Apple Leaf Diseases: Pictures and Identification

Most apple leaf problems give themselves away through a few features: the color of the spots, their shape, and where they sit on the leaf and the tree. Looking closely at one leaf, top and bottom, often narrows the cause to one or two possibilities. Not every spotted leaf is diseased, though, because nutrient shortages and chemical drift can leave marks that look almost identical to fungal spots.1Southern Appalachian Apples. Don’t Be Fooled by Nectrotic Leaf Blotch – Southern Appalachian Apples2Proceedings of the New York State Horticultural Society. Leaf Spotting: Causes and Solutions Most of these problems weaken a tree by making it drop leaves early rather than killing it, and fire blight is the main exception worth acting on quickly.

Apple Scab Olive-Green Velvety Spots

Scab spots usually show up first on leaves, most often on the upper surface.3Wisconsin Horticulture. Apple Scab They begin as velvety olive-green spots, the velvet being spores released into the air.4Washington State University Extension. Apple Scab5RHS Advice. Apple and Pear Scab: Prevention and Treatment Over time the spots darken to brown or black and take on a rough, scabby look.6Washington State University Extension. Apple Scab They are roughly circular with feathery edges, from pinhead size up to about half an inch across.7Wisconsin Horticulture. Apple Scab The same olive to black spots appear on the apples themselves.8Wisconsin Horticulture. Apple Scab

In bad years the spots merge and cover much of the leaf.9Wisconsin Horticulture. Apple Scab The tree often drops many leaves early.10Wisconsin Horticulture. Apple Scab Spots on or near the leaf stem can make a leaf fall even when the blade looks mostly healthy.11Washington State University Extension. Apple Scab

The fungus survives winter in diseased leaves lying on the ground.12PubMed. Effects of Shredding or Treating Apple Leaf Litter with Urea on Ascospore Dose of Venturia inaequalis and Disease Buildup13Agriculture, Ecosystems and Environment. Effect of leaf litter management on scab development in an organic apple orchard Spores from that leaf litter start new infections the next spring.14PubMed. Effects of Shredding or Treating Apple Leaf Litter with Urea on Ascospore Dose of Venturia inaequalis and Disease Buildup15Agriculture, Ecosystems and Environment. Effect of leaf litter management on scab development in an organic apple orchard Leaves can become infected in cool spring weather, needing about 18 hours of wetness at 6°C (43°F) and longer when it’s colder.16PubMed. Ascospore Release and Infection of Apple Leaves by Conidia and Ascospores of Venturia inaequalis at Low Temperatures Infection is most favored around 16–20°C (61–68°F) with about 20 hours of leaf wetness.17PubMed Central. Phenotyping, genetics, and “-omics” approaches to unravel and introgress enhanced resistance against apple scab (Venturia inaequalis) in apple cultivars (Malus × domestica)

Because the fallen leaves carry next year’s infection, rake and remove them in autumn. Running a mower over them speeds their breakdown. Compost them only if your pile heats well; otherwise bag or bin them. Cleanup reduces scab but won’t eliminate it if neighbors’ trees are infected.

Many newer apple varieties are bred to resist scab. Resistance can weaken under very wet weather or aggressive fungus strains, so it lowers the risk rather than guaranteeing a clean tree.

Cedar-Apple Rust Bright Orange Spots

Rust begins in spring as tiny yellow or greenish-yellow spots.18Illinois Extension. Cedar Apple Rust19Oklahoma Cooperative Extension Service. Cedar-Apple Rust The spots swell and turn bright orange, often ringed with red.20University of Minnesota Extension. Cedar-apple rust and related rust diseases21Illinois Extension. Cedar Apple Rust Small raised black dots then form in the center on the upper surface.22University of Minnesota Extension. Cedar-apple rust and related rust diseases By midsummer, cup-shaped bumps with very short finger-like tubes, under 1/10 inch, stick out from the underside directly below each spot.23University of Minnesota Extension. Cedar-apple rust and related rust diseases24Illinois Extension. Cedar Apple Rust25Oklahoma Cooperative Extension Service. Cedar-Apple Rust

Turn an orange-spotted leaf over and look beneath the spot; a hand lens or your phone camera’s zoom makes the structures easy to see. Bright orange spots with these structures underneath are a strong sign of rust.

