Fire blight on fruit trees – recognizing and fighting

In Germany, the occurrence of a fire blight must be reported. Even the suspicion must be reported. Depending on the federal state, reports are made to the state office or the state agency for agriculture. The legal basis is the ordinance to combat fire blight disease (fire blight ordinance) of December 20, 1985, in the current version.

Quarantine?

To prevent further spread, there are nationally and internationally applicable quarantine measures and trade restrictions. Unfortunately, not all countries implement uniform measures. The State Office for Agriculture can order a quarantine zone around infested properties, usually 5 kilometers. It can also be determined that highly susceptible and infested host plants must be destroyed in this area. Beekeeping is then not allowed, nor is the planting of susceptible host plants.

Trigger of the fire blight

As already mentioned, the cause of this disease is the bacterium Erwinia amylovora. It belongs to the enterobacteria. Most of these bacteria live in the gut, but this one doesn’t. A rod-shaped bacterium can be seen under the microscope. It is gram negative and viable even in the absence of air. The bacterium finds ideal growth conditions at temperatures between 21 and 28 ° C.

The spread of fire blight

There are numerous ways in which the pathogen can be spread and affect the plants. A distinction is made between infections before planting in the garden and afterwards. Fire blight can be brought in or attack the plants much later, at their location, so to speak.

• Contaminated plants
• Transport of plants in contaminated packaging material
• Contaminated cutting tools
• Weather events such as wind and rain
• Migratory birds
• insects
• Small mammals
• human

The bacteria spend the period of dormancy in the diseased parts of the bark, which are called necroses. The bacteria multiply in spring. From there, the spreading takes place in warmer and humid weather in spring and summer. The bacteria are excreted in huge quantities in the form of drops of mucus. In our home gardens, it is mostly spread by raindrops, wind and insects that visit the flowers.

How does the pathogen get into the plants?

How does the bacterium penetrate the plant tissue? This usually happens through natural entry ports, e.g. through a pore in the epidermis (cleft opening), through a cork pore (lenticels) in the area of ​​the bark, through a nectarium, i.e. a sap gland in flowering plants or through wounds, whether on leaves or shoots or branches. A rough distinction is made:

• Flower infection
• Drive infection
• Infection from infection sites that become active again

Most infections occur in spring and summer, but especially during the flowering period. Warm, humid weather is particularly ideal for spreading the pathogen. The flowers are extremely endangered. It is often transmitted by insects. The germs find ideal conditions and finally multiply explosively. Due to their mass alone, they overcome the plant’s natural defenses and penetrate.

How and how do you recognize fire blight?

Fire blight can be recognized by a few symptoms. The leaves and flowers of the infected plants suddenly wilt, always starting from the petiole. They turn brown or black, but stick. It is typical that the shoot tips curve downwards like a hook. It comes from the loss of water. The whole appearance of the plant, or parts of it, looks like it has been burned. This is where the name “fire blight” comes from.

Young plants die off pretty quickly, two to three weeks are enough. With older plants you can watch how the disease spreads over the years. Here, too, the disease leads to death within one or more years.

A typical symptom is that bacterial mucus emerges at the infection sites. That happens in summer and autumn. In winter the bark can sink in.

If you want 100 percent certainty that it is actually a fire blight, i.e. the Erwinia amylovora bacterium, you have to have a laboratory test carried out.

How severe the infestation is depends on a number of factors, e.g. the climate, the location conditions, the type of plant, sometimes also the variety, the state of health and the bacterial density on the plant. Often there are also interactions between the individual factors.

Typical host plants of the fire blight pathogen

There are numerous host plants. A total of more than 170 species from 40 genera in the rose family. Pome fruit plants are the main host plants. Only in these ways can the bacterium finally hibernate.

The following are particularly susceptible:

• Fruit trees
• Ornamental trees
• Ornamental and wild wood

Apple trees are often affected. Anyone who is new to planting should therefore opt for robust, less susceptible varieties. The following varieties are often affected by fire blight, for example: Cox Orange, Granny Smith, Elstar, Gala, Gloster, Jonathan, Jonagold, many cider apples and the M26 apple underlay. With pears it is mainly: Conference, Comice, Concorde, Gute Luise, Pastorenbirne and some cider pears.

In the ornamental trees, quince, medlar, service tree and service tree are particularly affected. In the wild trees, especially whitebeams, rowan berries, all apples, rock pear, chokeberry, ornamental quince, hawthorn, hawthorn, firethorn and others.

prevention

You cannot protect your plants 100 percent from fire blight. However, it is helpful to choose varieties that are robust or resistant to fire blight when replanting.

• Less susceptible apple varieties: Schöne from Boskoop, Schöner from Wiltshire, Danziger Kantapfel, Florina, Bell apple, Maunzenapfel, Rewena, Swiss orange apple, Remo and others
• Less susceptible pear varieties: Harrow delight, Harrow Sweet, Welsche Bratbirne, Bavarian wine pear …

It is important to regularly check your plants for infestation. The earlier a fire blight is discovered, the sooner appropriate action can be taken against it. It is also important to disinfect all cutting tools with 70% alcohol. The populations should be checked especially immediately after flowering. The dangerous time lasts until the end of early summer.

In some EU countries, an antibiotic is used as a preventive measure in commercial farming. But it is very controversial because it was found in honey. In addition, resistances must be expected. At some point the pathogen is immune.

Fire blight measures

After the disease has been properly reported, it must be prevented from spreading as soon as possible. For the home garden there are no ways of combating the fire blight with any means or substances. No pesticides are permitted. The only way is cutting, or sometimes felling.

Individual infected shoots can be cut back deep into the healthy wood. However, more strongly infested plants must be cleared. It is also important not to put infected parts or entire plants on the compost. They are also not allowed in the organic waste bin. It is best to burn everything. Since this is not allowed everywhere, it has to go to normal garbage in the garbage disposal. Whole trees have to be brought directly to the waste incineration plant.

Possible confusion

Symptoms similar to fire blight, i.e. wilting, browned and dried up flowers and shoots, can also be triggered by other pathogens.

• Bacterial infection
  • Pseudomonas syringae pv. Syringae – causative agent of bacterial blight in stone fruit and the lilac disease on lilacs
  • Phytoplasms – apple growth, pear decay – bacteria without cell walls that attack fruit trees

• Fungal pathogens
  • Monillia sp. – Fruit rot or peak drought – one of the most important plant pests on fruit trees

• Animal pests
  • Blood lice
  • Pear wasp

• other causes
  • Frost
  • dryness
  • Herbicides

Conclusion
Firebrand is not to be trifled with. The disease is spreading more and more. Whole orchards and orchards have already had to be cleared. Since there are no approved agents, prevention is the best way to fight the disease. It is therefore important to proceed with caution when selecting the types of fruit. If you have fruit trees in your garden, you should also be careful with the accompanying plants. Red thorns and hawthorns, as well as other popular trees, tend to be infested and this can lead to infection of the fruit trees. It is important to regularly check for infestations, especially immediately after flowering until early summer. Recognized at an early stage, something can still be achieved with cutting measures. On the other hand, if the disease has already spread, only clearing it usually helps.