One of the best-known pests that pose a threat to the shrub are the boxwood moth caterpillars. They feed on the leaves in spring and cause a lot of damage. Unfortunately, the offspring of the small butterfly are not the only threat to the plants: the psyllid, the gall midge and the spider mite also target the boxwood – if they are not discovered immediately, they literally suck the life out of the evergreen shrub. Below we will introduce you to the pests in more detail and reveal how you can get rid of the uninvited guests.
The boxwood moth (Cydalima perspectalis) is an invasive, non-native small butterfly. After the female butterflies lay their eggs on a bush, their offspring hatch just a few days later: the yellow-green caterpillars are easy to recognize with their black dots and fine bristles – but only if you look inside the plant, where the From mid-March onwards, pests up to five centimeters long satisfy their hunger first on the leaves and bark. Mostly undetected. However, urgent action is required at the latest when the caterpillars retreat into their white webs and cover the bush. The following methods should make it possible to successfully combat the boxwood moth pest:
It is only a few millimeters large, so it can hardly be seen with the naked eye. Nevertheless, the box tree flea (Psylla buxi) poses a danger to the evergreen shrub, although not as great as the box tree borer: Strictly speaking, it is its yellow-green larvae that hide under a white woolly wax layer and the plant – in the truest sense of the word Meaning – suck out the lifeblood. The infestation does not go unnoticed as the young leaves curl upwards in a spoon shape. This is due to the sticky honeydew that the offspring excrete. A black coating, so-called sooty mold fungi, and yellow discoloration on the leaves also indicate an infestation by the boxwood flea.
The adults can be found on the plants from June onwards to lay their eggs. The larvae hatch after a few weeks, but overwinter and do not become active until the next spring. So there is only one generation per garden year. If you discover a boxwood flea, it is important to act quickly: Cut off the affected shoot tips – in summer and autumn. Do not dispose of the leaves in the compost, but rather with household waste. If there is a severe infestation, you can also use a pesticide against sucking insects. It should also make a difference which types of boxwood live in your garden: “Blauer Heinz”, “Elegantissima”, “Angustifolia” and “Herrenhausen” are less susceptible to the boxwood psyllid.
The larvae of the box tree gall midge (Monarthropalpus buxi) are only a few millimeters small, but they have a huge appetite: after the female lays her eggs directly in the leaves from May onwards, she dies. Their orange offspring hatch after a few weeks and then eat their way through the inside of the leaves – for this reason the infestation is usually not recognized immediately. However, if there are visible bright, mostly yellow spots on the top of the leaves from August onwards, you should clearly recognize the symptoms. However, when you notice small bulges on the underside of the leaves, so-called galls, the shoots dry out.
The best way to combat the box tree gall midge is in spring by pruning in May – before the females hatch and lay their eggs. If you discovered the infestation too late, the larvae can be removed with a pesticide. The pest can be avoided if you choose boxwood varieties that are less susceptible to infestation: These include “Angustifolia”, “Handsworthiensis”, “Herrenhausen”, “Faulkner”, “Rotundifolia” and “Suffruticosa”. It is said that the box tree gall midge particularly likes to visit the “Green Mound” variety.
The pest, which comes from North America, has not been known in Germany for long: the box tree spider mite (Eurytetranychus buxi) was detected for the first time in 2000 – since then it has been able to form up to six generations per garden season. The tiny animals, which can hardly be seen with the naked eye, are kept in check by their natural predators such as lacewings, ladybirds or predatory mites. If it rains very often and a lot, the animals are actually washed out of the plants and the population is minimized. However, if it is very dry and hot for a long period of time, usually in the summer months, there is a risk of a severe infestation. You can tell whether your boxwood trees are infected with spider mites by looking at the following signs:
The boxwood spider mite lays its 0.1 millimeter eggs on the underside of the leaves in spring. They are flattened at the bottom and look yellow-brown. To prevent egg laying, it is recommended to use a plant protection product that contains the active ingredient azadirachtin. If you only notice the infestation in autumn, it is advisable to use an oil-based pesticide – this is intended to prevent the eggs from overwintering.
Sources: My Beautiful Garden, Plantura
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