Mulberry trees have the potential to thrive for at least 75 years and reach a striking height of 30 to 50 feet.
As robust as these stunning fruit trees are, they can be vulnerable to certain diseases when conditions are less than perfect. Let’s look at potential diseases of the mulberry tree and how to control them.
A tree disease can indeed be worrisome, but mulberry trees can, unfortunately, have other issues as well. Learn what to watch for and how to handle obstacles in my detailed guide, Mulberry Tree Diseases, Pests & Problems.
1. Powdery Mildew
This fungal plant disease shows up on leaves and twigs as a gray-whitish powdery coating and usually occurs when air can’t circulate well through the tree.
Improper watering and shady planting locations also contribute as moisture that can’t dry properly on the tree breeds mildew.
Powdery mildew can stunt new growth and cause general stress to the tree, inviting unwanted pests.
Help prevent it with adequate pruning to increase airflow, and clear fallen leaves beneath the tree, and dispose of them or burn them (don’t compost them) to prevent the fungal spread to other garden plants.
Planting resistant varieties can help too.
How To Manage
- Spray diseased foliage with systemic fungicide (products containing sulfur like this one or neem oil are very effective).
- For widespread infections, prune off all diseased leaves with sterile pruning tools, and disinfect between uses with rubbing alcohol.
2. Leaf Spot
Leaf spot appears as small circular gray/tan spots that eventually merge to form holes. Heavy rainfall and wind in summer cause spores of the pathogen to spread from fallen foliage onto healthy leaves.
In older trees, leaf spot can lead to defoliation and premature leaf drop, though this is benign on younger trees.
Whatever the age of your mulberry tree, you can keep this at bay by cleaning up all fallen foliage, weeds, and debris to prevent spores from overwintering on the ground.
Male fruitless mulberry trees tend to be most susceptible, so avoid planting these types where possible.
How To Manage
- Apply a broad-spectrum fungicide like this one for severe cases (defoliation).
- Remove and destroy infected leaves as you spot them.
3. Leaf Blight
Leaf blight can cause foliage to wilt and dry up, turning brown or black. Consistently warm and wet weather triggers this as certain bacteria thrive in these conditions.
Pollinating bees can also spread the disease around the tree on their travels.
In the long term, leaf blight causes entire twigs to hang down and develop a sunken, dark appearance, leading to large areas of dead foliage.
You can help prevent it by maintaining a well-ventilated canopy and avoiding fertilizer with excess nitrogen in spring as this encourages susceptible early growth.
How To Manage
- Prune dead or broken twigs and shoots in the fall and inspect the canopy for general crowding.
- Remove infected twigs or branches (i.e., sunken or blackened hanging growth), and disinfect pruning tools between uses.
4. Bacterial Blight
This causes small black spots to appear on the leaf surface, flowers, or fruit and can also appear as back stripes on the twigs.
Bacteria that survives on the soil surface spreads via rain splashes and is helped along by cool and moist spring weather.
Limbs affected by the bacteria struggle to produce new growth, and buds and twigs may dieback as summer temperatures arrive, leading to a sparse canopy.
Try to prevent bacterial spread by avoiding overhead watering and applying a preventative fungicide in early spring.
How To Manage
- Prune and destroy infected growth during the dry season when new infections are less likely.
- Soil-borne pathogens like bacterial blight can sometimes be treated and killed off with the help of soil solarization.
5. Bacterial Leaf Scorch
Foliage affected by this begins to brown around the edges as if scorched by fire before eventually dropping.
Dry soil conditions and high heat/humidity can contribute to bacterial leaf scorch, though glassy-winged sharpshooters are commonly known to transmit the disease-causing bacterium Xylella fastidiosa.
Left to fester, this can quickly spread to large areas of the tree. Deterring leafhoppers like glassy-winged sharpshooters from feeding is a good preventative step.
Apply diatomaceous earth to your soil, or spray trees with organic insecticidal soap.
How To Manage
- Prune infected leaves and improve your watering to maintain moist soil.
- Check if your soil has the necessary nutrients, and enrich where necessary.
6. Rust
This appears as irregular red or rust-colored pinhead-sized dots on the leaves that grow darker to dark brown spots over time. It’s often caused by a lack of air circulation during winter and rainy seasons.
