Although the lilac (Syringa) is considered to be quite robust and insensitive to diseases, it can of course still get it. The various pathogens - which include fungi as well as viruses and bacteria - are widespread in nature. You can only try to make the lilac strong and resistant to infection by choosing a suitable location, sufficient planting distance and good, species-appropriate care.
Diseases are usually first seen on the leaves
blossoms
If the lilac does not bloom, there is not always a pathogen behind it. In most cases, the location is just too dark or the plant is not getting enough nutrients. A possible waterlogging (caused, for example, by watering too often or too much rain) can also be behind it. In these cases, a change of location or a supply of fertilizer helps.
leaves
In many cases, diseases become noticeable on the leaves, although other parts of the plant such as branches and trunks can also be affected later on.
- Leaves turn yellow
If the lilac gets yellow leaves, there are usually location problems behind it: either it is too dark for the plant, too wet (waterlogging) or it lacks nutrients. Replant them or provide them with suitable fertilizer.
Leaves are light green
Light green leaves with dark green veins are a clear indication of iron deficiency. Treat the so-called chlorosis with the administration of an iron fertilizer. You should also check the location, because this phenomenon occurs mainly on soil unsuitable for lilacs. You should also remove any mulching (e.g. with bark mulch).
Leaves have brown spots
Brown spots on lilac leaves can look very different and accordingly have different causes. Fungi are usually behind it: Ascochyta syringae (large, brown-edged spots), Gloeosporium syringae (very large, brown spots), Heterosporium syringae (grey-brown spots with a velvety surface) and Septoria syringae (yellow-brown spots). Furthermore, the bacterium Pseudomonas syringae initially causes light to dark brown leaf spots and finally shoot rot. Appropriate measures in all cases: Remove or cut back infected parts of plants, remove fallen leaves and spray lilacs with field horsetail decoction. In the case of a severe infestation, a copper spray from the garden store will help.
Leaves have a whitish coating
Mildew fungi are quite common on lilacs. Special measures are basically not necessary, but you can prevent an infestation by spraying with field horsetail or garlic broth in the spring. Diseased parts of the plant are cut back and discarded.
shoots, branches and trunk
Wilting in lilacs can also have very different causes. For example, lilac disease caused by the bacterium Pseudomonas syringae and wilt disease caused by Verticillium fungi are common. In both cases, you should immediately cut diseased parts of the plant back deep into the healthy wood and dispose of the clippings in the household waste or burn them.
root
You also have to be careful with honey fungus, which likes to attack old lilacs and causes root rot. When infected, only uprooting the tree and eating the mushrooms will help.
tips
Many of the symptoms described do not necessarily have to be caused by pathogens. Many pests also like to feed on lilacs.