11 Common Problems With Magnolia Trees
Are your magnolia trees looking a little worse for wear? There can be a number of different issues that you run into with these popular trees. In this article, gardening expert Melissa Strauss looks at the most common problems you'll run into when growing magnolia trees.
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The lovely magnolia tree is the belle of Southern gardens and is also surprisingly cold-hardy sometimes. These sturdy trees are fairly unfussy and low maintenance, but magnolia tree problems can put a damper on the aesthetic and the health of your plants.
Research shows that deciduous species tend to be more vulnerable to pests, while evergreen species are more sensitive to environmental shifts.
Whatever the cause, it is distressing to see one of your trees ailing. Here are 11 common problems with magnolia trees, possible causes, and remedies for returning your tree to good health.
Discolored Foliage
A few different diseases can cause leaves to become discolored, covered in spots, or brown lesions. The most common are:
- Leaf spot
- Leaf blight
- Verticillium wilt
Phyllosticta leaf spot is caused by the fungus Phyllosticta magnoliae. Symptoms look like small black or purple spots that can gradually progress to larger spots with a halo and white center. This fungus is not a huge problem for mature trees but can be fatal to young trees that aren’t yet established.
Leaf blight is another disease that can cause brown or black spots on the leaves. It generally affects trees that are under stress already. This can happen during drought or when there is a lack of nutrients. Blight is a waterborne bacteria and can cause tip dieback on branches.
The third disease is the most serious and is called Verticillium wilt. This is a fungal infection that affects the water-conducting tissues of the plant. Leaves will turn yellow to brown, and foliage will appear wilted. A soil test is needed to diagnose this issue.
The Fix
Sadly, there is no fix for Verticillium wilt. Mature trees can outgrow the disease over several years, but the tree’s growth will be permanently stunted. The damage can be mitigated with pruning of affected tissues, proper watering, and fertilizing. Young trees are unlikely to survive. This fungus lives in the soil, so a tree that dies of this should be removed and disposed of. The fungus can live in the soil for up to 5 years.
Both Phyllosticta leaf spot and leaf blight can be helped by quickly pruning away affected foliage. Don’t be conservative about removing any branches you think may be infected. If blight reaches the tree’s trunk, it is fatal. Using hydroxide and copper sulfate sprays are common treatment methods for blight, but pruning is the most effective treatment.
Phyllosticta can be treated with a copper-based fungicide to control the infection. By doing this and careful pruning, this disease should be controllable. It typically does not kill a mature tree. An advanced infection in a younger tree can be fatal.
Shriveled Leaves
If you notice leaves beginning to shrivel and curl inward, you probably have an insect infestation. Insects like aphids, scales, and thrips like to feed on the sap of magnolia leaves. As they suck the sap from the leaves, they will begin to curl inward, which can look unsightly but is not typically threatening to the tree’s health.
A mature tree will usually be able to endure insect damage with little overall damage to the plant’s health. However, the tree may suffer if it is young or severely infested.
The Fix
Generally, no treatment is needed, as insecticides are damaging to beneficial insects as well as pests. Most pests have natural predators that will clean up the problem for you once they find it. If the infestation is severe, treating with insecticidal soaps or neem oil will help control the spread. Treating at night will help to mitigate the damage to pollinators. Try not to treat when the tree is in bloom.
Defoliation
Caterpillars are another common magnolia tree problem. There are several species of moths and butterflies whose larvae like to feed on the leaves. Sometimes this can look like leaves with irregular edges that have clearly been chewed on.
The fruittree leafroller, fall webworm, and cotoneaster webworm are all larvae that feed on magnolia leaves. You may notice that leaves are covered in webbing or have a lacy appearance, as some caterpillars will eat the soft tissue of leaves and leave only the veining intact.
Generally, a mature magnolia will support these insects through their larval stage with no real damage. However, if the infestation is severe enough, these insects can do enough damage to the tree to affect its overall health.
