Healthy magnolias are quite resistant to pest infestation and other diseases. A disease is therefore always to be seen as a symptom that your magnolia is weakened and therefore vulnerable due to an unsuitable location or incorrect care. In particular, the following diseases are common in weakened magnolias.
leaf spot disease
Leaf spot disease is caused by Pseudomonas bacteria, which are mainly found in raindrops or rainwater. It occurs mainly in warm but humid weather and is characterized by black spots surrounded by a yellowish halo or even holes on the leaves. As a result, affected shoots die. This very widespread plant disease is also a problem for deciduous magnolia species, because the bacteria overwinter in the shoots and often cause frost damage.
Combat leaf spot disease
Leaf spot disease is best combated through prevention: it is important that the crown of the magnolia is not too dense, but rather lets in enough light and air. The leaves should always be able to dry quickly, which is why you should never water from above (especially not with rainwater) in summer, but only directly at the roots. In the event of an infestation, the affected parts of the plant must be removed as quickly as possible.
mildew
There are two different types of powdery mildew, both of which initially show up as a whitish or greyish coating on the leaves. The leaves later turn brown and fall off. This plant disease is caused by Erysiphaceae fungi.
Prevent and combat powdery mildew
Powdery mildew can be combated very well with a garlic broth or lactic acid. For the latter, mix one part whole milk with nine parts water and mist the magnolia over a period of several days. In the case of a severe infestation, only fungicides can often help. Affected shoots and leaves should be removed immediately, as powdery mildew spreads very quickly.
pest infestation
Weakened magnolias are often attacked by whitefly or scale insects, whose excrement promotes fungal diseases (e.g. sooty mold) and aphid infestation. The roots, on the other hand, can be eaten by larvae or caterpillars that live underground and thus damage the tree. In particular, voles and weevil larvae like to feast on the juicy magnolia roots.
tips and tricks
Prevention is better than cure, so you can help endangered magnolias with a special fungicide fertilizer to get rid of annoying pests quickly. By the way, dried coffee grounds should also help.