The same cup-like spots can appear on young apples, leaving fruit small and misshapen.26Oklahoma Cooperative Extension Service. Cedar-Apple Rust Very susceptible apples and crabapples can also get infected twigs.27Illinois Extension. Cedar Apple Rust The disease takes its name from its need for nearby junipers (eastern red cedar) to complete its life cycle.

Look at junipers within a few hundred yards for brown galls that sprout orange jelly-like horns in wet spring weather. Those galls release the spores that infect apples. Removing neighbors’ junipers is rarely practical, so planting rust-resistant apple varieties is usually the better fix. Light infections seldom harm an established tree, though susceptible varieties may drop leaves early.

Powdery Mildew White Powder and Curled Leaves

Mildew forms gray or white felt-like patches, often on the undersides of leaves.28Pacific Northwest Pest Management Handbooks. Apple (Malus spp.)-Powdery Mildew29Cornell University College of Agriculture and Life Sciences. Apple Powdery Mildew Yellow spots may show on the upper side directly above a white patch.30Cornell University College of Agriculture and Life Sciences. Apple Powdery Mildew Powdery patches on the upper surface eventually turn darker brown.31Cornell University College of Agriculture and Life Sciences. Apple Powdery Mildew

Mildew also changes leaf shape. Infected young leaves grow longer but not wider, so they look narrow, with edges crinkled, curled, or rolled upward.32Pacific Northwest Pest Management Handbooks. Apple (Malus spp.)-Powdery Mildew33Cornell University College of Agriculture and Life Sciences. Apple Powdery Mildew Whole infected shoots are often stunted and coated in white powder.34RHS Advice. Apple Powdery Mildew: Symptoms and Care In severe cases leaves stay small and may shrivel.35RHS Advice. Apple Powdery Mildew: Symptoms and Care Unlike scab and rust, which mostly leave a flat spotted leaf, mildew distorts leaf shape and concentrates on new shoot tips.

Because the fungus survives in buds, prune off white, stunted shoot tips in winter and early spring. Dispose of the clippings rather than leaving them under the tree. Pruning for good air flow also helps the canopy dry and limits spread.

Brown Spots With Purple Rings Frogeye Marssonina and Alternaria

Frogeye appears 1 to 3 weeks after the petals fall, as tiny purple flecks.36Southern Appalachian Apples. Leaf Spots of Bother: The Troublesome 3 – Southern Appalachian Apples37University of Kentucky College of Agriculture. Frogeye Leaf Spot & Black Rot of Apple The flecks grow into round spots 1/8 to 1/4 inch across with tan centers and dark brown to purple rims, like a frog’s eye.38Southern Appalachian Apples. Leaf Spots of Bother: The Troublesome 3 – Southern Appalachian Apples39University of Kentucky College of Agriculture. Frogeye Leaf Spot & Black Rot of Apple Tiny black specks often form in the centers of older spots, easiest to see with a hand lens.40Extension. Frogeye leaf spot and black rot on Apple41University of Kentucky College of Agriculture. Frogeye Leaf Spot & Black Rot of Apple Heavy infection can yellow leaves and cause early leaf drop.42Southern Appalachian Apples. Leaf Spots of Bother: The Troublesome 3 – Southern Appalachian Apples

Frogeye is the leaf stage of black rot, the same fungus that rots apples and makes black specks on them.43Extension. Frogeye leaf spot and black rot on Apple The black rot fungus lives on dead wood, cankers, and old shriveled fruit in the tree, so removing dead branches and leftover mummified apples cuts the source. Rotten fruit with black specks on the same tree supports the diagnosis.

