Evaluation of foliar fungicides for control of potato late blight in Pennsylvania

摘要

Fungicides were evaluated on potato cv. Atlantic at the Penn State Russell E. Larson Agricultural Research Center at Rock Springs, PA. The soil type was a Hagerstown silty clay loam. The previous crop was corn. Potatoes were planted on 12 Jun. The experimental design was a randomized complete block with four replicates. Plots were three rows wide (36 in. spacing between rows) and 10 ft long with 8 in. seed piece spacing. Fertilization was 1199 lb/A of 10-5-5 (N-P-K) banded in row at planting. LiquidN fertilizer was applied at 30 lb/A on 12 Jul and 15 lb/A on 15 Jul during hilling. Precipitation was 6.54, 5.16, 1.97, and 2.20 in. for Jun, Jul, Aug, and Sep, respectively. On 8 Aug, spreader rows were spray-inoculated with a mixture of four isolates of Phytophthora infestans clonal lineage US-23, at a concentration of 9.3 x 10~4 sporangia/ml, to promote a uniform spread of the pathogen to all treatment plots. Overhead sprinklers were used for approximately one hour daily when the weather was dry andhot to increase humidity in the plant canopy after inoculation. Fungicides were applied with a tractor-mounted, N_2-pressurized side boom sprayer at 30 psi and 45 gal/A. The spray boom was equipped with drop nozzles and boom nozzles so that both sides and the top of each plant were uniformly sprayed. Disease ratings were determined by visually assessing each plot for the percentage of diseased foliage caused by late blight. The plots were rated on 25, 30 Aug and 3, 6, 10, 13, 19 Sep and the assessmentswere used to calculate the area under the disease progress curve (AUDPC). Plants were vine killed on 20 and 26 Sep with Reglone (2.0 pt/A). The middle row of each plot was harvested on 15 Oct. Tubers were sorted and yield data were collected. Disease data were subjected to analysis of variance and Fisher's protected least significant difference test (SAS v. 9.3, SAS Institute, Cary, NC).