The Fix
Remove all damaged foliage with clean hand shears. Inspect the trunk and branches for egg masses, and remove and dispose of them by dropping in a bucket of soapy water. Good hygiene practices such as fertilizing, pruning, and watering will keep your tree strong so it can rebound from the damage caused by these insects.
Dropping Leaves
If you notice your magnolia dropping leaves in the fall, you may have a deciduous species. This is a natural occurrence that takes place every year. Your tree is preparing for dormancy, and in the spring, it will grow its leaves back and most likely burst into bloom. Lucky you!
If your magnolia is evergreen, like the popular Southern Magnolia, it will lose some leaves naturally from time to time. If you notice a larger number of leaves dropping simultaneously, you’re most likely to see flowers soon. This is the tree’s way of redirecting resources to flowers and is not a cause for concern.
The Fix
This issue doesn’t usually warrant a response. Sit back and enjoy the flowers your beautiful magnolia tree is about to produce. On evergreen magnolias, pay attention to where the leaves drop from. If it is preparing to bloom, it will drop its oldest leaves. If more leaves begin to die off and a massive number fall, another issue is probably at play.
Leaf and Branch Dieback
This leads us to the dieback of leaves and branches. First, rule out the normal shedding of leaves by a deciduous tree in the fall or an evergreen’s natural shedding in early summer before the flowers bloom. If the leaf drop seems untimely, and entire limbs begin to turn brown and lose leaves, you may have a more serious issue.
The most likely culprit of this in an evergreen magnolia is cold damage. If you had a particularly cold winter, there might be frost damage to some of the outer limbs. Evergreen magnolias are cold tolerant to a certain point, but prolonged periods of extreme cold weather can cause death of the younger growth.
The Fix
Once the threat of freezing weather passes, prune off dead branches and allow the tree to recover. Giving the tree some fertilizer will help it to produce new, healthy growth, and it should be back to normal by the end of summer.
Yellow Leaves With Brown Edges
If your lovely magnolia leaves look faded and yellow with dry brown edges, the culprit is probably the weather. It sounds strange to say that sweltering dry weather and very cold weather would cause the same thing to happen, but this is precisely the case.
Very cold, harsh winds have the same effect on leaves that drought has. The leaves appear to be burned because the water evaporates very quickly under these conditions, leading to those dry, brown edges.
The Fix
The best thing to do is to prune away damaged growth as conservatively as possible and baby the tree for a while. There is not much else to do after the damage is done. You can prevent some of these issues with proper watering during drought, and if the tree is young and small, you can cover it if you know that there will be extremely cold weather.
Flower Discoloration
Magnolia flowers have different lifespans from one species to another. Some varieties, like the giant Southern Magnolia, produce lots of flowers that bloom in succession but only last one to two days each. Others, like M. soulangeana or the Japanese Magnolia, bloom in the spring, and the purple magnolia blooms can last for a week or more.
If you are concerned about flowers turning brown and wilting, the first thing to do is determine how long your specific tree’s blooms last. If the blooms are opening and already have a brown discoloration or look wilted from the beginning, it’s very likely a climate issue. Once again, extreme heat or cold can put stress on a magnolia, affecting the blooms.
The Fix
There is little to be done about the weather. The best solution here is to keep up with general tree health by watering, fertilizing, and pruning. A magnolia in optimal health will have the least reaction to environmental stress. Make sure to water weekly in times of extreme heat or drought.
If you live in a very cold climate, it’s best to plant your magnolia in a spot that has some shelter from freezing winds. It is the cold winds that typically do the most damage, not the actual temperature shift.
Not Flowering
If a magnolia tree is not producing flowers, the issue could be related to sun exposure or soil pH. Magnolias need a fair amount of sun. Most types prefer full sun and will produce the most flowers in this situation.
Soil pH is a little more complicated but can generally be rectified without transplanting. Magnolias like slightly acidic soil. The soil’s acidity helps to break down the nutrients in the soil and fertilizer so that the tree can best utilize them. If the soil pH is too high, meaning too alkaline, the tree will likely become malnourished, and the first thing to suffer will be flower production.
