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Even the beloved apple tree is not spared and can be afflicted by diseases. How to Identify Important Apple Tree Diseases

There are a variety of different apple tree diseases

Arguably every plant can be afflicted with dreaded and life-threatening diseases. The beloved apple tree (Malus domestica) in your own garden is not spared. Under certain circumstances and with early detection, an infestation can be prevented or an existing disease curbed through skillful care measures. We will show you how to counteract an infestation, how to recognize important pests and diseases in good time and what you can do if necessary.

Apple Tree Diseases: Factors Increasing Susceptibility

Although apple trees are easy to care for, they are also targeted by a number of pathogens and diseases. However, many factors that determine the susceptibility of trees can be influenced and are briefly presented here. If you follow these tips, you can usually prevent an excessive infestation.

These factors affect how he althy your apple tree is:

  • Selection of variety: The variety should be adapted to the chosen location. Not every apple variety will grow well in every location. There are also certain varieties that are better protected against some apple tree diseases from the outset. However, there are also particularly susceptible varieties that get sick all the time, even in the best locations.
  • Location: The vast majority of varieties do not tolerate humid, waterlogged and cold locations. In these places, special attention should be paid to choosing an adapted, robust variety. A sunny, rather sheltered place with nutrient-rich, permeable garden soil and sufficient water availability, on the other hand, appeals to most apple varieties.
  • Fertilization: If an apple tree is fertilized incorrectly, this can increase its susceptibility. These include, for example, nutrient deficiency induced by ion competition, unstable cell walls and a high crown density in which a warm, humid climate prevails. These are optimal living conditions for many pathogens and fungal spores. As yourWe explain how to properly fertilize apple trees in a separate article.
  • Pruning: Apple trees should be pruned once a year. If this is not done, this will lead to reduced fruit quality and increased crown density. As already described, many pathogens thrive here and fungal spores, eggs and larvae survive longer. We also explained in a separate article how to properly prune an apple tree.
  • Tool: A major problem that is often underestimated is infected tools. For example, when you prune your trees, you use pruning shears and saws to transport pathogens from one tree to the next, unintentionally aiding the spread of disease.
  • Sources of infection nearby: If, for example, the trees in the neighboring garden are infected, your trees are not far away. This is also a common reason for the outbreak of diseases, but unfortunately you cannot influence it very well.
The tool should be sterile so as not to transmit diseases

You can protect your apple tree from increased susceptibility to disease by taking the following simple measures:

  • Selection of resistant varieties.
  • Choose a variety suitable for the location.
  • Proper fertilization of the apple tree.
  • Cut and trim the crown regularly.
  • Use sterile tool.
  • Find out information about apple tree diseases in your neighborhood and then choose varieties that are not susceptible to them.
Apple powdery mildew can be avoided by good ventilation

Apple Tree Diseases: The Most Common Insect Pests

Many insects, such as bees, which pollinate the apple tree, or ladybugs, which like to eat aphids, help the apple tree. In addition to aphids, there are other insects that can damage the tree.

Apple Spider Moth

The apple spider moth (Yponomeuta malinellus) is a small white butterfly with black spots. However, it is not the flying moths that are unpleasant for the apple tree, but the caterpillars that hatch in spring. An infestation can be recognized by the white webs in the apple tree, in which the caterpillars feast on the leaves, so that they can bare entire trees. Combating the apple spider moth is not absolutely necessary, since apple trees usually survive an infestation. Even a bare tree will with a very high probabilitysprout again in the same year - although no more fruits are to be expected at harvest time. However, there is a lot that can be done about them, which is detailed in our article on apple spider moths.

In spring you can see the infestation by white webs

What to do about the apple spider moth?

  • Remove webs from the tree.
  • Biological control: Chalice wasps and parasitic wasps are natural enemies of apple gypsy moths. The small beneficial insects can be purchased in stores and used in a targeted manner.
  • Chemical control: This is available in specialist shops; be sure to inform about the application.
  • Prevention: Female apple spider moths cannot fly, a ring of glue prevents them from crawling up the trunk.

Codling moth

The codling moth (Cydia pomonella) is a brown-grey moth whose caterpillars are only two millimeters long and white or yellowish with a dark head. The infestation can be recognized by the tiny boreholes in apples and the typical feeding passages of the larvae to the core. Affected apples can no longer be stored and often fall off prematurely. But one is not powerless against the codling moth. For example, nematodes of the species Steinernema feltiae are natural enemies of codling moths and parasitize their larvae.

What can you do about the codling moth?

