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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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PATHOLOGY RESEARCH SUMMER 2010

December 15, 2010

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.

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