Efficacy of Vital and ZeroTol fungicides on preventive or residual control of impatiens downy mildew, 2012

摘要

Fungicides were applied as either foliar sprays using a hand-pressurized sprayer to runoff (Vital and ZeroTol) or as a drench (Vital) (0.68 fl oz/cell = 1pt/ft2) seven days prior to inoculation on 12 Oct to three-week old, seed-raised impatiens one day after transplant. The experimental design was a randomized complete block with four replications. Each replicate consisted of four plants grown in a 4-cell pack (2.5x2.5x3 in.3 per cell) containing Ball Professional Growing Mix. In addition, a foliar treatment of ZeroTol was applied on 18 Oct, thirty hours prior to inoculation. Plants were spray-inoculated with a suspension of Plasmopara obducens sporangia (3.7x 105 sporangia/ml = 1.1x 107sporangia/fl oz) on 19 Oct. The isolate of P. obducens used forinoculations was obtained from naturally infected I. walleriana plants growing in a trial field in Holland in Aug 2012 and subsequently established and maintained on seed-raised I. walleriana in a laboratory growth chamber. Inoculum was prepared by rinsing sporulating impatiens leaves in water with a drop of Tween 20. Plants were immediately bagged after inoculation to maintain 100% relative humidity and placed in a growth chamber with 62°F nights and 73°F days and 12 hr light/dark. The percentage ofplants with downy mildew sporulation (incidence) and the percentage of leaves, per plant, with sporulation were evaluated visually on 2 Nov.