Dealing with canker, woolly aphid and scab: the main fruit tree problems
If you grow apples or pears, you’ll know about these fruit tree problems – canker, woolly aphid and scab. Here’s how to recognise the signs and how to treat them. These are fungal diseases and pests that can seriously affect your crop and the tree’s health. However, there are measures you can take to limit the damage.
Apple canker
This is a fungal disease my old Cox’s Orange tree has battled with for years. Fortunately, the younger Red Falstaff tree is all clear so far. The fungus Neonectria galligena attacks the bark, causing a sunken area and, eventually, the death of the branch. New cankers form from mid-spring.
Sorbus species are attacked as are ash, beech and some other trees. On small branches and fruiting spurs, the infection may girdle the stem and kill it. On larger branches, cankers are perennial, with the affected area covered with dead bark showing concentric rings. You can see this in the photo above. Older cankers lose the bark, exposing dead wood in the centre. Eventually, the branch will die above the canker, progressively weakened as the bark is killed. Developing fruits are sometimes attacked and will rot and fall.
Fruit tree problems: pay attention to drainage
Canker is more serious on wet, heavy and/or acid soils, so pay attention to drainage and raise the soil pH by liming if needed. I used a soil-testing kit, a worthwhile purchase. My soil turned out to be pH 7 – neutral.
Copper-containing fungicides such as Bordeaux mixture are sometimes recommended, but I’m not keen on this. Studies have shown copper compounds build up in the soil and adversely affect helpful predators such as ladybirds and earthworms. I’ve learned to live with the canker on the old tree, cutting out the worst and making sure it is in the best health possible. Any parasite or predator will attack the weak.
Choosing canker-resistant apple trees
No apple or pear variety is completely resistant to canker, but these show some tolerance. Most are uncommon varieties that you will find at a specialist nursery like Tom the Apple Man.
Alfriston, Annie Elizabeth, Brownlees Russet, Cockle Pippin, Crawley Beauty, D’Arcy Spice, Emneth Early, Grenadier, John Standish, Katy (Katya), Lane’s Prince Albert, Lord Derby, Merton Russet, Newton Wonder, Orleans Reinette, Reverend W. Wilkes, Rosemary Russet, Winston.
Particularly susceptible popular varieties include Cox’s Orange Pippin, Lord Suffield, James Grieve, Ribston Pippin, Worcester Pearmain, Ellison’s Orange and Spartan.
Potted guide: how to deal with canker on fruit trees
- Cut out all affected smaller branches and spurs. With larger branches, cut out infected material.
- Remove all brown, infected bark and wood, cutting back to fresh green tissues.
- Use protective wound paint immediately to prevent the wounds from becoming reinfected and damaged.
Woolly aphids
One pest on my apple trees is the woolly aphid. It looks like mould or mildew, but the insects hide in a mass of white fluff they secrete. They also love Pyracantha and Cotoneaster horizontalis. Woolly aphids suck sap from woody stems. In the growing season, infested branches are covered with fluffy white material. Thinner bark around old pruning cuts is a prime site for insects in spring.
Affected branches develop soft, lumpy growths in the bark as a result of feeding. These can split in frosty weather and create entry wounds for cankers. One organic (and physical control) is scrubbing colonies with a stiff brush in spring/early summer before an extensive infestation has built up. Another method is using an organic winter wash, as nymphs overwinter in cracks in the bark. You can also blast them off with a hose.
Apple and pear scab
Apple scab and pear scab are caused by fungi Venturia inaequalis and V. pyrina, respectively. They spread by airborne spores and survive the winter on fallen leaves. Apple scab can also affect Cotoneaster, Pyracantha and Sorbus.
Symptoms include:
- Leaves: Olive-green spots or blotches appear, initially velvety as they release airborne spores, then darkening and falling early.
- Twigs: Blistering and cracking bark, leaving entry points for canker.
- Fruit: Familiar brown/black scabby patches which distort and crack the skin. Eating quality is hardly affected, but the fruit will become prone to rot and won’t store.
To control apple and pear scab, prune out blistered twigs. Clear the ground of fallen leaves and infected fruit to cut down on the number of spores able to spread next year. However, spores can be blown a long way by the wind.
Fruit tree problems: winter tree wash
One chore that’s worth doing is using a winter tree wash. The most popular organic sprays are a blend of natural plant and fish oils, but you can get garlic-based ones. Beware – they absolutely stink, and so will you, if you try and apply it on a windy day.
They’re used to control overwintering insect pests on fruit trees and bushes. I use Vitax’s Winter Tree Wash. It controls the eggs, larvae and nymphs of aphids and other pests on apples, pears, plums, cherries, gooseberries, blackberries, raspberries, blackcurrants and redcurrants.
Apply during calm, dry conditions using a pump-action sprayer, and thoroughly soak all bark surfaces, especially crooks of branches. If it is required, a repeat application can be made just before the trees’ buds break in early spring.
