Walnut tree: 6 recognizing and combating diseases and pests

Of the Walnut tree delights us not only with the tasty, versatile and healthy walnut, moreover The imposing tree enriches gardens, garden plots and orchards with its abundance and Grandeur. Every hobby gardener should be able to identify and combat diseases and pests at an early stage so that both the visual enrichment and the yield are permanently secured. Here you will find everything you need to know about the most common pests and diseases of the walnut in a nutshell.

Diseases

Although the number of diseases theoretically possible in the walnut tree is enormous, the diseases that actually appear can be limited to a handful of pathogens.

Bacterial burn

cause

• Xanthomonas juglandis bacterium

Appearance

• black, water-soaked round spots on leaves, young shoots and fruits
• partly with a yellow border
• in the further course the spots flow into one another to form extensive, mostly sunken black areas

transmission

• mostly overwintering or The latent pathogen is resting in dormant buds
• Outbreak with rising temperatures and high humidity
• subsequent infestation of young tissue, older tissue, on the other hand, usually less susceptible

follow

• Young shoots die off
• premature leaf and fruit drop

remedy

• no effective control possible, as effective pesticides are not available, infected areas are difficult to identify and finally to remove
• Disease to be accepted, especially in wet years

Anthracnose

(also Marssonina disease)

cause

•  Mushroom Gnomonia leptostyla (formerly also called Marssonina juglandis)

Appearance

• very similar to bacterial burn in the initial stage
• small black, mostly angular spots on leaves and fruits
• on the underside of the leaf in the area of ​​the spots, often rings of dark, brown to black dots - fruiting bodies of the pathogen

transmission

• Transport of the mushroom spores through the air after the mushrooms have been overwintered in frost-hard capsules in dead walnut leaves
• Release in damp weather by throwing off the spores and release into the air

Attention: In contrast to bacterial burn, old tissue on the walnut tree is far more susceptible than, for example, young leaf tissue!

follow

• premature shedding of severely infected leaves
• Infections of the leaf veins and shoots only very rarely

remedy

• Control is currently not possible, as the use of fungicides is currently not permitted

tip: The removal and destruction of the dry leaves under the walnut tree in autumn effectively prevents an infestation in spring and prevents an intensive infestation from the start!

Shell fragility

cause

not known

Appearance

• incompletely formed, thin shell of the walnut, so-called. "Paper nut"
• partially holey shell, especially on the nut tip

transmission

• not known
• Occurrence more often in rainy, cool years with little sunshine

follow

• Damaged nuts either fall off or are at least more susceptible to parasites and other pathogens
• If the skin is perforated, the fruit will usually spoil due to mold or rot

remedy

• not known, as the cause has not yet been clarified

In addition, there are other clinical pictures, but each of them occurs to such a small extent that they almost have to be regarded as exotic. A detailed consideration from the point of view of the hobby gardener does not make much sense because the exemplary one The selection would be just as arbitrary, the occurrence of exactly these selected diseases on the native tree. Examples of these unspecific and rarely encountered diseases are:

• Powdery mildew - recognizable by a whitish, floury coating on the leaves
• Stem and bark cancer - recognizable by changes and growths in the bark
• Wood rot - recognizable by changes in the wood structure up to the softening of entire trunk segments, as well as by the causing fungi, e.g. B. Hallimasch or sulfur pork
• Phytophthora diseases - lead to degeneration of the roots, recognizable by yellowed leaves, poor growth and drying young shoots

Pests

In addition to diseases, pests also threaten the walnut tree and the walnut itself. However, the most common pests can be easily identified and taken under control by taking appropriate countermeasures:

aphid

Appearance

• sucking pest with an elongated, transparent to greenish body
• Body length a few millimeters

Damage

• The accumulation of aphids can usually be seen on the underside of the leaves
• there biting of the plant veins for nutrition via the plant sap
• Actual damage only when it occurs enormously, then initially curling up, and later drying out of infected leaves

remedy

• in the case of moderate infestation, no immediate pressure to act
• Ideally, only cut off and remove affected twigs when the infestation is intense
• Combating severe damage with chemical or “natural” insecticides, for example by spraying with potash soap or rapeseed oil

tip: An intensive aphid infestation can be effectively prevented by the settlement of the aphid's natural predators. These include ichneumon wasps, ladybirds and lacewings.

Blue caterpillars

Appearance

• yellowish white body
• covered by point warts
• Body length up to 6 centimeters

Damage

• Dying of shoots and whole branches by drilling through the bark and creating feeding tunnels in the wood

remedy

• effective control hardly possible
• Cut off and remove affected shoots
• however, if the trunk is infested, it is usually necessary to fell the tree

Walnut fruit fly

Appearance

• yellow, elongated body with black tip on the abdomen
• The wings are transparent with black horizontal stripes
• Maggots yellowish-white
• but mostly more recognizable by the damage caused

Damage

• Damage to the walnut through penetration into the pericarp and duct corrosion
• initially black dots are formed on the nutshell, which is still green
• later watering of the peel and development of an increasingly soft consistency

remedy

• After infestation, collect infested nuts and dispose of them

Tip: In order to avoid an infestation and thus a reduction in the yield of the walnut right from the start, the flies can be kept away with yellow boards that are hung in the tree. Even more effective, but also more complex, is the tensioning of the entire tree with a fly net.

Leaf damage

Regardless of a single cause, numerous caterpillars and beetles cause leaf damage. However, as long as this occurs only sporadically, there is usually no danger for the tree or the hoped-for yield. If certain caterpillar species occur on a massive scale in individual years, a tree can be severely affected by this. In these cases it is worthwhile to identify the infesting species early and then to determine suitable control methods.

As with the clinical pictures, there are numerous other parasites that the walnut tree, however, does not specifically affected, but appear here in a very low frequency, as in many others Tree species. A detailed designation and explanation should therefore be dispensed with. These parasites include, for example:

• Willow Borer - Damage to the branches and trunk from duct drilling
• Gall mites - damage to the leaves caused by so-called "gall", in some cases complete destruction of infected leaves
• Butterfly caterpillars - recurring invasively, then unspecifically devouring entire tree populations