Marssonina spots appear on the upper side of mature leaves around mid-June.44Penn State Extension. Apple Disease – Marssonina Blotch They are 5 to 10 mm (about 1/4 to 3/8 inch), gray-brown to black with a purple tinge at the edge.45Penn State Extension. Apple Disease – Marssonina Blotch They are more irregular in shape than frogeye and easily mistaken for it.46Southern Appalachian Apples. Marssonina Madness on Malus Spots merge, the surrounding leaf yellows, and leaves drop as early as late June.47Penn State Extension. Apple Disease – Marssonina Blotch48Southern Appalachian Apples. Marssonina Madness on Malus Heavy early leaf loss weakens the tree and lowers the crop.49European Journal of Plant Pathology. Apple blotch disease (Marssonina coronaria (Ellis & Davis) Davis) – review and research prospects

Alternaria spots appear in late spring or early summer as small round purple to black spots, sometimes with a purple border.50Southern Appalachian Apples. Leaf Spots of Bother: The Troublesome 3 – Southern Appalachian Apples Older spots enlarge irregularly and darken.51Southern Appalachian Apples. Leaf Spots of Bother: The Troublesome 3 – Southern Appalachian Apples Unlike frogeye, they are spread evenly throughout the whole canopy.52Southern Appalachian Apples. Leaf Spots of Bother: The Troublesome 3 – Southern Appalachian Apples The fungus overwinters on fallen leaves, like scab.53Southern Appalachian Apples. Leaf Spots of Bother: The Troublesome 3 – Southern Appalachian Apples

To tell them apart, note when the spots first appeared: just after bloom points to frogeye, mid-June onward to Marssonina. Round spots with a clean ring suggest frogeye, while ragged ones suggest Marssonina or older Alternaria.

These look-alikes are hard to separate by eye, even for experts. A county extension office or plant clinic can confirm the cause from a bagged sample of leaves, which is worth doing because the timing of control differs from one disease to the next.

Fire Blight Blackened Shoots Bent Like a Hook

Fire blight is caused by bacteria, not a fungus.54U.S. Dept. of Agriculture eBooks. Fire-blight of apples and pears It kills blossoms and young twigs rather than making scattered leaf spots.55U.S. Dept. of Agriculture eBooks. Fire-blight of apples and pears Infected shoot tips wilt, turn brown or black, and bend over in a shape called a shepherd’s crook.56Davey Tree. Fire Blight of Apple & Pear Trees: Symptoms & Management57Cornell University. Fire Blight Leaves often darken along the central vein as bacteria move through the shoot.58Cornell University. Fire Blight Dead apple leaves turn dark orange-brown, while pear leaves turn black.59Cornell University. Fire Blight Young, fast-growing shoots are hit hardest, and symptoms often stop at older wood.60Cornell University. Fire Blight

Wilting from drought affects a tree more evenly and doesn’t form a tight hook. Dead leaves from fire blight tend to stay attached, looking scorched.

Because the bacteria can move into branches, act promptly. Prune infected shoots at least 8 to 12 inches below the visible damage, in dry weather. Disinfect pruners between cuts with alcohol or a diluted bleach solution, and bag and remove the cuttings rather than composting them. Avoid heavy nitrogen fertilizing, which drives the soft growth the bacteria favor.

Yellow Patterns From Mosaic Virus

In spring, sensitive varieties show pale yellow to bright cream irregular spots or bands along the main veins.61UC IPM. Apple Leaf Diseases: Pictures and Identification62Pacific Northwest Pest Management Handbooks. Apple (Malus spp.)-Apple Mosaic Some leaves develop large pale spots.63UC IPM. Apple Leaf Diseases: Pictures and Identification The virus is carried inside the tree, usually from infected grafting wood.

