In some parts of the U.S., there is pressure to reduce pesticide use on golf courses. This trend is more severe in Canada and Europe. At Oregon State University, researchers funded by the USGA Davis Program (read more from Kenna on the Davis Program here) have conducted two three-year experiments to evaluate alternative products to control Microdochium patch on annual bluegrass putting greens.

The first experiment, initiated in September 2018, compares iron sulfate versus chelated iron to suppress Microdochium patch on an annual bluegrass putting green in the absence and presence of phosphorous acid. In all three years, iron sulfate heptahydrate applications made in the presence or absence of phosphorous acid suppressed Microdochium patch compared to the non-treated control — except for when the team applied 0.1 lbs. per 1,000 square feet of iron as iron sulfate in the absence of phosphorous acid in the third year of the experiment.

Chelated iron applied as DTPA in the absence of phosphorous acid did not suppress the Microdochium patch compared to the non-treated control in any of the three years except in the first year for the 0.2 lbs. of iron per 1,000 square feet application. The application of phosphorous acid in combination with either iron source significantly suppressed Microdochium patch compared to the non-treated control.

The second three-year experiment evaluated the long-term impacts of winter applications of alternatives to traditional fungicides on Microdochium patch suppression, summer putting green performance and soil fertility on annual bluegrass greens.

In the third year, all treatments suppressed Microdochium patch compared to the non-treated control and were not statistically different from the fungicide control rotation. However, anthracnose was severe in June 2021 on plots that received treatments that included combinations of iron sulfate and phosphorous acid.

The fungicide control had the least amount of anthracnose in July, with 0.6 percent anthracnose compared to seven other alternative control treatments with an average of 20 percent or more anthracnose. The fungicide control received the last application on March 3, 2021, with an application of Ascernity (benzovindiflupyr, difenoconazole) at a rate of 1.0 oz. per 1,000 square feet and Heritage Action (azoxystrobin, acibenzolar-S-methyl) at a rate of 0.4 wt. oz. per 1,000 square feet.

Photo: Mike Kenna, Ph. D.

Mike Kenna, Ph.D., is the retired director of research, USGA Green Section. Contact him at mpkenna@gmail.com.