Poa trivialis is now common in sports fields, possibly due to as little as one contaminated seed source from the many overseedings done on sports fields. Once germinated, Poa trivialis spreads via stolons which may be further spread during every hollow tine aerification. Poa trivialis is shallow rooted, has poor wear resistance, is extremely susceptible to dollar spot, and often goes dormant with the heat of July and August. None of these qualities make for a good summer or fall use sports field. However, the constant overseeding and aerification required for a top-notch sports field almost dictates that Poa trivialis will become a problem. The only good solution right now is the relatively new herbicide called Certainty from Monsanto. It is labeled for use on commercial and residential turf including sod farms, cemeteries, golf courses, and other sites (read sports fields). Though the current version of the label does not provide specifics for Poa trivialis control in Kentucky bluegrass/perennial ryegrass sports fields, it does not prevent its use in sports fields. Our recommendation is to apply 0.25 to 0.50 oz product/acre starting in early June followed by a second application two weeks later. Apply a third application if needed two weeks later. Certainty is fairly slow to act and it should start yellowing the turf in a week or so with thinning shortly thereafter. It can cause phytotoxicity on some perennial ryegrass cultivars, so the lower rate may be warranted. Reseeding may be needed depending on density of Kentucky bluegrass or ryegrass. Our data with creeping bentgrass suggests waiting three weeks after the final Certainty application to seed and that appears to be similar with either Kentucky bluegrass or perennial ryegrass. Poa trivialis will likely be a long-term problem requiring multiple years of control, so aggressive fertilization in the fall and dormant-seeding Kentucky bluegrass after the season are required to increase the amount of Kentucky bluegrass in the field. Also consider experimenting on a practice field prior to trying this on the game field because cultivars, rates, weather, etc. may affect your results differently than what we would expect on our research plots. More information on Poa trivialis including biology and identification can be found at http://www.agry.purdue.edu/turf/pubs/AY-41.pdf . You can also see our latest research on Poa trivialis control and other sports field management techniques at our Field Day on July 17 ( http://www.agry.purdue.edu/turf/events/fieldday/fdregistration.pdf ).
