Boxwood: The most common diseases and pests

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Whether as a cut hedge, ball or artistic figure: boxwood has gained great popularity as a form of shrubbery in many hobby gardeners. In Central Europe, only the common boxwood (Buxus sempervirens) is native. The shrub loves warmth, but in our latitudes is quite hardy - but unfortunately also very susceptible to pests and diseases, which you can hardly get to grips with.

cydalima perspectalis

The boxwood tree (Glyphodes perspectalis) is probably the most common and most feared pest. The young caterpillars of the Zünslers are eight millimeters long and reach up to the pupation about five centimeters in length. They have a green body with light-dark back stripes and a black head. The adult moths are with spread-out wings about 40 millimeters wide and 25 millimeters long. The bright wings usually have a characteristic brown border.

Caterpillar of the Boxwood Borer

The boxwood borer is feared by hobby gardeners because he is hard to fight

The butterfly, which lives only a few days, is more likely to be found on neighboring plants. The caterpillars live in the inner part of the box trees and form there characteristic webs. Depending on the weather, wintering caterpillars feed on the leaves from mid-March. During its development a caterpillar destroys about 45 leaves. After the leaves, they also gnaw the green bark of the shoots down to the wood, which is why the overlying shoots dry up and die off. The eroded leaf ribs usually remain standing.
Fighting the boxwood condor is difficult and requires good timing, because the caterpillars can only be successfully controlled at certain times with biological preparations such as XenTari, which contains as active ingredient a parasitic bacterium called Bacillus thuringiensis. Mechanical methods such as blowing the boxwood with a high-pressure cleaner can also significantly reduce the infestation. The wrapping of the crowns of individual plants with dark foil has also proven itself - due to the resulting heat, the pests die off.

Boxwood dieback

Especially on warm, humid summer days, fungal diseases such as the well-known boxwood dying (Cylindrocladium buxicola) are spreading rapidly. The hobby gardener first establishes rapidly growing, dark brown spots on the affected leaves. On the underside of the leaves small white spore camps form at the same time. They are in addition to the black longitudinal stiffeners on the shoots the clearest identifying feature. A strong leaf fall as well as the dying off of the shoots are part of the damage picture.

Boxwood dieback

The boxwood instinct causes whole bookballs to die off

With a sunny-airy location and a balanced water and nutrient supply prevent you from possible infestation. Always pour your box trees from below instead of from above, so that the leaves do not become unnecessarily moist. In addition, avoid the pruning of your plants in warm, humid weather, because injured leaves are possible entry ports for the fungus. More resistant are some varieties of the small-leaved boxwood (Buxus microphylla), for example 'Faulkner'. Susceptible, however, are the popular border varieties 'Suffruticosa' and 'Blue Heinz'.

Boxwood psyllid

The widespread boxwood flea (Psylla buxi) can be recognized by its greenish, about 3.5 millimeters long body. He is winged and has jump legs, with which he can quickly leave the plant in imminent danger. The clearly flattened larvae are also yellow-green and usually covered by a white wax layer.
Once the plant is attacked by the boxwood leaf flea, the young leaves roll upwards in a bowl-this phenomenon is also referred to as spoon-leafing. The ball-like, one to two centimeters large bile include the larvae. The young animals go through to complete development, which is completed after about six weeks, up to five stages.

Damage of boxwood leaf flea

The so-called Löffelblättrigkeit is a typical damage image of a boxwood Blattflohs

Another symptom of Psylla buxi infection is yellow discoloration on the leaves. Often the affected parts of plants are covered by white wax threads, which were previously secreted by the larvae. The wax layer impairs the shoot growth of the plants. On the honeydew excretion of animals also like so-called Rußtaupilze form. On the one hand they reduce the ornamental value of the plants as a black coating, on the other hand they weaken the boxwood by impairing the metabolism and the photosynthesis.
Towards the end of May to the beginning of June you can observe the adult leaf fleas.From June and July, they then lay their yellow eggs in the outer bud shells of the box trees, where they also hibernate. In the following spring, the larvae finally migrate to the young shoots. One generation per year is formed.
If you notice an infestation, you should cut back all affected shoot tips in late summer and fall. Remove the affected clippings with household waste to prevent further spread of the pests. Also regularly check your stock for possible infestation and resort to less susceptible varieties such as 'Blue Heinz' or 'Elegantissima' when planting.

