Apple tree disease identification

My apple is covered in sooty spots

What you see: Black smudgy spots on apple skin
What it is: A fungus called sooty blotch
Eat or toss? Eat! You’re seeing a cosmetic issue, not anything that will hurt you. You can also quite easily rub or rinse off the sooty stuff.

This apple may look like it just took a bath in charcoal, and it may have a fungal disease called “sooty blotch,” but don’t abandon it just yet. You’re looking at a cosmetic issue, and nothing more.

This fungus only inhabits the apple’s natural wax, on the outermost layer of the fruit. In fact, the sooty blotch fungus likes wax so much it can live on wax paper, says Rich Marini, a horticulture professor at Pennsylvania State University. Which all means that the fungus isn’t in the apple’s crispy flesh. So, if you rub or wash off the black stuff, or peel the apple, you’ll never know it was there. Or, you could follow Marini’s lead and sink your teeth in.

“I’ve eaten a lot of it,” Marini says. “It’s not harmful to human health and you can’t really taste it.”

Sooty blotch is common and often pops up in residential trees and on organic orchards where fungicides aren’t used, Marini says. It tends to be worse in humid areas. Even on a single tree, it will be concentrated more on what’s literally the low-hanging fruit, because the lower branches, which get less sunlight, are wetter.


Rich Marini – Professor of Horticulture – Pennsylvania State University
Yard and Garden: Apples and Pears – Iowa State University Extension and Outreach
Sooty Blotch and Fly Speck of Apples – Royal Horticultural Society

Sooty Blotch in Apples Not a Health Concern —

Apple scab

Apple scab occurs on apple, crab-apple and other species in the genus Malus. A different but closely related species occurs on pear.

Disease cycle

The disease usually survives over winter under the trees, in the dead, infected leaves from the previous season. Occasionally twig infections, infected bud scales or infected leaves which remain on the tree over winter can provide an overwintering source of spores. Leaves infected with the apple scab fungus usually fall from trees in autumn or early winter. The fungus continues to live within the leaves during winter, forming small, flask-shaped bodies, in which spores (ascospores) develop. These ascospores mature in spring and are forcibly ejected during spring rains.

The time when ascospores mature coincides with the period of rapid development of buds, flowers and leaves. Ascospore discharge occurs over a period of about 8 –12 weeks. Mature ascospores are present by early September, and the greatest numbers of ascospores are released from late September to mid-November. This is the high-risk period for infection with apple scab. Small numbers of ascospores are released during December. The discharge of ascospores in spring depends on moisture, temperature and light. Some ascospores are released about 30 minutes after the start of rain, and about 75% of mature ascospores are released within three hours. Temperatures close to freezing decrease liberation of ascospores.

Most ascospores are released during daylight. Night discharge and any discharges into dew are less important. Wind currents carry ascospores to developing flowers, fruits and leaves, where they adhere quickly on contact, and resist removal by more rain.

Ascospores germinate and grow into the tissue if fruit or green leaves are wet when ascospores lodge, and if they remain wet long enough. The time needed for germination and infection varies with the temperature and is called the infection period (see Table 1).

The fungus grows under the cuticle of leaves and fruit and sends up stalks on which summer spores (conidia) are borne. This is when the typical scab lesions can be seen and happens after about 9-17 days (depending on the prevailing temperature, Table 1).

Table 1. Infection periods – the number of hours that leaves or fruit must remain wet at various temperatures for infection to occur, and the time after infection has begun for scab lesions to appear

Average temperature °C Hours of wetting required for infection1 Days required for scab lesions to appear2
5.5 30
7 20 more than 17
10 14 16
13 11 14
14-15 10 12
15.5 9.5 11
16-16.5 9 10
17-24 9 9
24.5 9.5
25 11

1Average temperature for the period determined from hourly readings
2Average temperature determined from daily maximum and minimum temperatures (after W.D. Mills)

Conidia, produced in large numbers, are washed or splashed to new locations during rain. They germinate and form new infections if temperature and moisture are suitable. This continues during summer and autumn rains. An important difference between ascospores and conidia is that release of the conidia does not depend on light. Infected leaves fall to the ground in autumn and the disease cycle continues.

