Weeping Crab Apple Problem - Knowledgebase Question

Toronto, ON
Question by dcalderisi
July 9, 2004
We've had this tree for more than 20 years. It has never had a problem before except for one year when I was remiss with pruning and the foliage suffered from lack of air flow. It produces, as per usual, a superb show of blossom at its usual time in early May. By late May I noticed that some of the foliage tips had turned brown and curled. I thought it might have been due to lack of water. I gave it a good soaking at that time and have maintained routine watering since then. The problem has continued however. Many end leaves have turned complete (dark) brown and shriveled amd some of the young fruit have turned almost black. Other leaves are spotted with dark brown. The problem hasn't yet progressed to the entire tree. A superficial look doesn't indicate a tree in distress, but a closer look reveals a general "dullness", what I might call in a human being a certain "lethargy." There are no signs of pests. I'm assuming it is a systemic problem but have no way of knowing where to start. Can you help? Thanks so much.

Answer from NGA
July 9, 2004


It sounds as though your crabapple has developed a fungal disease called apple scab. This disease attacks both apple and crabapple trees. Symptoms first appear in the spring as spots (lesions) on the lower leaf surface, the side first exposed to fungal spores as buds open. At first, the lesions are usually small, velvety, olive green in color, and have unclear margins. On some crabapples, infections may be reddish in color. As they age, the infections become darker and more distinct in outline. Lesions may appear more numerous closer to the mid-vein of the leaf. If heavily infected, the leaf becomes distorted and drops early in the summer. Trees of highly susceptible varieties may be severely defoliated by mid to late summer.

Fruit symptoms are similar to those found on leaves. The margins of the spots, however, are more distinct on the fruit. The lesions darken with age and become black and "scabby." Scabs are unsightly, but are only skin deep. Badly scabbed fruit becomes deformed and may fall before reaching good size.

Once the disease has infected a tree, it's very difficult to control. The first step is to avoid reinfection by raking up fallen leaves and fruit at the end of the season. This will stop fungal spores from splashing back up onto your tree during rainy weather.

Apple scab is more common when spring weather is wet, and if this past year was wetter than usual, your tree may not develop the disease again next year, especially since you've already done some pruning to open the tree canopy to better air circulation.

Some organic gardeners protect their apple and crabapple trees with sulfur sprays early in the growing season. If you're not opposed to using a preventative fungicide, sulfur sprays might be the answer if the problem continues in the years to come.

Hope this information is helpful.

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