Submitted to: Fungicide and Nematocide Tests
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/1998
Publication Date: N/A
Interpretive Summary: Grass seed is the second largest seed commodity for US export, and stem rust is the most serious disease in seed production of several grass species grown for seed in the Pacific Northwest. The current best control method for stem rust is the use of fungicides (usually 3 applications per season on perennial ryegrass), and one type of fungicide is used almost exclusively for this purpose. The research reported here was undertaken to test several different fungicides for ability to control stem rust and to test possibility of saving money by reducing the number of fungicide sprays per season. Several fungicides, including one (Quadris) that is relatively new and in the process of being labelled for grass seed crops, controlled the disease as well as the currently-used fungicide. Quadris improved the seed quality slightly more than the standard treatment. By using two fungicide applications instead of three, the disease was not controlled as well as it was with three applications (plants had more infections), but the yield was almost as high as it was with three applications. It is important to have more than one fungicide effective against stem rust because the repeated use of a single fungicide may allow fungicide resistance to develop in the rust pathogen population. These data also allow an assessment of the trade-off between the benefits of frequent fungicide applications (better disease control and yield) and the costs (environmental and economic costs of repeated applications).
Technical Abstract: Experiments were conducted in 1997 in a perennial ryegrass field to compare several fungicides for control of stem rust, and to assess the relative benefits of using a two- or a three-application fungicide program. Natural infection resulted in a rust epidemic that began on 10 April and reached 70% severity (modified Cobb scale) in the check plots by June 26. Fungicides were applied on May 29 and June 18 (two- application program), or on May 9, May 29, and June 18 (three- application program). Plots were rated for disease incidence July 5, and harvested on July 10. Yield of cleaned seed, and 1000-seed weights, were determined. Two-application treatments of Folicur + chlorothalonil were equivalent in disease control (not significantly lower than the check). Tile + chlorothalonil, and several treatments that contained Quadris (alone or in combination with other fungicides) gave better control. Total yield in all two-application fungicide treatments produced a higher yield than the check, and there were no statistically significant differences in yield among these treatments. The 1000-seed weights were likewise improved similarly by all fungicide treatments. In the three- application program there was a greater reduction in disease by the fungicides than in the two-application program, and all had significantly less disease than the check. But total yields were not significantly different among treatments in the three-application: all improved yield compared to the check. The 1000-seed weights were significantly higher in fungicide-treated plots than in the check, and Quadris at 9.2 fl. oz./gave a higher 1000-seed weight than any other treatment.