Control measures

Control measures are designed to interrupt the life cycle at various stages and to modify the orchard environment to reduce disease. When planning a new orchard:

  • Use scab-resistant varieties where practical
  • Avoid locations with high spring rainfall
  • Use dwarfing rootstocks and training systems to maintain an open and easily sprayed tree canopy
  • Avoid use of overhead irrigation, which could begin or prolong scab infection periods
  • Plan the orchard to allow for sanitation practices such as mulching of overwintering leaves.

At present the main methods of control are the use of protectant and post-infection sprays during spring, and sanitation practices to reduce scab carryover. Protectant spray programs remain the basis of effective apple scab control, especially where disease pressure is high. They may be supplemented by the use of post-infection sprays and autumn sanitation practices.

Protectant sprays

Protectant sprays of suitable fungicides are needed at green tip, pink bud and at regular intervals afterwards, to ensure that rapidly-developing leaves and fruits are covered with a fungicide residue that will prevent spores from germinating.

Post-infection sprays

Some fungicides have the capacity to kill or suppress established infections. The period of curative action is short. If curative fungicides are to be effective, they must be applied within a few days from the beginning of the wet period that started the infection period and not from when scab lesions are first visible.

Most fungicides will not cure an established apple scab infection after the lesion becomes visible to the naked eye, but some will suppress the formation and germination of spores on the established lesion as long as spray residue remains.

Both mechanical and electronic instruments that can record leaf wetness and temperature in the orchard are available. Data from these instruments, when combined with the table of infection periods (see Table 1) enable the grower to determine when scab infection conditions have occurred. This knowledge allows more precise timing of scab sprays. In orchards with a low risk of disease, such as those in irrigation districts where rainfall in spring is low, a control program based only on post-infection sprays can be followed. This may save several applications of spray when compared with a routine program of spraying protectants. Post-infection sprays, based on accurate knowledge of infection periods, can also supplement a program of protectant sprays.

Sanitation to reduce scab carryover

Primary infections of apple and pear scab are mainly caused by ascospores released from infected leaves that overwinter on the orchard floor (see disease cycle). The higher the density of ascospore inoculum, the faster and more intense the resultant scab epidemic . Sanitation practices can reduce the risk of scab build up in spring and improve the efficiency of scab control programs. Sanitation practices are defined as management practices which reduce or eliminate the development and production of primary inoculum (ascospores) before the start of susceptible tissue growth in spring.

Some practical sanitation practices are:

  • Treat leaves on the tree immediately before leaf fall with a nitrogenous fertiliser to hasten leaf breakdown.
  • Mulch the leaf litter after leaf fall. Sweep leaves into rows and use a mechanical shredder, slasher or flail mower to chop leaves into small pieces which then break down more rapidly. Leaf sweepers are available commercially.
  • Combine leaf mulching with a ground application of a nitrogenous fertiliser.

Storage scab

Infection periods that occur shortly before harvest can result in the development of storage scab. These spots develop slowly on fruit during storage as a result of infection in the orchard, and not from the contamination of fruit after harvest. Thus, it is important to apply suitable fungicide sprays if infection periods occur shortly before harvest and inoculum in the form of secondary infection is present in the trees.

Minimise resistance to fungicides

When planning a control program for scab, limit the use of fungicides which have a high risk of developing resistant strains of scab. Where possible, use multi-site fungicides (activity group Y) as they are at less risk from resistance than fungicides in all other activity groups.

Consult chemical resellers about the fungicides and most appropriate time to spray in your situation. Refer to the AVCARE fungicide activity group list for details of fungicide groups with similar modes of action.

Monitoring potential overwintering scab

Check levels of leaf infection in all blocks after harvest to estimate the potential level of scab which may overwinter and initiate primary infection in the following spring. Note that estimates of scab potential based on fruit scab levels are not a good indication of potential scab infection in the following season, because the disease does not carryover on infected fruit.

Refer to Note AG0159 Pear scab for information about this related disease.

The previous version of this note was published in June 2003.

The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.

