In apple and pear orchards, a silent enemy can compromise the quality of the harvests and the health of the trees: scab. This fungal disease is one of the most common in apple and pear trees and feared by many arboriculturists. Let’s learn to recognize the signs of this disease, understand what promotes it, and above all, explore the natural treatments that we have developed at Agrobiotop to protect your crops effectively.
Scab: a cryptogamic disease
Apple scab is a disease caused by microscopic fungi of the genus Venturia , which cause heavy losses in apple and pear orchards . In apples, Venturia inaequalis causes the infection, while Venturia pirina specifically attacks pear trees. These pathogens mainly affect leaves, young branches and fruits, where they cause significant damage.
This disease is particularly prevalent in areas where the climate remains humid for much of the year, such as Brittany or Normandy. Fungal spores develop rapidly in these environments, activating as soon as conditions become favorable. Once contamination begins, progression is rapid and affects the overall health of the trees as well as the quality of the harvests.
Scab does more than just weaken trees. By altering the fruit, it reduces its commercial appeal and complicates its conservation. Faced with this threat, it is essential for arboriculturists to adopt appropriate practices and to carefully monitor their crops to limit the impacts.
What are the factors that promote the development of scab?
The development of scab is directly influenced by climatic conditions. A mild spring between 7 and 25 °C accompanied by frequent rains creates an environment favorable to the dissemination of fungal spores. Persistent humidity on the foliage and young branches allows the fungus to quickly colonize the tissues of the tree.
Rainy summers amplify these initial infections by promoting secondary cycles, increasing disease pressure on orchards.
The presence of contaminated plant material , such as dead leaves or infected fruit left on the ground or on trees, acts as a reservoir of spores for subsequent seasons.
Certain cultural practices can also increase the sensitivity of trees. Excessive pruning stimulates rapid growth of tender shoots, which are particularly vulnerable to infection. Similarly, too generous an application of nitrogen fertilizers encourages this juvenile growth, further increasing the risks.
What are the symptoms of scab?
Symptoms of scab vary depending on which parts of the tree are affected, but their severity can quickly intensify.
On the leaves
The first signs of scab appear on the foliage, about three weeks after contamination. Small, round, olive-brown spots gradually develop and take on a characteristic velvety appearance. These lesions are accompanied by yellowing of the leaves, often followed by necrosis. This degradation leads to premature fall of the foliage.
On the young branches
Young, tender twigs are particularly susceptible to infection. Blackish spots and cankers form, as well as cracks in the bark. These changes weaken the structure of the twigs and can cause them to dry out. In young pear trees, these symptoms are sometimes so severe that they cause the entire tree to die back.
On the flowers
Flowers also show signs of infection. Dark spots develop on the sepals, peduncles and ovary . This phenomenon causes the fruits to abort before they even form and consequently impacts yields.
On fruits
Young fruits may become deformed due to infection or fall prematurely. More mature fruits are marked by corky, blackish-brown crusts , which reduce their visual and commercial quality.
How to fight apple and pear scab?
The fight against scab is based on an approach that combines prevention and natural treatments.
Preventive methods
Preventive practices play a central role in scab management. They aim to reduce the conditions favorable to the development of the fungus and to limit the sources of contamination:
- Choose resistant varieties : Varieties adapted to humid climates considerably reduce the risk of infection.
- Maintain tree vigor : Balanced fertilization and adequate irrigation during dry periods help trees remain robust and less vulnerable.
- Prune properly : Thinning out the branches improves air circulation and light penetration, creating unfavorable conditions for spore proliferation.
- Collect and burn contaminated leaves and fruit : In the fall, removing infected debris reduces the amount of spores present for the following season.
Agrobiotop biological treatment methods
When the disease is already present, biological treatments can strengthen the natural resistance of the trees and slow the progression of the infection.
For soil improvement (allows soil to be aerated, prevents moisture from stagnating in the soil)
Biostimulants to strengthen your fruit trees:
In processing:
