MEDIA RELEASE
June 11, 2003
Written by Lynn McNaughton, U of M Extension Service Horticulturist (507)
389-8146 or 1-888-899-7758
Healthy Crabapple Tree
Ornamental crabapple trees are one of the most popular small trees used in Minnesota. Most crabapples burst forth in spring with white, pink or dark rose blooms that are followed by small round yellow, orange or red fruits. Unfortunately, many a crabapple tree selected for its outstanding floral or fruit show has proven to be a disappointment in terms of disease resistance.
Crabapples are prone to numerous diseases, with apple scab being the most common. This disease infects new leaves in spring when weather conditions are right, and the cool wet weather conditions this spring have resulted in a bumper crop of leaf scab. Besides spring infection, wet weather throughout summer can spread apple scab as well.
Apple scab causes dark, olive-green to brownish spots on the foliage and fruits. The spots are often described as velvety-looking. Infected leaves drop early, and heavily infested trees may become almost totally bare by mid summer. Falling leaves may have a yellowish or reddish color to them.
To control scab on susceptible trees, start by raking up all dropped leaves and dispose of them. Next, selectively remove some branches here and there throughout the crown to allow in more light and better air circulation, both of which discourage disease development.
Trees known to get apple scab every year can be put on a spray schedule to lessen infection, however, this can be quite labor intensive. Start spraying crabapple trees with captan or an all-purpose fruit tree spray (with fungicide) when the green leaf buds are about ½ inch long, then every 7 to 10 days for five more sprays.
Many gardeners may wish to give up the fight and replant with a disease resistant cultivar. Because scab is such a widespread problem, plant breeders have been working hard to develop resistant crabapples. Here is a list of resistant crabapples, listed by name, followed by bud color, flower color, then fruit color. For example, ‘Adams’, red/pink/red has red flower buds, pink flowers and red fruits.
Scab Resistant Crabapples:
‘Adams’, red/pink/red; ‘Jackii’, pink/white/purple red; ‘Coralburst’, coral/double pink/red-orange; ‘David’, pink/white/scarlet; ‘Donald Wyman’, dark pink/white/glossy red; ‘Harvest Gold’, pink/white/gold; ‘Liset’, dark red/rose red/dark red; ‘Molten Lava’, dark red/white/red-orange; ‘Prairifire’, red/red/maroon; ‘Prof. Sprenger’, pink/white/orange-red; ‘Profusion’, dark red/rose-red/red; ‘Red Jewel’, white/white/red; ‘Sugar Tyme’, pink/white/red, ‘White Cascade’, dark pink/white/yellow; zumi ‘Calocarpa’, pink/white/red.
Keep in mind that resistant cultivars can still get some apple scab, but not nearly to the same degree as susceptible varieties.