David M. Kopec, Extension Turfgrass Specialist
Ryegrass stands at overseeding, winter performance and transition seem to vary from year to year, with sometimes not much "rhyme or reason."
Many superintendents are currently facing another year of poor transition back to bermudagrass. Last year we experienced the coldest May and June in over ten years, which prolonged the ryegrass at the expense of poor bermudagrass to boot. This year, it's been plenty hot and dry. For some clubs, there has been a loss of bermudagrass following transition, resulting in a complete loss of turf.
There are many reasons why poor transition can happen. Some occur during the overseeding itself (extreme verticutting, too early of an overseeding), or occur during the dry summer (cool weather, excess mat development, seed rate effects, poor irrigation, etc.). The direct effect of overseeding involves two components as far as bermudagrass is concerned, (1) direct competition (from the overseed) and (2) potential allelopathy (chemical suppression of bermudagrass. Allelopathy is nothing new in the plant kingdom. It's one of natures ways of eliminating your neighbor. Creosote bushes are prime examples. Ever see a weed underneath or near a creosote bush? Allelopathy from grasses has been demonstrated on certain tree crops and certain weeds are allelopathic as well.
The USGA has supported some research at the University of Arkansas which is investigating the potential for allelopathy within perennial ryegrass.
Using a seedling assay of duckweed, it has been preliminarily demonstrated that perennial ryegrass caused growth reductions of duckweed. Both endophyte and endophyte-free cultivars were tested. A second part of the test is investigating the potential allelopathic effects of perennial ryegrass on germinating seed of crabgrass. Early results show that ryegrass extracts inhibit directly and/or cause yellow seedlings to be short lived. The third project involves determining crabgrass suppression from overseeding perennial ryegrass into common bermudagrass. The connection here asks the question, does ryegrass provide allelopathy in a turf with bermudagrass. The third part of the test has not been finalized yet, but perennial ryegrass has exhibited suppression in the duckweed bioassay test. The crabgrass germination test also showed allelopathy from perennial ryegrass. These tests will probably be repeated and I will share all information as soon as it becomes available.
Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director, Cooperative Extension, College of Agriculture & Life Sciences, The University of Arizona. The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.