass often comes in as a contaminant in grass seed, especially K-31 tall fescue. Buying good grass seed is the first line of defense against this weed. Orchardgrass is a pasture grass and therefore is not found in the “weed seed” portion of the seed label. Rather, orchard- grass will be listed as “other crop seed.” Try to buy grass seed that has 0.0% “other crop seed.”
Control options are few and painful. Use glyphosate (Roundup, Killzall Weed and Grass Killer, Kleeraway Systemic Weed and Grass Killer and others) to spot spray orchardgrass clumps. Any lawn grasses you hit will be killed, so keep the spots sprayed as small as possible. Wait until the spots have turned brown and then cut out the clumps and replace with a small piece of sod. Large numbers of orchardgrass clumps may mean it is more practical to kill the entire lawn and start over. This should be done in the fall rather than now.
For information on identification of orchardgrass, including images, go to:
http://kswildflower.org/grass_details.php?grassID=15 (Ward Upham)