This blog carries detailed information about the major apple diseases, their symptoms and management strategies.

The planting of apples is frequently affected by several diseases each year. These diseases do not infect at the same time. Instead, they manifest in a comparatively predictable order dependent on the climate and the phenology or growth of the apple host, starting at dormancy and lasting until fruit is harvested. In order to harvest a high percentage of marketable fruit, a well-planned strategy for disease management is frequently required. Apple scab, Marsonina blotch, powdery mildew, Alternaria leaf spot, etc are among the most prevalent ones that affect apples.

The weather significantly impacts the frequency and severity of plant diseases. Therefore, diseases are typically the hardest to control in years of high temperatures, high humidity, plentiful rainfall, and cloud cover. As a result, understanding the identification of apple disease and its favourable conditions is essential to prevent them from affecting apple harvests.

Major apple diseases are:

• Apple scab
• Marsonina blotch
• Powdery mildew
• Alternaria leaf spot

Disease	Symptoms	Favourable conditions	Management
Apple scab	● Black, round patches on leaves. ● Later lesions turn brown and depressed, and their edges may be covered with spores.	● Summer and moist temperature.	● Clean cultivation, collecting, and removal of fallen leaves. ● Gather and burn plant material.
Marsonina Blotch	● Black spots on apple leaves and fruits. ● Dark green circular patches on the leaf’s upper part.Small black acervuli on leaves.	● The temperature of 20–25 °C and 100% relative humidity during a leaf wetness period of at least 40 hours.	● Clean orchards, trimming and using fungicides. ● Marssonina-infected leaves should be removed.
Powdery mildew	● Little clumps of white or grey powder on the underside of leaves. ● Curled leaf borders.	● Relative humidity (RH) is higher than 70%. ● Temperatures between 10 and 25 °C.	● Cleaning up the orchard. ● The use of resistant varieties. ● Use pruning and trimming techniques.
Alternaria leaf spot	● Leaf spot spherical, brown. ● Spots frequently turn from tan to ash-grey with age.	● Moist weather and temperatures between 77 and 86 °F.	● Maintain clean orchards and “gentle handling” of fruit. ● When the fruit is fully mature, harvest it.

Apple scab

The Apple scab disease was first discovered in Himachal Pradesh, India, in 1977, resulting in enormous apple output losses.

Symptoms

• The disease is typically seen on leaves and fruit.
• Affected leaves have twisted or puckered surfaces as well as black, round patches.
• The velvety spots on the underside of leaves have the potential to combine and cover the entire leaf surface. Severely impacted leaves may drop and turn yellow.
• Scab can also infect flower stems, resulting in the loss of blossoms.
• Later, the lesions turn brown and depressed, and their edges may be covered with spores.
• Fruit that has been infected develops distortions and may crack, allowing secondary pathogens to enter.

Favourable circumstances

• Moisture and temperature are the ideal circumstances for apple scab to spread. This cycle of secondary infections continues, throughout the summer, until the leaves and fruit start to fall from the tree at the start of winter.

Management

• To break the reproduction cycle, clean cultivation, collecting, and removal of fallen leaves and clipped materials should be done in the winter.
• Gather and burn plant material that is contaminated.
• After properly cutting and clipping the twigs and branches, burn them.
• To hasten the breakdown of fallen leaves, use dolomitic lime (2.5 tons/acre) in the fall and urea (2 kg/acre) at the pre-leaf fall stage in the spring.

Marssonina Blotch

A leaf spot fungus disease called Marssonina blotch was found to be the culprit behind the mid-season defoliation of trees that decimated apple crops in the Indian state of Himachal Pradesh in 1992.

Symptoms

• Black spots on apple leaves and fruits are typical indications of apple blotch, as well as premature defoliation that compromises the physiological balance of the host, reducing tree vigour and yields over the long run.
• Dark green circular patches on the upper surface of the leaf are the disease’s initial signs. These patches eventually develop into 5–10 mm brown leaf spots that eventually turn dark brown.
• It also grows on the underside of the leaf when it reaches maturity.
• Small black acervuli (the small fungal fruiting body that is asexual in nature) can be seen on the leaf’s surface.
• When there are several lesions, they group together and become huge, dark brown blotches, turning the surrounding areas yellow.
• The disease is spread through Conidia, the reproductive stage of the pathogen, and the infection itself persists in the diseased leaf litter on the orchard floor.

