Disease Identification RITCHIE FEED AND SEED INC. (613)

Apple-Cedar Rust  This is a disease that requires two hosts, apple/crabapple and eastern red cedar/junipers. It cannot spread from crabapple to crabapple, or from cedar to cedar, it alternates between the two. In spring spores from orange galls on cedars or junipers are blown to apple trees, as far as 2-3 miles away. These spores germinate during warm, wet weather, and they infect the leaves and fruit. Yellow spots appear on the leaves, gradually enlarging and turning orange, and causing premature leaf and fruit drop. In the summer small cups with fringed edges develop on the undersides of the leaves. These spores are blown back to cedars and junipers, causing new infections.

Apple-Cedar Rust Control: Where possible, avoid planting these two hosts within several hundred yards of each other. Remove any galls and destroy them. If cedar-apple rust is diagnosed on the leaves, it is too late to treat them. Early season fungicide applications, repeated at 7-10 day intervals may be effective.

Black Knot  This is a disease that most commonly affects plum and cherry trees. Greenish swellings form on twigs and branches, in time these develop into black, cylindrical corky galls which will kill the infected part. Black knot spreads more quickly during warm, wet springs.  Control  There is no chemical control for black knot. Prune infected branches late winter, cutting at least 4 inches beyond the infected area and spray with dormant oil. Sterilize pruning equipment with dilute bleach in between cuts. Repeat applications of fungicide every days. This may help to slow down the spread of the disease.

Fireblight

This is a bacterial disease that is a problem for trees in the Roseaceae family such as apple, crabapple, pear and mountain ash. The leaves and branches become blackened and look as though they have been burnt, and terminal branches bend over like a shepherd’s hook. Clear yellow liquid may ooze from infected branches. The disease can be spread by rain or wind, insects or by infected pruning tools. Controls: There is no chemical control for Fireblight. Pruning infected wood may slow down the disease, but it may also create more problems if not done properly. Pruning tools must be disinfected after each cut with diluted bleach to remove all traces of the disease. All cuts should be made at least 10” (25 cm) into healthy wood. Copper or sulphur sprays may be used, but effectiveness is questionable.

White Powdery Mildew This is a fungal disease that appears as a white, powdery coating on the surface of the leaves. Poor air circulation and high humidity conditions may increase the problem. Powdery mildew doesn’t usually kill a plant, but it is unattractive and my cause distortion of the leaves or premature leaf drop. Control: Increase air circulation if possible and remove infected leaves. Spray with sulphur.

Rust This is a fungus which appears as powdery orange spots on the underside of leaves. Infected leaves may drop prematurely. Control: As for any fungus, improve air circulation if possible. Remove infected leaves and spray with sulphur.

Sooty Mold This is a black fungus that grows on the sticky honeydew deposited on the foliage by various sucking insects such as aphids, scale and mealybugs. The mold is unattractive and may interfere with photosynthesis by blocking sunlight. Control: Treat insects causing sticky honeydew. Wipe off affected leaves with a damp cloth. Or apply a sulphur solution.