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ABC’s of Gardening: Fungus causes spots on apple tree leaves

Q. I have orange and red spots on my apple tree leaves. What is causing it and what can I spray? — C.B.

Q. I have orange and red spots on my apple tree leaves. What is causing it and what can I spray? — C.B.
A. The orange and red spots on your apple tree leaves are lesions caused by the cedar apple rust fungus, Gymnosporangium juniperi-virginianae.
This fungus needs two different host species, one host from the juniper family and the other from the rose family.
The symptoms of the fungus on apple trees include the orange and red “spots,” or lesions, that may be found on leaves, fruit or soft stem tissue.
Spores are then produced from tiny cuplike structures that develop in mid- to late summer. These structures develop typically on the undersides of leaves, but can be found anywhere if developing on fruit.
Spores are dispersed by the wind as they are from its juniper host.
The fungus, when on juniper hosts, resembles a gall or swollen woody tissue. In the spring, bright orange hornlike structures grow from the gall, where spores are produced and are taken by the wind to infect a member of the rose family. This gall structure is where the fungus can overwinter and produce spores for several years, though this is not always the case.
To control this fungus, a fungicide may be applied if it is a particularly bad infection. It is very important to look carefully when buying fungicides because there is not one fungicide that fits all; fungicides are usually used on specific plants and dependent on the fungus they are controlling. Don’t be afraid to enlist help when shopping for the correct fungicide to use. Be sure to read and follow all instructions when using a fungicide.
It is important to practice good plant hygiene when looking after the health of your plants. Rake up dropped leaves and apples in the fall and remove them from the area. It is not necessary to hunt down every juniper within a mile radius of your apple trees because this fungus can travel several miles on the wind. Treating your trees as necessary and continued good plant hygiene should make a difference in the health of your apple tree.
Q. I found a huge insect, with large pincers where the mouth is, on my patio. It is about 3 to 4 inches long and it flies. Do you know what it is? — M.J.
A. This large insect that you have found is an adult male Dobsonfly. Though it looks intimidating, it is nothing to fear. The large pincers that males have are used during mating and are not used to pinch a person. Adult females look similar to the males, but their pincers are much smaller.
Dobsonflies spend most of their lives in the larval stage, up to three years, in water. In this larval stage, often called hellgrammites, they are fierce predators that eat other insects. They are found in fast-moving streams that have a high amount of oxygen and a rocky bottom for hiding.
Hellgrammites are wormlike with projections of gills along their bodies. They look docile, but if handled they can give a good pinch to the handler. Adults are the docile ones and are rarely seen unless attracted to house or street lights.
Q. I have a big problem with Japanese beetles this year. What can I do to get rid of them? — F.R.
A. In just about every stage, this little insect creates havoc to humans. In the larval stage, the grub feeds on plant roots especially noticeable in our lawns. When they have eaten their fill, at about 10 months, they become adults. Adults have metallic green bodies with bronze-colored wing covers. They feed and fly during daylight hours, and tend to congregate on roses, raspberries and grapes, to name a few sites. When they feed, they eat between the leaf’s veins, giving the leaf a skeletal appearance.
When disturbed, the beetles will drop and either fly or land on another part of the plant closer to the ground. This is helpful when getting rid of them by hand. Fill an old coffee can or other container with warm, soapy water. Find a branch where the beetles are feeding, place the container under that
branch and gently knock the branch. The beetles will fall into the soapy solution and drown. This method is less harmful than insecticides, although it is time-consuming.
Using an insecticide may also be an option, but plants should not be treated when in flower or they will be damaged.
An option for the future is to use plants in your yard that are not as attractive to the beetles as the few mentioned above.
Also, check your lawn to see if the beetle’s life cycle is happening right in your yard. Look for mole runs or skunk diggings. Moles and skunks eat grubs, so signs of these creatures mean you have grubs. It is commonly thought that skunks or moles are going after plants or the lawn, but they are doing you a favor by eating the grubs. They do make a little mess in the process, but that is easily fixed.
Cut an area of sod and pull it up. If you notice C-shaped grubs, see how many and bring a sample to your closest Cornell Cooperative Extension office to get a positive identification. If needed, you can treat for the grubs before they become adults.
Q. My hollyhock leaves have orange spots on them that are fuzzy on the undersides. How can I get my plant healthy again? — D.P.
A. The symptoms you are describing are caused by hollyhock rust or the Puccinia malvacearum fungus. This fungus affects both hollyhocks and mallows (Malva rotundifolia), although, unlike the cedar apple rust, it has only one host site. The symptoms of the rust include the orange spots on the underside of leaves that you have found (most notable), as well as yellow spots on the upper side of leaves. The fungus produces spores from these pustules, which are then spread by the wind or by water splashing the spores onto new plants or plant parts. The rust spreads as the summer continues and by fall most of the infected leaves are dead.
This is a serious disease for hollyhocks, but it can be controlled with good plant hygiene. Cleaning up the leaves and cutting the stalks down in the fall and destroying these materials is very important in breaking the rust’s life cycle. When watering, water as close to the base of the plant as possible to minimize splash-up, and water in the morning so there is plenty of time for any water on the plant to evaporate. A fungicide may be used as treatment for a severe rust infection or it may be applied in early spring as a preventive measure. For fungicide information, see the cedar apple rust question above.
“The ABC’s of Gardening” is submitted by the master gardeners of the Cornell Cooperative Extensions of Orange, Sullivan and Ulster Counties, on a rotating basis, in response to questions from callers to the Master Gardener Volunteer Helpline. Maggie Pichura is a master gardener at the Cornell Cooperative Extension of Sullivan County.
Need help?
For answers to your gardening questions, call your local Master Gardener Volunteer Helpline:
Orange County — 18 Seward Ave., Middletown. Calls are answered “live” by master gardeners 9:30 a.m.-12:30 p.m. Monday, Wednesday and Friday, April-October. At all other times, leave a message at 343-0664 or e-mail [email protected]
Sullivan County — 69 Ferndale-Loomis Road, Liberty. Calls are answered 8:30 a.m.-4:30 p.m. Monday-Friday, 292-6180.
Ulster County — 10 Westbrook Lane, Kingston. Calls are answered 9 a.m.-noon Monday, Wednesday and Friday, March-October, and 9 a.m.-noon Fridays only, November-February; otherwise, leave a message, 340-3478.
Master gardeners are also available in the Cooperative Extension offices for soil testing and plant and insect identification. The cost is $5 for plant and insect identification and $3 for a soil pH test.

