| Abstract/Contents: | "Fungicides were evaluated for preventative control of Pythium blight and gray leaf spot. This trial was conducted at the Lake Wheeler Turfgrass Field Laboratory in Raleigh, NC on 'Rebel III' tall fescue that was established from seed (10 lbs/1000 sq ft) in Oct 05 and maintained under home lawn conditions. Mowing was performed two times weekly at a height of 3.5 in. with clippings returned, and the site was irrigated daily with 0.13-in. at 8 PM to enhance disease development. Fertilizer was applied as 25-6-12 on 28 Feb, 29 Mar, and 16 Jun (1.0 lb N/1000 sq ft respectively). Barricade 65WG (0.75 lb ai/A) was applied on 7 Mar for pre-emergent weed control. ProStar 70WP was applied on 16 Jun, and 5 and 28 Jul (2.25 oz/1000 sq ft) to prevent brown patch development. Plots were 5 ft x 6 ft and were arranged in a randomized complete block with four replications. Fungicides were applied in water equivalent to 2 gal per 1000 sq ft with a CO2-powered sprayer at 40 psi using TeeJet 8004 nozzles. All treatments were initiated on 21 Jul and were reapplied on 14 day intervals as indicated in the table. The experimental area was inoculated on 17 Jul using rye grain infested with an isolate of P. Aphanidermatum to encourage Pythium blight development. Percent turf area exhibiting Pythium blight symptoms was assessed on 3 and 16 Aug. Percent turf area exhibiting gray leaf spot symptoms was assessed on 17, 25 and 30 Aug; and 6 and 15 Sep. Turfgrass quality was evaluated on 31 Aug, using a 1 to 9 scale (9=best, 5=acceptable) based on color, density, and uniformity. Data were subjected to analysis of variance and means separation by Waller-Duncan k-ratio t test (k=100). Pythium blight developed slowly after the 17 Jul inoculation due to night temperatures consistently below 70° F. Pythium blight incidence reached a maximum of 4.5% in untreated plots on 3 Aug, 13 days after the first fungicide application. On this date, all treatments, with the exception of Rhapsody, were providing significant disease control. On 16 Aug, 13 days after all treatments were reapplied, excellent control was noted in plots treated with Heritage, Rhapsody + Heritage, Signature, Subdue MAXX, Cyazofamid (0.45 fl oz), Cyazofamid + Alude (0.45 fl oz + 10 fl oz), Disarm applied alone or in combination with either Subdue MAXX or Vital Sign, the three-component mixture of Disarm + Banner MAXX + TM-90109, Alude, CL-EXP-11, and Insignia. Gray leaf spot symptoms were first observed in the experimental area on 17 Aug, resulting from a natural infestation of the Pyricularia grisea. The disease progressed rapidly, causing severe foliar blight and reaching a maximum incidence of 56.4% on 15 Sep. Significant differences in gray leaf spot incidence were observed on 6 Sep (20 days after the 17 Aug fungicide application) with excellent control provided by Heritage, Rhapsody + Heritage, Insignia, Rhapsody + Insignia, Disarm, Disarm + Banner MAXX + TM-90109, Disarm + Subdue MAXX, Disarm + Vital Sign, and CL-EXP-11. On 15 Sep, the same treatments continued to provide good control of gray leaf spot, with the exception of CL-EXP-11. Significant gray leaf spot suppression was also provided by both rates of V-10161, V-10162, Signature, and Subdue MAXX on 15 Sep. Good turfgrass quality was observed in plots treated with the QoI fungicides Heritage, Insignia, and Disarm, and in mixtures containing these fungicides." |
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