Apricot Tree Diseases: How to Identify, Treat, and Prevent Apricot Tree Diseases

If you have apricot trees, or even one apricot tree, chances are that you have made a special effort to grow a special crop. Apricot tree diseases can undo years of work in just a few days, but most apricot tree diseases are identifiable, treatable, and sometimes preventable. Here is what you need to know about the most common apricot tree diseases.

Armillaria Root Rot (Oak Root Fungus, also known as Apricot Fungus)

Symptoms and Signs

Sometimes apricot trees go through a general decline one year and just don’t come back the next spring. A frequent cause of this kind of apricot decline is armillaria root rot, which is also known as oak root fungus.

Apricot trees affected with this disease show a general decline in vigor a year or two before the whole tree collapses. Usually there will be a circular area in an orchard where every tree is affected as the fungus spreads. The fungus spreads along the roots of infected trees to healthy trees. Sometimes a tree will leaf out and die in late spring, but more often the tree just doesn’t leaf out.

Peaches can also get armillaria root rot. You can tell the difference between Armillaria and Phytophthora root rot by the yellow, fan-shaped mats of fungus between the bark and the wood. Sometimes the fungus puts out dark brown or black “horns” above the soil from the roots.

What You Need to Know About This Apricot Tree Disease

Armillaria root rot can survive in the soil for years after the tree dies.

How You Can Manage This Disease

Apricot trees with this fungus cannot be saved. Trees that are grafted on Marianna 2624 rootstocks are more resistant to this fungus than most, but aren’t completely immune.

Bacterial Canker

Symptoms and Signs

Bacterial canker also becomes obvious in the spring. Sometimes limbs die back, but more often the first sign is amber-colored ooze on the trunk. There can be spots on the leaves and odd formations on young shoots. Called blasts, these formations encase the shoot in a clear ooze before it dies.

There can be orange and red flecks on the tree outside the areas killed by the canker. The tree may try to survive by sprouting numerous suckers near ground level or from limbs before the parts of the tree that are affected by the disease.

The organism that causes bacterial canker, Pseudomonas syringae, lives on the surface of the tree and is spread by splashing rain. It multiplies when the weather is warm and rainy in the spring. Healthy plants won’t get the disease when it splashes on them, but stressed trees are. 

What kinds of stress will cause apricot trees to get bacterial canker? Spring frosts weaken apricot trees so they come down with it, as will nematodes.Commercial growers will fumigate the ground to prevent the disease.

What You Need to Know About This Disease

Bacterial canker is worse in trees planted in shallow soils, especially if there is hard pan clay about 3 feet (a meter) down.

How You Can Manage This Disease

Anything that keeps apricot trees healthier, such as irrigation when needed, winter fertilizer in appropriate amounts builds resistance to bacterial canker. It can also help to wait until spring to do pruning.

Apricot Tree Diseases: Brown Rot 

Symptoms and Signs

Brown rot starts with the death of young blossoms and the twigs and leaves near them. The infection moves from flowers to twigs as it forms cankers in the bark of limbs. There will be a gummy substance at the base of infected flowers. The cankers will have tan centers and black margins. In a rainy spring, grayish-brown spores will be visible on the dead flowers.

What You Need to Know About This Disease

This fungus survives from year to year on mummified fruits left on the ground beneath the apricot tree. It spreads to new apricot trees when splashes of rain carry the fungus from the ground to the limbs of the tree.

How You Can Manage This Disease

There is a lot you can do to control brown rot:

• Remove mummy fruit from under apricot trees immediately after harvest or during the winter.
• Cultivate the soil underneath the tree to break up and cover mummified fruit.
• Apply bloom fungicides two or three times to control brown rot flower and twig blight, two in normal weather, three if you are having a rainy spring. The best time to apply fungicide is when the flower buds first turn red.
• Spray every two weeks to ensure continuing protection. If you have an extended rainy spell, spray fungicide every 7 to 10 days..

Eutypa Die Back 

Symptoms and Signs

Eutypa die back, also known as gummosis, causes whole branches to die in the late spring with their leaves still attached. The bark will be discolored and covered with am amber gum. The cambium and xylem inside the branch will be discolored brown.