Best product
for Cedar Apple Rust

Cedar apple rust (Gymnosporangium juniperi-virginianae) is a fungal disease that requires juniper plants to complete its complicated two year life-cycle. Spores overwinter as a reddish-brown gall on young twigs of various juniper species. In early spring, during wet weather, these galls swell and bright orange masses of spores are blown by the wind where they infect susceptible apple and crab-apple trees. The spores that develop on these trees will only infect junipers the following year. From year to year, the disease must pass from junipers to apples to junipers again; it cannot spread between apple trees.

On apple and crab-apple trees, look for pale yellow pinhead sized spots on the upper surface of the leaves shortly after bloom. These gradually enlarge to bright orange-yellow spots which make the disease easy to identify. Orange spots may develop on the fruit as well. Heavily infected leaves may drop prematurely.


  1. Choose resistant cultivars when available.
  2. Rake up and dispose of fallen leaves and other debris from under trees.
  3. Remove galls from infected junipers. In some cases, juniper plants should be removed entirely.
  4. Apply preventative, disease-fighting fungicides labeled for use on apples weekly, starting with bud break, to protect trees from spores being released by the juniper host. This occurs only once per year, so additional applications after this springtime spread are not necessary.
  5. On juniper, rust can be controlled by spraying plants with a copper solution (0.5 to 2.0 oz/ gallon of water) at least four times between late August and late October.
  6. Safely treat most fungal and bacterial diseases with SERENADE Garden. This broad spectrum bio-fungicide uses a patented strain of Bacillus subtilis that is registered for organic use. Best of all, SERENADE is completely non-toxic to honey bees and beneficial insects.
  7. Containing sulfur and pyrethrins, Bonide® Orchard Spray is a safe, one-hit concentrate for insect attacks and fungal problems. For best results, apply as a protective spray (2.5 oz/ gallon) early in the season. If disease, insects or wet weather are present, mix 5 oz in one gallon of water. Thoroughly spray all parts of the plant, especially new shoots.
  8. Contact your local Agricultural Extension office for other possible solutions in your area.