If left untreated, rust will cause entire leaves to yellow before dropping prematurely.
Where possible, prevent rust disease from taking hold by spacing mulberry trees far apart to promote better airflow (trees require between 8 and 30 feet spacing for dwarf and full-sized mulberries respectively).
How To Manage
- Affected foliage can be treated with a spray of carbendazim fungicide, though mild symptoms may subside on their own.
7. Armillaria Root Rot
Armillaria root rot usually manifests as yellow or browning leaves that drop prematurely. Red or brown mushrooms can also appear at the base of the trunk.
This fungal disease occurs when mycelium fungi survive in the decaying wood of nearby stumps or dead trees.
This disease is notoriously hard to control once present and can cause entire branches and trees to die, so planting disease-resistant stock is recommended.
Preventing general tree stress with good watering practices, fertilizer, and pest control measures can also help.
How To Manage
- Diseased plants and stumps should be dug up and removed if possible. Consult the help of a professional tree surgeon when in doubt.
8. Cotton Root Rot
Cotton root rot causes leaves to turn yellow/bronze before wilting and is caused when new roots come into contact with decaying roots or old diseased material in the soil.
Left to fester, this root-rotting disease can lead to reduced vigor and the fast decline and death of your tree within weeks. Maintaining healthy soil conditions is key to preventing cotton root rot.
The fungus thrives in compacted and perpetually moist clay soils with a high pH. Using fertilizers with excess nitrogen can reduce the soil’s protection against microbial diseases, so make changes as needed.
Also, avoid planting white mulberry trees as this species is most susceptible to cotton root rot.
How To Manage
- Improve soil drainage and add sulfur products to lower high soil pH.
- Allow soil to dry well in between watering.
- Consult a professional arborist for a full diagnosis as cotton root rot can spread to surrounding plants.
9. Canker
Sooty canker displays symptoms such as discolored wet spots on branches, peeling bark, and wilting leaves.
This fungal disease commonly affects stressed trees with exposed cambium tissue due to sunburn or over-pruning.
Once spores have entered this exposed inner tree tissue, they can spread and kill off entire trees within years.
Maintain good watering and fertilizer practices to keep trees in vigorous shape, and take care when pruning or using machinery near your tree to avoid bark damage.
How To Manage
- Prune and destroy all infected branches and leaves, and be sure to disinfect tools between each use.
- Paint wounded areas of bark with canker paint (a copper fungicide such as Bordeaux mixture).
10. Mulberry Ringspot Virus
Trees with the ringspot virus develop a yellow line or mosaic pattern on the leaves, sometimes resembling the outline of an oak leaf.
This virus is thought to spread through infected seeds and plant propagation methods. It’s also believed that bees transmit pollen infected with ringspot virus.
Adult trees can show recovery from symptoms, but young trees may suffer from long-lasting stunting if the ringspot virus gets out of hand.
Where possible, always try to plant certified virus-free mulberry tree cultivars, and consult tree nursery specialists about this as some nurseries use thermotherapy to eliminate the virus.
How To Manage
- There is no cure for the virus other than to remove infected trees, so young saplings may need to be removed by hand to prevent further infection.
11. Mulberry Yellow Dwarf Virus
Yellowing leaves due to reduced photosynthesis ability and generally stunted growth can be signs of mulberry yellow dwarf virus, which is normally spread by aphids transmitting the virus to leaf cells as they feed.
Long-term effects of this virus can result in poor foliage yield so employing aphid deterrents throughout the season is crucial.
Planting pungent companion plants next to your mulberry tree such as garlic, onion, and nasturtiums is recommended.
How To Manage
- Spray foliage with organic insecticide sprays to control aphid numbers before the infection becomes widespread.
12. Mulberry Dwarf Disease
Mulberry dwarf disease causes leaves to grow small and yellow and is caused by the bacteria phytoplasma. This is commonly transmitted by leafhopper insects via their salivary gland secretion as they feed.
Trees that are significantly affected by the virus can experience stunting and a deformity in the wood known as “witch’s broom” in which a dense mass of growth grows out from one point.
