Final Report: Fungicide Alternative Management Practices for Microdochium Patch

Clint Mattox, Alec Kowalewski and Brian McDonald
Department of Horticulture, Oregon State University

Microdochium patch can be observed year-around in some cool, humid regions, and damages nearly all grass species in Western Canada and the Pacific Northwest.  Historically, more money has been spent on fungicides to combat this disease in Western Canada and the Pacific Northwest than any other turfgrass disease.

Currently, fungicides applied every 3 to 4 weeks to putting greens throughout the 9 month period of disease activity are the primary means for providing control of this pathogen, which equates to roughly $20,000 annually per golf course. 

In recent years, increasing pesticide bans and restrictions have affected turfgrass management.  Considering this, little information exists regarding alternative integrated management strategies that might significantly reduce or eliminate the need for fungicide applications.  Due to increasing pesticide restrictions it was the goal of this research to first identify fungicide alternative control measures, then research the practical application of these products and practices, and finally develop an integrated pest management program for the control of Microdochium patch that does not use traditional fungicides. 

Alternatives to Traditional Fungicides:
In continued exploration of fungicide alternative products and practices for management of Microdochium patch, a series of experiments were initiated at the Oregon State University Lewis Brown Horticulture Farm and at the Washington State University Goss Research Farm, Puyallup, WA on September 26, 2013 and lasted until the end of Microdochium patch disease activity. The trials were repeated in identical fashion for a second year beginning in September 2014. Objectives of these projects were to explore the effects of i) dew removal, ii) winter applied Civitas One, sulfur and potassium phosphite, iii) winter applied combinations of nitrogen and iron sulfate on Microdochium patch activity. 

Results:
In regards to objective one which focused on dew removal, we determined that rolling significantly reduced disease cover (Image 1).  Following rolling, frequent applications (twice weekly) of the wetting agent Revolution also provided a reduction in disease activity.  Daily treatments with a blower (buffalo blower with a sand-devil attachment), drew brush and dew whip produced slight reductions in disease populations in comparison to the control.   

In regards to objective two, promising results were observed with treatments that included Civitas One applied at 8.5 oz/1,000 ft2 applied with either Sulfur DF applied at 0.25 lbs. of elemental S/1,000 ft2 or potassium phosphite (PK Plus) (image 1a) applied at 6.0 oz/1,000 ft2. These treatments provided greater than 95% control of Microdochium patch with or without the addition of rolling.  However, rolling applied in combination with Civitas One did result in some abiotic damage over the course of the study at the Corvallis location, likely made worse as a result of the turf being under stress due to shade and wet conditions.

In regards to objective three, promising results were observed with treatments that included iron sulfate plus nitrogen applied at 2.0 lbs. FeSO4 and 0.10 lbs. N/1,000 ft2 (image 2). This treatment provided greater than 95% control of Microdochium patch without fungicides. One future concern is reduced visual quality due to the blackening of turf as a result of the iron sulfate additions.  While these findings show that applications which include sulfur and iron sulfate provide significant Microdochium patch control, continued application of these products at these rates have been linked with increased anthracnose disease.  Our current recommendation for annual sulfur applications per year is 1.5 lbs. of elemental sulfur/1,000 ft2/yr. with no more than 0.5 lbs. sulfur/1,000 ft2 per month.

Exploring the Effects of Sulfur on Annual Bluegrass:  
In response to concerns associated with repeated sulfur applications, researchers at Oregon State University have also initiated work intended to balance or offset the potential detrimental effects associated with elevated rates of sulfur and iron sulfate (i.e. acidic soil conditions) on annual bluegrass putting greens, which the above treatments will likely produce.

Objectives of this research are to i) determine if sulfur applied with and without various calcium sources can reduce the number of annual fungicide applications necessary to manage Microdochium patch, ii) evaluate the effects of various sulfur applications rates applied with and without differing calcium sources on annual bluegrass health and vigor, and finally iii) explore potential correlations between soil pH, turf health and Microdochium patch incidence. 

Results:
In comparison to the control, sulfur applied at 3.0 and 6.0 lbs. sulfur/1,000 ft2 annually, reduced March infection centers from 12.3 per 30 ft2 plot to 3.6 and 0.3, respectively (Table 2).  Sulfur applications not only slowed the infection process, but also resulted in fewer curative fungicide applications.  Plots without sulfur required an average of 3.9 fungicide applications to manage the disease over an 8 month period, while plots receiving 3.0 and 6.0 lbs. sulfur/1,000 ft2 annually required 2.9 and 2.3 fungicides applications, respectively.  However, sulfur did decrease turf color and increase anthracnose activity the subsequent August.  It is important to note, that fungicides were not applied to these plots after May 2014.  While summer fungicide applications for anthracnose would have likely prevented the disease, the disease association with sulfur and the decreased turf color observed in May are a concern.  Calcium source and the interaction between sulfur rate and calcium source had no effect on the response variables evaluated. 

Future Research:
In response to concerns associated with repeated Civitas One applications (i.e. abiotic damage when rolling was applied to the Civitas treatments), a new trial will explore ways of better understanding the minimum effective rates of Civitas One used in combination with sulfur and/or Potassium phosphites as well as the most effective application timings.  In addition, replicated golfer traffic will be included in the trial to give a better understanding of how these treatments will perform in real-world conditions. A second trial will look at ways of incorporating calcium sources to offset the effects of long-term sulfur applications on Poa annua putting greens. Finally, collaborative work between OSU and the USDA has suggested that biochar applied to agriculture soils suppresses fungal activity, therefore as a means of continuing the search for alternative control practices, a proposal for a new experiment that looks at the novel use of biochar and activated charcoal incorporation and its effects on Microdochium nivale infection will be explored.

The Oregon State University Turfgrass Program would like to thank the following association and foundations for support of this research initiative:   
• Western Canada Turf Association
• Northwest Turf Association
• Western IPM Center
• Oregon Golf Course Superintendents Association
• Oregon Turf Foundation • Golf Course Superintendents Association
• United States Golf Association  

 Editors note:  Download a pdf file of this report using the link below.  The pdf version includes tables and images.