The Norway maple is very robust, but the plant is not immune to some diseases. Verticillium wilt in particular can cause considerable damage to Norway maples.
The Norway maple (Acer platanoides) is a robust plant. The plant is very well adapted to our climate and even finds a habitat in the cities. Nevertheless, diseases and pests are not entirely absent. It is not uncommon for care errors to be the cause of ailing plants. Thus, hobby gardeners can do a lot to keep the Norway maple he althy.
The Norway maple is particularly susceptible to the following diseases:
- Powdery mildew
- Verticillium Wilt
- Tar spot disease
Read below how to identify diseases and pests and what you can do about them.
Powdery mildew - common but harmless
Powdery mildew infestation is common in specimens planted in cities. Uncinula tulasnei is a type of powdery mildew found on Norway maples. Although powdery mildew occurs quite frequently, no lasting damage to the plant is to be feared.
Recognize:
An infestation cannot be overlooked visually. The leaves are covered with a white coating reminiscent of flour.
Fight:
Remove all infected leaves. These do not belong in the compost and should not be left on the ground. The fungus would survive the winter on the leaves and cause damage to the shoots again in the spring.
» Tip: Burn infested plant parts or dispose of them with household waste.
Powdery mildew can be combated quite reliably with a proven household remedy. Mix fresh milk and water in a ratio of 1:9 and spray the leaves vigorously with it. This treatment should be carried out every other day until no more infestation can be detected. It becomes more difficult with larger trees where you can no longer easily reach the leaves. In this case, remedies should be used that can be administered via the irrigation water.
Verticillium Wilt - The Aggressive Fungus
Verticillium wilt is widespread and affects hundreds of plant species. More than 70 trees are affected. In addition to the maple, elms and lindens are also increasingly at risk. The damage caused by Verticillium wilt on strawberries or hops is particularly drastic and associated with considerable economic damage. The soil-borne fungus has clearly been on the rise in the last 20 years.
Recognize:
The fungus wilts leaves and flowers. Cracks appear in the trunk, especially on maple. Brown to greenish discolorations appear. Trunk necrosis occurs particularly in the lower part of the trunk. At first glance, the hobby gardener might think his Norway maple lacks water. It can happen that the leaves begin to wither and fall off in the middle of summer. This is usually not the result of a watering error, but can be explained by the fact that the fungus is blocking the water channels of the plant.
» Tip: When Verticillium wilts, the older leaves are affected first. Younger leaves initially continue to grow as usual. In the later course, the younger parts of the plant also fall off and the entire plant dies.
The fungal disease often occurs in hot summers and during longer periods of drought.
Fight:
Verticillium wilt is quite aggressive, especially since no suitable means have yet been found against the pathogen. All parts of the plant affected by the fungus must be removed immediately. Cut back into he althy tissue.
» Warning: Norway maple does not tolerate pruning very well. A lot of sap escapes and the tree threatens to bleed out if the wounds are not closed with a special agent.
However, these measures often come too late and the plant can no longer be saved. To stop the fungus from spreading further, remove the entire plant along with its roots and replace the soil before replanting.
Prevent Verticillium Wilt
You can already do a lot for the he alth of the Norway maple when planting. Create optimal site conditions and ensure an adequate supply of water and nutrients. A sunny to partially shaded location is best for the Norway maple. Young plants need adequate watering. The plants should not dry out, but should not be too wet either. This quickly creates waterlogging, which thedamages roots. Ailing plants are far more susceptible to Verticillium wilt.
Avoid susceptibility through proper plant care
❶ Make sure the soil is permeable, which allows the irrigation water to drain off well and protects the plant from waterlogging.
❷ Be careful when planting and don't damage the sensitive roots.❸ Mix compost and horn meal (e.g. available here) into the substrate. This ensures natural fertilization and keeps the plant he althy.
When pruning, use sharp and clean gardening tools and seal the cuts of the plant with clay or pruning compound.
Tar spot disease - danger for the leaves
Tart spot disease is also quite common on maples. The infestation can be easily recognized by the black leaf spots. The mycelium appears more distinct from year to year, developing from small, yellow-edged black spots to conspicuous black bulges on the leaves. The spots are about one centimeter in size and the yellowish edge is clearly visible. Initially, the leaf spots still appear yellowish-green. The entire leaf is affected.
Tar spot disease is also known as maple wrinkle scab. In the spring of the following year, the fruiting body develops from the fungal networks, which are also known as the stroma. The black leaf spots bulge and get a rather irregular structure. Spores are shed in spring and infect young leaves.
Fight:
No further action is usually required. Leaves should be carefully removed and disposed of in autumn. If the infestation is massive, it can make sense to use appropriate means to combat it in spring.
» Tip: Tar spot disease is far less common on trees planted in cities than on forest trees where regular leaf removal is not performed.
At a glance:
| Diseases | Features | Combat |
| Powdery mildew | There is a whitish coating on the leaves, reminiscent of flour. | Sprays with a water and milk mixture can help.
In the case of larger trees, add suitable agents to the irrigation water. Remove and discard affected leaves. |
| Verticillium Wilt | The leaves wither and fall off.
First are the older leavesaffected. Sudden leaf drop occurs in the middle of the growing season. The damage resembles a plant that has not been watered enough. | So far, no suitable means exist.
The disease can be prevented by optimal site selection and nutrient supply. |
| Tar spot disease | Black spots with yellow edges are visible on the leaves. These grow into ulcer-like necrosis. | The leaves must be completely removed and disposed of in autumn so that the fungus cannot spread further. |
Is the Norway maple attacked by pests?
The aphid is a permanent guest on the plants. However, there is no risk of lasting damage from the pests. The hobby gardener does not have to intervene here. The work is done quite reliably by the predators of the aphid.
Anyone who lives in rural areas should protect the trunks of the Norway maple from deer browsing. Rabbits especially prefer maple trunks.