SportsTurf provides current, practical and technical content on issues relevant to sports turf managers, including facilities managers. Most readers are athletic field managers from the professional level through parks and recreation, universities.
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www.stma.org March 2015 | SportsTurf 17 years. I have conducted research on most of these. While some appeared promis- ing, and I occasionally got excited about the results, every one of them has had the same problem. They work on some biotypes of Poa annua and not on others. There are literally thousands of biotypes of this species. While these biotypes are all genetically classed as Poa, they vary widely in their response to postemer- gence herbicides. It's not unusual to see multiple types on the same golf course and it is assumed that this is also the case on sports turf. This is Poa annua's strength and our downfall. It always has a way of getting around us. If a product is found that controls 99% on a given site (I rarely see more than 80% control) the remaining Poa that is resistant to the her- bicide will produce seed and simply turn over the population. This is the primary reason why I wrote earlier that I do not think that we will ever see the "magic bullet" herbicide that will completely take out Poa. This genetic variability is the best guarantee of sur- vival that a weed can have. These postemergence herbicides can also be quite variable in their effect on desirable turf species. One of the most effective postemergence herbicide that I worked with has been Prograss (etho- fumesate). This product is very effective at killing most Poa biotypes from peren- nial ryegrass. The catch is the perennial ryegrass. It easily damages Kentucky bluegrass and other species commonly used in sports turf areas. If your field is perennial ryegrass only, Prograss may be the product that you need, but this is rare. Tenacity (mesotrione), a recent postemergence material from Syngenta, can also be effective in some situations. This product, though, is limited to use in Kentucky bluegrass. It will kill bentgrass and can damage perennial ryegrass and tall fescue. This product does hold some promise for Kentucky bluegrass sports fields, but again, the biotype problem with the Poa is a concern. I have seen some promising trials and some that were less promising (Fig. 5). With Tenacity, persistence is important and more than one applica- tion within the limits of the label will be necessary. Xonerate (amicarbaxone) is an herbi- cide used primarily for the removal of Poa annua from both cool- and warm-season perennial grasses. While the golf market was the primary thrust of its develop- ment, it is labeled in many states for other turf areas, including sports fields. Its use in the golf market has been somewhat limited because of phytotoxicity problems with creeping bentgrass. For use on sports fields, follow the label very carefully. It should not be applied to Kentucky blue- grass when air temperatures are expected to exceed 85 F within 3 weeks of its application. It can also damage seedling Kentucky bluegrass and should not be applied to Kentucky bluegrass areas that are less than 12 months from establish- ment. It also should not be applied to turf that has been treated with Embark within the past 3 months. It is best applied for Poa annua control in the spring, when it can be applied at 2 oz/acre in 14 to 21 day intervals, or split into 4 one oz/acre appli- cations separated by 7 day intervals. Dr. Shawn Askew of Virginia Tech reports that a combination of Tenacity at 4-5 oz/A in a tank mix with Xonerate at 1 to 1.5 oz/A is proving to be a good combination for control of Poa annua in Kentucky bluegrass sports fields. Velocity (bisprybic-sodium) is another postemergence herbicide that shows promise for Poa annua control in creeping bentgrass turf on golf courses. It can cause discoloration of creeping bentgrass and there are clearly biotype differences in the response of Poa. It is generally limited to use on creeping bentgrass, or on perennial ryegrass. It can also be used on bermudagrass turf over- seeded with perennial rye. These are very limited situations in athletic fields, and its use in sports turf is quite limited. The newest postemergence, selective product is PoaCure (methiozolin). This product is also known in the industry in the US as the "Korean product" because it comes from Moghu Research Center in South Korea. PoaCure has a new mode of action and works by inhibiting cell wall formation. This product has been very promising in early testing in golf course turf. It has been used under an experimental use permit (EUP) for limited testing in 34 states this year in the US. They hope to begin marketing in 2016. It has provided the best results of any new product that I have seen for many years. However, as more results are being reported, it is evident that there is variability in its control of various Poa biotypes. This product is generally more effective in fall than in spring. It can be used for control in Kentucky bluegrass turf, although Dr. Askew reports varia- tions in phytotoxicity among different cultivars of Kentucky bluegrass in tests conducted in Virginia. Research on sports fields will be an important issue once it has reached the market for golf course use. The company has not tested it in the US on sports turf, but they report that it is widely used in Korea to take Poa from Kentucky bluegrass soccer fields. To this day, the most effective solution to the problem has been the develop- ment of Roundup (glyphosate) Ready creeping bentgrass. This method involves the genetic manipulation of creeping bentgrass. Scientists from O.M. Scotts Co., Marysville, OH, and Monsanto, St. Louis, have successfully inserted a gene into creeping bentgrass that makes the grass tolerant of glyphosate. Creeping bentgrass is normally susceptible to glyphosate, as are most weeds found in bentgrass turf. The susceptible spe- cies include Poa annua, and this makes it possible to remove the Poa without damaging the bentgrass. My students and I did a lot of work at Iowa State on Fig.5. Tenacity (mesotrione) turning Poa annua white in Kentucky bluegrass turf. Courtesy of Tim Van Loo CSFM, Iowa State.