What You Need to Know About This Disease

Disease organisms infect freshly pruned wood in the early spring if you prune just before it rains. The disease can also infect apricot trees that are pruned in the summer or fall just before they are irrigated, or it rains. The disease also spreads if you do not remove all infected wood when you prune.

How You Can Manage This Disease

Remove infected limbs in the summer after you harvest the fruit during dry weather. Don’t irrigate your trees for a couple of weeks after pruning. Except when you are pruning your apricot tree during an extended period of hot, dry weather, paint all pruning wounds with organic or chemical fungicide.

Powdery Mildew

Symptoms and Signs

Powdery is the familiar white, web-like growth that can appear on plants of all kinds overnight. Apricot trees affected by powdery mildew may have scabs and red or purple splotches. They are OK for making jams and pies at home, but they aren’t salable.

What You Need to Know About This Disease

Apricot trees most often get powdery mildew from infected rose bushes. Different species of fungi cause the condition in spring, summer, and fall. Winter cold will kill them.

How You Can Manage This Disease

Don’t plant apricot trees near roses. Begin spraying for powdery mildew as soon as blossoms have opened in the spring. It is important to stop mildew at the earliest stage of fruit development possible. Apricot fruit becomes resistant to new infections after the pit begins to harden, but older infections may still affect the fruit.

Ripe Fruit Rot

Symptoms and Signs

Ripe fruit rot is probably the most disappointing apricot tree disease. This fungal infection causes brown, circular, firm spots to spread over ripening fruit overnight. Tan masses of spores will pop up in the middle of the spots. Ripe fruit rot most often affects fruit that is within a day or two of harvest. Diseased apricot fruits that stay on the tree will become a source of ripe fruit rot the next year.

What You Need to Know About This Disease

Ripe fruit rot is most likely to occur when it rains on ripe fruit. The disease won’t occur if overnight temperatures fall below 67 degrees Fahrenheit (19 degrees Celsius).

How You Can Manage This Disease

There are things you can do to prevent ripe fruit rot:

• Avoid giving your apricot trees too much nitrogen fertilizer.
• Irrigate in the morning, not in the afternoon, and absolutely not at night. Overnight humidity gives the fungus a chance to grow.
• Control blossom rot (see above) in the early spring.

Shot Hole Disease

Symptoms and Signs

The fungus that caused shot hole disease causes spots on leaves that fall as if they had been shot out with a BB gun. A severe infestation of this disease can cause all the apricot tree’s leaves to fall in the spring. It can also cause brown areas of decay with dark purple margins to appear on the top edges of ripening fruit. As the fruit ripens, it may become covered with scabs.

What You Need to Know About This Disease

This is another fungus that is spread by rain. It can overwinter on infected twigs. There is a similar condition caused by summer fog, but fog spot does not affect the leaves.

How You Can Manage This Disease

You can prevent shot hole disease by applying fungicides in the winter. The more it rains in the winter, the more spraying you will need to do.

Verticillium Wilt

Symptoms and Signs

It’s hard to miss verticillium wilt. The leaves on one and usually more branches, often on just one side of the apricot tree, turn yellow, wilt, and fall off in late spring. The shoots on which they were growing will curl up, die, and dry up. If you cut off an affected limb, you will see dark discoloration inside. 

Verticillium wilt is  usually a disease of younger trees. Mature trees are not affected. Even when leaves and branches do not die and fall off, fruit yields may be affected.

What You Need to Know About This Disease

Verticillium bacteria accumulate in the soil of ground used to grow cotton or tomatoes.

How You Can Manage This Disease

Verticillium wilt is something you can prevent but you can’t treat. The summer before you plant apricot trees, cover the soil with clear UV-stable plastic to heat it up so microorganisms in it will die. Then, after you set out your apricot trees, surround them with a ring of black plastic to make sure the bacteria don’t get into the tree’s root system from somewhere else on your property. Never plant apricots, tomatoes, or melons in the same location.

Wrapping Up Apricot Tree Diseases

If you have any questions about any other apricot tree diseases, can’t identify what you’re dealing with, or have any general questions, leave a comment below.

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