Stages of Apple Tree Growth: What to Expect After Planting

An apple tree, much like a person, develops and changes as it matures. New to planting apple trees? Look through these stages of apple tree growth.

“It is remarkable how closely the history of the apple tree is connected with that of man.” — Henry David Thoreau

Year 1: Apple Variety Budded/Grafted to Rootstock

At Stark Bro’s, in the first year of a grafted apple tree’s life, it begins as an apple rootstock and a budded/grafted variety. This method is true for all varieties, including Fuji, Golden Delicious, Granny Smith and more.

The rootstock determines certain characteristics for your tree as it grows, including its mature size and tolerance of water and cold weather. We choose these rootstocks for your trees to help you enjoy the best results when planted in your yard.

When you order your new apple tree, you will choose which size you want it to be at maturity: a dwarf (8-10 feet tall and wide), a semi-dwarf (12-15 feet tall and wide), or the occasional standard (18-25+ feet tall and wide). Be careful to choose the size best suited to your needs and available space. For more information on the differences in tree size, explore our article on Fruit Tree Sizes.

Year 2: Development of Top Growth (Dormant)

The apple tree will be shipped to you around the time of its second growing year. It will arrive bare-root (without a pot, and without soil around the root system) and dormant, in either spring or fall. The tree will also have been professionally pruned to help ensure transplant success from our nursery to your yard.

To see why we professionally prune your trees, check out our Pre-Pruning Fruit Trees article and accompanying video.

Year 2: Development of Top Growth (Leafed Out)

As your new apple tree gets established and breaks dormancy, you will see it put on new leafy growth. It is at this point that you will begin applying fertilizer and starting your growing season spray routine. Make sure you always follow product labels when it comes to applying any fertilizer or spray.

You can find additional suggestions in our article, Fruit Tree Care: Spray & Weed Control.

Years 3-4: Limb, Leaf, & Root Growth

A few years after planting in your yard, your healthy apple tree will have put on many branches and leaves and the trunk will have increased in diameter.

In the spring, you may start seeing your apple tree bloom and start setting its first fruit after pollination. If you prune while your tree is dormant, fertilize as needed in the spring, and keep your tree clear of weeds, disease and pests year round, it will be well on its way to producing crops of luscious apples for you to enjoy!

Years 5-6: Established Apple Tree

Your apple tree will be familiar with its environment and it will have developed a regular routine of when to grow, when to produce, and when to rest. It may be regularly blooming and fruiting by this point! Since there is variation in cultivars and environments, your results may differ.

Overbearing and other blooming problems may be on your radar, but can be easily avoided. Overbearing may could cause your tree to only bear biennially (every other year). We discuss 4 Benefits to Thinning Fruit Trees here in regard to overbearing and how to prevent it.

This article and these images should give you a good idea of what to expect, but keep in mind that each apple variety responds differently in its environment. That said, one thing that never changes (no matter what the variety) is the importance of quality care to ensure that your tree grows and bears properly throughout its life.

What stage are your apple trees at? Share your apple tree photos with us!

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Apple: Diseases and Symptoms

Disease symptoms

  • The disease usually noticed on leaves and fruits.
  • Affected leaves become twisted or puckered and have black, circular spots on their upper surface.
  • On the under surface of leaves, the spots are velvety and may coalesce to cover the whole leaf surface. Severely affected leaves may turn yellow and drop.
  • Scab can also infect flower stems and cause flowers to drop.
  • The lesions later become sunken and brown and may have spores around their margins
  • Infected fruit become distorted and may crack, allowing entry of secondary organisms.

Survival and spread

  • The pathogen survives through perithecia in the soil debris.

Favourable conditions

  • Suitable temperatures and moisture promote the release of V. inaequalis ascospores. This cycle of secondary infections continues throughout the summer, until the leaves and fruit fall from the tree at the onset of winter.

Marssonina leaf blotch (pre mature leaf fall)

Disease symptoms

  • The disease symptoms appears in form of dark green circular patches on upper surface of leaf giving rise to 5-10 mm brown leaf spots which become dark brown in due course.
  • On maturity it also develops on lower surface of the leaf.
  • Small black acervuli are visible on the surface of leaf.
  • When lesions are numerous, they coalesce and to form large dark brown blotches and the surrounding areas turn yellow.

