Evaluation of foliar fungicides for control of potato early blight in Wisconsin, 2013

摘要

A field trial was conducted at the University of Wisconsin Agricultural Research Station in Hancock, WI to evaluate fungicide programs for control of foliar blights on potato. A total of 47 treatments were included for early blight and late blight control. Seed pieces, approximately 2 oz in size, were cut mechanically from US#1 'Russet Burbank' tubers on 21 Apr. Seed pieces were allowed to heal prior to planting on 5 May. No seed treatments were applied unless noted in the table. A randomized complete block design with four replications was used for the trial, and treatment plots consisted of four 24-ft-long rows spaced 36 in. apart with 12 in. spacing in the row. To minimize soil compaction and damage to plants in the treatment rows, drive rows forpesticide application equipment were placed adjacent to the plots. Fungicide treatments were initiated on 2 Jul after the P-day value (generated from a crop physiological model used for early blight prediction and fungicide initiation) reached 300. Subsequent applications were applied on a weekly basis to all four rows of each plot on the following dates: 9 Jul, 16 Jul, 23 Jul, 30 Jul, 6 Aug, 13 Aug, 20 Aug, 27 Aug, and 3 Sep for a total of ten fungicide applications. Vine kill was initiated 5 Sep withan application of Diquat E 1.5 pt/acre followed by a second application on 12 Sep. Treatments were applied with a plot sprayer consisting of a tractor-mounted boom, pressurized with an air compressor, using TeeJet Hollow Disc Cone D3-23 nozzles (16 nozzles at 8-in. spacing). Fungicides were applied at a rate equivalent to 35 gal water/A at 40 psi. Plots were not inoculated but relied on natural dispersal of inocula for disease establishment. Early blight severity across 20 ft of the two center rows wasrated on 25 Jul, 5 Aug, 18 Aug, and 2 Sep using the Horsfall-Barratt rating scale (0-11 rating with 0=no disease, 11=100% disease severity). The Area Under the Disease Progress Curve (AUDPC) was determined by trapezoidal integration and then converted into Relative AUDPC (RAUDPC), i.e. percentage of the maximum possible AUDPC for the whole period of the experiment. Plots were harvested and graded on 24 Sep. A subset of 12 tubers from each plot was tested for specific gravity at time of grading. Total precipitation in Hancock during the potato production season was 17.2 in. Supplemental irrigation was applied 32 times during the potato production season for an additional 13.7 in.