The robust lilac (Syringa vulgaris) has been growing and thriving in gardens and pots in Germany for many hundreds of years. The shrub or small tree is considered to be less susceptible to disease and easy to care for - but you have to be particularly careful with fungi, especially after unfavorable weather or a wrong cut there is a risk of fungicidal infection.
Brown leaves are often an indication of a fungal disease
Lilacs are prone to fungal diseases
Above all, fungi are targeting the lilacs, which are susceptible in this respect: There is a risk of infection after severe pruning if the fresh wounds cannot close quickly enough or if the cutting tool has not been disinfected before use. But also a location that is too damp (perhaps with heavily compacted soil), damp weather, severe winter frost or fertilization with a strong emphasis on nitrogen can promote the penetration and growth of fungi. Brown leaves are mainly caused by these pathogens:
- Lilac disease or lilac blight (Pseudomonas syringae)
- Leaf spot disease (Ascochyta syringae)
The only thing that helps with both causes is a strong pruning deep into the healthy wood. Only cut with disinfected tools on a dry, frost-free day that is as warm as possible.
Brown spots often come from the lilac leaf miner moth
The lilac leaf miner or lilac moth (Gracillaria syringella or Caloptilia syringella) occurs not only on lilacs, but also on other woody plants. An infestation is indicated by the feeding spots on the leaves, which are black-brown in color and irregular. If you look closely, caterpillars should also be visible in early summer. The leaves later dry up and fall off. Control is mainly possible when the leaves shoot out, then you should spray the lilac several times with neem.
tips
If you cultivate your lilac in a bucket, you shouldn't just cut it back above ground every two years: the roots also need to be cut back by around a third. Otherwise, the plant will soon no longer have enough space in the bucket and will respond with poor growth, no flowers and brown leaves.