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Dollar Spot Disease 2010, Tim Sibicky, CDGA Turfgrass Research Manager

September 30, 2010

Warmer temperatures this week have provided suitable environmental conditions for dollar spot (Sclerotinia homoeoecarpa) development on fairways. We are now beginning to see a late season surge in damage as we enter the autumn months. Thinking back to the beginning of the 2010 season, we set out to investigate the effectiveness of early season dollar spot programs and if you look (Figure 1) we are able to see the progression of the disease at a variety of different locations surrounding Chicago. So I ask, was it worth it to spray early in April-May? At our locations for this year’s Biorational study, ranging from North Shore Country Club in Glenview, IL Coyote Run Golf Course in Flossmor, IL and Briar Ridge CC in northwest Indiana, it is evident that the disease failed to take off until the middle of summer.
 

As an additional note: each of our locations vary in turfgrass composition with Coyote Run having a blend of Southshore and L93, Briar Ridge CC with Penncross and North Shore CC having a mix of creeping bentgrass and Poa annua. We tested seven treatments, Rhapsody 10 fl oz, Ecoguard 20 fl oz, Dew Cure 4.0 fl oz, Urea 0.15 lbs, Daconil 3.2 oz, Daconil 3.2 oz curative (as needed using 5% damage threshold).

Treatments are being applied at 14 day intervals at label rates and the plots at all locations are scouted weekly. If disease infection centers exceed an average of 5% area affected a curative application of 3.2 oz of Daconil is applied over the biorational treatment. We are able to understand the effectiveness of the different treatments by comparing visual quality, percentage of disease, and number of curative fungicide applications. Our goal is to reduce fungicide use and maintain turfgrass quality at levels required for fairways.

Results (Table 1). At Coyote Run GC, we have been able to maintain the Dew Cure treatment below the 5% threshold without applying a single curative application of Daconil! At this location we were also able to see a recuperative effect within the Urea treatment, only requiring a single application. At North Shore Country Club we were able to reduce the curative applications by two when using DewCure. All other plots required the same amount of curatives, four apps. At Briar Ridge with DewCure, we were able to reduce the number of curative required by one. At Briar Ridge we did observe phytotoxicity by DewCure. On August 10 an application of all products were made at a time when temperatures were 90+ degrees and turf was entering drought stress. This resulted in severe injury by DewCure alone.

These biorational products may play more important roles in disease management programs as we continue to progress into a reduced input future. As we continue to learn and understand the benefits and limitations, superintendents will be able to make better and more informed decisions. We may as well investigate alternatives now before we run out of options.

The final picture shows a plot treated with Dew Cure resisting dollar spot without receiving any curative applications during the summer of 2010 at Coyote Run GC.

Tim Sibicky
TSibicky@cdga.org
Chicago District Golf Association
11855 Archer Avenue
Lemont, IL 60439

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PATHOLOGY RESEARCH SUMMER 2010-3rd POST

December 20, 2010

Here is the 3rd post by undergraduate student Steve Johnson on his pathology project at ISU during the summer of 2010.
 

Steve Johnson, Soph. Summer Intern Blog #3

Following my last blog I will discuss the results of the experiment.

Assessments of the turf were made by my instructor Mark Gleason, Professor of Plant Pathology and Horticulture at Iowa State University. Data were recorded on 2 July, 15 July, 26 July, and 18 August at the Turfgrass Research Area of the ISU Horticulture Research Farm near Gilbert, IA, and at a green near the WOI Building on the ISU campus. Dollar spot was recorded as a percentage of the area in a 5-ft x 4-ft plot that was covered with the disease; all treatments had 4 replicate plots, arranged in a randomized complete block design. Turf quality ratings were set on a qualitative scale of 1 to 10 where 10 indicated no disease, excellent quality, and a 1 indicated very poor turf quality. Data were analyzed using the GLM procedure and SAS (statistical analysis software) with mean separations determined by Fisher’s protected LSD at P<0.05.

Weather conditions for the 2009 summer hit record highs in heat, rainfall, and humidity. Heavy rainfall caused extensive flooding in the Ames area which persisted from 11-13 August. There were no signs of phytotoxicity seen on the turf for the duration of the trial for either location. However, worth noting is that all four sub-plots for treatment 11 (a pre-mix of chlorothalonil and propiconazole) at the Hort Farm displayed a darker green coloration and sometimes slight browning on 15 and 26 July.

At the Hort Farm, dollar spot was light to moderate in disease intensity over the course of the summer. Intensity peaked in late July with a decline occurring by August. However, due to variation among subplots, most treatments did not vary significantly from the untreated control. Turf quality had similar results, with most of the treatments showing a consistent decline in the quality as the summer progressed.

However, many fungicide treatments exhibited significant difference in dollar spot severity on 2 July and 26 July. In addition, a few of the treatments maintained good quality the entire summer, indicating that that these treatments proved effective against dollar spot and preserved adequate turf visual quality despite the stressful growing conditions.

For WOI, the data were in question due to a severe outbreak of crabgrass. Creeping bentgrass at the location was overwhelmed to such a degree that WOI will not be used again for future experiments. There were two reasons for this. Golf course maintenance was inhibited due to tree damage from a storm in mid July that produced 70-mph winds, as well as severe flooding from 11-13 August. While I have made available the data in Tables, the results are questionable for WOI.

I have attached 4 Tables showing the data that were collected on check dates over the summer. Data Tables include: dollar spot % severity at the Hort Farm and WOI, as well as turf quality for the Hort Farm and WOI. On 26 July, Mark and I independently assessed % dollar spot severity at the Hort Farm. As was explained in the earlier blogs, this was to improve the reliability of the disease % ratings of dollar spot on turf by combining the impressions of two raters. The data was averaged between Mark and myself and was recorded under 26 July column for the Hort arm % dollar spot Table.

Despite the numerous and overwhelming weather issues and outburst of crabgrass at WOI, this experiment still yielded some good data concerning the effectiveness of fungicide treatments. Also valuable is the method of averaging disease ratings from multiple raters to reduce individual biases. The amount and reoccurrence of fungicide sprays are factors determined by accurate readings which can save money and resources as well as prevent over-applications of fungicides which can lead to phytotoxicity of grass blades. It is methods and good data learned from studies such as this one that can prove quite useful in telling how well established a disease is and aid owners in deciding upon a proper integrated disease management program for optimal disease prevention.






 

 

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