Powdery mildew on apples is as a result of the fungus referred to as Podosphaera leucotricha.
It develops as a white mass on the new terminal growth of apple trees.
This will ultimately encompass the apple trees’ shoot tips.
These symptoms will lead to stunted growth of nonbearing apple trees
Also, it will cause possible effects on yield and return bloom of bearing tress and loss of vitality.
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Additionally, powdery mildew fruit infection will cause russeting if you don’t manage the disease before the fruit is present.
The fungus is unique in that it will infect apple trees without wetting from dew or rain.
While this fungus doesn’t kill their hosts, they certainly do several on them.
And that’s especially true for powdery mildew of crabapples and apples.
This powdery mildew will attack both wild and cultivated crabapples and apples.
The disease happens in all apple producing areas globally.
It will attack each stage of the apple plant; fruit, new shoots, buds, leaves, and flowers.
Powdery mildew can be so severe that there’s no fruit formation.
While the regular treatments are fungicides, you can find some cultural practices to help in controlling apple powdery mildew.
Unlike the majority of fungal diseases, powdery mildew spores on apples don’t need moisture for germination.
Thus, this infection is referred to as “dry weather disease.
Here are steps to show you how to diagnose and treat powdery mildew infection on the crabapple and apple tree.
Primary infection symptoms
If this disease infects your apple tree, first, you’ll see a delay of up to 4 days in the opening apple buds in the spring months.
Usually, spores cover these buds.
After that, fungal spores cover the flowers and leaves as they surface from their buds.
These spores resemble a white or light gray powder, and there is a curling of infected leaves.
This powder will cover both sides of the tree shoots and leaves.
The blossoms do not produce fruit, are often greenish-white, and grow abnormally.
The cycle of apple powdery mildew
This disease overwinters in leaf and fruit buds.
In addition, the first symptoms take place on the shoots and flower trusses that surface from infected buds in the spring season.
These leaves infected spores cause secondary mildew infections on leaves of apple shoots.
This quickly extends throughout the spring and early summer months.
Newly created buds in leaf axils will get infected by spores from all sources.
For roughly a month, fruit buds on spurs are prone to powdery mildew infection.
Leaf buds are prone to infection for roughly 30 days after emerging in the leaves axils on extending laterals.
However, the terminal buds on laterals might get infected all through the lateral growth period.
Infected buds are usually not killed; however, they offer the main primary infection source become next season.
Difficult to stop the infection
The wind blows away these spores quickly and causes secondary infections on the fruit, leaves, and shoots.
Provided that the apple shoots keep growing, the shoots and leaves will continue getting infected.
The infections usually take place during the night at 65 – 80 degrees Fahrenheit when the relative humidity exceeds 70 percent.
While this may seem high, it’s popular on the lower surface of leaves.
First, apple powdery mildew on the leaves takes place on the bottoms and might resemble chlorotic spots on the leaves’ top part.
As time goes by, the infected tissues grow the silver-gray powdery mildew look.
Infected fruit will get discoloration and netlike reddish brown shades. It might get dwarfed and distorted as well.
There are two ways that high powdery mildew levels at the end of the growing season will damage the apple tree.
To start with, the number of infected buds will increase, so come next spring, and the infection level will be high.
Second, it will slow down flower buds formation, so there will be no or less fruit production in the coming season.
And worse, a heavily infected apple tree will become prone to additional infection types.
Natural ways of treating apple powdery mildew
There are lots of natural remedies that apple growers use for preventing and treating this disease.
- Apple cider vinegar
- A milk mixture
- Neem oil
- Potassium bicarbonate
- Baking soda also referred to as bicarbonate sodium
It is best if you prune any shoots that look white in the early spring season, so they will not spread spores.
You should avoid using too much fertilizer, particularly in the late summertime.
This helps prevent the growth of succulent new tissue that’s infected by the powdery mildew easily.
Planting the apple tree in a sunny area is another thing that can help you protect your tree.
The reason being, poor circulation, high humidity, and too much shade all increase infection chances.
As it is hard to control powdery mildew, and it’s important to get rid of the spores that will continue infecting your apple tree, you might decide to apply fungicides.
Make sure you select those labeled, especially for fruit trees.
You can go for low toxicity fungicides such as horticultural oils.
They include neem oil, jojoba oil, and spray oils made for fruit trees.
Classic fungicides used against apple scab, like sterol inhibitors, are very effective in controlling apple powdery mildew.
These fungicides include fenbuconazole and myclobutanil.
As powdery mildew overwinters inside apple buds, you have to begin treating the tree early in the season before the flowers begin showing a pinkish shade.
One of the most popular mistakes made in controlling powdery mildew is not spraying before the flowers open.
Be certain and repeat the sprays two to three-week intervals until the growth of new shoot stops.
This can mean as many as eighteen sprays if the cultivar is highly at risk.
Additionally, keep on spraying even if there’s dry weather.
Unlike the majority of other foliar pathogens, this disease keeps growing and producing spores in dry conditions.
Applying the fungicides properly can minimize the need for applying in the future.
Controlling apple powdery mildew
You can control this disease by:
- Protecting the buds from infection by spraying
- Modify the surroundings so that it is less conducive to infection
- Getting rid of infected buds
- Make sure that before the symptoms emerge, you spray sulfur fungicides.
- Be cautious with sulfur. The plant can get damaged if you apply when the temperatures exceed 90 degrees Fahrenheit.
This group of fungicides will include the classic Bordeaux of lime and copper sulfate.
This mixture is certified organic and is very effective at helping to prevent apple powdery mildew.
You can purchase a pre-packaged combination made for small gardens.
The best method to prevent powdery mildew is planting resistant varieties.
Some of the most common cultivars are the most prone; Rome, Jonathan, and Granny Smith, for instance.
Some of the more popular resistant cultivars include:
Apple drop threat
Though the fungus won’t technically kill the plat, it will incapacitate the tree to such a degree that it might not produce any fruit.
Apple powdery mildew is prevalent on cultivated and wild crabapples and apples globally where they are grown.
For that reason, it’s important that you know the symptoms of this disease, so you can act fast when you see infected tissue.
You will have to use some type of fungicide to spray; sterol, horticultural oils, or sulfur inhibiting fungicides.
A stern spray timetable might help in saving your tress from this destructive pathogen.