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A major challenge in organic apple production in humid production regions is the available fungicide options for apple scab [Venturia inaequalis (Cooke) Wint.] management. The standard sulfur/lime sulfur fungicide program can be injurious to the applicator, the apple ecosystem, and the apple tree itself. The objectives of this study were to compare the efficacy of three potential alternative fungicides [potassium bicarbonate (PB), neem oil (NO), and Bacillus subtilis (Bs)] with a standard organic sulfur/lime sulfur (SLS) fungicide program and a non-treated control (NTC) for management of apple scab and to evaluate potential non-target impacts on pest and beneficial arthropod populations. The five treatments were applied to ‘Empire’ trees arranged in a completely randomized design with five single-tree replications at the University of Vermont Horticultural Research Center in South Burlington, VT. Fungicides were applied with a handgun to drip using maximum label rates. Applications began on 26 Apr. 2007 and 23 Apr. 2008 and continued on approximately a weekly schedule through the end of June and then every 2 weeks through 23 July 2007 and 17 July 2008, respectively. The standard SLS treatment resulted in the best scab control in both years. The NO treatment reduced foliar and fruit scab compared with the NTC and the other alternatives at the end of the 2008 growing season and had insecticidal activity. However, both the SLS and NO treatments had disadvantages, including phytotoxic burning on the fruit and/or significantly more russeting on the fruit at harvest. In each year of the study, one or more of the alternative treatments, particularly Bs, resulted in higher insect damage than the non-fungicide-treated control. This research showed that PB, Bs, and NO do not offer advantages over the standard SLS fungicide program in organic apple production and in some cases offer distinct disadvantages in terms of non-target impacts. Chemical names used: potassium bicarbonate (Armicarb “O”), Bacillus subtilis (Serenade MAX), neem oil (Trilogy), sulfur (Microthiol Sulfur)/lime sulfur (Miller Lime Sulfur)

The objective was to systematically quantify the dose response from applications of several alkaline materials recommended for raising pH in acidic media. A 70 peat: 30 perlite (by volume) medium was mixed with a pre-plant nutrient charge, a wetting agent, and between 0 and 1.5 kg·m3 of a dolomitic hydrated lime resulting in six starting-pHs between 3.4 and 6.4. The supernatant from a solution of Ca(OH)2, 2.5 to 40 mL·L-1 of a flowable dolomitic limestone suspension, 99.5% KHCO3 between 0.6 to 9.6 g·L-1, 85% KOH between 0.056 and 0.56 g·L-1, 15N-0P-12K water-soluble fertilizer at 50 to 400 mg·L-1 N, and a distilled water control were applied at 60 mL per 126-mL container with minimal leaching as a single drench (except the 15N-0P-12K that was applied about every three days). All chemicals increased medium-pH within one day, and pH remained stable until day 28 except for Ca(OH)2 which showed a 0.2 unit decrease in pH from day 1 to 28. The Ca(OH)2 and KOH drenches raised medium-pH by less than 0.5 units, and there was a slight decrease in pH from the 15N-0P-12K for starting-pHs lower than 5.0. Flowable dolomitic lime and KHCO3 raised pH by up to 2 pH units, averaged across starting pHs and 1-28 days after application. The effect on medium-pH increased as concentration of flowable lime and KHCO3 increased. Effect of flowable lime was greater (up to 2.9 units) at lower starting-pHs, whereas KHCO3 was less affected by starting-pH. Medium-EC increased by -1 following single applications of all solutions.

Powdery mildew in euonymus (Euonymus japonica Thunh.) plants, caused by Oidium euonymi-japonica (Arcang.) Sacc., was controlled by applying various polymer coatings or an aqueous solution of sodium or potassium bicarbonate plus horticultural Sun Spray (SS) Ultra Fine Oil 1% (v/v) to plant foliage. The combined treatment (bicarbonate + oil) was more effective than either of the two materials alone. The results indicate that sodium or potassium (but not ammonium) bicarbonate solutions mixed with SS seems to be a useful biocompatible fungicide for controlling powdery mildew in euonymus plants. Some of the polymer coatings effectively reduced disease levels when applied immediately after the symptoms first appeared. Powdery mildew disease caused by Oidium euonymi-japonica is severely destructive to euonymus plants from early spring until early autumn (Koul, 1980; Tokushige, 1953). Nademejad ( 1966) reported serious damage to E. japonica plants caused by the pathogen and stressed the need for chemical treatment to control powdery mildew. Chemical fungicides often fail to control foliar diseases, mainly because the pathogen develops resistance (Dekker, 1976). Various epidermal polymer coatings were effective in controlling powdery mildew on some other crops (Elad et al., 1990; Hagiladi and Ziv, 1986; Kamp, 1985; Ziv and Hagiladi, 1984). In China, the antitranspirant Masbrene (dodecyl alcohol; Aefachemi, Sheng Wan, Hong Kong) effectively controlled 12 foliar diseases on nine diverse hosts (Han Jing-Sheng, 1990). Newton, Mass.), to powdery mildew (Sphaero- theca fuliginea Schlechtend; Fr. Pollacci) on cucurbit foliage were demonstrated in green- house and field trials (Ziv and Zitter, 1992). The purpose of this work was to evaluate the use of various coatings and bicarbonate solutions in controlling powdery mildews in E. japonica. One day after the symptoms of a natural powdery mildew infection appeared on a few leaves, the products were hand sprayed to run- off. The plants were sprayed three times at 10- day intervals. In the second trial, plants were also treated with bicarbonate solutions; with or without 1% (v/v) SS, they were sprayed weekly, starting 27 Mar., for a total of five applications. Five branches of the same age and size on each of four plants were selected for each