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How to Identify and Treat Kumquat Diseases

If you like to grow your own fruits and vegetables, you’re probably familiar with how devastating diseases can be to your crops.

Closeup of kumquats growing on a tree.

There are many different kumquat diseases with various causes, so it’s important to know what you’re dealing with to save your plants.

Keep reading this article to learn all about kumquat diseases, what to look for, how to treat them, and how to prevent them in the first place.


General Symptoms of Kumquat Diseases

Yellow or browning leaves that fall before they should are always an indicator that your tree is struggling. Lesions on leaves and fruit are another troubling sign of kumquat diseases.

Lemon tree leaf with signs of fungal disease.

Deformed fruits are definitely a symptom as well. If your tree just doesn’t look right in general, it’s time to carefully assess your tree to determine if it’s been infected.

The earlier you can catch kumquat diseases the better. The best way to do that is to check your tree regularly so you know as soon as any symptoms appear. Many kumquat diseases can be fatal if they’re allowed to progress, so don’t let them get that far.

It’s crucial that you accurately identify the kumquat disease afflicting your tree so you can properly treat it and prevent it from recurring in the future. Each disease has specific prescribed treatments.

Many kumquat diseases are transmitted by pests, and trees are more vulnerable when attacked by pests. Pest control is an important facet of disease avoidance.


Root Rot

Mushrooms -- a telltale sign of root rot, a common kumquat disease.
Mushrooms are a sign of root rot.

There are many different types of root rot, but all generally have the same effects and treatment.

Too much moisture in the soil causes the roots to degrade and can eventually kill the entire tree. As root rot takes hold, without being able to gather nutrients from the soil the tree will fail to thrive and will often drop leaves prematurely.

This is usually a result of overwatering or, if you live in a rainy climate, too much natural rainfall.

Treatment/Prevention

Root rot can typically be fixed by replacing all the soil around the roots and watering less frequently. A better watering method is to water further apart and in larger amounts to strengthen root systems. As a bonus, this will also make trees more resilient in drought conditions.

Opt for soil that drains well so the roots aren’t constantly sitting in wet earth. Our article on the Best Soil for Kumquat Trees will help you choose the right one for your tree.


Citrus Scab

Diseased grapefruit
Citrus scab lesions.

Citrus scab is a fungal kumquat disease that attacks the twigs, leaves, and fruit of the tree.

Symptoms are raised or flat irregular scab-like growths on leaves and fruit that start out grey or pink and darken with age. The fruit is still edible, but it’s not exactly pretty.

This kumquat disease can also cause younger plants to grow in bushier and struggle to bud out.

Humid climates will usually see more cases of citrus scab because it mainly spreads through contact with water. It can also be introduced by other plants that are already infected.

Treatment/Prevention

To treat, remove all affected areas on the tree and apply a fungicide according to the directions on the bottle.

Avoid citrus scab by using well-draining soil and be careful not to plant trees too close together.

Choose a sunny and dry area to plant your tree, control weeds around the tree, and prune the tree diligently for improved airflow.

Water trees from the base only to keep excess moisture off branches, leaves, and fruit.


Exocortis

An oak tree with gummosis.

Exocortis is a kumquat disease that affects the bark of the tree, which is its protective layer.

Signs of exocortis are lifting, drying, or cracked bark. You’ll often observe gum droplets where the bark has lifted; this is called gummosis.

It will also lead to stunted growth of the entire tree.

While it’s often not much of a risk to younger trees, exocortis can still affect older trees. This can lead to fewer fruits on the tree and also make the tree vulnerable to other problems.

Treatment/Prevention

This kumquat disease is highly contagious and incurable; fortunately, it’s unlikely to actually kill your kumquat tree on its own.

You can try being extra careful by sanitizing all of your gardening tools and anything else that will touch the affected tree. This can help other trees from succumbing as well.

However, the best way to stop it from spreading is to remove infected trees and destroy them.


Citrus Blast

Also known as black pit or bacterial blast, citrus blast is a type of fungus.

It usually gains access through damage from pests or other injuries to the plant, including where leaves have fallen off as a result of the disease.

Early signs of this kumquat disease are lesions on the leaves and wilted leaves. Next, you’ll see scabbing and twigs will begin to die off. Eventually, black spots will begin popping up on the kumquats themselves.

These symptoms will typically appear on the south-facing side of the tree. Without enough leaves to photosynthesize, your kumquat tree may eventually die.

Treatment/Prevention

Copper-based fungicide is your best option to resolve a case of citrus blast.

You can prevent it from returning by using wind protection for trees to avoid damage. You should also remove any diseased parts from the tree as soon as possible with a very sharp, sanitized knife or trimmer.


Algal Leaf Spot

A leaf with algal leaf spot on it.

Growers in warm and humid climates will have to watch out for algal leaf spot.

This parasitic alga enters through small cracks in the barn of kumquat trees.

It typically affects the leaves, but can also show up on twigs, branches, and even the fruit.

Leaves will begin to yellow and drop as this kumquat disease progresses. Canker will start to form on the bark, ultimately killing the branch it’s on.

Blotchy spots can be circular or irregular and gray-green to brownish in color. They will turn velvety and reddish-brown in summer when the alga reproduces.

Treatment/Prevention

In superficial cases, these spots can wash off in the rain or with a thorough spraying. A mild infection can be resolved by removing affected leaves and branches. In these situations, this kumquat disease is not typically a major threat to your tree.

For more extreme infections, regularly apply a copper fungicide.

Since this disease usually affects stressed plants, proper management will help prevent it entirely. Healthy plants are unlikely to die as a result of algal leaf spot.


Greasy Spot

Black spots on a citrus tree's leaves.

Another common kumquat disease in warmer areas is greasy spot.

Greasy spot is characterized by yellow, dark brown, or black lesions under mature leaves. These spots become darker as the disease progresses and will eventually show through to the top of the leaf.

Leaves will drop in fall and winter, putting the tree at a major disadvantage heading into the cold season.

Fruit will also show signs, with small necrotic black spots surrounded by green.

Greasy spot spreads on decaying leaves on the soil. The spores are disturbed and distributed when leaves get wet from rain or irrigation, then picked up by the wind and carried to nearby trees.

Treatment/Prevention

This kumquat disease is best treated with an oil and copper-based spray applied through May and June.

Be disciplined about cleaning up leaf litter to avoid allowing it to spread to your trees.


Anthracnose

Anthracnose in a citrus fruit.

Anthracnose, also known as blight, refers to several types of fungal kumquat diseases.

It usually appears in spring when conditions are wet. Visible signs include spots, lesions, and dead areas on leaves, dying twigs, leaves and fruit dropping prematurely, and spots on the kumquats. It will also likely cause stunted growth for the entire tree.

Treatment/Prevention

To treat a case of anthracnose, remove as much infected material as you can and weed carefully around the tree.

Apply horticultural oil to kill off the fungus and continue to do so several times throughout the year. Be careful not to water the tree from above, and prune your kumquat tree to allow sunlight and airflow to keep leaves and branches dry.


Protect Your Plants From Kumquat Diseases

Dealing with kumquat diseases can be disheartening, but don’t despair! These common afflictions can usually be treated.

Person holding a single kumquat in their palm.

Monitor your trees closely for signs of disease and treat them as soon as possible for the best chance of saving your tree.

Check out our Kumquats page for everything you need to know about growing these amazing trees!