Long-Term Effects of Alternative Microdochium Patch Management Techniques

Oregon State University Turfgrass Final Report - Clint Mattox, Alec Kowalewski, Brian McDonald, Emily Braithwaite, & Alyssa Cain

Since 2013, research at Oregon State University focusing on the management of Microdochium patch in the absence of traditional fungicides has made great strides.

Many different techniques using multiple products have demonstrated that managing this turfgrass disease using iron sulfate, phosphorous acid, sulfur, and mineral oil is possible. The long-term effects of these product applications, however, is currently unknown. For this reason, a trial began on the 4th of September 2018 and is on-going in the same location in order to quantify any long-term effects of these treatments on summer turfgrass quality and changes in available soil nutrients. 

Figure 1: Microdochium patch pressure on 24 January 2019 in Corvallis, Oregon.

Multiple dependent variables are being considered in this experiment. All diseases that appear on the trial are being recorded, with the primary diseases being Microdochium patch in the winter and anthracnose in the summer. Yellow patch and dollar spot also appeared on the trial, although these diseases were not spread uniformly across the experimental area and no significant differences between treatments were found. Table 1 lists the Microdochium patch data at the peak of disease for the first two years of this experiment.  The mean disease for all treatments was ≤ 2% with the exception of sulfur or phosphorous acid applied alone. The non-treated control had an average of 40% disease in January 2019 and 72.5% in February 2002 (Table 1 and Figure 1). Anthracnose appeared on all of the treatments except for the fungicide control plot (Table 1 and Figure 2).  Iron sulfate applied at 0.5 lbs. per thousand square feet applied in combination with phosphorous acid caused the largest increase in anthracnose severity. It is unclear why the higher rate of iron sulfate did not produce the same effect. There is evidence in previous research that sulfur applications may increase the risk of anthracnose.  While sulfur did not increase anthracnose activity in this study, it is speculated that sulfur will increase activity in future years.

Table 1. Microdochium patch and anthracnose severity on an annual bluegrass putting green in Corvallis, Oregon.

zTreatments applied every two weeks from September through April unless indicated otherwise. yS=Sulfur applied as Kumulus DF at 0.25 lbs. S per 1,000 ft2, xPA=Phosphorous acid applied as Duraphite 12 at 0.075 lbs. H3PO3 per 1,000 ft2, w=mean turfgrass percent disease v=means in the same column sharing the same letter are not significantly different according to Dunn’s test (alpha ≤ 0.05). uMO=Mineral oil applied as Civitas Turf Defense at 8.5 oz. per 1,000 ft2.

Figure 2. Microdochium patch symptoms as observed on 10 January 2019.

Figure 3. Anthracnose symptoms as observed on select treatments on 19 September 2019.

Soil samples are collected each May to assess the long-term impacts of treatments on soil nutrient levels, and pH. The results for the first year (May 2019) are displayed in Table 2 and the samples collected in May 2020 will be available in the future on the Beaver Turf website (www.beaverturf.com). It is difficult to establish trends in the data with only one year of soil test results. Some things to point out are the higher sulfur levels in plots receiving sulfur and iron sulfate, which would suggest a projected reduction in soil pH in future years. It will be interesting to observe if the addition of phosphorous acid leads to higher phosphorus levels over time as well as higher iron levels from the iron sulfate treatments.

Table 2. Soil test results from soil samples collected 8 May 2019 from a depth of 3” using a ¾” diameter soil probe with the top 1” removed for future analysis.

zTreatments applied every two weeks from September through April unless indicated otherwise. yS=Sulfur applied at Kumulus DF at 0.25 lbs. S per 1,000 ft2, xPA=Phosphorous acid applied at Duraphite 12 at 0.075 lbs. H3PO3 per 1,000 ft2, w=means in same column sharing the same letter are not significantly different according to Tukey’s HSD (alpha<0.05). uMO=Mineral oil applied as Civitas Turf Defense at 8.5 oz. per 1,000 ft2.

