Apple scab is the most common disease of apples, and in a wet spring it can turn a promising crop into a disappointment. The leaves develop olive-green to brown blotches that darken and grow, the leaves yellow and drop early, and the fruit develops dark, scabby, cracked spots that make it unsightly and prone to rotting in storage. A tree that is badly hit year after year weakens, flowers less, and produces less fruit, and the fruit it does produce is often too damaged to store. The disease is rarely fatal, but it is the reason many home orchards produce apples that look nothing like the ones in the shop.

The fungus is Venturia inaequalis, and it is a specialist that attacks apples and crabapples. It overwinters in fallen leaves, and in spring it releases spores that infect the young leaves and fruit during wet weather. The infection needs leaves to stay wet for many hours, so the disease is worst in rainy springs and in humid climates, and it is rare in dry regions. The control is a combination of resistant varieties, which are the single most effective step, and the cultural habits that keep leaves dry and remove the overwintering fungus — airflow, spacing, and autumn leaf cleanup.

What apple scab looks like: symptoms

  • Olive-green blotches on leaves: irregular olive or grey-green spots on the young leaves, which darken to brown or black and grow as the season goes on.
  • Leaf yellowing and drop: badly spotted leaves yellow and fall early, starting in midsummer, and a badly hit tree can lose most of its leaves by autumn.
  • Dark scabby spots on fruit: circular, dark, rough spots on the fruit that may crack as the fruit grows, opening the way for rot.
  • Deformed fruit: fruit that is infected young may grow unevenly and be small and misshapen, with the scabby spots covering much of the surface.
  • Spots on leaf stalks and shoots: in severe cases the fungus spots the leaf stalks and young shoots, and the shoots may be weakened.
  • Poor storage: scabbed fruit rots more easily in storage, even if the spots looked superficial at harvest, so the crop does not keep.
  • Weakened tree: repeated severe defoliation over several years weakens the tree, reduces flowering, and makes it more vulnerable to winter cold and other problems.

Apple scab starts in spring, when the first young leaves open and the first wet weather arrives. The spores from last year's fallen leaves infect the young foliage, and the first blotches appear within a week or two. Through summer, each rainy spell produces a new wave of spots on the leaves and the fruit, and the disease climbs the tree. In a wet year the fruit can be heavily spotted by midsummer and the leaves can be dropping by August. In a dry year the same tree may show only a few spots all season. The disease slows in hot, dry weather and stops when the leaves stay dry, which is why the same tree can look terrible in a rainy May and recover with clean new growth in a dry September.

Which plants get apple scab

Apple scab attacks apples and crabapples, and a closely related fungus causes pear scab on pears. Some apple varieties are very susceptible — many older favourites are among the worst — while others are notably resistant, and the resistant varieties are the best investment a gardener in a wet climate can make. The disease does not attack other fruit trees, vegetables, or ornamentals, so it is a problem for the apple tree alone. Young trees are hit as hard as old ones, and the disease is worst on trees in shade or in crowded plantings where the leaves dry slowly.

Conditions that favour apple scab

Apple scab needs wet leaves and mild temperatures in spring: roughly 60 to 75 degrees Fahrenheit with leaves wet for many hours. The fungus overwinters in fallen leaves, and the spring spores are released during rain, so a wet spring is the danger period. Crowded, shaded trees dry slowly and are hit hardest, and young, soft growth is more easily infected than mature leaves. The disease is worst in humid climates and in rainy springs, and it is rare in dry regions. A tree that was not cleaned up in autumn starts the spring with a heavy load of spores at its base, which is why autumn cleanup matters so much.

How apple scab spreads

Apple scab spreads by spores: the spring spores are released from fallen leaves and travel on the wind and in rain to the young leaves above, and the summer spores spread from leaf to leaf in splashing water. The spores do not travel far — most infections come from the tree's own fallen leaves — which is why cleaning up the leaves under a single tree makes a real difference. The fungus does not spread on tools or hands to any significant degree, and it does not travel in seed or in nursery stock in the way some diseases do. The practical rule is that the fallen leaves are the source, and removing them is the control.

How to tell it apart from lookalikes

Apple scab is sometimes confused with other leaf spots, but its olive-green blotches that darken with age, and its scabby spots on the fruit, are distinctive. Powdery mildew on apple makes a white powdery coating on young shoots rather than olive blotches. Fire blight blackens shoots and bends them into a shepherd's crook, which scab does not do. Cedar-apple rust makes orange spots on the leaves and orange galls on junipers nearby. Insect damage makes holes or stippling rather than blotches. If the leaves have olive blotches and the fruit has dark, cracked, scabby spots, apple scab is the most likely answer.