To help prevent this, plant pathogen-free varieties where possible, and maintain sanitary tree practices such as using sterile pruning tools, promptly removing weeds and debris, etc. to limit contamination.
How To Manage
- Prune out branches with infected foliage.
- Control and deter leafhopper numbers with the use of sticky traps, predatory insects, and other methods.
13. Fusarium Wilt
As the name suggests, trees infected with the Fusarium fungi will display wilted foliage. Lower leaves can also appear yellow and turn dry.
Fungal spores can spread via infected cuttings, contaminated tools, hands, or plant debris and enter the soil, reducing water transportation in the tree.
Tree roots can rot in the later stages of the disease, and large parts of the tree can die back.
Taking care to practice good sanitation around your tree (wearing gloves and disinfecting pruning tools in a bleach solution or rubbing alcohol) can help.
How To Manage
- Remove weeds as these can host the fungi.
- Apply the biological fungicide Mycostop as a soil spray/drench with water to send the fungicide to the root zone.
14. Verticillium Wilt
This is caused by the soil-borne fungi Verticillium dahliae, which enters through the roots and suffocates the tree’s water-conducting tissues.
Shriveled or yellowing lower leaves and branch dieback are common symptoms as well as brownish or black streaks on the tissue beneath the bark.
Hot weather can cause most or all of the tree to suddenly wilt, and trees may recover in cooler or wetter conditions.
Verticillium wilt cannot be cured, but trees may be able to live with the disease with regular watering to prevent stress and therefore severe infection.
How To Manage
- Prune dead or discolored branches, and carefully disinfect pruning shears with a 70% alcohol or 10% bleach solution.
- Destroy diseased twigs, branches, and leaves to prevent further soil contamination.
15. Wetwood
Bacterial wetwood or slime flux appears as large discolored dark patches on the bark with a rancid-smelling slimy ooze that can be pink or orange on closer inspection.
Wetwood is caused by various bacterium and yeast microorganisms that overwinter in soil or water and splash up into tree wounds via rain and wind.
Prolific wetwood infections can cause widespread branch dieback and foliage wilt.
Wetwood cannot be cured, so wound prevention is best. Take care to avoid injury to the bark and wood with pruning tools and equipment.
How To Manage
To limit the unsightly appearance, the University of Wisconsin Horticulture Extension advises inserting a long plastic tube at the site of the infection to direct the ooze away from the trunk toward the ground.
16. False Mildew
Similar in appearance to powdery mildew, false mildew displays a cobweb-like film on the undersides of the leaves that is gray instead of white like true mildew.
High humidity and stagnant airflow in the canopy help these fungal spores survive, leading to stunted growth and general stress if the mildew is left to spread.
Prevent reinfection of the fungus by clearing away leaf litter and debris and pruning broken or crossing/rubbing branches to promote better circulation and sunlight exposure.
How To Manage
- As soon as infection appears, spray leaves with a mildew-treating fungicide until signs of the disease subside.
17. Popcorn Disease
As the name suggests, this disease causes the mulberry fruit to swell, resembling unpopped corn kernels!
This usually only occurs in the southern states and is caused by the fungal pathogen Ciboria carunculoides, which invades during flowering and contributes to greatly enlarged ovaries.
Popcorn disease causes mulberry fruit to mature and drop prematurely, where the infection cycle risks repeating in the soil.
Avoid planting Morus alba (white mulberry) hybrids as they are prone to this disease, and collect and destroy all fallen fruit and debris.
How To Manage
- After removing infected fruit, apply Bordeaux mixture fungicide to help control the spread.
Closing Thoughts
Diseases can be spread to your mulberry tree by a cocktail of pest transmission and extreme weather conditions, but these diseases can take hold and cause greater damage if you are not vigilant with your tree care and maintenance.
As most diseases love shade, moisture, and poor soil conditions, assess your everyday care habits to keep stress to a minimum. Try to plant disease-resistant varieties when possible too.
The more you know, the more equipped you’ll be to tackle any tree problem that comes your way. Learn more by reading these articles next:
- 20 Common Mulberry Tree Pests To Watch For (+ Solutions)
- 16 Common Mulberry Tree Problems and How To Correct Them