Fire blight
This disease, which mainly affects orchards, but not only, and which is most often fatal for plantsis also called “fire disease”.
Moreover, under European Directive 2000/29 EC, the bacteria which is responsible, Erwinia amylovora, is the subject of compulsory control, whether in nurseries, in professional orchards, green spaces, hedges and private gardens, and in the event of manifestation of this disease, sanitation must be carried out, or even l uprooting the affected tree or trees. This explains why this disease is so feared.
The bacterium Erwinia amylovora
The spread of this bacteria responsible for fire blight is generally natural, it can be by wind, rain, birds or insects, but it can also be human, by tools, watering method, etc.
As for contamination, it generally occurs through flowersbut it can also be through buds, wounds on the plant, etc. Once the bacteria has entered the tissues, it multiplies and spreads throughout the plantfrom the roots to the tips of the branches and twigs, and nothing seems to be able to stop this progression.
You can’t even count on the winter cold to do the cleaning, because this bacteria resists it and begins to multiply again when the nice weather returns.
Trees and shrubs susceptible to fire disease
Whether fruit trees or ornamental plants, not all are susceptible to fire blight. Let’s see which ones are the most sensitive and require your vigilance:
- Among the fruit trees, apple trees, quince trees, pear trees and medlar trees are among the most sensitive host trees. Moreover, the Passe-Crassane pear is so sensitive that it is banned in France. The good news is that cherry trees, plum trees and apricot trees are absolutely not susceptible to this bacteria.
- Among ornamental plants, it is pyracanthas, mountain ash, cottoneasters, Japanese quince or hawthorn which are sensitive to this bacteria. As with the Passe-Crassane pear, the multiplication, sale and planting of certain species and certain cultivars of Cotoneaster are prohibited in France.
Unfortunately, other plants can harbor this dreaded bacteria and pass it on without you realizing it.
Recognizing fire blight
If you take the time to monitor the leaves, branches and twigs of trees and shrubs most likely to contract this bacteria, the appearance of certain signs should alert you. Here are which:
- To begin with, you may notice brownish or rust-colored spots located along the midrib of the leaves. These spots may be elliptical or irregular in shape. At first, they are visible at the tips of the leaves, then quickly spread until they reach the peduncle, giving the impression that the leaves are burned, hence the name given to this disease. Even when burned in this way, the leaves do not fall, nor do the flowers or fruits which have withered.
- You can notice drying and browning of flower buds.
- As for the branches, you can see thatthey dry and curl to form a crook.
- As the disease progresses, you may notice thatParts of branches, or even entire branches, dry out.
- Another sign that should alert you is the presence of cankersthat is to say necrosis of the bark, on the trunk and branches.
- Finally, but more rarely, you can spot the appearance of a whitish exudate. In humid weather, this viscous liquid oozes from the cankers in the form of droplets.
Reduce risks
Although there is no treatment for this disease, it is possible to reduce the risks through good practices such as:
- Carry out winter pruning to eliminate fruit and flower mummies. If you notice the presence of cankers, you should also remove them.
- Carry out regular checks of plants likely to be infected. If you notice symptoms that sow doubt in your mind, do not procrastinate and quickly eliminate contaminated plants or branches.
- Proceed to uproot diseased trees.
- During planting, favor varieties that are tolerant.
- For size, always use disinfected tools.
Despite these precautions, it is possible for trees and shrubs to contract fire blight.
Conditions conducive to the development of the disease
This type of disease is developing all the more when temperatures are high and the atmosphere humid. This means that during periods of stormy weather, you need to be even more vigilant. Indeed, under such conditions, the cankers will exude even more, which will lead to an increase in the spread of the bacteria by birds, wind, rain, insects, etc.
The period when the disease is most active extends from spring to fall, with a peak at the time of resumption of vegetation and, above all, after flowering. Waist-related sores can also be a gateway for disease.
Treatment of fire illness
There is no chemical or natural treatment for fire blight. The only thing you can do is limit contagion by acting quickly in the following ways:
- Peel the bark to check if it is red-brown in color. In this case, it is a sign of an infection.
- When the disease occurs, cut off the infected parts immediately. For small branches, do not hesitate to cut at least 30 cm of healthy wood. For larger branches, you can go up to 60 cm.
- Burn contaminated parts.
- When the subject is too affected, it is important to remove it.
- Remove secondary flowers before they open.
Plants contaminated by fire blight must be burned. Furthermore, it is important to systematically disinfect tools, even outside periods of infection.