Date of Award

2009

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Plant and Soil Science

First Advisor

Berkett, Lorraine

Abstract

A major challenge in organic apple production in Vermont is the available fungicide options for apple scab management. The standard lime sulfur/sulfur fungicide program used can be injurious to the applicator, the apple ecosystem, and the apple tree itself. Because of these drawbacks of the standard program it is necessary to evaluate potential alternative fungicides for organic apple production. The objectives of this study were to: (i) compare the efficiency of potassium bicarbonate, neem oil, and Bacillus subtilis to a standard organic lime sulfur/sulfur fungicide program and a non-sprayed treatment for control of apple scab and other fungal diseases; (ii) evaluate potential non-target impacts of these fungicides on pest and beneficial insect populations; and (iii) conduct a preliminary experiment evaluating the potential of raw milk as a fungicide in organic apple production in Vermont. Five treatments (potassium bicarbonate, neem oil, Bacillus subtilis, lime sulfur/sulfur, and a non-sprayed treatment) 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 April 2007 and 23 April 2008 and continued on approximately a weekly schedule through the end of June and then every two weeks through 23 July 2007 and 17 July 2008, respectively. Data obtained were analyzed by analysis of variance and significance between means was determined by Fisher‟s Protected LSD Test (P ≤ 0.05). None of the alternatives managed disease as well as the standard lime sulfur/sulfur fungicide program. The neem oil treatment showed more activity against apple diseases than the other alternative fungicides. Both the lime sulfur/sulfur and neem oil treatments had disadvantages, including phytotoxic burning and/or significantly more russetting on the fruit at harvest. The neem oil treatment had significantly more fruit clean of insect damage than the other alternatives and the non-sprayed treatment in 2007 and more than all treatments in 2008, which is attributable to its insecticidal properties. However, the insect management from the neem oil treatment was not commercially acceptable. The overall quality of the fruit was not at commercially acceptable levels. No treatment had above 40% of the harvested fruit placed in marketable grades. This research shows that potassium bicarbonate, Bacillus subtilis, and neem oil do not offer substantial advantages over the standard lime sulfur/sulfur fungicide program in organic apple production in Vermont. In a preliminary study at the University of Vermont Horticultural Research Center, the efficiency of a 30% v/v raw milk dilution was compared to a non-sprayed treatment. Treatments were applied to „McIntosh‟ trees in a completely randomized design with three single-tree replications. Milk applications were made on approximately a weekly schedule from 26 Apr 2007 to the end of June and every two weeks through 23 Jul 2007. Overall, milk did not provide management of disease and caused premature leaf yellowing and defoliation of the apple trees.

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