Recognize diseases and treat them successfully

The most common diseases of the elm

• the Dutch elm disease
• fungal leaf spot pathogens

The Dutch elm disease

It starts with the elm sapwood beetle. Once the pest has transmitted the wilt fungus, the elm usually dies within 2-5 years. Dutch elm disease is considered the most dangerous disease of the deciduous tree and has claimed numerous victims since it spread across Europe and North America. The disease originally comes from Asia and came to the Netherlands via timber imports. The fungus cuts off the water supply to the elm, so to speak, by clogging the channels in the trunk. Some species of elm, such as the golden elm, are less susceptible to this disease, while others, such as the field elm, are severely affected. Unfortunately, experts are still looking for a reliable control agent.

Fungal leaf spot pathogens

Fungal leaf spot pathogens include

• the Phloespora leaf spot disease
• and Platychora leaf spot disease

You can recognize the former disease by yellowish spots on the leaves of the elm, which turn brownish after only a short time. In addition, fruit bodies develop on the underside of the leaves, which soon produce white, fluffy tufts. A layperson often confuses Phloespora leaf disease with a mineral deficiency due to the similar symptoms. Don't be too sure if the fungus suddenly disappears. It only hibernates in fallen leaves, but reappears next summer. A fight applies only to the optics. The fungus does not cause much damage.
Shady locations and high humidity promote the infestation that causes Platychora leaf spot disease. The black spots, bordered by a dark green halo, are clearly visible with the bare eye recognizable. The fall foliage is primarily affected, which means that this fungus is also relatively harmless.