The Fix
When choosing a spot to plant your magnolia, ensure the area gets at least 6 hours of direct sun daily. If soil pH is the issue, a soil test will give you the necessary answers. Magnolias need a pH of around 6, give or take.
To raise the pH of your soil, add organic material like manure, pine mulch, or compost. Soil acidifiers are also available, but they tend to be more costly. Although they work faster, they do not last as long as amending the soil with organic materials.
Slow Growth
Magnolia trees are not fast growers, to begin with. Expect to see 1-2 feet of growth per year, with smaller trees maturing at about 10 years and larger species taking as many as 60 years to reach their full height.
If your magnolia is growing at a snail’s pace, there could be various reasons, from malnourishment to pest infestation. If you’ve ruled out all the other growth-inhibiting factors on this list, nutrition is probably the culprit.
The Fix
The short answer: fertilizer. But first, make sure your soil pH is right because if the soil is too alkaline, the nutrients in the fertilizer won’t break down in a way that makes them useful to the tree. Check the pH and then make sure you are fertilizing properly.
Magnolias don’t need a ton of fertilizer, but they do like a strategic fertilizing schedule and will flourish when given this. Magnolias should be fertilized 2-3 times during their growing season with a balanced fertilizer.
Spread a granular fertilizer (8-8-8 or 10-10-10 will work great) around the plant’s base in early spring, late spring/early summer, and mid-to-late summer. Fertilizing is particularly important during the tree’s early years.
Black Mold on Leaves
Black sooty mold is a common magnolia tree problem in the garden. If you notice a fine coating of black mold on the undersides of leaves, there is one nearly certain culprit… honeydew. This sweet, sticky substance is the result of insect infestation.
That’s right; it’s insect excrement. Insects such as aphids, mealybugs, and scales suck the sap from plants and leave behind this sticky substance, creating the perfect host for sooty mold to grow on.
The Fix
First, make sure that you treat the underlying issue, or this issue will crop up again and again. As long as there is an infestation of some sort, there will be honeydew, and there will be mold. While black sooty mold won’t necessarily kill a mature tree, it can inhibit photosynthesis, which will stunt the growth and lead to a generally ailing tree.
Black sooty mold has to be wiped away by hand, although over time, it will wear away on its own. In the meantime, it can negatively impact on the tree’s health. So it is best to get out there with a damp rag and wipe it off as much as possible.
Unusual Bark Growths
Three different diseases can manifest as irregularities in the bark of your magnolia:
- Wetwood
- Wood decay
- Canker
Wetwood, or slime flux, is a bacterial disease. Most of the time, the tree will heal itself in time. However, if the tree is already weakened by another factor, this disease can exacerbate its decline.
Wood decay manifests as wounds with rotten tissue in the tree’s trunk. This fungal disease can cause the trunk’s interior to decay over time. This typically occurs during times of excessive humidity or rain. You may notice mushrooms forming around the base of the tree and leaf or limb death.
The third bark-affecting disease is canker, which is another fungal disease that causes darkened lesions and eventually opens cankers in the bark of the tree. It is very rare for canker to kill a magnolia tree, but the cankers can be unsightly and damaging to the ornamental value of the tree.
The Fix
Prevention is the best defense against these issues. By that, I mean proper tree care. Pruning away crossing branches to allow proper airflow to the tree’s interior will greatly help prevent fungal infections. Proper watering, fertilizing, and placing your tree in a spot with good sun exposure are all factors that will create a strong tree resistant to disease.
When these issues arise, the best way to deal with them is to remove infected wood. Prune away any affected branches and cut out galls with a sharp knife. If the affected area cannot be removed, clean it with a solution of bleach and water or alcohol for bacterial infection and fungicide for fungal infections. Treating during cool, dry weather will help control the spread and maximize treatment.
Final Thoughts
Magnolias are typically hardy trees that, when planted in the proper place, flourish with very little care or attention. If you see the beginnings of any of these ailments, take action swiftly to preserve the greatest amount of foliage and give the tree its best shot at recovery.
