Although the walnut tree is one of the most robust tree species, it is not completely immune to diseases. In this guide, you will learn about the most important problems and learn how to deal with them.
The Marssonina fungus leaves ugly stains
Overview of the most common walnut tree diseases
Essentially can
- fungi and bacteria as well
- Insects (including larvae)
lead to diseases in the walnut tree.
Walnut diseases caused by fungi and bacteria
- Marssonina leaf spot disease
- Bacterial walnut burn
- Powdery mildew fungus
- Fungi of the genus Nectria
These four diseases occur on the trunk and bark and provoke the development of bark canker.
- honey fungus
- Sulfur Porling
- Shaggy Schillerporling
- Scaly Porling
- ash tree fungus
These five fungal species are broad-host-spectrum pests. They are responsible for wood rot.
Walnut tree diseases caused by insects
- walnut toad gall mite
- Striped walnut ornamental louse
- Woolly scale insect
These three insects trigger leaf damage. In young plants, they can cause stunted growth.
- willow borer larvae
- blue sieve larvae
Both of these genera cause structural damage to the trunk of the walnut tree.
The maggots of the so-called walnut fruit fly are also a typical problem.
Note: In addition, Phytophtora can damage and degenerate the roots of walnuts. Phytophtora refers to a genus of plant-damaging protists. These are microscopic creatures. Symptoms of Phytophthora disease: stunted shoots, yellowed leaves, light crown.
A portrait of selected walnut tree diseases
We give space to Marssonina leaf spot (most common walnut tree disease) in a separate article. Here we want to focus more intensively on bacterial walnut smut and walnut fruit flies - two other diseases or pathogens that often occur.
Bacterial walnut burn
Bacterial blight is a walnut tree disease that can be found in Germany as well as in other European countries.
Rain and wind spread the bacteria. Crevices, cracks and other wounds on the leaves and wood allow the pests to get in - moisture acts as a catalyst.
The bark of the walnut tree is usually attacked in autumn. From the following spring, the plant will show signs of
- Bark canker (woody growths) or
- Bark blight (dark bark, top layer peeling off).
The leaves of the walnut reveal light spots. As a result, they turn brown. Finally the leaves fall off. Affected flowers appear burnt.
Here’s how you can fight (or prevent) bacterial walnut smut:
- plant resistant varieties
- Avoid nitrogen-rich fertilizers
- Thin out the crown regularly
- only cut with disinfected tools
- Perform pruning on dry days
- Cut off the affected areas down to the healthy wood
- DO NOT dispose of infested plant parts in the compost
walnut fruit fly
Walnut fruit flies are insects that lay their eggs in walnut fruit. Up to 30 larvae hatch inside and eat their way out through the pulp. Luckily, the actual walnuts remain intact and are still safe to eat.
Note: In commercial agriculture, infested nuts have to be cleaned in a time-consuming process in order to be salable.
Here's how you can fight (or prevent) walnut fruit flies:
- Gather walnuts daily
- from mid-June lay a close-meshed net under the crown of the tree
The second measure prevents the maggots from hatching. In hot summers, fruit flies even die under the warm net.