Survival and spread

  • The pathogen survived in infected leaf litter on orchard floor in the form of conidia and the sexual stage of pathogen
  • Diplocarpon mali is also intercepted in nature.

Favourable conditions

  • This disease favoured by high rainfall and moderate temperature ranging from 20-22°C during the fruit development stages of apple.

Black rot canker

Disease symptoms

  • Leaf symptoms first occur early in the spring when the leaves are unfolding.
  • They appear as small, purple specks on the upper surface of the leaves that enlarge into circular lesions 1/8 to 1/4 inch (3-6 mm) in diameter.
  • The margin of the lesions remains purple, while the center turns tan to brown. In a few weeks, secondary enlargement of these leaf spots occurs.
  • Heavily infected leaves become chlorotic and defoliation occurs.
  • As the rotted area enlarges, a series of concentric bands of uniform width form which alternate in color from black to brown. The flesh of the rotted area remains firm and leathery. Black pycnidia are often seen on the surface of the infected fruit.
  • Lesions resulting in canker formation usually are associated with a wound in the bark.

Survival and spread

  • The pathogen survives through ascospore (cysts) in the soil debris which is the source of primary infection.
  • In the spring, the black pycnidia and perithecia release their respective conidia and ascospores and causes secondary infection.

Favourable conditions

  • 20-24°C temperature and moist situation is responsible for the disease development.
  • Winter injury in plants is favourable for the development of the diseases.

Collar rot

Disease symptoms

  • Phytophthora collar rot attacks the lower 30 inches (76 cm) of apple trunks.
  • Most infections start at the junction of a lateral root with the trunk.
  • Infected bark becomes brown and is often soft and mushy or slimy when wet.
  • Dark streaks often occur near the cambium and extend beyond the canker margin. If a canker enlarges for several years, only the marginal areas show the typical color and texture of newly killed tissue.
  • The development of the canker is rapid, horizontally and vertically. The ultimate effect of collar rot is to girdle the affected limb, roots, or trunk, resulting in the death of that organ or of the entire tree.

Survival and spread

  • Fungus overwinters as dormant resting spores or as mycelium within infected tissues. New infections occur when the pathogen releases motile spores that are carried via water to susceptible hosts.

Favourable conditions

  • Soils that are saturated from rain or over-watering provide the moist conditions necessary for Phytophthora spp. to thrive and spread.
  • The lack of oxygen in saturated soils may also increase the rootstock’s susceptibility to this disease

Powdery mildew

Disease symptoms

  • Disease appearswhen the buds develop into new leaves and shoots.
  • Small patches of white or grey powdery masses on under surface of leaves occur.
  • Leaves grow longer and narrower than normal leaves and the margin is curled.
  • Twigs covered with powdery mass.
  • Aff ected fruits remain small and deformed and tend to develop roughened surface.

Survival and spread

  • The fungus survives in the form of a resting mycelium or encapsulated haustoria in the buds and the secondary spread occur through wind borne conidia.

Favourable conditions

  • Powdery mildew infections occur when the relative humidity (RH) is greater than 70%.
  • Infections can occur when the temperature lies between 10 to 25°C.

Sooty blotch and fly speck

Disease symptoms

  • Sooty Blotch: Sooty blotch appears as sooty or cloudy blotches on the surface of the fruit. The blotches are olive green with an indefi nite outline.
  • The blotches are usually one fourth of an inch in diameter or larger, and may coalesce to cover much of the fruit.
  • The “smudge” appearance results from the presence of hundreds of minute, dark pycnidia that are interconnected by a mass of loose, interwoven dark hyphae.
  • The sooty blotch fungus is generally restricted to the outer surface of the cuticle. In rare cases, the hyphae penetrate between the epidermal cell walls and the cuticle.
  • Flyspeck: Groups of a few to 50 or more slightly raised, black and shiny round dots that resemble fly excreta, appear on the apple fruit.
  • The individual “fly specks” are more widely scattered and much larger than the pycnidia of the sooty blotch fungus.
  • The flyspecks are sexual fruiting bodies (pseudothecia) of the fungus, and are interconnected by very fine hyphae. The blemishes can be removed by vigorous rubbing or bleaching.

