Farming and Agriculture Gardens and Outdoors

12 Common Apple Tree Diseases (And How to Treat Them)

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There are many diseases that can impact your apple trees. Some of them shouldn’t be very concerning as the most damage you can expect is slight cosmetic issues. Other diseases can be more damaging and reduce the amount of fruit produced or even cause tree death. While treating apple tree diseases represents a good solution to try, the best option is to prevent diseases by planting varieties that offer disease-resistant properties.

If you have a small apple tree orchard, it’s safe to say that aesthetic problems won’t bother you that much. Although they don’t seem that damaging, cosmetic diseases can be very troublesome for large-scale growers. If you want to sell your apples, they need to be marketable. When it comes to fruit, that usually refers to looking appealing to the customer’s eye. Before trying to treat apple trees of diseases, it’s essential to figure out the best prevention methods. Check out the most common apple tree diseases to stay prepared in case of more difficult scenarios.

1. Fire Blight

One of the most common apple tree diseases that you might have to deal with is fire blight. This is a bacterial disease that can get particularly difficult to control. If left unchecked, fire blight can devastate your apple tree orchard as it affects all important parts of the tree. An easy sign to identify this disease involves checking for browning of the leaves or blossoms. An infected tree in a more advanced stage can show damage to its branches. The same browning may be accompanied by open cankers. Fire blight overwinters and can easily spread during the rainy season or with the help of insects.

Symptoms of fire blight will usually develop in spring and summer. Some apple tree cultivars are particularly susceptible to this disease. Examples include Jonathan and Granny Smith. There are a few things that need to be done for successfully managing this devastating disease. Eliminating infected tissue represents an essential aspect of the treatment process. Make sure pruning takes into account a few extra inches below the visible infection of the twig. Another important detail is to remember cleaning the pruning shears to prevent the spread of the bacterium.

2. Powdery Mildew

Powdery mildew is a common apple tree disease that also affects popular ornamental plants. It’s not as dangerous as fire blight but it can severely weaken the tree. This is a fungal disease that you won’t have too many troubles recognizing. You will see white felt-like growths on the leaves. As the disease progresses, leaves will become wilted and the growth of the tree is affected. Finding the cause of powdery mildew can pose some difficulties due to how the disease can be easily spread by fungus spores. It’s not just the wind or insects that represent causes for concern as the spores can land on the tree’s leaves because of heavy rainstorms.

Due to the fact that powdery mildew overwinters in fallen leaves, it’s highly recommended to prevent the disease from spreading further by cleaning up the leaves in autumn. Moist conditions seem to favor the development of the disease so consider good air circulation when planting new apple trees. Overhead water can also be a risk factor for powdery mildew. A good treatment option is to get the trees sprayed with lime sulfur. Pruning whitened terminal shoots is another great solution to control this disease.

3. Apple Scab

Prevalent in rainy weather and affecting lots of apple varieties, apple scab is an extremely common disease that can have serious effects on your trees. This is another fungal disease that can be hard to control as fungus spores can easily reach vulnerable leaves in the spring. To identify this disease, it’s important to check for lesions on new leaves. It’s usually not very difficult to spot as the lesion has a darker color. Make sure you look carefully under leaves as lesions there can have a slightly lighter hue.

While apple scab has some potential to become a serious problem, the good news is that it’s fairly easy to prevent with regular observation. Infestations can be tough to spot unless you’re regularly looking for signs of the disease as a prevention measure. Don’t let infected leaves on the ground in autumn as apple scab overwinters. If your apple trees get more badly infected, there are many issues you will have to deal with. The tree gets more vulnerable to other diseases as it can get completely defoliated. The scabs on the leaves can also be discovered on the fruit surface in case the disease is mild enough to allow for fruit production.

4. Cork Spot

Although it may initially look like hail or insect damage, the small dimples on developing apples are actually caused by a disease. It’s called cork spot because dimples have a corky or soft appearance on the skin of the fruit. Apple trees get this disease due to poor soil conditions. The cause is usually a calcium deficiency or low soil pH. While cork spot isn’t really a big issue for small-scale growers, those that depend on the apples’ aesthetic appeal can be more severely impacted.

Treating this apple tree disease will usually involve correcting the soil problems. The first step to consider is a soil test analysis to determine the pH. Depending on the results of the test, it might be necessary to add lime to the soil. Trees can benefit from some calcium chloride supplementation. A water-based calcium solution sprayed on affected trees should help control cork spot disease. Make sure you apply it multiple times, ideally after the apple tree is in full bloom for best results.

5. Phytophthora Rot

Phytophthora rot is another common apple tree disease to watch out for. It’s named after the fungus that causes vigor and growth declines in affected trees. Multiple tree parts can be damaged by Phytophthora rot. Suspected infections are not easy to spot but you can start by checking the color underneath the outer bark. If it’s orange or brown, that could mean you’re dealing with a Phytophthora disease. There are many possible sources of contamination for this disease and the fungus thrives in wet soils.

When the disease gets to a more advanced stage, you will notice yellowish leaves that become purple in the autumn season. Treating Phytophthora rot can be hard to control if you rely on fungicides. Good prevention methods are recommended if you’re a small-scale apple tree grower. Aside from avoiding possible contaminated sources like soils or irrigation waters from different places, it’s recommended to be careful when planting new apple trees. Choose loamy soils and add compost while avoiding excessive moisture. Using raised beds represents a great solution to fight against poor drainage issues.

