Each fall, a surprising amount of fruit is left to rot under often aging trees. Whether solitary by the roadside or clustered in backyard orchards, most are relics of old farms and homesteads. These old trees can be surprisingly prolific, despite their age, and while gleaners reap some of the wealth for local food banks, many are sadly unusable. Here in the humid Maritime Northwest, apples and pears are often affected by a funky fungal disorder called scab. It’s an apt name, as the lesions do indeed look like scabs on old wounds. Yuck, right?
Although mangy fruits are unsightly, fruits that are only moderately affected can still be used to make juice and cider. Once peeled, the slightly scabby fruit can be eaten raw or cooked. Advanced scab lesions quickly ruin the fruit, as they cause the skin to crack and crack, creating a ready-to-eat assortment for scavengers, from birds to beetles and insects. (Some birds even enjoy the fruit as it ferments, which makes for some pretty amusing moments for sober observers.) Open wounds in the skin also provide ideal opportunities for disease just waiting for a chance to invade. .
Although apple scab and pear scab are caused by different species of fungi, they are very similar. Like athlete’s foot for fruit, scab is very much at home in the Maritime Northwest. Mushrooms go dormant in hot, dry weather, but wake up and begin to spread from fall to spring as cool, misty mornings create perfect conditions for mushroom growth. Affected fruit will first develop small, pimply spots, which coalesce into flat, discolored spots, then gradually form darker masses that rise above the surrounding skin. After a hot, dry summer like this, scab may not show up clearly until the rainy season returns, when small lesions will develop rapidly.
The very first sign of scab usually appears in the spring, when dark green or brown spots form on new leaves. Severely affected trees may develop leaf scab, which completely covers the leaves, causing them to fall from the branches. These dead leaves remain in the soil, loaded with fungal spores that thrive in the moist leaf litter. In the spring, the fungal spores explode into action. To avoid this disastrous outcome, remove leaves from under affected fruit trees, then spread horticultural lime and several inches of mature compost from the trunk to several feet beyond the drip line. If you have a hot, active compost bin, add the leaves, as the beneficial biota will quickly consume the scab spores. If you don’t, put the affected leaves and fruit in the green waste bin. To make home composting more effective in controlling fungus, layer a nitrogen source like corn gluten or cottonseed meal with the affected plant material.
Once the fungal cycle is broken, your trees can become disease free (unless they are particularly susceptible to disease). If they become re-infected, it might be time to consider replacing disease-prone trees with disease-resistant varieties. At the Mount Vernon Research and Extension Station, rigorous decades-long trials of apples and pears have found a number of reliable varieties that resist scab and other diseases, even when the weather conditions are harsh. unfavorable. Suggested lists of productive and disease resistant apples for growers and orchards in the Maritime Northwest include Belmac, Crimson Crisp, Dayton, Enterprise, Gold Rush, Johnafree, Liberty, Prima, Redfree, Sundance, William’s Pride and Wynooche. Among European pear cultivars with good scab resistance, Arganche, Barnett Perry, Batjarka, Brandy, Erabasma, Harrow Delight, Muscat and Orcas are the highest rated varieties.
Contact Ann Lovejoy at 413 Madrona Way NE, Bainbridge Island, WA 98110 or visit Ann’s blog at http://www.loghouseplants.com/blogs/greengardening/ and leave a question/comment.