Trunk applications of phosphite fungicides for management of apple scab and powdery mildew, 2007

摘要

A trial was conducted at the New York State Agricultural Experiment Station in Geneva NY to evaluate the potential of single dormant trunk applications of phosphite fungicides to manage apple scab. The orchard site is a mature planting of 33-yr-old McIntosh trees on MM.106 rootstocks. Treatment programs consisted of eleven trunk-applied programs, an untreated check, and two foliar programs. Phosphite fungicides evaluated for apple scab management by trunk application included Agri-Fos (53.6% mono- and di-potassium salts of phosphorous acid), ProPhyt (54.5% potassium phosphitea), and Phostrol (53.6% mono- and dibasic sodium, potassium, and ammonium phosphites). Trunk-applied treatment programs using Sovran were also included to evaluate the approachusing a conventional fungicide. Trunk applications were made only once at 100% silver tip using a low-pressure, 2-gallon, hand-pump sprayer using measurement rates in terms of amount per gallon. Materials were applied to drip to the trunk up to a heightof 36 in. and out 1ft onto scaffold limbs below 36 in. On average, the trees required 0.15 gal for treatment. All trunk applications included PentraBark, a nonionic wetting agent (99.8% alkylphenol ethoxylate, polysiloxane polyether copolymer, propyleneglycol). Foliar treatments were applied dilute (300 gal/A) to drip using a handgun (200 PSI) at forecasted infection events (27-29 April – half inch green + 10-11 May – pink/boom). Prior to a petal fall (PF) infection event (16-17 May) and at first cover (29 May), all trees, including untreated checks, were treated (foliar handgun application) with Dithane 75DF 3 lb/A plus Microthiol sulfur 3 lb/A. After an infection event at second cover (3-4 Jun), all trees were treated again (foliar handgun application) with Dithane 75DF 3 lb/A plus Sovran 4 oz/A. The development of powdery mildew and apple scab symptoms was evaluated on terminal leaves on 22 and 29 Jun, respectively. The incidence of these diseases was expressed as the number of terminal leaves with scab or mildew symptoms out of 10 fully expanded leaves counting back from the terminal end of the shoot with 20 terminals assessed for four replicate trees. The incidence of fruit scab at harvest was evaluated on 14 Aug as the number of fruit with apple scab lesions out of five collected fruit with 10 collections assessed for four replicate trees. Disease incidence data was subject to analysis of variance (ANOVA) for a randomized block design using accepted statistical procedures and software (e.g. General Linear Model (GLM) procedure of SAS (version 9.1; SAS Institute Inc., Cary, NC). All percentage data was subject to arcsine square root transformation prior to analysis.