New Zealand Garden Swap Newsletter

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NO SPRAY ORGANIC APPLES

The first point to keep in mind is that few gardeners face all of the apple pests that fill growers' manuals, and that home gardeners need only concern themselves with a few key problems and the best methods for managing them. Below we describe specific stages of apple tree development and the important tasks for each period. We also discuss the most common pests. No treatise on organic growing is complete without emphasizing the importance of building rich soil. Your plantings rely on the billions of microorganisms teeming in good compost. In late fall or early spring spread an inch or two of compost within the tree's drip line.

Test the pH of your soil, and if it's acidic, use either a ground limestone or powdered oyster shell to raise soil pH to between 6.3 and 6.8. If the pH tests within that range and if a soil test shows that soil calcium is low, use gypsum. A plentiful supply of calcium in soil is important to prevent bitter pit, a physiological disorder of apples.

Apple Pests

The diseases and insect pests that most often ruin home apple crops. The diseases are apple scab, powdery mildew, and rust. The insect pests are codling moth and apple maggot. Scab, powdery mildew, and codling moth are nearly universal. Scab is generally considered the most serious apple disease. Initially the fungus causes olive green spots, which darken and harden over time. Scab develops in the mild temperatures and high humidity of spring. During particularly wet summers, subsequent scab infections, called "secondary scab," will cause problems through the summer if you were unsuccessful preventing infection in spring.

Scab is the most common and most potentially damaging apple disease. It starts in spring about the time buds show their pink colour, and that's the time for you to spray Scab spores overwinter in infected leaves, so if the disease is common where you live, rake fallen leaves every fall and destroy them. Alternatively, scatter ground limestone over the fallen leaves under the tree after harvest, and follow up with an earthworm-friendly layer of compost. This hinders spore reproduction that normally occurs at that time.

Powdery mildew is common to many kinds of plants besides apples. Infected leaves are covered with a thin layer of white fungus. The disease develops fastest when days are warm and nights cool. It does not require high humidity. Spores overwinter in already infected buds. Even though scab and powdery mildew are very different diseases, when you spray for scab, you also prevent powdery mildew. Control both diseases with sprays of sulphur. Many forms of sulphur are available; which one you choose depends on how you plan to apply it. Also even though sulphur is an ancient and safe pesticide, it is a potential irritant, so protect your eyes, ears, and nose.

Control Codling moth: This is the most famous insect pest of apples and it occurs virtually everywhere apples grow. The time to take action is petal fall and early summer. Many kinds of fruit moths and their caterpillars strike in different regions of the country, leaving behind entrance holes marked by sawdust-like frass, winding feeding depressions in the skin, deep sunken areas of light corky tissue, or clusters of tiny circular excavations on the fruit beneath a touching leaf. But codling moth is by far the most prevalent. Adult moths lay eggs on leaves and twigs about the time petal fall begins. Within days, larvae find their way to fruits and tunnel inside them, often beginning with the tiny openings left by the flower. Home gardeners might sufficiently protect their trees with codling moth traps, which contain a hormone attractant that lures males and traps them, provided that wild or unmanaged fruit trees are not within 100 yards. Make sure traps are in place when bloom begins. Use two per standard-sized tree, one per dwarf tree, and replace them after eight weeks. If codling moths are a persistent problem, spray with insecticide. Add fish oil to the spray mix to help stick the bacterium to leaves and slow its breakdown. At least three sprayings are needed, and timing is critical: spray initially 15 days after petal fall begins, and subsequently at 5-day intervals. Note when petal fall begins and mark the spray days on a calendar.

Apple maggot earned the name railroad worm long ago for its meandering tunnels beneath the apple skin and eventually throughout the flesh. A practiced eye can pick out the puncture where the fly laid its egg by catching the slightly depressed sting mark in the right light. Apple maggots overwinter in the soil after emerging from fallen fruits. That's why the first step to reduce their numbers is picking up and disposing of fruit when it drops from the tree. Control apple maggots during the growing season by trapping them on fake apples that are coated with sticky insect trap coating. These hang on the tree like Christmas ornaments. You need six traps for a standard-size tree, and they must be in place three weeks after petal fall.

Tools and Supplies

Decide on your strategy and gather your materials while trees are still dormant. Most likely you'll include a sulphur-containing spray or dust, a sticker-spreader, especially if you live in a rainy area, traps for codling moth and apple maggot, and maybe a spray to aid control of codling moth. You'll also need a spray applicator.

The seasons of an apple tree

Exactly when and how fast your apple tree progresses from dormancy through bloom depends upon your climate and the weather. But to track that progress, apple growers long ago identified and named specific stages of spring growth. Those stages for the tree are then linked to the various pests that prey on apple trees and fruits. By observing the stage of the tree, you can know the stage of the pest.

Dormant:

In fall, rake and clean below your tree to minimize overwintering scab disease. Or scatter ground limestone over the leaves to hinder scab reproduction and to maintain optimum soil pH. Prune your tree while still dormant and shortly before spring growth begins. Prune to open the tree to air and light, a key to disease prevention. Remove prunings from garden area to prevent rot spores from establishing on cut branches.

Green or silver tip stage:

Spread compost 1- to 2-inches thick under dripline of each tree. Apply gypsum if fall soil testing indicated calcium levels are moderate to low.

Quarter-inch green stage

Apply an organic fertilizer blend. Cultivate a circle several feet in diameter around newly planted trees the first several years as well.

Pink bud stage

Now begins primary scab season. Apply liquid sulphur with sticker-spreader before next predicted rain. Spray sulphur now and 10 days later to minimize and powdery mildew.

Petal fall stage

Primary scab season usually ends with a daytime rain soon after petal fall. Be sure to have fresh sulphur spray in place before this rain if more than a week has passed since the previous sulphur spray. Repeat sulphur spray 10 days later to control powdery mildew. Hang codling moth traps and lures. Spray for first-generation codling moth approximately two weeks after petal fall. Repeat every 3 to 5 days at twilight over a two-week period.

Summer:

Hang sticky red spheres (fake apples) to trap apple maggots. Place them at eye level in direct sunlight but surrounded by developing fruit. Scrape away dead insects and renew the adhesive every three weeks. Replace codling moth traps and lures. Thin young fruits, leaving only the largest fruit in each cluster. After thinning, fruits should be 6 to 8 inches apart. Dispose of any infested fruits.