Some fields that incurred damage last fall may be thin or have bare soil in heavy traffic areas. These thin or bare soil areas will quickly become infested with Poa annua, knotweed or crabgrass if a plan is not in place to get desirable grass in those areas as soon as possible.

In addition to trying to prevent weeds from emerging in those areas, some fields may have mature weeds, like Poa annua, that are creating problems on the field. Poa, while green and offering at least some kind of grass cover, will usually go dormant or die in the summer heat and it is shallow rooted, so easily torn or kicked out during games. As well as not being a suitable grass for athletes to play on, it does not blend well with the darker perennial ryegrass or Kentucky bluegrass, so stands out and generates unfavorable comments about field aesthetics.

Here are some tips this spring to have a plan in place to deal with Poa, from both a pre-emergence and post-emergence stand-point:

* PRE-EMERGENCE HERBICIDES. Prevent new Poa seeds from germinating by applying a pre-emergence herbicide that does not injure mature favorable grasses, or impede desirable grass germination. Tenacity (mesotrione) can be applied at the time of seeding to prevent Poa from emerging without adversely affecting desirable grass or new seedlings. If another pre-emergence herbicide is used, check the label for re-entry periods as many of them do not a allow you to re-seed with desirable grasses for 3-4 months.

* REGULAR OVERSEEDING WITH PERENNIAL RYEGRASS. Over-seed thin areas and bare spots continually. On athletic fields, over-seeding is not a 1 x per year operation. Rather, it should be done each time the turf gets thin or is lost. Heavily trafficked fields should be over-seeded weekly. The quickest grass to achieve ground cover is perennial ryegrass and it offers the best chance to out-compete the Poa annua plants.

* SOUND CULTURAL PRACTICES. Maintain fields to favor the desirable grasses (perennial ryegrass and Kentucky bluegrass). In essence, this means mowing at the correct height and applying fertilizer and water judiciously. Mowing too high allows Poa to produce abundant seedheads (see picture, top left). Mowing too low (i.e. ~ 1-inch) stresses Kentucky bluegrass and favors Poa. Perennial ryegrass is more inclined to compete with Poa at low mowing heights. Being shallow rooted, Poa thrives in wet, fertile soils, so irrigation and applications of quick release N should be limited. Poa will also grow in compacted soils when the desirable grasses will not, so regular aeration in high traffic areas is key.

*NON-SELECTIVE HERBICIDE, THEN SEED OR SOD. If there are large isolated spots of Poa annua, they can be spot treated with a non-selective herbicide like glyphosate and reseeded with perennial ryegrass or sodded with Kentucky bluegrass. Sodding is a great way to get Kentucky bluegrass back onto an athletic field. High traffic areas like goal mouths and between hashes could be re-sodded each year, if the budget allows.

Posted by Pam Sherratt & Dr. John R Street,

SportsField Management