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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

In the next few weeks, I'm going to upload a series of posts from ISU students who have been working on research projects and from those who were on internships last summer. They submit written reports on their experience and many of these are excellent.

The post below is from an undergraduate named Steve Johnson. He worked for Mark Gleason in pathology this summer and established some trials at the research station. This is the second of three posts from him. The first was on Sept. 27. This is the second one and the third one will come in a few days.

Steve Johnson, Soph. Summer Intern Blog #2
 

In continuation from my first blog I will go over the methods I used to carry out the experiment. However, while the idea of improving disease ratings by using multiple raters to average the results was the primary purpose, useful information on the effectiveness of specific fungicides to combat dollar spot was also gained through the experiment. The overall idea was to rate and evaluate the effectiveness of 19 fungicide treatments against a selected fungus disease, dollar spot, at two locations and in the process improve the disease ratings by using two raters to average the results.

The first plot was located at the ISU Horticulture Farm near Gilbert, Iowa, and the second at an old golf green located just north of Roy J. Carver Co-Lab on the northwest edge of the Iowa State campus. This location was called the WOI green, since the former WOI-TV building is also located nearby. Turf cultivars were ‘Emerald’ at the Hort farm and ‘Washington’ at WOI. Four sub-plots were needed for each of the 19 treatments making 76 plots. Four more plots were added as a control and not sprayed, totaling 80 sub-plots per location.

The first step to setting up the experiment was creating the sub-plots. By using Pythagoras’ theorem, accurate plot dimensions were insured for both site locations. A method that uses nails and a ball of white string, which is represented by the pictures, was utilized so that the corners of every 5-ft x 4-ft subplot could be seen temporarily. Orange spray paint was then used to mark the corners of each subplot so that the string could be removed and the subplots could still be located. Re-spraying the subplot corners for both locations was necessary every few weeks, especially following a heavy rain. Assignment of the spray treatments to specific sub-plots at both locations was randomized and then marked on maps for both the Hort Farm and WOI.

After the individual plots were marked the Hort Farm plot was ready to be inoculated with dollar spot. The WOI plot was not inoculated. Rye grain seeds were infested with Sclerotinia homoeocarpa, the fungus that causes dollar spot, which were then spread evenly across the surface of the 80 sub-plots. The green was kept moist but not water- logged for five days without mowing to incite fungal growth.

Following the inoculation a spray calendar was made based on the experiment’s protocol. The first spray began on 7 June, except for treatments 18 and 19 which began 24 May, and ended on 17 August. Re-application of the fungicides depended on the protocol, which had varying spray intervals. Backpack sprayers were used to apply the fungicides at 30 psi and a dilution rate of 5 gal per 1000 sq ft.

The day before a spray was to be made, the fungicide treatments were weighed out at the ISU Curtiss Farm plant pathology lab south of the ISU campus. The treatments were put into 2- liter bottles. Only about ½ inch of water was added to make a slurry. The rest of the water would not be added until right before the sprays, so that the chemical reaction would occur during the spray and not the day before, when measuring took place. On spraying days the weighed samples, in a slurry form, were transported to both spray locations and filled with the appropriate amount of water. After the bottles were filled with 1.5 liters water, the treatments were immediately driven to the plots and then sprayed.

Marked stakes were placed at every sub-plot according to a map that indicated the location of every spray treatment. These stakes would be placed in the middle of every sub-plot and then pulled out after the spraying had finished.

Tyvek suits and dual-cartridge, full-face respirator masks, with the appropriate filter necessary for pesticides, were worn for protection during sprays. During a spray date all walking took place on the borders of the sub-plots. This prevented fungicide treatments spreading to sub-plots with different treatments which, if it had occurred, would have made the data unreliable.

The treatments were evenly coated at a consistent rate of application speed, moving up and down each sub-plot. The person spraying would spray one sub-plot at a time by going north and south, and then going in an east-west direction, so the spray occurred from two directions, thus fully and evenly coating a sub-plot.

In my next and final blog I will discuss the results of the experiment as well as the impact of natural events that plagued the experiment over the course of the summer.

Nails are placed appropriately on the outside perimeter of the total plot. The nails held the string tightly in place so that the corners in the inside not measured out or marked held by nails can be seen and marked with spray paint. A single continual piece of string was used to mark out the entire plot

One of the last of the inside corners, not supported by nails but now visible because of the string, is being sprayed.

Filling the backpack sprayer with a fungicide treatment that had been weighed out the day before in our Curtiss laboratory and then transported (dry) to the location in a 2 liter bottle and then filled with 1.5 liters water right before the spray.

Applying the fungicide treatment by backpack sprayer on previously marked out 5-ft x 4-ft plots at the WOI green.