Organic Apple Production

Published: April 28, 2014

(excerpted from the 2013 Fruit and Vegetable Research Report, University of Kentucky)

University of Kentucky scientists recently studied the feasibility of producing Redfree, Crimson Crisp and Enterprise apples organically. Trees were on a B.9 (dwarfing) rootstock and were planted at a 6 ft. (in-row) x 18.5 ft. (between row) spacing in 2007 in Lexington. Trees were trained to a slender spindle system and were fertilized with Nature Safe fertilizer at 100 lbs nitrogen/acre each spring. A mixture of lime sulfur plus Organocide (fish oil + sesame oil) each at 2.5% v/v was applied at petal fall to thin fruit, followed by additional hand thinning. Organically-approved products (Table 1) were applied for pest control and a Weed Badger was used to till underneath trees to reduce groundcover growth.

Total and marketable yield were recorded for each tree annually (Table 2). To obtain total yield, every fruit was harvested from trees, whereas marketable yield included fruits of acceptable size without significant disease or insect damage. Results indicated that Enterprise trees were more productive than the other cultivars. Redfree, the earliest ripening cultivar, had the greatest percentage of marketable fruit.

Early results of this study demonstrated that the organic-approved thinning agents were effective with additional hand-thinning. However, some lime sulfur products are no longer manufactured and may become increasingly difficult to purchase. All three apple cultivars are resistant to apple scab and moderately resistant or resistant to fire blight. However, CrimsonCrisp is susceptible to cedar apple rust, whereas the other two cultivars are resistant to this disease. Because scab, fire blight, and rust are common diseases, fruit yields were likely enhanced by their level of resistance, but fruit loss due to pests was still high. Brown marmorated stink bugs were not present in this orchard, but they could cause substantial damage to fruit since organic certified insecticides that provide specific control of this pest are currently unavailable. Although ground cover growth was limited, vegetation underneath trees was sufficient to provide a habitat for voles. These small rodents feed on trunks of trees and in severe cases, can cause tree mortality. Researchers will continue to evaluate pest control strategies to enhance marketable yield.

Table 1. Organic products used for pest control in an apple trial in Lexington, Kentucky during 2011 to 2013.

Table 2. Total and marketable yield of Redfree, CrimsonCrisp, and Enterprise apple trees grown at Lexington, Kentucky during 2011 to 2013.*

*Spring frost likely reduced crop in 2012.