Survival and spread

  • Flyspeck: In late spring, this fungus produces both ascospores and conidia that are wind-borne and survive into orchards from other plants.
  • Sooty blotch: The pycnidia on host plants produce large numbers of spores (conidia) that ooze out of infections and collect in a gelatinous mass.

Favourable conditions

  • Moist condition and 18 to27°C temperature are essential for infection and disease development

Apple mosaic and other virus diseases

Disease symptoms

  • Apple trees infected with apple mosaic virus develop pale to bright cream spots on spring leaves as they expand.
  • These spots may become necrotic after exposure to summer sun and heat.
  • Other viral diseases are symptomless in most commercial cultivars, but may cause symptoms in certain cultivars, scionl / rootstock combinations, and ornamental varieties. Symptoms of apple chlorotic leaf spot virus may include chlorotic leaf spots, leaf distortion, chlorotic rings and line patterns, reduced leaf size, and stunting.
  • Apple stem grooving virus produces symptoms on ‘Virginia Crab’ such as chlorotic leaf spots, stern grooving and pitting, union necrosis, and swelling of the stem above the graft union.


  • Transmission of ApMV to C. quinoa and C. sativus was obtained under greenhouse conditions. C. quinoa reacted with mottling, whereas C. sativus showed chlorotic local lesions followed by systemic yellowing and stunting

Alternaria leaf spot/blight

Disease symptoms

  • Leaf spots appear on the leaves in late spring and early summer. Initially, they are 1/8 to 1/4 inch in diameter, round, brown, and occasionally have a purple border.
  • As spots age, they often turn tan to ash gray. Some spots undergo secondary enlargement, becoming irregularly shaped.
  • Heavily infected leaves often abscise, resulting in defoliation. (Defoliation is greater when mites are present.) Fruit infections result in small, dark, raised pimple-like lesions associated with the lenticels.
  • Twig lesions, which are somewhat sunken, round, blackish spots bordered by cracks, occur on susceptible cultivars such as Indo but have not been observed on Delicious.

Survival and spread

  • Primary infection occurs about one month after petal fall the following year

Favourable conditions

  • The disease is favoured by temperatures between 77 and 86 °F (25–30 °C), and by wet conditions. Infection occurs at optimum temperatures with 5.5 hours of wetting and an outbreak can become serious within two days of infection.

Core rot

Disease symptoms

  • Common injuries that can lead to Alternaria rot include mechanical or chemical injury, sunscald, or chilling injury.
  • Browning occurred most frequently with the occurrence rates of core rot.
  • Infection can occur before or after harvest, although it is more commonly a post-harvest problem.

Survival and spread

  • The fungus is soil borne and Primary infection occurs by spores survives in the soil.

Favourable conditions

  • Warm weather and high humidity favour the development of diseases.

Brown rot

Disease symptoms

  • Enlarged rots are soft but not mushy.
  • Circular and medium brown during the early and medium stages of development.
  • Decayed area enlarges; small black spots about 1/8 inch across gradually develop at the lenticels
  • Entire fruit is decayed and under warm conditions turns black and develops a velvety sheen.
  • In warm, moist conditions gray to tan fungal tufts develop, either in varying size patches or scattered over the decayed surface.

Survival and spread

  • The fungus over-winters in mummified fruit on the ground or in the tree and in twig cankers.
  • Secondary Infection: Spores produced on blighted blossoms provide a source of infection for ripening fruit

Favourable conditions

  • Prolonged wet weather during bloom may result in extensive blossom infection.
  • Humid wet conditions are when the fruit trees are most at risk from infection.
  • Young green fruit can be infected just before autumn, but the infection often remains inactive until near maturity of the fruit.

White rot / root rot

Disease symptoms

  • Infection can occur on large roots or at the tree collar.
  • In fruit trees, the base of the trunk at soil level can show signs of a dark, wet rot, especially if kept moist by weeds or wet weather.
  • As the disease progresses, the infected tissue becomes rotten.
  • Trees develop a generally unthrifty appearance with leaf yellowing, cessation of root growth, small leaves, premature leaf fall and small, shrivelled fruit. Infected trees will eventually die.

