Poa Trivialis: Friend and foe
Poa trivialis (rough-stalk bluegrass) is gaining recognition. That much is certain. However, not all of it is favorable. That, too, is certain. This turfgrass is becoming a bane to turf managers who frequently find it difficult to obtain turfgrass seed that isn't contaminated with Poa trivialis. Nevertheless, it is an increasingly popular choice with superintendents, who find that its qualities make it an excellent grass for overseeding dormant bermu-dagrass in the Southeast, the Gulf states and the Southwest.
First, the good news Poa trivialis is adapted to wet and shaded situations, and turf managers have used this species for such sites for many years. However, superintendents find that the superior playing surface and generally low cost of Poa trivialis make it a desirable species for winter overseeding on golf courses. Thus, its use is steadily increasing for both fairways and putting greens, and suppliers have brought several improved varieties to the marketplace to satisfy this demand.
Superintendents often mix Poa trivialis with perennial ryegrass for fairway overseeding. This mix provides a better playing surface than ryegrass or Poa trivialis alone and reduces total seed costs. Joe O'Donnell, with Sunbelt Seeds (Norcross, Ga), supplies many superintendents with Poa trivialis seed. He states that an 85:15 mix of ryegrass and Poa trivialis is typical for fairways. However, on greens, pure Poa trivialis provides a decidedly better putting surface than ryegrass, and this is the destination of most Poa trivialis seed.
Poa trivialis establishes easily compared to most turfgrass species. Not quite as easily as ryegrass, perhaps, but it germinates only slightly more slowly and requires less surface preparation. This ease-of-establishment-in addition to a superior putting surface-is a major reason for Poa trivialis' popularity as an overseeding species.
Preparation for overseeding Poa trivialis is similar to that of perennial ryegrass-some combination of scalping, verticutting and topdressing. No single standard exists, however. O'Donnell notes that, "There are almost as many ways of overseeding preparation as there are superintendents." In addition to cultural techniques, some superintendents use plant growth regulators to suppress the bermudagrass and reduce its competition with the germinating seedlings.
Overseeding takes place at varying times, depending on the region. In North Carolina, the process begins in late September. Farther south, the time for overseeding gradually becomes later, until you reach South Florida where the process doesn't begin until November. In the arid Southwest, a similar timetable applies, with most overseeding occurring in late September and October.
O'Donnell notes that seed size is an important aspect of Poa trivialis' usefulness. It allows you to overseed and then return later with follow-up seedings. This is possible because the seeds' small size allows them to filter down through the turfgrass canopy to a suitable environment for germination without additional surface preparation. Thus, according to O'Donnell, many superintendents initially put down around 8 pounds of seed per 1,000 square feet and then "dust" their greens with 1 to 2 pounds of seed in two, three or even four follow-up applications. This is similar to the recommendation you find on many seed labels, which commonly advise overseeding 4 or 5 times in consecutive weeks, using 2 to 4 pounds each time. Repetitive applications improve the playing surface in a way that the large-seeded perennial ryegrass does not allow because it requires surface preparation.
The overall seeding rate for Poa trivialis varies from 8 to 20 pounds, according to O'Donnell. Heavier seeding rates will, of course, create a solid stand more quickly. Thus, if a course is planning for an upcoming event, the superintendent may elect to use higher rates.
Of equal importance for an overseeding species is spring transition Poa trivialis' lack of heat tolerance is the primary reason it transitions more readily than ryegrass in this critical regard. O'Donnell notes that at any given site, management factors are the primary determinant of the progression of transition. Further, transition is a little different each year. However, "All else being equal, Poa trivialis transitions more easily than ryegrass. This definitely is a selling point with superintendents," says O'Donnell.
Now for the bad news To many turf managers, including lawn-care contractors and superintendents in cool-season areas, Poa trivialis is nothing less than a curse. It contaminates commercial turfgrass seed with what many people feel is increasing frequency, and there seems to be no ready solution to the problem. Seed companies have even had to defend themselves in court against claims that their seed was the source of Poa trivialis contamination. The trouble stems from several factors, each compounding the others:
* Seed cleaning. Poa trivialis seed is difficult to separate from others, especially Kentucky bluegrass and bentgrass. * Patchy appearance. Even tiny amounts of Poa trivialis contamination can cause big aesthetic problems. Because Poa trivialis spreads in dense patches-with a bright-green color that contrasts badly with desirable turf-just a few plants ruin turf appearance. Additionally, with its lack of heat and drought tolerance, Poa trivialis dies out in summer, leaving bare, unsightly patches where it thrived in cooler weather. * No selective control. Because no selective control exists for Poa trivialis, turf managers must constantly rogue out patches, and lawn contractors often must perform "make-goods" after unknowingly using contaminated seed. * Seed analyses. Existing seed analyses may not be adequate to ensure Poa trivialis-free seed. Detecting Poa trivialis seed takes an experienced seed technician, especially when the task is to distinguish it from Kentucky bluegrass, to which it is almost identical in appearance. It's likely that some labs are better than others at this task. Plus, standard seed samples may be too small (often just 2.5 grams-about a tablespoon) to reliably detect contamination.
