Magnolia’s Pests And Diseases
Magnolias are very tough plants and are seldom seriously troubled by insects and diseases. However, some times slugs may attack very young magnolia plants, but you can use modern baits to control these pests easily. Occasionally, leaf miners also attack magnolia leaves – these pests not only gnaw the leaves, but the flowers too. Most growers face this problem in the southern regions of the United States. Employing systemic insecticides will help to keep these insects under control. However, these insecticides are extremely toxic. Moreover, as these pests do not kill the plant they inhabit, you may opt for other means to get rid of them or even decide to continue with the problem.
Apart from slugs and leaf miners, the magnolia species that bloom during the summer may also be troubled by the Japanese beetle. In fact, Magnolia grandiflora is commonly affected by this problem. You may, however, pick these insects by hand. However, this is not possible if the magnolia trees are large or you are dealing with a vast population of these pests.
People residing in places having cold climatic conditions have an advantage vis-à-vis these pests. In fact, these pests are killed naturally when the temperatures drop drastically during the winter. In addition, you can also use any good insecticide to get rid of the pests. However, prior to using any insecticide, you need to consider the benefits of using them and the damage that the chemicals can cause to the plants.
Magnolias are also affected by various other diseases like leaf spots that include powdery mildew and magnolia scab. In fact, usually controls are neither required nor feasibly in dealing with this problem, especially if your tree is large. This is because you can hardly reach all the areas of the tree that may be affected by this condition. However, you may spray a sulfur compound on the affected leaves that are reachable. On the other hand, you can deal with a variety of cankers like dieback, nectria canker and trunk decay by straight away cutting down the diseased or dead branches. However, none of these diseases will lead to the death of the magnolia.
On the other hand, the condition called magnolia scale (scientific name Neolecanium cornuparvum) is a more serious problem that affects magnolia trees. These scales have a brown color and round shape, measuring roughly 1/4 inch (0.50 cm) across. Their body is often coated with a white, dust-like wax. Similar to other scales, magnolia scales also extract the plant’s sap and when this occurs continuously, the tree may eventually die. The plants excrete the surplus sap in the form of honeydew, which forms the base for the development of fungus sooty molds. This causes the leaves as well as the branches of magnolias to appear blackish. It is advisable that before you purchase any magnolia plant, examine it carefully to see if there are any scales present on it.
When you notice magnolia scales on the trees in your garden, you may spray horticultural oils (also called summer oils) on the insects as well as the entire stages of their life cycle. These chemicals will effectively kill the scales by choking them. However, it will be more effective if you remove as many scales as possible by hand before applying the horticultural spray oils. In fact, these horticultural oils prove to be more effective when they are applied to crawlers (the young scales) that are settled some time during August end. Subsequently, you should apply a dormant oil between October and November and once again in March. Ensure that the leaves as well as stems of the plant are completely wet when you apply the dormant oil.
The trees that are attacked most commonly include the star, saucer, cucumber and lily tree magnolias. In addition, magnolia scales also feed on Virginia creeper and Daphne.
Magnolia scales possess effective sucking mouthparts and when they invade a plant in large numbers, they usually cover the branches completely, eventually causing the branches to die. In the initial stages of their infestation, they suck out the life-giving sap from the magnolia branches and twigs making them weak and also retarding their growth. Even the leaves on the affected branches and twigs are affected, as they tend to be under-developed. When a magnolia tree is attacked continuously, it often leads to the death of the tree. Similar to majority of the other soft scales, the surplus sap of the plant is expelled in the form of honeydew – a sweet and sticky substance. This excess sap eventually drips on the branches and foliage of the magnolia. The honeydew that drops on the magnolia branches and foliage give rise to a dark-hued fungus known as black sooty mold that affects the leaves changing their color to black. This actually destroys the leaves’ ornamental worth. What is worse is that ants, flies, wasps and bees are drawn by honeydew, which forms their food. These insects also harm the trees to some extent.
During the winter months, magnolia scale inhabits the twigs of young plants – usually those that are in existence for one or two years. During this phase, the scales appear as dark-hued nymphs. When the temperatures begin to warm up with the onset of spring, the magnolia scales start sucking the sap from the plants and by the time it is early May, they would have normally molted (shed their coating) once. In early May, you will usually find two different forms of magnolia scales – male and female scales. The male magnolia scales continue to be small; measuring just 1/8 inch and their color soon changes to lucid white. After the color of the male scales become white, they appear as minute gnats whose color may vary from pink to yellow and they appear as other insects that have two elongated wax-like threads emerging from their abdomen’s tip.
On the other hand, the body of the female magnolia scales keeps on growing and by the beginning of June, their color changes to brownish-purple. In fact, this is the time when the scales suck out excess sap from the plants forming large quantities of honeydew. By the time it is July, the body of the female magnolia scales is swathed with white, powdery, wax-like substance and this makes their color look more yellowish than tan. Some days later – from the end of July to August, the adult female scales start giving birth to their offsprings called crawlers. These minute, moving crawlers keep moving till they discover a proper feeding site on the tree, where they settle, feed and stay put throughout the winter months.
You can also control scale by employing contact insecticides. However, the success of using these insecticides depends on the timing of their use. You can obtain the best results if the sprays are applied to scales that are in their crawler stage and during the period between the end of August and the beginning of September. While the adult magnolia scales are brown in color, those in the crawler stage have different hues – brown, orange and purple, and when they crawl they appear as moving dusty spots. It is, however, important to go through the manufacturer’s instructions that come along the product, before using any horticultural oil or insecticide on your magnolias. There are a number of other scales that attack magnolias and these include the tulip tree scales and wax scales. You may follow the same treatment for these insects as those that are used for magnolia scales.
