In Transition

The transition period from perennial ryegrass to bermudagrass in the spring is a critical time in managing turfgrasses that are overseeded. A timely transition is the key to ensure the health of the bermudagrass. Failure to remove perennial ryegrass in a timely manner will ultimately result in a decline in the bermudagrass stand. Unfortunately, over the past few years, there has been a trend to hold bermudagrass in as long as possible in the spring/summer (often too long), and in the fall overseed too early. The reason for this is to lengthen the perennial ryegrass season, yet if it is lengthened too long, bermudagrass will disappear over time. Bermudagrass is also not tolerant to shade. In addition, bermudagrass cannot grow into areas that are being occupied by perennial ryegrass. The objective should be to remove the perennial ryegrass in a timely manner that will allow a full bermudagrass recovery in time for overseeding in the fall. A full recovery includes not only 100 percent ground cover, but also rhizome and stolon growth. Previous research and observations indicate that bermudagrass needs approximately 100 days of growth in the absence of perennial ryegrass competition. Failure to provide growth conditions without perennial ryegrass competition can result in significant shading of the bermudagrass canopy and lead to substantial bermudagrass stand loss.

In some areas, perennial ryegrass will transition out without herbicides, particularly when you use management practices that promote bermudagrass growth and discourage ryegrass growth in the spring. This is true in areas such as Florida or south Texas and other areas with a similar climate. However, in most areas, you need to use herbicides to kill the ryegrass in order to provide 100 days of bermudagrass growth free of ryegrass competition. Fortunately, in recent years, several new herbicides have been approved by the Environmental Protection Agency for use that can help tremendously with transition. These new herbicides all belong to the sulfonylurea herbicide family. They include Revolver (foramsulfuron), Monument (trifloxysulfuron) Tranxit (rimsulfuron), and Manor or Blade (metsulfuron), which has been around for several years. Monument is the newest product, having just been labeled at the end of 2003, while Revolver was labeled in the spring of 2003. Tranxit has been labeled for a couple of years.

SPEED OF CONTROL

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There are five herbicides labeled for removing perennial ryegrass from bermudagrass. This list includes Manor/Blade, Monument, Revolver, Tranxit, and Kerb (not a sulfonylurea herbicide). All five of these are effective, but the speed at which they kill perennial ryegrass differs. You should note that the speed at which herbicides kill ryegrass is not inherently considered a negative or a positive. The differences in speed let you customize your program and determine the speed at which you want to kill ryegrass. For instance, Kerb is effective for removing perennial ryegrass, but it is also the slowest of all available products for doing so. Some turfgrass managers like the fact that it kills ryegrass slowly because the activity is so gradual that there is seldom the appearance of dying turf. Other turfgrass managers prefer a very rapid kill. The main difference in products that remove ryegrass is the speed at which they remove perennial ryegrass. The order of kill of perennial ryegrass (from slowest to fastest) is the following: Kerb is slower than Manor/Blade, and Manor/Blade is slower than Revolver, Tranxit and Monument.

The speed at which Revolver, Tranxit and Monument kill perennial ryegrass provides insight into when you should use it. Because Revolver, Tranxit and Monument kill ryegrass very rapidly, you should use these products as late transition aids. The underlying bermudagrass must be actively growing before you use these products. If you use Revolver, Monument or Tranxit too early (before the bermudagrass is actively growing), then the ryegrass will die before the bermudagrass is able to fill in the voids left from the perennial ryegrass. The resulting overall turf quality will be poor.

To determine when you should remove perennial ryegrass from bermudagrass, consider these two issues:

  • First, when does bermudagrass reach its summer growth pattern in your area?

  • Second, how long is the period of removal in spring/summer to overseeding in the fall?

Your answers should add up to at least 100 days. Because most turf managers prefer to leave perennial ryegrass in as long as possible, Revolver, Tranxit and Monument fit well for transition aids because they allow them to hold the ryegrass longer and remove it more quickly.

REVOLVER

Revolver was first introduced in the spring of 2003. Revolver is sold as a suspension concentrate (0.19 SC formulation) and the rates range from 0.2 to 0.6 fluid ounces per 1000 ft2. Research has shown that it is effective for removing perennial ryegrass from overseeded bermudagrass. It is also effective on Poa annua and has activity on goosegrass, among other weeds. It has been tested extensively on Tifway, Tifsport, Tifgreen, Tifdwarf and Vamont bermudas as well as Meyer zoysiagrass. Other bermudas and zoysias have tolerance, but you should test them for tolerance prior to widespread use. You can also use Revolver on bermudagrass putting greens. In addition to the removal of perennial ryegrass, it will also remove overseeded Poa trivialis from bermudagrass putting greens.

Another important use for Revolver is to control clumpy perennial ryegrass. When ryegrass escapes the overseeding area, such in roughs when only fairways are overseeded or areas around greens, the ryegrass can get clumpy because it is growing at a low density. The clumps become even larger when the plant survives the summer. When this occurs, it can be very difficult to control the clumpy ryegrass. Because of widespread overseeding, clumpy perennial ryegrass has become one of the major weeds throughout areas that utilize overseeding of bermudagrass. Revolver is highly effective in controlling clumpy ryegrass when applied at 0.4 ounces/1000 ft2.

MONUMENT

Monument is the most recently registered herbicide with the EPA granting full registration in late 2003. It will be available for use during the spring transition period this year. Monument will be sold as a 75 percent water-dispersible granule (75 WG) and the rates will range from 0.1 to 0.56 ounces/acre. The rates for removing perennial ryegrass from bermudagrass range from 0.1 to 0.3 ounces/acre. In my research, 0.3 ounces/acre has been more consistent in the complete removal of perennial ryegrass from bermudagrass. Like Revolver, Monument controls Poa annua but also is highly effective on perennial sedges such as yellow and purple nutsedge and the perennial kyllingas (green and false green kyllinga). Monument is not approved for use on bermudagrass putting greens.

TRANXIT

Tranxit has been labeled for use in bermudagrass for a couple of years. It is sold as a 25 percent water-dispersible granule (25 WG) and the rates range from 1 to 2 ounces/acre for turfgrass use. Removal of perennial ryegrass can easily be obtained with 1 ounce/acre. As with Revolver, Tranxit can be used on bermudagrass putting greens.

TREATMENT TIMING

In most areas that are overseeded with perennial ryegrass, removal with herbicides is necessary in order to provide adequate bermudagrass recovery in summer. Failure to provide approximately 100 days of bermudagrass growth in the absence of perennial ryegrass competition is necessary for complete bermudagrass recovery. If bermudagrass does not have adequate time to recover, decline in the bermudagrass stand will occur over time. In many cases, a total loss of bermudagrass can occur. New sulfonylurea herbicides such as Revolver, Tranxit and Monument offer you effective tools for the removal of perennial ryegrass. Transition with these products is fast, so proper timing is critical for successful use.

Fred Yelverton, Ph. D. is a professor of turfgrass science at North Carolina State University (Raleigh, N.C.).

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