What can turf managers do? You can insist on a more complete analysis than what's listed on the seed label. Unfortunately, Poa trivialis counts as "other crop" on seed tags. Thus, even if the seed analysis for that lot detected Poa trivialis, the label wouldn't explicitly say so. However, suppliers often have more complete analyses on hand (or they know where to get them). If your supplier can't or won't provide you with it, don't purchase their seed-or don't complain if it contains Poa trivialis. As more customers begin asking for this information, more seed suppliers will be sure to have it available.
Another option is to hire a seed lab to conduct an analysis of the lot you wish to purchase. You then can ensure that the sample is larger than a standard analysis, which increases the odds of spotting contamination. Malcolm Sarna, chief of the Turf and Seed Section of the Maryland Department of Agriculture, notes that, "When reviewing a test report, it is important to know what quantity of seed the analyst examined for a given contaminant." Sarna states that, "[some] tests may have had as little as 1 gram.examined for Poa trivialis!" Twenty-five grams is better and many seed laboratories suggest 50 grams. Paying for an analysis that costs $100 or more is not cost-effective for small purchases, but you definitely should consider this for larger purchases, such as for golf courses.
Yet another option is to use Gold Tag seed. This is "sod-quality" seed that already comes with a complete, specific list of everything-nothing is lumped into generic categories like "other crop." Unfortunately, Gold Tag seed may not be available in all areas, and it is relatively expensive. It also does not completely avoid the fact that even "complete" analyses can, apparently, sometimes overlook Poa trivialis. Nevertheless, it's the best-quality seed available on the open market.
No strategy for dealing with Poa trivialis contamination is foolproof. To say, "Be picky about the seed you buy" oversimplifies the problem. However, if you are willing to search for a conscientious supplier and are ready to pay more for higher-quality seed, you at least can significantly reduce the chance of Poa trivialis contamination. Several suppliers go to extensive efforts to combat this problem. Ask questions about this, and purchase seed from those that show the greatest diligence.
Another side of the debate needs telling, however. Dr. Richard Hurley, an expert on Poa trivialis with Lofts Seed, cautions against jumping to conclusions. Hurley states that, "Poa trivialis has been intentionally seeded in shade sites for many years." Further, "Millions of pounds of Poa pratensis, or Kentucky bluegrass.was imported during the first 60 or 70 years of this century. Much of this seed carried with it.Poa trivialis as a crop contaminant. This provided a large seed pool which has assisted in naturalizing Poa trivialis across the United States and Canada."
The fact that Poa trivialis grows naturally in so many areas makes it difficult to pinpoint a source of contamination-if there is one. Hurley states, "I have walked [golf course] construction sites and on most occasions found significant numbers of Poa trivialis plants already present.. This fact is evidence that no matter what turfgrass seed is selected to establish a new golf course, patches of Poa trivialis will be present two or three years after establishment."
Some people note that the Poa trivialis infesting their turf closely resembles improved varieties and cite this as evidence that the plants came from contaminated seed. However, Hurley has observed naturally occurring specimens that appear quite similar to improved varieties. Consistent with this, DNA analysis has shown that plants originally thought to have resulted from contaminated seed were actually genetically similar to native populations growing in the area. Hurley does not deny that contamination is occurring or that the seed industry should exercise vigilance to combat the problem. However, turf managers cannot automatically assume that contaminated seed is to blame for Poatrivialis growing in their turf. Many cases of alleged contamination are really nothing more than native Poa trivialis plants.
If you already have an infestation of Poa trivialis, you have few chemical options. Non-selective herbicides can eliminate patches (and then force you to re-establish turf in that spot), but no selective control for Poa trivialis exists. Hurley has a suggestion, however. "The best advice.is to water sparingly and provide good soil drainage. Dryer soil will encourage desirable grasses to be more competitive against Poa trivialis. I have observed the disappearance of Poa trivialis from a mixed stand of Kentucky bluegrass after a few years. This appeared to be related to dry soil conditions. So there is hope."
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