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Introduction

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There is more interest in organic tree fruit production than the actual number of certified orchards reflect and some growers are taking a new look at organic production, particularly organic apple production, given some recent research advances that address long-standing obstacles.

In the past, very few growers in the Northeast have attempted to produce apples and other tree fruits organically in part because of the practical difficulties involved in managing pests in this region with organically-approved pesticides. Wet weather in the spring and summer coupled with the disease-susceptible apple cultivars present significant challenges in disease management, particularly apple scab. In addition, a large number of both native and introduced arthropod pest species attack apples and other tree fruits grown in commercial orchards.

Management of pest complexes is particularly challenging in New England, because unlike more arid production regions in the country, fruit orchards in New England are commonly in close proximity to semi-wooded areas with an abundance of naturalized and wild host species that can harbor populations of certain tree fruit pests. However, during the last 10-15 years studies have been conducted to develop management tactics that address key pests that can be incorporated into an organic program. For example, recent studies have shown that application of kaolin clay in organic orchards can help to successfully manage plum curculio. Also, the trend of planting apple cultivars less susceptible to disease than ‘McIntosh’ may make organic production more feasible.

In addition, recent research in New York state and elsewhere has shown that pheromones can be deployed in orchards to disrupt mating of key lepidopteran species such as codling moth and borer species, and substantially reduce damage from these pests. In addition, traditional management methods such as selective fruit thinning, pruning, sanitation (frequent removal of pest–infested, dropped fruit), removal of wild hosts near commercial plantings, and exclusion of pests, have been shown to reduce populations of some types of pests. Experience in Vermont has shown that non-managed Malus species can present significant inoculum for development of apple scab, fruit rot, and European apple sawfly outbreaks in adjacent organically managed apple blocks.

Ideally, organic fruit production is the synthesis of an entire suite of practices intended to take advantage of natural ecosystem interactions and minimize chemical intervention. In apples, such a system should start with the selection of disease-resistant cultivars to circumvent the need for the majority of normal disease sprays. This one tactic could eliminate or substantially reduce the need to manage apple scab, powdery mildew, cedar apple rust, and/or fire blight (Ellis et al., 1998). Many high-quality scab resistant apple cultivars, including ‘Liberty’, ‘Crimson Crisp’, ‘Topaz’, and others are commercially-available and worthy of trial in commercial New England orchards (Brown and Maloney, 2008). While resistant to apple scab, these cultivars are susceptible to other diseases which will require management during the growing season. Furthermore, genetic resistance to apple scab in commercially-available cultivars is largely dependent on a single gene, and in some production regions the apple scab fungus has evolved to overcome this resistance. To reduce the likelihood of breakdown of apple scab resistance in your orchard, scab-resistant cultivars should not be interplanted with unmanaged, scab susceptible cultivars. Additionally, fungicide sprays may be warranted on scab-resistant cultivars during peak infection periods from pink to petal fall to reduce likelihood of germination of resistant spores. In lieu of cultivar resistance to apple scab, a combined strategy of orchard sanitation and frequent applications of organic fungicides, such as elemental sulfur, throughout most of the season would be necessary.

However, overapplication of sulfur or lime sulfur fungicides to manage apple scab and other diseases should be avoided because those materials have significant negative impacts associated with their use. Both sulfur and lime sulfur have been shown to reduce net photosynthesis in trees following application, which may reduce tree growth, fruit set, crop yield, and fruit size. Both materials also have been shown to reduce populations of predacious mites, e.g. and fruit size. Both materials also have been shown to reduce populations of predacious mites, e.g. T. pyri, which contribute to biological management of phytophagous (i.e. plant-feeding) mite species. Finally, both sulfur and lime sulfur may impact fruit finish, especially when applied prior to hot weather greater than 85°F.

Because spray materials acceptable under organic certification tend to have less target efficacy than many non-organic materials, organic IPM programs should include all available management options. Pest management can be improved by addressing biological and physical components of the orchard system, including orchard architecture that promotes good airflow and spray penetration within the trees, strict orchard sanitation, predator introduction and conservation, good tree nutrient and groundcover management, and regular scouting for orchard pests. Sprayer operation is more critical under organic management programs, requiring careful calibration to ensure effective material application. Sprays should penetrate fully into the top and interior of each tree without excessive drift occurring. It is therefore important to use the best sprayer on the farm for applications of organic materials, keeping in mind that most certifiers require a dedicated sprayer that is not also used to apply materials that are incompatible with organic certification in non-organic blocks. One good way to quickly assess spray coverage is to observe the white surface residue if Surround (kaolin clay) is applied. The extent of the resulting residue will give some indication of the coverage of your sprayer. This is not a replacement for full annual sprayer calibration as discussed elsewhere this Guide.