The magnolia tree is known for its beautiful spring blossoms and spreading branches. Just like a variety of other ornamental trees, it is susceptible to fungal disease as well as infestation by pests. Among these pests are sap suckers that attack the magnolia tree by sucking the sap, weakening the tree. The amount of damage caused to the magnolia depends upon the amount of infestation and the pest involved. Sap sucking pests include aphids, scales, spider mites and white flies.
An aphid infestation will produce the following symptoms on a magnolia: new growth will exhibit leaf distortion, deposits of honeydew and sooty mold. Aphids suck the sap from plants and cause the leaves to curl up, wilt or die. Honeydew--waste material--is excreted by the aphid. If the magnolia tree has been infested by a large number of aphids, the honeydew will be a problem. This sticky substance can cover patios, sidewalks and leaves and branches. A large amount of honeydew will cause sooty mold, which forms on the waste material. Aphids do have natural enemies, such as lady beetles, flower fly larvae, lacewing larvae and parasitic wasps. They can also be controlled by insecticides.
Scales are yet another pest that suck the juices of the tree. There are two types of scales: armored scales and soft scales. A severe infestation of armored scales can lead to the death of the tree. A heavy infestation of scales will produce small, round growths on the tree. The sap-sucking insect is underneath this growth and feeds or sucks on the juices of the tree. Armored scale produces yellowing leaves that eventually fall from the tree, dying twigs and limbs and possible cracking of the bark. Scales attack a weak tree, so it is important to keep your tree healthy through watering and fertilization. Insecticides can be applied to control an infestation of armored scales.
Soft scales are also a problem but they will not kill the magnolia tree–they will weaken the tree. Soft scales also produce a great deal of honeydew (waste material) that can also lead to sooty mold. Natural enemies of armored and soft scales are small parasitic wasps and ladybird beetles. Insecticides can also be applied to control an infestation of soft scales.
Spider mites are arachnids that attack the magnolia tree by sucking on the leaves. Infestation symptoms are a yellowing and dropping of leaves. Severe infestations produce webbing on the leaves and branches. It is hard to detect spider mites because of their miniscule size. You will only know that they are present when the symptoms are apparent. Natural enemies include ladybugs, lacewing larvae, minute pirate bugs and some predatory mites. Spider mites will attack a stressed or weakened magnolia tree, therefore maintaining the health of your tree is of the utmost importance to avoid pest infestations. You can hose off the undersides of the leaves to dislodge the spider mites.
White flies, which are small, whitie-winged insects, also suck the sap from magnolia trees. They are very difficult to detect due to their size (size of a pinhead). Yellowing and dying leaves indicate an infestation of white flies. Honeydew will also be present, which can then cause sooty mold. White flies do not do any serious damage to mature trees. However, they can weaken a young tree.