In order to replicate the closest possible real-world conditions, simulated golfer traffic of 73 golf rounds a day was performed by walking over the trial with golf shoes. No abiotic damage was observed resulting from the treatments, although thinning of the sward was visible where iron sulfate was applied leading to a reduction in turfgrass quality (Table 3). Treatments in the group with the highest turfgrass quality rating included mineral oil and phosphorous acid combinations rotated with mineral oil and sulfur, mineral oil and phosphorous acid combinations applied in the milder months with sulfur and phosphorous acid applied in the winter months, and the fungicide control. Normalized difference vegetation index (NDVI) is an unbiased method of quantifying plant health by measuring how light is absorbed and reflected. Higher numbers indicate the area is greener (i.e. healthier in this case). Treatments that often had the lowest NDVI values included the non-treated control because of disease or treatments that included iron sulfate because of a thinning of the sward (Table 3). All other treatments were in the same grouping regarding NDVI values.

Table 3. Monthly turfgrass quality ratings along with monthly NDVI data provide a good indication of the overall appearance and health of the turfgrass in the plots.

zTreatments applied every two weeks from Sep through Apr unless indicated otherwise. yS=Sulfur applied as Kumulus DF at 0.25 lbs. S per 1,000 ft2, xPA=Phosphorous acid applied as Duraphite 12 at 0.075 lbs. H3PO3 per 1,000 ft2, w=mean turfgrass quality rating of 1 to 9 with a 6 or greater considered acceptable, v=means in the same column sharing the same letter are not significantly different according to Dunn’s test (alpha ≤ 0.05). uMO=Mineral oil applied at Civitas Turf Defense at 8.5 oz. per 1,000 ft2. t=mean NDVI recording of 5 sub-sample readings using a FieldScout CM 1000 NDVI meter. S=means in the same column sharing the same letter are not significantly different according to Tukey’s HSD (alpha ≤ 0.05).

Other dependent variables quantified in this study include putting green speed and water infiltration using a double ring infiltrometer (Table 4 and Figure 4). Putting green speed was calculated by taking the average of 3 ball roll distances from opposite directions using the “2X” notch on the USGA Stimpmeter because the plots were only 8 feet in length. As expected, the summer ball roll distances were not affected. After multiple treatment applications, data in October and November showed that the mineral oil and phosphorous acid treatments every two weeks was in the group with the lowest ball roll distance and the sulfur treatment was in the group with the highest ball roll distance. Water infiltration was tested in May 2020 prior to soil sampling and aerification in order to quantify any effects of the treatments on water movement post eight months of treatments. The data does not indicate that the treatments are creating any differences in infiltration. 

Table 4: Infiltration rate and putting green speed on an annual bluegrass putting green in Corvallis, Oregon.

zTreatments applied every two weeks from September through April unless indicated otherwise. yPutting green speed was recorded by taking the average of 3 ball roll distances from opposite directions using the “2X’ notch on the USGA Stimpmeter. xInfiltration recorded using a double ring infiltrometer. Rates listed are the infiltration of the second inch of water. wS=Sulfur applied as Kumulus DF at 0.25 lbs. S per 1,000 ft2, vPA=Phosphorous acid applied as Duraphite 12 at 0.075 lbs. H3PO3 per 1,000 ft2, u=means in same column sharing the same letter are not significantly different according to Tukey’s HSD (alpha<0.05). tMO=Mineral oil applied as Civitas Turf Defense at 8.5 oz. per 1,000 ft2.

Figure 4. Water infiltration data collection on 07 May 2020.

In conclusion, the data indicate that a mineral oil and phosphorous acid treatment combination rotated every two weeks with a sulfur and phosphorous acid treatment combination significantly suppresses Microdochium patch to levels comparable to a traditional fungicide rotation. The same alternative treatment rotation also provided similar turfgrass quality ratings and NDVI readings as a traditional fungicide treatment combination, indicating that this treatment is a viable means of suppressing Microdochium patch. The incidence of anthracnose remains a concern, especially for treatments that include iron sulfate or sulfur. Initial soil tests indicate that pH will likely be affected by the treatments over time and mitigation using lime may be necessary over the course of the experiment. Future soil analyses will provide details in the long-term effects of other soil nutrients such as iron, phosphorus, sulfur, and copper.