Apple scab is a fungal disease that affects apple trees and ornamental crabapples. Managing apple scab disease is necessary as it is the most common and serious disease of apples worldwide, causing significant losses to fruit growers.
Apple scab can infect leaves, fruit, and twigs, and can cause premature leaf drop, fruit distortion and cracking, and reduced fruit quality and yield.
What is Apple Scab Disease?
Apple scab is caused by the fungus Venturia inaequalis. The fungus overwinters in fallen leaves and produces spores in the spring. The spores are carried by the wind and infect new leaves, fruit, and twigs.
The fungus grows inside the plant’s tissues and produces more spores, which can spread the disease to other parts of the tree and to other trees.
Apple scab infections start in early spring from spores from leaves infected the previous year. These spores overwinter on the ground in the orchard or nearby. Once infected, the tree produces more spores that can spread the disease quickly in wet spring and early summer weather.
Host Plants for Apple Scab
Apple scab primarily affects apple trees (Malus domestica). However, it can also infect other plants belonging to the Rosaceae family, such as pears, mountain ash, and certain ornamental flowering plants.
How to Identify Scab Diseases in Apple?
The symptoms of apple scab vary depending on the part of the plant that is infected.
- Scab can occur on any apple tissue, most commonly on leaves and fruit.
- First appears as small, raised, fuzzy, olive-colored spots on fruit cluster leaves near bloom, or on early vegetative leaves and immature fruit after petal fall.
- Leaves: The first symptoms of apple scab on leaves are small, pale yellow or olive-green spots. As the disease progresses, the spots become larger and more numerous. The leaves may also become distorted, puckered, and yellow. In severe cases, infected leaves may drop prematurely.
- Fruit: Apple scab can cause fruit to become distorted and cracked. The lesions can be small and superficial, or they can be large and deep. Severely infected fruit may be unmarketable or inedible.
- Twigs: Apple scab can also infect twigs, causing them to become blighted and die.
In storage, fruit infected at the end of the growing season may develop small, dark spots called “pinpoint scab”
Lifecycle of Apple Scab
The lifecycle of apple scab begins in the spring, when spores are released from fallen leaves. The spores are carried by the wind and infect new leaves, fruit, and twigs.
The fungus grows inside the plant’s tissues and produces more spores. The spores can spread the disease to other parts of the tree and to other trees.
The apple scab fungus can produce multiple generations of spores per season. The number of generations and the severity of the disease depend on the weather conditions. Cool, wet weather favors the development and spread of apple scab.
Also Read: Potato Spindle Tuber Disease
Treatment for Apple Scab
Managing apple scab disease is necessary as the disease affects the yield and quality of the fruit. The disease can be prevented by chemical and cultural methods.
Chemical Methods
Captan: Captan is a multi-site fungicide that is effective against a wide range of fungal diseases, including apple scab. It is a protectant fungicide, meaning that it must be applied to the tree before infection occurs.
Captan is typically applied as a foliar spray every 7-10 days during the growing season.
Myclobutanil: Myclobutanil is a systemic fungicide that is absorbed by the plant and translocated throughout the tissues. It is effective against a wide range of fungal diseases, including apple scab.
Myclobutanil is typically applied as a foliar spray every 10-14 days during the growing season.
Sulfur: Sulfur is a multi-site fungicide that is effective against a wide range of fungal diseases, including apple scab. It is a protectant fungicide, meaning that it must be applied to the tree before infection occurs.
Sulfur is typically applied as a foliar spray every 7-10 days during the growing season.
It is important to note that chemical control of apple scab should be used in conjunction with other cultural practices, such as planting resistant cultivars, pruning infected leaves, and avoiding overhead watering.
Chemical control should also be used judiciously to avoid the development of fungicide resistance.
When to Apply Chemical Treatments
The timing of chemical treatments for apple scab depends on the weather conditions and the stage of crop development. In general, the first treatment should be applied early in the spring, before bud break.
Subsequent treatments should be applied every 7-14 days, depending on the fungicide and the weather conditions.
How to Apply Chemical Treatments
Chemical treatments for apple scab should be applied according to the label directions. This includes using the correct rate of fungicide and applying it at the correct time of day and under the correct weather conditions.
It is also important to wear appropriate personal protective equipment (PPE) when applying chemical treatments.
Cultural Methods
Planting resistant cultivars: There are a number of apple cultivars that are resistant to apple scab. Planting resistant cultivars is one of the best ways to reduce the need for fungicides and other control measures. Some examples of resistant cultivars include Gala, Fuji, Liberty, and McIntosh.
Pruning: Pruning trees to improve air circulation and rapid drying of leaves can help to reduce the risk of apple scab infection. Remove diseased branches and any branches that are crossing or rubbing against each other.
Removing fallen leaves: Fallen leaves can harbour the fungus that causes apple scab. In the fall, rake up and dispose of all fallen leaves. You can compost them, burn them, or bury them deep in the ground.
Sanitation: Keep the orchard area clean and free of debris. This will help to reduce the risk of apple scab infection.
Water management: Avoid overhead watering, as this can spread the fungus. Instead, water trees at the base of the trunk.
Mulching: Mulching around trees can help to suppress the growth of the fungus. Mulch also helps to improve drainage and soil fertility.
Cultural methods of control are most effective when used in combination with other control measures, such as fungicide applications.
Here are some additional tips for controlling apple scab using cultural methods:
- Plant trees in a sunny spot with good drainage. The fungus that causes apple scab thrives in wet, shady conditions.
- Avoid planting trees in areas where apple scab has been a problem in the past.
- Space trees properly to allow for good air circulation.
- Fertilize trees regularly to keep them healthy.
- Monitor trees regularly for signs of apple scab infection. If you see any infected leaves or fruit, remove them immediately.
By following these tips, you can help to reduce the risk of apple scab infection and keep your trees healthy and productive.
Conclusion
Apple scab is a disease caused by fungus, effecting apple worldwide, it is serious disease that causes significant losses to apple production. Premature leaf drop, quality reduction and yield is caused by this disease.
In early spring scab starts from spores that infects leaves in the previous year. Primarily the disease affects apple crop, but the disease can also cause damage to plants, belongs to Rosaceae family.
Managing apple scab disease is necessary it can be managed by using chemical and cultural methods, chemical method includes captan, Myclobutanil and sulphur, cultural methods includes planting resistant verities, pruning, mulching, removing fallen leaves etc.,