Prevention: cultural steps that work

  • Plant resistant varieties — this is the single most effective step, and it is worth choosing a resistant variety even if it means giving up a susceptible favourite.
  • Plant in full sun with generous spacing and good airflow, and prune for an open canopy so leaves dry quickly after rain.
  • In autumn, rake up and dispose of every fallen apple leaf, and do not compost diseased material. Mowing the leaves to shred them can also help them break down faster.
  • Prune out crowded growth in late winter so air moves through the canopy.
  • Avoid overhead watering, and water at soil level in the morning if you water at all.
  • Feed moderately and avoid heavy nitrogen that pushes soft, vulnerable growth.
  • Thin the fruit so the remaining apples have room to grow and air can move between them.

Treatment step by step

  1. Rake up fallen leaves from under the tree in autumn and dispose of them with household waste — this removes the source of next spring's spores and is the most important treatment there is.
  2. Prune out crowded growth in late winter to open the canopy, and remove any dead or weak shoots.
  3. Pick off badly spotted leaves in summer if you can reach them, and dispose of them rather than leaving them on the ground.
  4. If you choose to spray, a fungicide labelled for apple scab can protect new growth, but it must be applied from bud break through the wet spring weather, and it will not cure spots that are already there. Apply it exactly as the label directs.
  5. Thin the fruit so the tree is not overloaded, and pick the fruit as soon as it ripens so it does not sit on the tree in wet weather.
  6. Feed the tree moderately after the worst of the disease has passed so it can replace its leaves, but do not overfeed with nitrogen.
  7. Keep up the autumn cleanup every year — a single year of thorough cleanup can cut the next spring's disease sharply.

What recovery looks like

Recovery from apple scab is visible in the new growth: leaves that open after the wet spring has passed should come through clean, and the tree will start to fill in again. The spotted leaves will not heal and will drop, and the fruit that is already scabbed will stay scabbed, but the tree itself is rarely badly damaged in a single year. Full recovery is a next-season matter: a tree that is cleaned up in autumn, pruned in late winter, and given sun and air in spring will often stay nearly clean the following year, even if it looked terrible the year before. The recovery is fastest and most complete when the tree is a resistant variety — on a very susceptible variety in a wet climate, scab will return every year no matter how good the cleanup is.

When a plant is beyond saving

An apple tree is rarely beyond saving from scab alone, because the disease attacks leaves and fruit, not the roots or the trunk. A tree is in serious trouble only when it has been defoliated several years running, when its growth is weak and its flowering poor, and when it fails to leaf out properly in spring. Even then, a hard prune, good feeding, and a season of clean culture can often revive it. The time to replace a tree is when it is a very susceptible variety in a wet climate where scab returns every year despite good care — in that case, a resistant variety in a sunnier position is the better investment.

Frequently asked questions

Can I eat apples with apple scab?

Yes, generally — the spots are on the skin and the flesh underneath is usually fine once the spot is cut away, though badly cracked fruit may have started to rot and should be discarded. Scabbed apples do not store well, so eat them fresh rather than keeping them. If you are unsure, check your local extension service.

Will apple scab kill my tree?

Almost never on its own, but repeated severe defoliation weakens the tree over several years, reduces flowering and fruiting, and makes it more vulnerable to winter cold and other problems.

Can I compost apple leaves with scab?

No. Home compost rarely gets hot enough to kill the fungus, so composting infected leaves returns the disease to the orchard. Bag the leaves and put them with household waste, or shred them by mowing so they break down in place over winter.

Why do my apples get scab but my pears do not?

Apple scab and pear scab are caused by closely related but different fungi, and a variety that is susceptible to one may not be susceptible to the other. The weather during the spring infection period matters too.

Do I need to spray for apple scab?

Spraying can help on a susceptible variety, but it must start at bud break and continue through the wet spring, and it never cures existing spots. Resistant varieties and autumn cleanup are the foundation, and any spray is an addition to them, used as its label directs.

Getting help and going further

If you are unsure which disease you are dealing with, take clear photos of the symptoms and check your local extension service — they can confirm a diagnosis from a sample and advise on the varieties and the timing that work best in your area. You can also try our plant disease checker to narrow down the problem, and browse the guides hub for related disease guides. For growing advice, see growing apples. For growing advice, see zone 5 apples. For growing advice, see growing peaches. Related guides: fire blight, brown rot fruit, peach leaf curl. Whenever you remove diseased material, dispose of it with household waste — do not compost diseased material, since home compost rarely gets hot enough to kill the organisms that cause these diseases. Good record-keeping helps too: note the date, the weather, and the variety when a problem first appears, so you can spot the pattern next year and act earlier.