Evaluation of residual activity of apple scab fungicides, 2008.

摘要

This trial was designed to compare the residual/redistributive capabilities of various fungicides by monitoring disease development after a single spray was omitted at the time that trees entered the period of rapid terminal shoot growth.The test orchard was established in 1991 and contained two-tree plots of Jerseymac and Ginger Gold on M.9 rootstocks. Trees within plots were spaced 8.5 ft apart, with 17 ft separating trees in adjacent in-row plots and 20 ft between rows. Plotswithin rows were separated by large cedar trees that provided inoculum for rust diseases and limited spray drift between plots. All treatments were replicated four times. Jerseymac bud stages were 7 Apr - green tip, 17 Apr – half-inch green, 22Apr - tight cluster, 25 April - pink, 2 May – full bloom, 11 May - petal fall. The first apple scab infection period occurred 28- 29 Apr (33 hr, 48 deg F), with additional infection periods 1-4 May (41 hr, 49 deg F), 9-10 May (28 hr, 49 deg F), 15-17 May (34 hr,51 deg F), 21-22 May (21 hr, 51 deg F), 31 May-5 Jun (78 hr, 66 deg F). There were 10 additional secondary infection periods in June and seven in July. The first scab lesions appeared in unsprayed trees on 14 May. Treatments were applied by spraying trees todrip using a high-pressure sprayer and a handgun at 200 psi. Manzate 75DF 1 lb/100 gal was applied to all plots except unsprayed controls on 8, and 17 Apr. Test treatments listed in the tables were applied on 25 Apr, with the next spray delayedfor 16 days except that the standard mancozeb program (treatment 2) received a spray of Manzate 1 lb/100 gal on 3 May. All plots except controls were subsequently sprayed with Manzate on 11, 22, and 30 May, so any differences among treatmentsare attributable to residual activity of the fungicides applied on 25 Apr. During the extended spray interval between 25 Apr and 11 May, the test fungicides were exposed to rainfall as follows: 27-29 Apr — 1.58 in.; 1-4 May — 0.27 in.; 9-10 May —0.5 in. During this same time period, tree phenology advanced from pink through bloom to petal fall, and terminal shoots unfolded 3-5 leaves. Captan 80WDG 30 oz/A was applied to the entire block, including control plots, on 13 Jun using anairblast sprayer. Flint 50WG 2 oz/A was similarly applied to the entire block on 25 Jun. No other fungicides were applied thereafter. Scab pressure was very light due to extended dry periods from 10-27 Apr. Details of rating methods are providedin table footnotes. Data was analyzed using SuperANOVA software from Abacus Concepts.