Evaluation of foliar fungicides for control of potato late blight in Pennsylvania, 2014

摘要

Fungicides were evaluated on potato cv. Atlantic at the Penn State Russell E. Larson Agricultural Research Center in Rock Springs, PA. The soil type was a Hagerstown silty clay loam. The previous crop was wheat. Potatoes were planted on 16 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 966 lb/A of 20-10-10 (N-P-K) banded in row at planting. Liquid N fertilizer was applied at 33 lb/A on 18 Jul during hilling. Precipitation was 5.71, 3.84, 5.52, and 1.38 in. for Jun, Jul, Aug, and Sep, respectively. Natural infection of Phytophthora infestans clonal lineage US-23 occurred in the middle of August.Overhead sprinklers were used for approximately one hour daily when the weather was dry and hot to increase humidity in the plant canopy after infection. Fungicides were applied with a tractor-mounted, N2-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 late blight diseased foliage. The plots were rated on 17, 24, 30 Aug and 3, 7, 12, 18 Sep and the assessments were used to calculate the area under the disease progress curve (AUDPC). Plants were vine killed on 23 and 26 Sep with Reglone (2.0 pt/A). The middle row of each plot was harvested on 10 Oct. Tubers were sorted for marketability and yield data was collected. Disease and yield data were subjected to analysis of variance and Fisher's protected least significant difference test (SAS v. 9.4, SAS Institute, Cary, NC).