6. Apple Rust Diseases

There are multiple apple rust diseases that are characterized by rusty spots on the apple tree’s leaves. Of all the forms of rust diseases affecting apple trees, Cedar-apple is the most common. The typical yellow-orange stains can be found on other parts of the tree, not just the leaves. Inspect the branches and fruits to check for the severity of the disease. Cedar-Quince is another type of apple rust disease that can be spread from another plant near the apple trees. This is because the fungus requires a host plant to spread further.

The fungus can grow a lot on the host plants so the best treatment is to get rid of them to prevent damage to the apple tree. There’s not much else you can do to fight against this disease aside from trying to stick to more resistant varieties such as Redfree, Freedom, and William’s Pride cultivars. Lime sulfur spraying can help to fight against the fungal spores that spread apple rust diseases.

7. Black Rot

Caused by Botryosphaeria obtuse, the black rot disease can affect the fruit of your apple trees. If you notice brown spots on the fruit’s end, it’s safe to say that you’re dealing with this disease. As black rot progresses, those brown spots become larger and turn to black color. This is where the name of the disease comes as apples start to rot at this stage. Leaves can also get damaged with spots or holes. If left unchecked, the disease can prove fatal for the entire tree as black rot spreads to the branches.

The best solution to treat this disease is to catch it in its early stages. Once infected tree material is detected, it has to be carefully pruned out or burnt. While black rot is not as common as other apple tree diseases, keep in mind that it can be particularly insidious for trees that are already affected by fire blight. It’s recommended to get the infected trees sprayed with sulfur or Captan before it starts to spread to all the parts of the tree.

8. Sooty Blotch

Sooty blotch is not a dangerous disease but still quite common. Affected apple trees will have fruits covered in black or grey spots. It’s caused by a fungus and it’s very similar to another non-lethal disease called Flyspeck where similar spots appear on apples. The damage is simply cosmetic in nature because the fruit remains edible. Even if that’s the case, many apple tree growers will find it difficult to sell the apples at the market due to unsightly discolorations.

Dealing with sooty blotch involves repeated chemical sprays but the best solution is to modify the environment. The fungus grows well when humidity is high. Another risk factor is poor air circulation. It’s important to impose some prevention measures so that apple trees won’t fall under the ideal conditions for the development of the disease. Unfortunately, once the infection becomes established and apples become really stained with sooty fungal bodies, you won’t be able to do much besides cleaning the fruit really well. Under-pruned trees seem to be more vulnerable to this disease.

9. Apple Mosaic Virus

Most apple tree varieties can get infected with the apple mosaic virus. Recognizing the disease can be done easily by checking the leaves in early spring. The virus creates yellowish spots that start small but can grow larger as the infection progresses. It may not appear very damaging initially but once the summer weather comes, leaves start to get wilted and die prematurely. As you can expect, tree growth and yields will be affected.

Apple mosaic virus disease can be spread by propagation or root grafting. Ensuring that you’re not relying on contaminated propagation sources represents one solid method to avoid the apple mosaic virus. As there’s no treatment available for this disease, the only solution is to detect the infected tree early and remove it from the orchard. The fruit yields can be severely impacted by this disease. Depending on the apple tree variety, the virus can create more pronounced effects with conspicuous symptoms. Jonathan and Golden Delicious are some of the most susceptible apple tree varieties.

10. White Rot

More common in southern climates, white rot is an apple tree disease that only affects the wood and fruit. Infected branches show small spots and blisters that can turn the bark to an unhealthy orange color as the disease advances. The disease can cause girdling of the twigs and branches. In serious cases, you can expect to face the girdling of the whole tree. Apples are also affected by brown or white spots depending on the fruit color variety.

This apple tree disease overwinters and relies on rotten tree material like cankers and dead bark for hosts. This is similar to other fungal diseases when it comes to spreading. Weather events like heavy storms have the potential to spread the infection to other trees. Keeping the trees healthy represents a good prevention method. Fungicide can be considered as a treatment solution during the growing season. It’s very important to remove all the infected wood and prune the apple tree thoroughly to minimize the effects of the disease.

11. Crown Gall

Crown gall is a bacterial disease that can often affect apple trees. Injured tree roots can become infected through the soil. The most important symptom of crown gall is the lack of proper tree growth. All areas of the tree can be affected but it’s more noticeable when fruit-bearing trees offer very reduced yields or none at all. There are other diseases and problems that cause stunted tree growth so you will need to inspect the ground level to put an accurate diagnostic.

As its name suggests, crown gall disease will create woody growths that are called galls. Check the roots for these tumor-like growths. This can be usually done only after the tree has died. Fortunately, the disease isn’t usually that deadly as the growths develop over fairly long periods of time. They restrict the flow of nutrients to the tree causing the growth problems. Some fire blight sprays have been shown to be able to control this disease.

12. Anthracnose

There are lots of wet weather diseases that can affect apple trees. One of them is called anthracnose. It’s spread by a fungus through rain and irrigation. The disease can be identified by observing the bark of the tree. If you see little canker spots on it, that’s the first sign of an infection. The cankers have a more distinctive color when wet as they can turn to a reddish hue. The bark spots turn to darker shades of orange and brown as they grow.

The leaves and apples can also be affected by spots but the bark seems the most impacted. Old cankers can cause disintegration problems and expose wood fibers underneath the bark. Anthracnose is not a particularly deadly disease as cankers take a long time to grow. If you detect it early, it’s relatively easy to control by removing small branches and twigs. Another treatment method involves the use of neem oil or fungicide sprays.

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