Normally, magnolias are rarely attacked by pests or other diseases. Nevertheless, two pests in particular - scale insects and whiteflies - are quite common on magnolias and can permanently weaken the tree.
scale insects
Scale insects belong to the plant lice and are quite small insects, depending on the species between 0.8 and 6 millimeters long. Mealybugs and mealybugs in particular attach themselves to young shoots as well as to the underside of leaves and leaf axils and suck out the nutrient-rich leaf sap. The high-sugar food also leads to very sweet excretions, the so-called honeydew. This, in turn, magically attracts aphids and ants - so as soon as you notice large concentrations of ants on your magnolia, you should be suspicious. A greasy, black coating indicates a colonization of the honeydew with sooty mold, a fungal disease. Mealybugs spread very quickly and are difficult to get rid of.
Prevent and fight scale insects
Scale insects primarily attack weakened plants or plants that have been over-fertilized with nitrogen. Incorrect hibernation of the magnolia - for example in a warm living room - also promotes the infestation. If the magnolia is already affected, spraying the affected shoots and leaves several times with garlic, nettle or onion broth can help. Loosen the soil in the tree disc without hacking or digging deep. Mulch your magnolia or plant nasturtiums underneath.
white bow tie
In particular, the tiny ash whitefly (Siphoninus phillyreae) often afflicts weakened and/or over-fertilized magnolias. The insect, which is only about 1.5 millimeters long, lays its numerous eggs on the underside of the leaf. The larvae that hatch from them, as well as the adults, also feed on the plant juices that they suck from the leaves of the magnolia. They also excrete honeydew, which in turn promotes the formation of mold and sooty fungus. As a result, the magnolia sheds more leaves.
Fight whitefly
The whitefly has numerous natural enemies, including ladybugs and parasitic wasps. However, these are difficult to target on magnolias planted freely in the garden, so a special insecticide can help.
tips and tricks
If your magnolia sheds its leaves for no apparent reason, root damage by certain larvae, grubs, caterpillars or even voles can also be the cause. The vine weevil larvae in particular like to gnaw on the roots and leaves of the magnolia, they prefer - like their host plant - loose and humus-rich soil.