Survival and spread

  • The fungus survives in soil or plant debris which is the source of primary inoculums.

Favourable conditions

  • The disease is favoured by cool and moist soils.

Seedling blight

Damage symptoms

  • The most distinct symptoms and signs occur at the collar of the tree.
  • Small, round, light brown to yellow resting structures of the pathogen, known as sclerotia, can be found appressed to or in the soil adjacent to infected trees.
  • If conditions are moist, a white web-like mycelial growth may also be present.
  • Aff ected cortical tissues in the collar of the tree are often shredded.

Survival and spread

  • The fungus survives in soil. Primary infection occurs by soil and secondary by conidia through rain or wind.

Favourable conditions

  • High humidity, high soil moisture, cloudiness and low temperatures below 24° C for few days are ideal for infection and development of disease.

IPM for Apple

To know the IPM practices for Apple,

Source: NIPHM, and Directorate of Plant Protection, Quarantine & Storage

Apple Tree Diseases | How to cure. 

Gardenseeker Main › Fruit Main › Apples Main › Apple Tree Diseases

The first thing to assess when you think that you have a diseased apple tree, is whether in fact your apple tree is actually ‘diseased’ or is affected by a ‘pest’! A pest is a living insect or mite, whereas a disease is normally a fungal infection. It can also be a virus.

Basically, if it has legs – it is a pest. An insect of sorts that can be treated with an insecticide. Insecticides are no use whatever in treating diseases. (However, some diseases are spread by insects, so there is sometimes a case for treating a disease bearing insect!) Some pest look like diseases, which does not help. Woolly aphid in particular, is often confused as a fungus because of its cotton wool appearance.

Fortunately, there are not too many diseases that commonly affect apple trees, and the identification can normally be positive. Most of the diseases on Apple Trees are caused by fungus, and can be controlled by fungicides or other physical control.

The most common disease affecting apple trees is some form of Canker or other. The image shows an early attack, which can develop into large lumpy growths – affecting the tree quite severely unless treated.

Apple Scab is a fungal apple tree disease, and normally appears in the later part of autumn, or early in spring. It shows as brown or black pimples on leaves, and ultimately to the fruit of the apple tree.

It is spread by wind, so can easily take hold if not checked in early stages. Leaves will not stay on the tree, and signs on the apples are maturing unevenly – eventually cracking and spoiling.

The scab looks as its name sounds!

Prune any affected areas and burn the debris. Affected fruit should not be stored. There can be lasting damage to the apple tree from Apple Scab Disease.

Powdery Mildew on Apple Trees

The name is very descriptive of this disease of apple trees. It is a disease that also affects many other garden plants.

It is normally to be seen in periods of high humidity, but thrives in hot dry conditions also.

If left untreated, Powdery Mildew Disease will cause severe weakening of the tree, starting with young growth. This will result in the death of the terminal bud of the twig. It is relatively common member of the apple tree diseases

A strong healthy tree will survive the disease without too much ill effect. Aim for good air circulation between the branches, and control with a fungicide or sulphur spray.

Fire Blight on Apple Trees

Fire Blight Disease is again aptly named, for the apple tree will look as though a fire has been started nearby – scorching the foliage up one side of the tree.

It is a serious disease that can also affect many other plants of the same genus as Apples – The Rose family. (Pyracantha, Hawthorn etc are also affected.)

Affected young shoots will wither and die – as will any flowers.

Prune back hard, any affected branches and burn the debris.

Black Rot of Apples

Black Rot Apple Tree Disease will be visible on mature fruit – just as they are nearly ready to harvest – typical!

Often, the apple has already been wounded by some physical force or other. This will include bruising damage as a result of windy conditions.

The disease is first noticed as small brown spots on the apple fruit, which will then grow – turning first dark brown and then black!

If caught early enough, then the fruit can be treated with a sulphur spray.

It can spread to the bark of the tree and will overwinter – ready to affect the tree in the spring growing season. A good fungicidal spray in early winter will help this and other fungal diseases of apple trees.

  • Brown Leaves and Spots
  • Winter Wash for Fruit Trees
  • Lichen on Apple Trees

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