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Dollar Spot Expression
The effects of fertility on dollar spot expression; 2008 Guelph research station
To determine the effects of the sponsor's fertilizer programs on dollarspot disease and general performance of creeping bentgrass putting green turf maintained at fairway height. Data collected included the duration and strength of the color response following application(s) of the tested products, turf quality, uniformity, and density, and resistance of the turf to disease and drought stress. Background Information: The effects of nitrogen on dollar spot expression have been well documented. Nitrogen has been used as a tool to “grow out” lesions by improving the plants tolerance to infection. To further reduce the effect of dollar spot, we need to review the plants ability to utilize its natural defense mechanisms. This process is known as plant resistance. Turf performance – visual ratings.   Visual quality ratings of treated plots indicated high quality turf throughout most of the trial period, though by 7 weeks after the first treatment, the dollarspot disease infestation in the Clubgreen and untreated plots was reducing the quality compared to the Mineral Builder treatments (Table 2). Turf performance – canopy reflectance.  The canopy reflectance data showed a very similar pattern to the visual quality data, with significant differences among the treatments on all observation dates (Table 3).  The values of the NDVI were very close among all the treatments, but the two Mineral Builder treatments had higher absolute index values (Figure 2).  When the data were corrected to remove the background variation (by subtracting the control plot means), the treatment response became more evident (Figure 3).  The two applications for the Mineral Builder treatments resulted in a clear response to the second application, in comparison to the single application of the NPK Control. The uniformity of the turf can be assessed by examining the coefficients of variation of the NDVI values.  Generally the uniformity of the turf increased (coefficients of variation were reduced) as the NDVI values increased across the trial period, and the Mineral Builder  treatments were more uniform.  Towards the end of the trial, as the dollarspot infestation increased and turf quality declined, the control and NPK treatments became much less uniform (Figure 4). Dollarspot disease.  There was a little bit of dollarspot across all treatments in the first two weeks after the first application (Table 4).  By three weeks after the start of the trial, the trend in dollarspot disease presence was clear, with less dollarspot present in the two Mineral Builder treatments than in the control or NPK control treatments (Figure 5).  By 5 weeks after the start, the pattern was statistically significant There were consistent and significant differences among the treatments in turf quality and resistance to dollarspot disease.   Generally the two Mineral Builder treatments were significantly better quality and had much less dollarspot disease than either the NPK treatment or the control.  There was a slight enhancement of performance of the treatment with micronutrients, but it was not significantly different in many cases.  The NPK treatment had higher quality than the control early in the experiment, but the improvement had disappeared by the end of the experiment.
"by 7 weeks after the first treatment, the dollarspot disease infestation in the Clubgreen and untreated plots was reducing the quality compared to the Mineral Builder treatments"
The objective of this research project was:
V I S I O N  +  I N N O V A T I O N
Figure 1.  Plot area September 4, 2008.
Figure 3.  Fertilizer response as estimated by NDVI measurements in treated plots, corrected to remove background variation (Control=0).  Curves are fourth order polynomials fitted to plot means (R2 values are 0.14 [NPK control], 0.31 [Mineral Builder], and  0.52 [Mineral Builder + micros]).
Figure 5. Typical dollarspot disease symptoms in untreated check plot, October 3, 2008.