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The following is a report on a dollar spot trial conducted at the research station this past summer.  The primary objective of the work was to evaluate the effect of an experimental adjuvant on disease control, but there is a lot of good information comparing the different fungicides.  We had a great year for dollar spot at the station.

KALO FUNGICIDE/ADJUVANT TRIAL-2015
Nick Christians and Dan Strey
Iowa State University

Objective: To compare the control of Dollar Sport caused by the fungi Sclerotinia homeocarpa on creeping bentgrass turf with 7 commercial fungicides applied with and without Kalo’s  KA-9107 experimental adjuvant.  

Materials and Methods: The trial was conducted at the Iowa State University Horticulture research station near Gilbert, Iowa.  Plots were located on a mature stand of creeping bentgrass and were arranged in a randomized complete block design with 3 replications. Each plot measured 5 x 5 ft, for a total of 25 ft² per plot. Bentgrass was a mixed sward of ‘1019’, ‘1020’, and ‘Penncross’ maintained at 0.5”.  Soil at the site was a 1:1:1 mix of sand:peat:soil with a particle size of 13.7% sand, 56.9% silt, and 29.5% clay.  Soil pH was 7.6 with soil P and K contents of 17 and 58 ppm, respectively.  Soil type was a Nicollet clay-loam (fine-loamy, mixed, mesic, Typic Hapluldoll). 

The full list of treatments appears in Table 1.  All products were applied through TeeJet 8002VS nozzles in a spray volume equivalent to 2 gallons/1000 ft² powered by carbon dioxide supplying 40 pounds per square inch. The products were generally applied on 14 day intervals.

Results: The two week interval of application was too long to get satisfactory control of dollar spot with chlorothalonil (Table 2). The addition of the KA-9107 to chlorothalonil did provide numerically better control in most data collection dates.  These differences were significant on Sept. 2, Sept. 24, Oct. 2 and for the grand mean of all dates.   Fathom 14.3 MEC, Briskway, and Renown also provided less than desirable control. Control with Briskway was improved by KA-9107 on July 8 and July 27, as was the control with Renown.  The control with Fathom 14.3 MECwas improved by the adjuvant on August 25.  Emerald, Secure, and Velista were the most effective controls of dollar spot.   While at most dates, there was a numerical advantage to adding KA-9107 to these materials, there control was so effective, that none of these differences were significant.

Overall means comparing fungicides with adjuvant and those without adjuvant were calculated and orthogonal contrasts were performed to compare the means (Table 2) (Figure 1).  Significant improvement in activity of all fungicides that included KA-9107 were observed on July 8 and July 27.   The grand mean of all treatments over all dates showed a decrease of from 22 % dollar spot to 18 % dollar spot when KA-9107 was used as an additive.  The level of significance for this difference was 0.08.

It is apparent that KA-9107 can boost the activity of some fungicides for the control of dollar spot on creeping bentgrass turf.  Future studies could include the application of KA-9107 without a fungicide to determine if it provides any suppression on dollar spot development by itself.  It would also make sense to test the most effective materials with and without the adjuvant at longer intervals between treatments to determine if KA-9107 extends the activity of these products.