Control of apple scab and cedar apple rust with Flint 50WDG, Inspire Super EW ProPhyt and Agri-Fos

摘要

Phosphite fungicides have provided excellent scab control in some trials but not in others. This trial was designed to evaluate the activity of two phosphite formulations against scab and rust diseases when both were applied at different rates and viahandgun or with an airblast sprayer. Treatments were replicated four times in a randomized block design in a 15-yr-old orchard containing trees on MM.111 rootstocks with M.9 interstems. Trees were planted with 25 ft between rows, 10 ft between trees, and 20 feet between plots within rows. Each plot consisted of one Golden Delicious tree and a second tree on which the lower scaffolds were McIntosh and the top part of the tree was Ginger Gold. Plots within rows were separated by 10-ft-tall cedar trees that limited drift from one plot to another, and cedar hedges of a similar height were located on two sides of this triangular orchard. As a result, apple trees in this block were exposed to extremely high concentrations of inoculum for cedar apple rust. Handgun applications were made with a tractor-powered high-pressure sprayer at 250 psi, and trees were sprayed to drip. Two treatments were applied using a Unigreen Turboteuton Mistblower sprayer (Uni-green Crop Protection, S.p.A., Reggio Emilia, Italy).This three-point-hitch tower sprayer has five double-nozzled air plenums on each side and was calibrated to deliver 88 gal/A using the assumption that trees were spaced with only 18 ft between rows (as would occur in commercial orchards with trees of this size). The sprayer was driven at 2.5 miles per hour adjacent to the tree canopy when airblast treatments were applied. Each plot was sprayed from both sides, and the airspeed from the sprayer fan was adjusted as needed by using various combinations oftractor gears and engine/PTO speeds (without changing travel speed or the volume/A) so that most of the spray plume stayed within the tree canopy regardless of wind direction the time of application. All of the airblast applications were done when wind speeds were less than 2 mph. The experimental plan was to apply treatments four times at 7-day intervals before switching to cover sprays of contact fungicides at petal fall. Unfortunately, no scab infection periods occurred prior to full bloom, so test products were applied only twice, on 7 May (McIntosh full bloom) and again on 15 May (McIntosh petal fall). After that the entire orchard was sprayed with Manzate 75DF 3 lb/A plus Microthiol Disperss 80DG (sulfur) 3 lb/A on 21 May and with Manzate 75DF 3lb/A plus Flint 50WDG 2.5 oz/A on 27 May. No fungicide cover sprays were applied to this this block between 27 May and 23 July so as to allow secondary scab infections to develop in trees where primary scab was not effectively controlled. Incidence of apple scab, cedar apple rust, rust-related leaf disorders, and impacts of the various treatments on leaf shape and leaf size were collected as described in the table footnotes. Scab incidence on fruit was evaluated by observing 75 Ginger Gold fruit per tree on 14 Aug and 60 McIntosh fruit per tree on 22 Aug. Data was analyzed using SuperAnova (Abacus Concepts Inc., Berkely, CA).