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To find out what’s attacking and eating your magnolia plants, you need to get down and close up to the leaves themselves. Maybe even with a magnifying glass. Actually, it’s a good idea to make a point of doing this regularly so you can deal with any bug infestation as soon as it starts. It’s much easier to tackle an infestation while it is small and they have caused limited damage.
Here are some of the most common culprits that often take a liking to magnolias.
We’ll start with scale insects as they attack pretty much every plant in the garden. The bugs themselves look like a legless brown or tan bump on the leaves. You may more easily notice what they leave behind – a sticky substance called honeydew on the leaves and stems, and sometimes you will notice ants then feed on the honeydew. Scale insects not only eat the leaves but they weaken the tree in general, leading to poor health.
What to do
The good news is that scale insects are easily dealt with. Thoroughly spray the stems and leaves with insecticidal soap. But you may have to use a pesticide if this infestation has spread over much of the tree.
If the culprits of eating your magnolia leaves aren’t scale insects, then check for vine weevils. You probably won’t catch them red-handed, so to speak, as they hide in the soil during the day and climb the tree at night to feast on the leaves.
It’s actually their larvae that cause more damage if grown in pots as they eat the roots and can cause a lot of damage to the root systems and even kill the shrub.
What to do
It won’t hurt to place a sticky trap at the base of the tree to catch them. You can also spray plants with a pesticide and for plants grown in pots, use a pesticide drench through the soil.
These insects are tiny and are either white or grey as pictured above. They have quite a few legs to move about in your leaves. They don’t so much eat the foliage as suck all the juice out of it, leaving behind a stick substance called honeydew. And that’s not the end of the story as fungus loves to grow on that stickiness, causing further problems with fungicides. Another sign of these bugs is that the twigs on the tree start to die without any other apparent problem.
What to do
Mealybugs are a serious problem and you need to treat the leaves immediately with a pesticide, the good news is most pesticides from garden centres will treat mealybugs.
If you spy small, black or tan, moth-like insects with really feathery wings, you’ve got thrips. These suck the juices out of plants and attack both the underside of the leaves and flowers. This weakens the tree and makes it susceptible to other diseases.
Another sign of a thrip infestation is a discoloured flecking in a silver colour on the surface of the leaf. You need to really get at these as they fly from plant to plant, spreading diseases.
What to do
Using insecticides is a last result. You need one that contains the active ingredient pyrethrin. Any insecticide kills off good bugs as well as the bad ones. Start by trying out insecticidal soap and hosing down the tree leaves with that. Or go bio-friendly and introduce parasite insects such as lady bugs which believe it not you can actually buy from Amazon.
The magnolia borer is well named as it attacks young magnolia trees. This is a beetle that lays its eggs in the tree trunk. When the eggs hatch they bore their way into the trunk, working their way down into the roots. Parts of your tree start to look soft and spongy. The beetles are dark brown or black so you might not see them directly. But you’ll notice that your leaves are dying and your tree doesn’t look healthy.
What to do
Carefully prune the infested limbs and twigs. And pay extra attention to your tree’s care and maintenance, making it as strong as possible to outlast this infestation.
Learn more about how to grow a magnolias tree here as well as why your magnolia might not be flowering here and even what pests might be eating your magnolia leave in this guide