Efficacy of fungicides for the control of Cercospora leaf spot in processing table beet, 2015

Abstract

The experiment was conducted at the New York State Agricultural Experiment Station in Geneva, NY. The crop was planted on 22 May using a Monosem planter at the rate of 17 seeds/ft with 30 in. row spacing. Fertilizer (700 lb/A 5-5-15) was applied at planting and the herbicide Dual Magnum (0.67 pt/A) was applied directly following planting. Weed management was conducted using a mixture of machinery cultivation and by hand. On 21 Jun, 8 and 22 Jul, 50 lb/A of 22% nitrogen was applied by hand along the rows. Irrigation was provided as necessary using overhead solid-set sprinklers. Treatments were arranged in a randomized complete block design with five replications, including a nontreated control. Individual plots consisted of 20-ft sections of two adjacent rows, with a nontreated buffer of 4-ft between plots within rows. Two nontreated rows separated adjacent plots. Treatments were applied with a CO2-pressurized backpack sprayer (21.7 gal/A), with four TJ 8002VS flat fan nozzles spaced 19 in. apart along a 38 in. boom. Fungicide applications were made on 12, 19 and 24 Aug. On 8 Jul, a mycelial suspension (3 × 103 cfu/ml and 0.01% Tween-20) was applied to the two outer rows of each plot using a backpack sprayer. A second inoculation was conducted on 21 Jul during which the entire plot received a mycelial suspension of 1 × 104 cfu/ml and 0.01% Tween-20. Inoculum consisted of a mixture of eight Cercospora beticola isolates collected from diseased table beet fields in NY. Plant density (number of plants/m) was assessed prior to the application of fungicides on 25 Jun by counting the number of plants in two, 0.5 m2 lengths in each of the two inner rows of each plot. Assessments of disease intensity used an individual leaf as the sampling unit. Ten leaves were systematically selected from each of the two inner rows within each plot (n = 20/plot). Disease severity was assessed by counting the number of lesions on each leaf. Disease severity was assessed on 10 (prior to fungicide application) and 31 Aug. The effect of treatment allocation on plant density as a potential covariate and fungicides on disease severity was analyzed using a generalized linear model and means were separated by a Fisher’s protected least significant difference test (Genstat Version 17.1)