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Magnolias are one of the most stunning types of trees, with the Magnolia ‘Yellow River’ being my ultimate favourite with its yellow tulip-shaped flowers, but I also have Magnolia ‘Stellata’ and Magnolia ‘Susan’ planted in my garden.
This charming tree produces large blooms that are both a remarkable sight and some varieties have a lovely scent. While Magnolias look majestic when fully matured, they need some maintenance to promote healthy growth and that includes understanding what is attacking its leaves, stems and flowers and more importantly how to spot and treat them.
Below I have highlighted some of the causes behind Magnolia leaves appearing to have holes, yellow spots, common and some less common symptoms.
Insects that attack Magnolia trees
Magnolias are resilient trees but sometimes they attract insects and other pests that can cause damage. Common pests associated with Magnolias include the following (which we have listed below) and I have tried to start with what I consider the most common:
Vine weevils are persistent beetles that feed on your plants, but if you happen to grow your Magnolias in pots, the grubs can also damage the roots enough to actually cause damage to kill them.
However, if you have holes in the leaves it is the adult beetles that crawl up the plant at night to feed, leaving behind devastated leaves with holes in them or edges that have been eaten away.
Vine weevils usually start to damage the leaves around spring and summer. If the infestation is left unchecked, these weevils then move to the roots in autumn and winter; therefore, causing the demise of the plant. As previously mentioned though, it is the grubs (that look like tiny maggots) that do the most damage to the roots.
How to kill vine weevil on Magnolias
The easiest way to deal with vine weevils is to place a sticky surface at the bottom of the tree. This will deter the insects from going up the tree and causing damage. You can also introduce bird or rove beetles that naturally prey on beetles.
There is also the option of using insecticides, but make sure the insecticide is not toxic to other animals around or the soil. If you grow Magnolias in pots and they are eating the roots, you can all but drench the pot and soak the roots with water which should kill the grubs.
- Scotts Bug Clear Ultra Vine Weevil Killer
Magnolia borers do more damage to young trees rather than older ones due to the strength of the bark. These parasitic insects feed on plant tissue and lay their eggs waiting to hatch. Once the eggs hatch, the insects bore into the trunk and continue through the tree. Borers are detrimental to Magnolia trees because they eat down to the roots.
Once the roots are affected, the tree will start to die slowly presenting a sunken and spongy texture.
Read next: Cordyline problems and how to fix them
How to treat Magnolia borer
You must prune off any infected branches. You can also use a pesticide that can be effective or horticultural oil which you usually apply in August and then reapply around October to treat the overwinter form of this pest and then again around March. It’s a long process.
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Scale insects on Magnolias
A scale insect infection is usually noticeable when the tree’s branches and leaves start manifesting multiple lumps. These lumps are caused by the scale’s sticky waxy secretions that if left unchecked could lead to a very unhealthy tree, or even death if the infestation is bad enough.
Scale insects extract the plant’s sap for nutrients, which eventually leads to yellowing leaves, stunted growth and branch dieback.
These insects not only feed on the tree’s sap but also attract other insects like ants. This is because of scale insects’ sticky secretions otherwise known as honeydew that ants and other insects love to feed on.
How to kill scale insects
It is best to remove the infected branches, apply insecticides repeatedly as recommended on the pesticide container, or introduce parasitic wasps that are scale insects’ number one enemy. Introducing parasitic wasps is a long-term strategy for Magnolia trees that keep getting re-infested.
- Up to 2 weeks control of a wide range of pests
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- Targets lily beetle, whitefly, scale, greenfly, red spider mite, blackfly, mealybug, thrips and leaf hopper
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Thrips are winged insects that enjoy feeding on Magnolia leaves, especially the under surface. After munching through the leaves, they move towards the shoots, blossoms or buds depending on the level of infestation. The tiny insects get their nutrients by ingesting delicate plant tissue and pollen, which in turn cause the plant to suffer stunted growth.
Thrips are manageable through the use of horticultural oil available from garden centres and nurseries, or pesticides. Keeping the area around the tree free from debris can also help and even introducing ladybirds or lacewings which are their natural predator can help. Did you know you can even buy them from Amazon? It’s also worth noting a mixture of soapy water in a spray bottle can also kill thrips on contact.
Bearing soft bodies with no wings, mealybugs are whitish/grey in colour. These insects are the same as scale insects as they feed on the plant’s sap. They are not dangerous to Magnolias unless the infestation is widespread though. Mealybugs also produce honeydew, a sticky waxy substance that promotes the development of sooty mould which then becomes another problem. You can tell they are mealybugs by their appearance and yellowing leaves that curl.
Treating Magnolias from mealybug infestations includes the use of insecticides and other predator insects like ladybugs and lacewings. Alternatively, you can employ the use of neem oil or horticultural oil to control the infestation over time.
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Unlike the rest of the pests above, the Hoplia beetle does not attack the leaves or stem. They instead cause damage to Magnolia blooms leaving unsightly holes. To deal with Hoplia beetles, you can remove them by hand or place water in a bucket with some detergent. The water will attract the beetles that will then fall in and drown. A nice easy solution though not nice for the Hoplia beetle.
If not pests, its diseases
In some cases, pests are not the cause behind Magnolia’s damaged leaves. Magnolia trees are also susceptible to fungus and bacteria. Bacterial blight is a common disease in Magnolias as well as verticillium wilt, canker disease, powdery mildew, wood decay and crown gall.
These diseases usually occur when the environmental conditions are humid and warm and therefore, preventative measures are required.
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- Use at the first sign of infection for best results
Promoting good ventilation by clearing mulch, weeds, or dead matter around the tree base helps to lower the risk of infection. Once you notice patchy leaves, wilting or discolouration, make note of the visible symptoms and check online for help or contact a professional. In general, most fungicides can be treated with a fungicide spray and by removing affected leaves.
Taking care of your Magnolia tree
Magnolia trees can pretty much look after themselves; however, they do need regular tending to promote healthy growth and to get the best out of them. Some of the things you can do to take care of your Magnolia trees include:
- Plant your Magnolias in an area with plenty of sunshine to prevent recurrent fungal infections caused by high humidity.
- Use well-fertilised acidic or neutral soil to promote optimal growth.
- If you have young Magnolia trees, ensure they are well hydrated to prevent the sun from damaging them especially in summer. You can try drip irrigation to try to mitigate the heat.
- A little pruning, especially around spring or early summer, ensures the tree remains in good condition by shedding unwanted weight from dead branches or stems.
Keep your young Magnolias away from areas with foot traffic. This is because Magnolias have shallow roots that are damaged easily.
Last update on 2023-02-01 / Affiliate links / Images from Amazon Product Advertising API