Fruit disease is the quiet thief of the fruit garden: it rarely kills a tree outright, but it ruins the crop, weakens the tree year after year, and turns a promising harvest into spotted, cracked, rotting fruit. The good news is that most fruit disease is preventable, and the prevention is mostly the same set of habits for every fruit: choose a resistant variety, plant it in sun with room to breathe, prune for airflow, keep the ground clean, and water the soil, not the leaves. A spray can help, but it is the last resort, not the first.
The diseases you will meet depend on your fruit and your climate. Apples and pears suffer from scab, which spots the leaves and cracks the fruit, and from fire blight, which blackens shoots. Peaches, plums and cherries suffer from brown rot, which turns the fruit into a brown, mummified husk, and from bacterial canker, which oozes gum from the bark. Grapes suffer from powdery and downy mildew. Berries suffer from grey mould, which rots the fruit in wet weather. All of these are worse in damp, crowded, shaded plantings — which is why the cultural steps matter so much.
The single most effective decision you make against disease is the variety you plant. Resistant apple varieties, for example, can make scab a non-problem in a garden where a susceptible variety would be badly hit every year. Ask your nursery which varieties are resistant to the diseases common in your area, and be willing to give up a susceptible favourite for a resistant one that actually crops. If you are unsure about a variety, a spray, or a diagnosis, check your local extension service — its advice is matched to your climate and soil.
Scab, brown rot and the diseases you will meet
Apple and pear scab is the most common fruit disease in wet climates: olive-green blotches on the leaves that darken and spread, and dark, cracked, scabby spots on the fruit. The fungus overwinters in fallen leaves, so autumn leaf cleanup is the single most effective control. Brown rot attacks peaches, plums, cherries and apricots: the fruit develops a brown, spreading rot, shrivels into a mummy and hangs on the tree, releasing spores the next spring. Remove every mummified fruit, in the tree and on the ground, and thin the fruit so it does not touch — brown rot spreads fastest where fruit clusters together. Powdery mildew coats young shoots and leaves with a white powder, worst on gooseberries, grapes and apples in a dry, humid summer; prune for airflow and avoid overfeeding with nitrogen, which pushes the soft growth mildew loves. Fire blight is the most serious: it blackens shoots and bends them into a shepherd's crook on apples and pears, and infected wood must be cut out well below the damage and destroyed. Our guides to apple scab and brown rot cover two of these in detail.
Resistant varieties: the decision that matters most
Resistance is not immunity, but it is the difference between a tree that crops cleanly with no spraying and a tree that needs constant attention. For apples, several modern varieties are resistant to scab, and they are worth choosing if scab is common in your area. For peaches, choose varieties resistant to leaf curl if that disease is a problem where you live. For grapes, choose mildew-resistant varieties if you garden in a humid climate. For raspberries, choose varieties resistant to the root diseases that kill canes in wet soil. For strawberries, choose varieties resistant to the wilts and rots that build up in old beds. Your nursery and your extension service can tell you which diseases matter in your area and which varieties resist them. A resistant variety is not a compromise on flavour — many resistant varieties are excellent eating — and it is the cheapest disease control you will ever buy, because you pay for it once, at planting time.
Airflow, sunlight and spacing: the cultural triangle
Fungal disease needs wet leaves to infect, and wet leaves dry fastest in sun and moving air. That is why spacing, pruning and site matter more than any spray. Plant fruit in full sun, give each tree or bush the space its mature size needs, and prune every winter to keep the centre open so light reaches the fruit and air moves through the canopy. A tree you can throw a hat through is a tree whose leaves dry quickly after rain. Do not plant fruit in a frost pocket or a damp hollow, and do not let grass or weeds grow right up to the trunk, where they hold damp against the bark. For berries, thin raspberry canes to six or eight strong ones per foot of row, and space strawberry plants so air moves between them. For grapes, keep the vine to a single cordon or a simple framework rather than a tangled mass. Every cut that opens the canopy is a cut against disease.
Watering, mulching and feeding for disease prevention
How you water matters as much as how much you water. Water at the base of the plant, in the morning, so the leaves stay dry and any splashes dry quickly. Overhead watering and sprinklers wet the foliage and spread spores from leaf to leaf, and they are the worst way to water fruit. Drip irrigation or a soaker hose is the best way, because it puts water at the roots and nowhere else. Mulch with straw or bark to stop soil splashing onto low fruit and leaves — soil splash is how many diseases reach the plant — and keep the mulch away from the trunk. Feed moderately: heavy nitrogen pushes soft, leafy growth that is easily infected by mildew and scab, and late feeding pushes soft growth that frost damages and disease enters through. Compost in spring and a potash feed as fruit swells is enough for most fruit. The watering calculator can help you plan a routine that keeps foliage dry.
Sanitation: the autumn cleanup that prevents next year's disease
Most fruit diseases overwinter in the garden, in fallen leaves, fallen fruit, mummified fruit hanging on the tree, and dead wood. The autumn cleanup is the most underrated disease control there is. Rake up and dispose of every fallen apple and pear leaf, because scab overwinters in them. Pick off every mummified plum, peach and cherry, in the tree and on the ground, because brown rot overwinters in them. Prune out dead and diseased wood and burn it or bin it — do not compost diseased material, because a home compost heap does not get hot enough to kill the spores. Clear fallen strawberries and raspberries from the bed, and remove old strawberry leaves in spring. Clean your tools between trees if you have been cutting diseased wood. It is unglamorous work, and it is the work that decides whether next year's crop is clean or spotted. Keep a note of which trees were hit and how badly, and prune those trees first and hardest the following winter.
When to spray, and when not to
In a home fruit garden, spraying should be the last step, not the first, and for many gardens it is never needed at all if the variety is resistant and the culture is good. If you do spray, use a product labelled for the disease and the fruit, apply it at the time the label directs — usually from bud break through the wet spring weather for scab, and at blossom time for brown rot — and understand that a fungicide protects new growth, it does not cure spots that are already there. Never spray while the tree is in flower, when bees are working the blossom. A winter wash of the bark can help against overwintering pests and disease on apples and pears, and a copper spray is sometimes used on peaches for leaf curl, but both should be used exactly as the label directs. If a disease is severe and spreading, or if you are unsure what it is, the plant disease checker can help you name it, and your extension service can confirm a diagnosis before you treat it.
Frequently asked questions
What is the best way to prevent apple scab?
Plant a resistant variety, prune for airflow so leaves dry quickly, water at soil level, and rake up and dispose of every fallen leaf in autumn, because the fungus overwinters in them.
Why are my plums rotting on the tree?
Almost certainly brown rot. The fruit rots, shrivels into a mummy and hangs on the tree, spreading spores. Remove every mummified fruit, thin the crop so fruit does not touch, and clear fallen fruit daily.
Do I need to spray my fruit trees?
Usually not, if you choose resistant varieties and keep the trees open, sunny and clean. If you do spray, use a product labelled for the disease, apply it at the right time, and never spray in flower.
What is fire blight and how do I deal with it?
Fire blight blackens shoots on apples and pears and bends them into a shepherd's crook. Cut the infected wood out well below the damage, disinfect the tools, and destroy the prunings — do not compost them.
Why do my grapes get white powder on the leaves?
That is powdery mildew, worst in dry, humid weather on crowded vines. Prune for airflow, avoid heavy nitrogen feeding, and choose a mildew-resistant variety next time you plant.
Disease prevention in fruit is mostly good gardening: a resistant variety, a sunny, airy site, clean ground and dry leaves. Do those four things and most diseases never get a foothold. For help naming a problem, use the plant disease checker, and for the individual fruits, see the growing guides.