There is no cure, but many infected trees still bear reasonably well. Symptoms are often strongest in spring and fade in summer heat. Don’t use wood from an infected tree for grafting, and buy certified virus-free nursery stock for new plantings.

Leaf Problems That Aren’t Diseases

Iron shortage turns leaves yellow with a fine net of green veins.64Pacific Northwest Extension Publication. Nutrient Disorders in Tree Fruits In severe cases edges and patches die, and all or part of the tree may be affected.65Pacific Northwest Extension Publication. Nutrient Disorders in Tree Fruits Nitrogen shortage gives smaller, pale green leaves and short shoots, sometimes with reddish bark.66Pacific Northwest Extension Publication. Nutrient Disorders in Tree Fruits Magnesium shortage yellows areas between veins or at the edges of older leaves in late summer, which may brown and drop.67Pacific Northwest Extension Publication. Nutrient Disorders in Tree Fruits

On Golden Delicious, irregular brown blotches 0.5 to 1.5 cm suddenly appear, usually bounded by larger veins.68Ohio State University Extension. Necrotic Leaf Blotch of Golden Delicious Apples Within days many leaves yellow and drop at once.69Ohio State University Extension. Necrotic Leaf Blotch of Golden Delicious Apples This necrotic leaf blotch is a growth disorder thought to be linked to zinc shortage, not an infection.70Southern Appalachian Apples. Don’t Be Fooled by Nectrotic Leaf Blotch – Southern Appalachian Apples It is worst on Golden Delicious and milder on its offspring.71Southern Appalachian Apples. Don’t Be Fooled by Nectrotic Leaf Blotch – Southern Appalachian Apples

The fungicide azoxystrobin, even at tiny drifted amounts, can spot McIntosh and Gala leaves in a way that looks just like frogeye.72Proceedings of the New York State Horticultural Society. Leaf Spotting: Causes and Solutions Drift spotting appears suddenly, evenly across the canopy, and only on McIntosh-related varieties while neighbors stay clean.73Proceedings of the New York State Horticultural Society. Leaf Spotting: Causes and Solutions Damage that stops sharply at one variety is a strong sign of a chemical rather than fungal cause.74Proceedings of the New York State Horticultural Society. Leaf Spotting: Causes and Solutions Apple rust mites can also bronze leaves and roughen fruit skin, another non-disease mimic.75Koppert. Apple Rust Mite (Aculus schlechtendali) | Damage & Biological Control

Patterns that follow the veins or affect the whole tree evenly suggest nutrition, though spray drift can also appear evenly. Infections usually spread gradually and vary with wet weather.

To confirm a nutrient problem, a soil test and a leaf analysis through extension show what’s actually short. High-pH soil often causes iron yellowing even when iron is present. Correct the soil or use foliar sprays rather than guessing with fungicides.

Using Phone Apps and Photos to Identify Leaf Problems

Computer programs trained on large sets of apple leaf photos can sort common diseases accurately.76PubMed Central. A systematic review of deep learning techniques for apple leaf diseases classification and detection In tests they correctly identified about 97–98% of leaf photos.77PubMed Central. The Plant Pathology Challenge 2020 data set to classify foliar disease of apples78PubMed Central. AppleLeafNet: a lightweight and efficient deep learning framework for diagnosing apple leaf diseases Leaves with several problems at once, however, were identified correctly only about half the time.79PubMed Central. The Plant Pathology Challenge 2020 data set to classify foliar disease of apples An app answer is a good starting point but not final when symptoms look mixed.

To get a useful answer, photograph both the top and underside of a typical leaf in daylight. Include a close-up of one spot and a wider shot of the branch, and note the variety and the date symptoms first appeared. If the app’s answer seems uncertain, send the same photos to an extension office. If symptoms stop at one variety, consider spray drift, which no app will recognize.

A Seasonal Calendar for Spotting Problems

Walk the tree weekly from bud break through June, the busiest disease period, and keep a simple log of dates and photos so repeat problems stand out.