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Nitrogen Source, Rate, Timing and Fungicides on Dollar Spot Incidence (2006)

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Nitrogen Source, Rate, Timing and Fungicides on Dollar Spot Incidence (2006)

Abstract: Dollar spot (DS) (Sclerotinia homeocarpa) is a major disease problem on golf course greens, tees, and fairways. Low nitrogen (N) fertility and dry soils contribute to an increase in DS incidence, while disease development is favored by warm, humid weather and cool nights that produce heavy dew. Limited data exists regarding N source, and timing, including fertilizer applications in conjunction with low label fungicide rates on DS severity.

Objective: This research topic was initiated to determine the effect of N source (foliar v. granular), rate (0.125 v. 0.250 lb N/M), timing (7 v. 14 day interval), and low label fungicide rates combined with fertilizers on DS incidence and color response of creeping bentgrass (CB) (Agrostis stoloniferous L.).

Method and Results: Fertilizer treatments were split, with no fungicide and 1.6 oz/M Daconil Ultrex (half rate) applied on a 30 day interval. Without fungicide, DS was less for fertilized compared to unfertilized CB, while the effect of N source, rate, and timing was not significant. With a fungicide, both rates of foliar applied fertilizer sources (7 day application interval) exhibited significantly less DS than unfertilized treatments, specifically when disease pressure was high (Figure 1). N applied at the higher rate (0.250 lb N/M), regardless of source, contributed to less DS (Figure 2). Most fertilizer treatments provided better CB color than unfertilized treatments and when applied at the higher rate produced the best color (Figure 3).

Conclusion: The results of this study document the importance of 1.) N rate on DS control 2.) More frequent application intervals 3.) Foliar rather than granular N application 4.) N rate/frequency in conjunction with low label fungicide rates for DS suppression and improved turf color.

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Figure 1. Effect of foliar fertilizer treatments (7 day interval and 0.250 lb N/M), with or without low label fungicide rates, on dollar spot incidence (% DS)

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Figure 2. Effect of fertilizer rate in combination with low label fungicide rates (1.6 oz Daconil Ultrex) on dollar spot incidence (% DS) on Aug. 20, 2006

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Figure 3. Effect of fertilizer treatments and rate on creeping bentgrass color on Aug. 28, 2006