Favourable conditions

• The fungus pathogen survives the winter on fallen leaves and fruits. When it’s warm and humid outside in the spring or early summer, fungal spores on diseased waste are released and spread by wind and rain splash, infecting leaves (primary infection). 
• The necessary circumstances for epidemic outbreaks include a temperature of 20–25 °C and 100% relative humidity during a leaf-wetness period of at least 40 hours. In fields during a season, recurrent secondary infections cause disease outbreaks, making it more evident in the late summer. 
• The development of the disease is favoured by frequent rain and moist weather in the spring and summer.

Management

• You can prevent Marssonina blotch yearly if you manage apple scab.
• Disease control is handled similarly to apple scab by maintaining clean orchards, trimming, and using fungicides. 
• The level of infection can be lowered by removing overwintered leaves from the ground. 
• Marssonina-infected leaves can be removed if you regularly adopt a method to remove scab leaves (flail mowing, urea). 
• Collect fallen fruit and leaves, then scatter them by burying or burning them. To promote air circulation in the canopies, prune trees properly.
• This disease is easily controlled by conventional fungicides, which are frequently used for early and summer apple diseases.
• Applications of fungicides may shield leaves from the disease and reduce spore generation on affected leaves.

Powdery mildew

Apple powdery mildew is a devastating disease rapidly spreading in orchards in warm weather.

Symptoms

• When the buds turn into fresh leaves and shoots, the disease starts to occur.
• Little clumps of white or grey powder can be seen on the underside of the leaves.
• The border of the leaves is curled, and they become longer and narrower than typical leaves.
• Twigs are covered in a powdery substance.
• Fruits that have been infected tend to have a roughened surface and remain small and deformed.

Favourable circumstances

Powdery mildew infections happen when the relative humidity (RH) exceeds 70%.

Temperatures between 10 and 25 °C are conducive to the development of infections.

Management

• Cleaning up the orchard
• The use of resistant varieties can prevent the disease
• Pruning infected terminals overwintering (6–8″ below the infection) can prevent the disease.
• Use pruning and trimming techniques to lower the humidity.

Alternaria leaf spot

Apple Alternaria leaf spot is a destructive and economically significant disease that results in severe early defoliation and decreases tree vigour, reducing apple production.

Symptoms

• In the late spring and early summer, leaf spots start to form on the leaves. 
• They are spherical, brown, and 1/8 to 1/4 inch in diameter. Occasionally, they also have a purple border.
• Spots frequently turn from tan to ash-grey with age. Some areas experience secondary expansion and take on an atypical shape.
• Defoliation frequently occurs when leaves that are severely diseased abscise. (Defoliation is increased in the presence of mites.) Small, black, raised pimple-like lesions that are connected to the lenticels are the outcome of fruit infections.
• Twig lesions, which appear as somewhat sunken, rounded, blackish spots surrounded by fractures, affect vulnerable cultivars like Indo but not Delicious.

Favourable circumstances

Moist weather and temperatures between 77 and 86 °F (25 and 30 °C) favour the disease. Within two days of infection, a major outbreak can develop. Infection happens at ideal temperatures with 5.5 hours of wetness.

Management

• Farmers can reduce the disease pressure in the next season by shredding leaf litter during the fall season (this will also help prevent apple scab). 
• To successfully eradicate Alternaria blotch, red mite populations must be under control. The fungicides that contain strobilurin are the most effective at preventing Alternaria blotch.
• Maintain clean orchards and “gentle handling” of fruit.
• When the fruit is fully mature, harvest it.
• Handling the fruit carefully during sorting, cleaning, and packing is essential.
• Fruits should be kept between 0 and 4 °C.

How can Fasal assist?

• In order to increase apple yield and output, plant protection is a crucial component of horticulture. Therefore, artificial intelligence (AI) approaches have recently been established to precisely control crop pests and diseases. Plant protection measures should be followed on a community basis to ensure the successful management of pests.
• Fasal is making strides in the horticulture industry with its AI-powered automated device. 
• The Fasal IoT-based system is powered by solar and battery power and is simple to install on any horticultural farm. 
• Fasal device is equipped with a number of sensors that monitor the macro- and microclimates at the farm level, as well as rainfall, soil moisture, soil temperature, wind direction, leaf wetness, etc., to detect the conditions that lead to disease breakout in farms.
• Apple growers are alerted about the potential disease and pest infestations by the Fasal Disease and Pest Prevention System, which also provides information on the best preventive sprays to minimise damage. Farmers have reduced pesticide use by 15-30%, lowering the environmental impact.
• Farmers are also informed via the Fasal app on their smartphones, giving them access to a complete image of their orchards and allowing them to take corrective and preventive actions to avoid diseases.