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Common diseases that affect fruit trees

By Michael Allen

ly lethal, diseases of fruit trees accompanied by pointers on how to detect them and what to do about them in terms of prevention and treatment. The following treatments are strongly recommended for dealing with all the diseases. (1) It is highly recommended that all diseased, infected


leaves and twigs be collected and placed in the trash, or where permitted, burnt right away. Leaves must not be left on the ground over winter. (2) Fertilize affected trees and woody shrubs in the

spring (May to early June, or late September to October) to improve their vigour and chances of fighting the disease. Thoroughly water the tree after fertilization. Annual ferti- lization for at least three years may be needed to continue

s an expert on trees, I have noticed that all kinds of fruit trees are becoming more susceptible to disease. The following are five common, potential-

holding back the disease. (3) Spray the tree with a copper fungicide or any other

approved fungicide three times starting in late May and repeating the spraying procedure about every two to four weeks. Repeat treatments in the following two to three years if possible. (4) Prune off all infected twigs and dried leaf areas at

least one foot into the healthy looking branches. Always prune back to a nearby branch junction. After each prun- ing cut always sterilize the pruning tool with diluted bleach (one part bleach to nine parts water), or with dena- tured alcohol, or with methyl hydrate if the cuts were made between April and September inclusive. Sterilizing tools is not required for pruning in late fall and winter. (5) Where possible select new fruit trees whose cultivars have a high resistance to the disease.

Apple Scab Disease (Venturia inaequalis) This is more of a disease on the leaves of crab

apple than of the fruit. Cool, wet, early summers can favour this disease causing the leaves to turn yellow or yellow orange with prominent dark fungal spots. The disease causes the leaves to drop prematurely in the early part of summer. The overwinter leaves contain microscopic struc- tures that release disease spores at their maturity which occurs about the same time as the winter buds start to open. Over time the untreated tree dies as it can no longer manufacture the sugars and starches it needs to overwinter as the process of photosynthesis is seriously compromised.

Here is the typical sign of a leaf with severe apple scab disease.

Fire Blight Disease (Erwinia amylovora) Fire blight disease affects virtually all fruit-

ing trees and shrubs in the rose family. It is a major killer of apple, crab apple and pear trees. The disease is often transmitted by bees and wasps in the spring. Early signs of this disease may be all or one of the following: infected flow- ers that have a brownish shriveled appearance; or shriveled leaves that turn brown, orange, red, dark purplish-brown or black; or curled ends of twigs that have a dark brown or black (pear especially) colour. Often the inside of the bark will be discoloured reddish-brown when the bark is peeled back. After pruning cuts have been made use a tree

Apple fire blight twig and leaf symptoms. 12 • Summer 2015

pruning inert tar wound sealer or a wax based sealer to cover over each cut. This will prevent any further disease from entering the exposed twig or branch.

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