Fruit tree diseases in France: Fruit scab

Quick read / the essentials on fruit scab

Apple scab is a major fungal disease that primarily affects pome fruit trees, such as apples, pears, and quinces. Caused by fungi of the genus Venturia ( Venturia inaequalis for apples and Venturia pyrina for pears), it causes significant losses by affecting the quality and marketability of the fruit. Its development is favored by humid and temperate conditions, making prevention essential to limit its impact.

At Arboriverse, a specialist wholesale supplier of fruit plants , we know that the best defense against scab is effective preventative management. Choosing resistant varieties , particularly for apple and pear trees, is a sustainable solution to reduce the susceptibility of orchards. Proper pruning improves air circulation and limits humidity on the foliage, thus reducing the conditions favorable to the development of the fungus. Removing infected leaves and fruit is essential to reduce fungal pressure from one year to the next.

A drip irrigation system , rather than a sprinkler system, limits the spread of spores. Balanced fertilization, without excess nitrogen, strengthens the natural resistance of trees.

In organic farming, Bordeaux mixture , applied before leaf fall and before flowering, is an effective method for limiting infection. Alternative solutions such as baking soda as a curative or talc as a preventative can strengthen tree protection. In conventional farming, the use of copper and specific fungicides is sometimes necessary to contain the disease, while respecting regulatory doses and deadlines.

At Arboriverse, a specialist wholesale supplier of fruit plants , we offer plants selected for their vigor and disease resistance. Buying apple, pear, and quince plants from a specialist guarantees a healthier crop and better protection against scab.

Fruit scab: identification, prevention and control

Apple scab is one of the most common fungal diseases affecting pome fruit trees. Caused by fungi of the genus Venturia , it causes significant losses in orchards, affecting the quality and marketability of fruit. Its spread is favored by humid and temperate conditions, and its management relies on a preventive approach and appropriate treatments.

Fruit tree species concerned

Apple scab primarily affects pome fruit trees, including apple, pear, quince, nashi (Japanese pear) and cider apple.

Stone fruit trees such as apricot, almond, cherry, nectarine, peach and plum are generally not susceptible to this disease.

Symptoms of the disease

Scab manifests itself by specific symptoms on leaves, fruits and twigs.

On the leaves, brown to olive spots with a velvety appearance appear, developing into necrotic lesions. These symptoms cause weakening of the tree and can lead to premature leaf fall.

On fruit, the disease appears as olive-brown spots that develop into a corky, cracked appearance. Fruits may be deformed and their growth is often stunted. Heavy infestations can render fruit unsaleable due to aesthetic damage and impaired taste.

Blackish pustules may appear on the branches, accompanied by cracks in the bark. These lesions weaken the structure of the tree and constitute sources of infection for the following seasons.

Means of prevention

Prevention is the main lever for limiting the appearance and spread of scab in orchards.

Varietal selection is an effective strategy for reducing disease incidence. Some apple and pear varieties are bred for their resistance to scab, which helps limit the use of fungicide treatments.

Proper pruning promotes good aeration of the foliage and reduces humidity within the canopy, conditions unfavorable to the development of the fungus. Well-aerated vegetation limits water stagnation on the leaves and fruit after rainfall.

Plant debris management is essential to reduce infection pressure from one year to the next. It is recommended to collect and destroy diseased leaves and fruit that have fallen to the ground or remain attached to branches to eliminate overwintering spores.

A proper irrigation system helps limit moisture on the foliage. Drip irrigation is preferable to sprinkler irrigation, which promotes the dispersal of fungal spores.

Balanced fertilization strengthens the trees' resistance. Excess nitrogen should be avoided, as it stimulates rapid foliage growth, making tissues more vulnerable to infection.

Means of control and treatments

When scab is established, appropriate treatments must be implemented to limit its spread and protect the trees.

In organic farming, several natural solutions are available. Baking soda is used as a curative treatment to block the growth of the fungus. It should be applied at a concentration of 3 to 10 g/L, with a maximum of eight applications spaced ten days apart.

Talc is an effective preventative treatment. It forms a physical barrier on leaves and fruit, preventing the adhesion of fungal spores. Its application must be repeated every two to three weeks, with three to five treatments per season.

Willow bark tea is a natural alternative with recognized antifungal properties. It can be sprayed regularly on the foliage to limit the appearance of the disease.

In conventional agriculture, the use of copper products is recommended. Copper hydroxide is more effective than copper sulfate or copper oxychloride. The treatment should be applied in three stages: just before leaf fall, before bud swelling, and just before flowering.

The application of approved fungicides for the protection of fruit trees is a last resort in cases of high disease pressure. It is imperative to respect the doses and application conditions to minimize environmental and health impacts.

Conditions favorable to the development of the disease

Scab is caused by several species of the genus Venturia , notably Venturia inaequalis for apple trees and Venturia pyrina for pear trees.

Its development is favored by humid and temperate climatic conditions. The disease generally appears in spring when temperatures are between 10 and 20°C and humidity is high. The presence of water on the foliage for several hours is a determining factor for spore germination.

Prolonged periods of rain followed by cool days are particularly conducive to the spread of the fungus. Increased vigilance is necessary during these periods to anticipate preventive treatments.

Impacts and monitoring of the orchard

Apple scab can cause significant economic losses in commercial orchards. Uncontrolled infection leads to fruit deterioration, reducing its market value. In severe cases, premature leaf drop weakens the tree and jeopardizes future harvests.

Regular monitoring of trees is essential to detect the first signs of the disease. Careful monitoring allows for rapid intervention with appropriate preventive or curative measures, thus limiting the spread of scab in the orchard.

Conclusion

Apple scab is a serious disease that can hamper the production of apple, pear, and quince orchards. Its management relies primarily on preventative measures, including varietal selection, pruning, plant debris management, and proper leaf ventilation.

When treatment is necessary, biological or conventional solutions can limit the impact of the disease. An integrated approach combining prevention, monitoring, and targeted interventions is essential to ensure the quality and profitability of fruit production.

To summarize: how to protect your fruit trees against scab?

Apple scab is a disease that compromises harvest quality and can weaken pome fruit trees. Its prevention relies on rigorous crop management, preventative practices, and targeted treatments to limit its spread.

Arboriverse, a specialist wholesale supplier of fruit plants , supports arborists with varieties selected for their robustness and disease tolerance. Purchasing apple, pear and quince plants from an expert is a strategic solution to guarantee the sustainability and profitability of orchards.

Orchard maintenance plays a key role in limiting the fungus. Proper pruning , which promotes leaf aeration, reduces humidity and slows the progression of the disease. Removing contaminated leaves and fruit , as well as good management of plant debris, reduces fungal pressure from one season to the next. Controlled irrigation , without wetting the foliage, also helps limit the appearance of infectious foci.

When treatments become necessary, several solutions exist. In organic farming, Bordeaux mixture applied in late winter and early spring effectively protects young leaves and buds. Baking soda as a curative and talc as a preventative offer natural alternatives to limit infection. In conventional farming, specific fungicides must be used carefully to avoid the development of resistance and minimize environmental impacts.

Regular monitoring of the orchard and rapid intervention can control the disease before it causes irreparable damage. At Arboriverse, a specialist wholesale supplier of fruit plants , we put our expertise at the service of professionals by offering robust and resistant plants , guaranteeing efficient and sustainable cultivation. Buying apple, pear and quince plants from a specialist is a strategic choice to ensure the profitability and quality of fruit production.