Boxwood cancer

Damage of boxwood crab

If the boxwood is attacked by the boxwood cancer, the leaves first turn pale green to brown and then fall off

The boxwood canker Volutella buxi is caused by a fungal pathogen that infects the trees primarily through wounds, injuries and interfaces. He shows as damage image twisted and adjacent leaves that turn pale green to brown and later fall off. Especially young shoots and leaves are affected. Typical of an infestation are the drying of whole branches and the formation of pink to orange pustules. The clearly visible spore bearings form on the shoots as well as on the undersides of the leaves.
Especially already weakened and sick plants are prone to infection with Volutella buxi. Avoid humid locations, low pH, drought stress and nutrient deficiencies. You can prevent the spread of boxwood cancer by cutting back affected plants all the way to the healthy shoots. Then remove all diseased plant parts including the fall leaves, as the spore bearings are still highly infectious.

Boxwood Welke

The boxwood wilt is triggered by a fungus called Fusarium buxicola. Mostly only individual branches, twigs or leaves are attacked, which first turn yellow and then quickly die off.
As a rule, the fungal disease does not spread, so it remains in an infestation of individual shoots. The fact that your boxwood is affected, you can tell by the bark: This often shows dark spots, which are a bit softer than the healthy bark. In some cases, it comes to an early leaf release of the affected plants.
The fungal disease affects the boxwood mostly only when the plants are already weakened and sickly anyway. However, as an infestation is usually not severe, a pruning of the affected areas is sufficient. Make sure you have an optimal location and an optimal supply of shrubs to protect them from infestation right from the start.

The boxwood spider mite

The boxwood spider mite (Eurytetranychus buxi) has its origins in North America. In Germany it is known only since 2000 as a pest on boxwood. The spider mite prefers a dry-warm weather, so it is usually a problem in the field only in very hot summers. Otherwise, the animals are well controlled by naturally occurring predators such as predatory mites.

Damage of boxwood spider mites

Lightening on the leaves is a sign of an infection with boxwood spider mites

Boxwood spider mites overwinter as an egg on the underside of the leaves. The 0.1 millimeter eggs are yellow-brown and flattened below. The pests develop over several stages. In the first stage, the yellow-green juveniles have only six legs, older spider mites take on a reddish-brown color and have an extended pair of legs. The females are slightly larger than the male animals. The life span is about one month. Depending on the prevailing environmental conditions, up to six generations per year can form, preferably in sunny and warm locations. Heavy precipitation, on the other hand, drastically reduces a population.
The typical damage pattern are streaky lightening on the upper side of the leaf and the lower side, which show marked leaf leaflets later in the disease. Especially young leaves are affected. In a very strong infestation, the branches of boxwood may be covered with filaments, then in some cases leaf fall indicates an infestation.
If you notice an infestation in autumn, you can use a pesticide-based plant protection product to prevent the eggs of the spider mite from hibernating on the leaves. In the spring, the application of pesticides with the active ingredient azadirachtin (included in, for example, in pest-free neem by natures) prevents eggs from being laid. Who wants to rely on natural control methods, can use predatory mites.

The boxwood gnat

Similar to the boxwood cones, the larva is the actual pest in the circa four millimeter boxwood gallbladder (Monarthropalpus buxi). The gallmuck lays its eggs in a circular shape from May onwards with its long, curved laying drill. After about two to three weeks, the 0.5-millimeter, legless young hatch. The orange larvae develop well hidden in boxwood leaves and begin quickly with their feeding activities.An infestation will be apparent from August, when initially on the upper leaf side bright yellow spots occur and then bump-shaped bulges occur on the underside of leaves. In heavy infestation, the individual galls flow together to form a large bladder.

Damage boxwood gallbladder

An infestation with the boxwood gnat can be recognized by yellow spots on the leaves

If the infestation is manageable, a pruning in the spring is sufficient before the gall bladders begin to hatch in May and start laying eggs. In heavy infestation it comes to leaf fall and dried out shoots. Susceptibility to Monarthropalpus buxi is dependent on the variety. Less susceptible are Angustifolia, Rotundifolia, Faulkner and Herrenhausen.

Rust on book

The mushroom Puccinia buxi causes the so-called box tree rust. In comparison to the previously presented damage pictures of boxwood, this fungus is rare - at least in Germany and Austria. Affected is the species Buxus sempervirens, there especially the older stocks. The infection of the leaves takes place in early spring. As the fungus grows inside the leaf, there is a thickening of the leaf tissue. It is not until the following autumn that conspicuous rust-brown spore bearings on the upper and lower sides of the leaves become noticeable.
A deciduous waste occurs in contrast to other rust fungi in the rust on Buchs barely or not at all, so that the infected leaves serve longer as a source of infection. Remove affected shoots immediately. Also, avoid over-watering your plants.

Video Board: What's Wrong with My Boxwood?.

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