Bag Apples for Spray-Free Disease and Insect Control
Dr. Robert Tomesh, UW-Extension Specialist
Apple scab, cedar-apple rust, apple maggot, coddling moth and curculio are the most destructive pests of apples grown in backyards. Each year these pests present themselves during the growing season and degrade fruit. The season long spray applications to control pests are a frustration for many homeowners who find the weekly spraying a real inconvenience.
Common apple insect and disease pests such as apple scab, cedar-apple rust, curculio, codling moth, and aphids can severely damage trees and/or fruit. Other pests and diseases such as stink bugs, flyspeck, and sooty blotch reduce the aesthetic and keeping quality of the fruit. Knowing that pests are likely to appear, some gardeners may use seasonal fruit spray applications and may be left wondering whether or not their apples are safe. Most insect pests, with exception of the curculio, become problematic after petal drop. While impractical for commercial growers, bagging of fruit on the tree provides an effective alternative to pesticide sprays throughout most of the season.
Begin home orchard by selecting disease resistant varieties which will provide protections to tree leaves and fruit. Sanitation reduces the number pest initiation sources in the area. Picking up and properly disposing of fallen apples prevents the larvae from burrowing into the ground. Raking and disposing fallen leaves is a way of discarding fungal infected leaves which serve a as an infection source for the coming year. However, many backyard orchardists have no control over their neighbors' apples or abandoned apple trees which are sources of insects and pathogens.
Insects can be prevented from laying eggs on apples and disease spores can be prevented from contacting apple fruit by placing a plastic bag over the apple. Many types of bags will work to control pest infections. About 10 days after petal drop, when fruit is about the size of a dime, place the bag on the apple prior to the arrival of insects and diseases. Tie or staple the bag loosely around the fruit stem. With plastic bags, cut about ¼ inch piece off the bottom corners of the bag to prevent the build-up of water in the bag.
Several choices of protectant products exist: nylon stocking bags, plastic bags, brown paper bags, commercial paper bags (gray bags, specifically used for bagging fruit in orchards), plastic film ("Saran Wrap"), and zipper closure plastic bags.
Our experience has been that the most successful product and method was stapling the zipper closure plastic bags. We could apply 30-plus bags per hour. We stapled the bag one third of the way across the zipper, slipped the plastic bag over the apple, zipped it closed and secured in place by another staple on the other side of the apple stem.
Using ordinary household plastic bags, we could bag 30 to 40 apples in an hour to protect from insects and diseases the remainder of the growing season. Once bagging the anticipated number of apples needed to meet family consumption needs, forget the rest of the apples on the trees, only to pick-up and discard when dropped by the tree.
All trees should be pruned normally and receive a thorough dormant oil spray during the late winter or early spring. Plum curculio attacks the apples before the fruit are large enough to bag. Select fruit that do not have egg laying scars (1/16 of inch crescent mark). Petal fall is when all of the petals have fallen off of the blossoms. Organic growers may select Rotenone to control plum curculio. These would be the last pesticide application of the year.
When the fruit are about 1/2 to 3/4 of an inch in diameter, the fruit should be thinned to a single fruit per fruit cluster with approximately one fruit per six to seven inches of limb. This will help to produce large fruit and encourage return bloom next year. The fruit can be thinned at the same time that the apples are bagged.
When the apple fruit reach 1/2 to 3/4 of an inch in diameter, they are ready to be bagged. This should be about two to three weeks after petal fall. Continue to apply bags to the rest of the fruit on the tree. Once the fruit have been bagged, no additional pesticide sprays should be needed for the remainder of the season. This bagging will work for plums, pears and other larger tree fruits.
Clear plastic bags do not impact fruit coloring and thus can be left on the fruit. If paper bags are left on the fruit until harvest, the fruit will not color properly. Even red apple varieties will be light yellow in color when ripe. So the paper bags need to be removed three weeks before harvest to allow the fruits to color properly. Generally, during this late summer period, no additional sprays are needed.