Marssonina leaf spot is the most common fungal disease in walnut trees. In this article you will learn everything about the causes, symptoms and how to combat the dreaded walnut disease.

The Marssonina fungus leaves ugly stains

Portrait of Marssonina leaf spot

Marssonina juglansis, as the disease is known in Latin, is also known by the names walnut scab, leaf blast and anthracnose.

The pathogen Gnomonia leptostyla acts as a trigger. Interesting fact: This pathogen was originally called Marssonina juglansis and thus gave its name to the disease.

Like any mushroom, Gnomonia leptostyla also thrives particularly luxuriantly in damp weather and moderate to warm temperatures.

Symptoms of Marssonina disease

First, the appearance of the leaves and pericarp changes. Similarities to another walnut tree disease, walnut blight, cannot be denied in the early stages.

Both diseases show brown, square-shaped spots on the leaves and pericarp. These spots quickly grow in size until they cover almost the entire leaf or fruit and eventually even merge.

Bright centers are commonly revealed in these brown spots. The brown spots look like they have been burned and are so dry that some of the tissue is breaking out and only the veins and stalks remain. Sometimes the leaves fall off too.

On the underside of the leaf there are small, black-brown, ring-shaped dots with typical spore appearance. This collection of spores allows differentiation from bacterial blight.

If the fungal infestation is severe, it weakens the entire walnut tree, which can also lead to premature fruit drop. However, the direct effect on the walnuts is much worse: the spores attack the green fruit shell and often penetrate into the kernel (especially in young fruits with a soft wooden shell) - the consequences are

  • a black wooden bowl,
  • an infested nut kernel and
  • blight.

Good growing conditions for the fungus

  • wet springs and summers
  • rain showers and wind*

* Rain showers and wind "help" wash away and spread the spores.

Incidentally, here (in contrast to bacterial blight infestation) older leaves are significantly more susceptible than young ones - they offer the spores more breeding ground.

Combating Marssonina disease in a targeted manner

  • Carefully collect the foliage and fruit of infested walnut trees.
  • Do NOT put the collected plant parts on the compost, but burn them if possible or otherwise throw them in the organic waste bin.

Prevention of Marssonina leaf spot

Regular pruning will prevent this walnut tree disease.

In addition, when planting new plants, you should always choose varieties that have a basic resistance to the pathogen (Gnomonia leptostyla).

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Vegetable garden