  • Remove affected apples as early as possible.
  • Pheromone traps can be used to monitor the flight of moths and thus to determine the optimal time to control them. Many pesticides are only effective on young larvae, which hatch about 7-15 days after mating.
  • Prevention: Check fruit tree trunks for pupated codling moth larvae in winter and spring and collect larvae if necessary.
  • Fighting with nematodes: Nematodes, for example our Plantura SF nematodes against fungus gnats, codling moths & ants, parasitize the larvae and thus prevent the codling moth from reproducing. With nematodes you are opting for a simple method of combating them that is harmless to people and the environment. The best application period is from September to March, when most of the larvae overwinter in the bark on the trunk.
  • Spraying trees with granulosis viruses. Since these only affect larvae that have just hatched, the first spray should be given 10 - 14 days after the first moth flight and then repeated at least three times at intervals of 6 to 8 days.

TheCodling moth is one of the most common pests on apple trees. That's why we go into more detail about setting up traps and using sprays in our article "Fighting codling moths".

The codling moth is also known as the fruit maggot [Tomasz Klejdysz/ Shutterstock.com]

Aphids

Aphid is not just an aphid. On the apple tree, the mealy apple aphid (Dysaphis plantaginea) probably causes the most damage, but also the apple weed aphid (Rhapolosiphum insertum) or various apple aphids ( Dysaphis spp.) target apple trees. An infestation with aphids can of course be recognized by the small animals themselves, by the curling and malformations of the leaves and by the so-called honeydew, the sugary excretion of the animals, sometimes together with black sooty mold fungi, which settle on the sticky honeydew. Due to the more sensitive cell walls, aphids are mainly found on younger shoots. Fertilization that is too high in nitrogen, which leads to increased sprouting of shoots with spongy tissue, therefore entails a higher risk of aphid infestation. But you don't have to take action as soon as you spot the first aphid. Apple trees can usually tolerate a light infestation and in most cases a natural balance between beneficial insects such as ladybirds and the aphid population is established by itself. However, aphids are also disease vectors.

What helps against aphids on apple trees?

  • Promote beneficial insects: natural enemies are, for example, ladybugs or earwigs.
  • If possible, avoid the use of chemical pesticides in the home and garden.
  • Prevention: Remove affected branches during summer pruning; Create mixed cultures.

Tip: Place upside down clay pots with wood shavings in the apple tree to attract earwigs. Neem supplements are also effective against aphids. However, the agent may only be used on apple trees by people with a certificate of expertise, such as trained gardeners.

Neem preparations may also be used on apples by trained gardeners

Apple Tree Diseases: The Most Common Fungi and Bacteria

In addition to the insects that can tamper with the apple tree, there are also some fungi and bacteria that damage it. In order to prevent the pathogen from spreading, particular caution is required here.

Apple Scab

You can recognize

apple scab (Venturia inaequalis) in sensitive varieties as early as spring. It is visible as olive green to brown spots on the leaves. These dry up from the middle and turn brown. The leaves become wavy or bumpy because the diseased leaf tissue stops growing. The infected foliage falls to the ground prematurely. Apple trees that are particularly badly affected are therefore almost bare as early as August. The fruits also show brown, often torn sores. They are still edible, but less easy to store. Rot fungi can penetrate faster through the cracked shell. Apple scab is favored by a mild and rainy spring.

Apples have brown, often torn sores

How to get rid of apple scab?

  • Remove infected leaves immediately.
  • Spray treatment with approved fungicide (advice from specialist dealers).
  • Prevention: Removal of leaves in autumn, thinning cuts and airy location; Silicic horsetail broth as a preventative tonic.
  • Use of scab-resistant varieties.

Powdery mildew

Powdery mildew is one of the most well-known diseases of apple trees. The fungus spreads at high speed and can sometimes lead to a total failure of the apple harvest. Symptoms of powdery mildew can be a mealy coating on the twigs, white and mealy spots on the leaves or a net-like russeting of the fruit skin.

What can be done about powdery mildew?

  • Targeted cut to keep the crown airy.
  • Cut out infected areas generously and burn infected plant material.
  • In the case of severe infestation, use approved pesticides after professional advice.
Powdery mildew can be recognized by white and mealy spots on the leaves

Firebrand

Fire blight is caused by the bacterium Erwinia amylovora. Affected are the blossoms and young shoots, which turn dark brown to black, become crooked and therefore appear "burned". Sticky bacterial slime can appear on the affected plant parts of the apple tree. Fire blight is easily transmitted via insects, but can also be spread to other plants by humans. Since the course of the disease is so tragic, the transmission is so easy and the spread is correspondingly rapid, the infestation withFire blight notifiable. If you spot a plant showing symptoms of fire blight, do not hesitate to inform the plant protection office responsible for your area.

The fire blight bacterium can severely damage apple trees within a short time

What can be done about fireblight?

  • Infected plants cannot be treated: possible death within 24 hours
  • Report infestation: There is an obligation to report this disease
  • Trees are cleared, infested plants and cleared wood are completely burned
  • How to Protect Yourself: Choosing Fire Blight Resistant Varieties

The choice of apple variety in particular has an impact on how susceptible an apple tree is to diseases. We present the best apple varieties for the home garden in a separate article.

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Fruit