Taking an environmentally sensitive approach to pest management


Missouri Environment & Garden



AUTHOR

Michele Warmund
University of Missouri
Division of Plant Sciences
(573) 882-9632
warmundm@missouri.edu

A New Year’s Resolution - Better Quality Apples

Michele Warmund
University of Missouri
(573) 882-9632
warmundm@missouri.edu

Published: January 1, 2010

This is the time of year we all make resolutions, including striving for a healthy lifestyle. As you make those resolutions, consider a simple practice such as enclosing individual apples in bags to increase the pest-free fruit from your trees. While this resolution may not result in losing ten pounds or omitting a particular vice, it will result in more useful fruit harvested from your trees with a bit of early season effort. Bagging fruit is commonly used world-wide on dwarf trees to improve the fruit finish and peel color for upscale markets. When used by homeowners, bags can also be an effective barrier against summer diseases and insects.

Before bagging fruit, a few pesticides may be applied before flowering. Dormant oil should be applied in late winter before the buds open to control mites and scale. Also, plum curculio and codling moth can infest trees before fruit are large enough to bag. Organic growers can apply Rotenone to control plum curculio. For non-organic growers, recommended pesticides for early season use can be found in the Fruit Spray Schedule at http://extension.missouri.edu/publications/index.aspx. Diseases such as apple scab, cedar apple rust, and fire blight should also be controlled. Most often this is done by selecting and planting a diseaseresistant cultivar such as Enterprise or Liberty. However, if you don’t have these cultivars, you may apply early season fungicides. When bagging apples, pesticides may be applied until three weeks after petal fall. After this, no other sprays are applied for the rest of the season.

Hand thinning the fruit is another cultural practice is done before bagging. When the fruit are about the size of a dime, remove all but one apple from the cluster. Also, space one fruit about ever six inches. This will allow space for the bags and result in large fruit this growing season and enhance fruit set the following year.

About three weeks after petal fall or when the apples are about one-half inch in diameter, they are ready for bagging. Two types of bags can be used. Japanese apple bags have been designed specifically for enclosing fruit and are used by commercial growers. These bags have two paper layers, with a slit for a stem and a wire embedded in the opening to secure it around the fruit. Japanese fruit bags cost less than $15 for 100 bags from a supplier such as Wilson Irrigation & Orchard Supplies (http://www.wilsonirr.com/catalog_i4342079.html?catId=272951). Once bags are securely fastened around the fruit, they are left in place until three weeks before harvest. If bags are not removed before harvest, the pigments in the fruit do not develop properly and red-skinned cultivars will be pale yellow at maturity.

If Japanese apples are unavailable, a three-pound paper bag can also be used that has been cut to about six inches in length. Although not tested, a white bag would likely be a good choice as it would be more reflective than a brown bag and prevent an increase in temperature with the bag. A wire twist tie can be used to secure the bag around the fruit. In other states, ziploc bags have also been used to enclose the fruit with holes cut in the bottom corners of the bag to allow moisture that collects in bag to drain. However, in heat stress experiments conducted at the University of Missouri, ziploc bags on sun-exposed apples increased the fruit surface and flesh temperatures by more than 10º F during the warmest hours of the day. This increase in temperature over a five day period resulted in poor red color development on the peel of apples and decreased the sugar content and acidity of the fruit.

For the best quality fruit, plan now to reduce pesticide usage and harvest nutritious apples in the fall. While other resolutions may not last, this one will be year-long.

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REVISED: October 23, 2012