- This pest especially attacks small plants. Nevertheless, slugs can actually completely strip a small tree of all its leaves. Therefore, it is essential to get rid of them before they destroy your plants. As slugs come out of their hiding place when it is dark, the best way to overcome this problem is to visit your garden late at night and pick and destroy them.
- Honey fungus
- Magnolia trees/ shrubs are extremely resilient. Usually, they are not vulnerable to this fungal disease. However, when a plant is under immense stress for any other reason, they can be susceptible to honey fungus.
- A soil with a poor drainage is mainly responsible for this disease. When a magnolia tree is affected by phytophthora, its roots will start rotting and the health of the plant will deteriorate rapidly. As of now, there is no cure for phytophthora. Hence, the best remedy is preventing it by preparing the planting hole appropriately.
- Red spider mites
- These pests are very small, but extremely versatile. Plants grown under glass or polythene sheets during summer are especially vulnerable to red spider mites, which have the ability to cause severe “cob webbing” and speckling on the leaves. The damages caused by these pests may actually retard the growth of a magnolia tree/ shrub. You can avoid this problem by growing your magnolias in high humidity conditions. In addition, they can also be kept under control by employing predators like Phytoselius persimilis.
- This problem is quite common during spring and it affects the robustly growing leaves of magnolia. To some extent this condition is attributed to the cold conditions that often prevent the plants from uptake of nutrients. You can only treat chlorosis by providing the plants with foliar feeding at regular intervals.
- The magnolia trees’ bark is a favourite of rabbits. Therefore, if you have a problem tree in your garden, you need to protect it by using guards or encircling the bark with nets. Apart from rabbits, deer may also pose a problem for the magnolia trees and, hence, they too need to be protected from browsing deer.
Among other diseases that affect plants of this species are leaf spots. In fact, magnolia trees are susceptible to leaf spots by the bacterium Pseudomonas syringae. In addition, a great number of fungi may also damage the magnolia leaves. You will seldom require using chemical controls to get rid of this problem. Instead, just identify the affected leaves, pick them manually and destroy them to prevent the problem from spreading to healthy leaves.
A fungal disease called canker disease actually kills healthy branches. Fungi that cause this disease inhibit the branches and cause the bark in the area to die. It is very difficult to control this disease and once it affects the branches of your magnolia tree, simply prune the branch. However, providing the trees with sufficient fertilizers and watering them regularly during the dry weather will not only keep the trees healthy, but also help to prevent the occurrence of this disease.
Another condition called verticillum wilt may also kill some branches of your magnolia. Sometimes, this condition may even kill the entire magnolia tree. Therefore, as soon as you notice any dead branch, prune it out. At the same time provide the tree with fertilizers containing high amounts of nitrogen to keep the tree healthy.
Other diseases in Magnolia trees
In addition to the pests and diseases discussed above, magnolia trees are also affected by a number of other diseases, including powdery mildew, black sooty mold, and wood rot. A brief discussion regarding these diseases, their causes, symptoms and the means to control them is presented below.
- Black sooty mold
- This fungal growth is not a very harmful disease. This occurs on magnolia leaves and stems, especially on trees that are heavily infested by other pests like aphids and scales. Black sooty mold gives out a white, sticky material known as honeydew that forms the base for the growth of a black, velvet-like fungus. While this fungal growth does not cause a tree to die, it definitely hinders the growth process of the affected trees. Precisely speaking, black sooty mold adversely affects photosynthesis of the magnolia trees. The damage is more when the infestation is heavy and the fungus engulfs the leaves and stems of the tree completely. This menace may be controlled by taking pest control as soon as you notice the development of honeydew on your tree. It will help to eliminate the fungus. When you have done away with the infestation, you need to cleanse the affected areas or mold using water.
- Powdery mildew
- This is also a fungal problem and is distinguished by formation of powdery, white patches on the magnolia leaves as well as stems. In majority of instances, powdery mildew does not cause much harm to the trees. Nevertheless, it can still distort the form of the leaves; result in untimely shedding of leaves as well as deformation of the plant’s buds and blooms. In order to save your plants from this condition, you need to use fungicides immediately when the symptoms come to your notice. In case of attack by powdery mildew, you should remove all the leaves that have been infected by the fungus and avoid watering the plants from the top. In addition, it is essential to ensure that the trees are provided with adequate air circulation and sufficient sunlight. These will be beneficial for the trees to overcome the menace and also protect them from powdery mildew.
- Wood rot
- This is another fungal disease that affects magnolia trees. When a magnolia tree is affected by wood rot, its wood starts decaying. The symptoms of this condition vary and they largely depend on the fungus that attacks the magnolia trees. Usually, the fungus gets into the tree through its scars and wounds. Wood rot is usually recognized by conks or fruiting fungal bodies that appear on the trunk of the trees that are infected by the fungus. Generally, this disease is more widespread in older magnolia trees and it can even result in their death. The best way to protect your magnolias from developing wood rot is to ensure that they are not injured or damaged. However, if the disease has already affected your magnolia tree, cut down the dead branches and those infected by the fungus as soon as you notice the symptoms. It is also important to dispose these dead and diseased branches appropriately to ensure that the fungus does not spread to the healthy parts of the tree.
History of magnolias
Propagation of magnolias
Cultivation of magnolias
Landscaping with magnolias
Symptoms and possible causes of magnolia diseases