Whether stringently designed hedge or solitary planting in free form, the boxwood, or also Buxus sempervirens, enjoys great popularity due to its high creative diversity. The disappointment is all the greater when pests and diseases destroy the painstakingly created and well-kept appearance. Knowledge of the most well-known diseases and pests will help you to classify the type of damage found and to take the necessary countermeasures.
boxwood diseases
Hardly any plant is seen in the gardens as often as the boxwood. Whether as a hedge or a solitary plant - it offers endless design options. It is all the sadder when Buxus sempervirens is attacked by diseases. Below is an overview of the most common boxwood diseases.
Recurring diseases of Buxus sempervirens
Boxwood dieback
(Cylindrocladium buxicola)
identifying features
- increasing, dark brown spots on leaves
- simultaneously formation of white spore deposits on the underside of the leaves
- black vertical stripes on the shoots
pathogen
- host-specific fungus
- favored by warm, humid weather in summer
consequence
- heavy leaf fall
- then the shoots die off
measures
- Control with fungicides
- Prevention through a sunny and yet airy location for rapid drying after precipitation
- However, water only in the root area and not over the leaves to avoid fungus-promoting moisture on the leaves
sooty mold
(Capnodiales)
identifying features
- grey-black, flat coating on the upper sides of the leaves
pathogen
- different mushrooms
Follow
- Reduction of metabolism and photosynthetic performance of Buxus sempervirens
- in the long run, this results in a significant weakening of the plant
measures
- Use of approved fungicides
- In the case of intensive infestation, remove affected parts of the plant, since fungal spores overwinter in dead leaves
- Regularly remove and dispose of dead leaves
boxwood canker
(Volutella buxi)
identifying features
- twisted and flat leaves, initially pale green, later turning brown, finally drying up and falling off
- Easily recognizable spore beds on the underside of the leaves in the form of pink to orange pustules
- typically infestation of entire shoots, preferably young shoots and shoot tips
pathogen
- fungal pathogen that mainly enters the plant through injuries and cuts
Follow
- Leaf discoloration with later drying out
- then shoots and branches die off
- Bark dries up, cracks and detaches
measures
- Generously remove and eliminate affected areas
- Prevention by avoiding conditions that favor infestation: locations with high humidity, low soil pH, drought stress, nutrient deficiency
danger: All removed plant parts including dead leaves should be completely removed and disposed of as the spore stores of Volutella buxi are still highly infectious!
boxwood wilt
(Fusarium buxicola)
identifying features
- yellow discoloration with rapid death of typically individual branches, twigs or leaves
- dark, somewhat softer areas on the bark
pathogen
- Fungus that attacks already weakened plants
Follow
- Apart from the affected areas, there are normally no relevant consequences for the entire plant, since the spread is very low
measures
- Remove affected shoots
- Prevention by avoiding debilitating conditions, such as water or nutrient deprivation
boxwood rust
(Puccinia buxi)
identifying features
- Thickening of the leaf due to fungal growth inside the leaf
- rust-red spore deposits on the upper and lower sides of the leaves that are only clearly visible in the following year
pathogen:
- mushroom
- infection in early spring
- especially older stocks
Follow:
- Weakening of metabolism and other leaf functions
- overall reduced growth performance of the plant
- due to the lack of leaf fall in most cases, rapid spread due to permanent spore deposits on the affected leaves
measures:
- immediate removal of all affected shoots
- Preventing rapid spread by avoiding overhead watering (spreading of spores through irrigation water)
notice: Boxwood rust is very rare in Germany. However, if it occurs once, action should be taken quickly and consistently once it has been detected, since the spore deposits can only be identified very late and are permanently present on the plant as a source of infection due to the lack of leaf fall.
recurring methods by similar pathogens
If you look carefully at the list of diseases, you will notice that in almost all cases fungi are the primary causes of diseases on boxwood. Although the damage can be very individual in each case, the help is usually similar.
Usually work fungicidal agents against the fungus, provided that the agent has a way of getting to the fungus. In addition, the containment of a spread is always successful by removing the fungal spores and their spore stores. A quick removal and at the same time disposal of infested areas is actually always effective. In many cases, this also includes dead leaves. In general, neither composting nor shredding should be done, as the fungal spores survive these procedures without damage and are thus even further spread. On the other hand, a great help is the disposal in the residual waste, or the burning of the shoots, if permitted and feasible on the garden property.
Pests on boxwood
In addition to the numerous boxwood diseases, there are also some pests for which the boxwood is a favorite food. A selection of malware and countermeasures can be found in the following overview.
box tree moth
(Glyphodes perspectalis)
Box tree moth, Cydalima perspectalis
cause
- Green caterpillars with black and white longitudinal markings and a black head
- Body length of 8 millimeters
- Young caterpillars up to 5 centimeters just before entering the pupation
damage picture
- characteristic webs inside the crown of Buxus sempervirens
- initially from about March intensive leaf damage
- subsequently eating away the bark of young shoots with subsequent drying out and death of the shoots
combat
- Biological control agents from the trade are only very specifically effective in a certain development phase of the caterpillars
- mechanical removal of the caterpillars
- for example by blowing out the bushes with a (cold) steam jet
- Enveloping the crowns with dark foil and thus killing the caterpillars by increasing the temperature inside the foil
danger: The box tree moth is one of the most feared and common pests affecting Buxus sempervirens. However, the actual butterflies are harmless and are rarely found on the boxwood itself. The caterpillars, on the other hand, can spread like epidemics and cause enormous damage due to their high feeding rate. Regular monitoring and early inclusion of countermeasures is therefore essential for success.
Boxwood flea
(Psylla buxi)
cause
- Leaf flea, recognizable by its greenish body, about 3.5 millimeters long
- winged and with jumping legs
- when approached, usually jumping up well recognizable
- Larvae yellow-green and flattened
- often covered with a whitish layer of wax
damage picture
- Development of spoon-leaves (rolling up of the leaves on all sides into a spherical shape in which the larvae are located)
- yellowing of the leaves
- Affected areas streaked with white wax threads
- Restriction of plant growth due to interference from the wax layer
- Honeydew excretions are also a breeding ground for sooty mold fungi
Spoon leaves on boxwood caused by boxwood leaf fleas
combat
- Remove and discard infested shoot tips to prevent further spread
Boxwood spider mite
(Eurytetranychus buxi)
cause
- Mite, different manifestations in the course of development
- Eggs are only 0.1 millimeters in size and yellow-brown, mostly found on the undersides of leaves
- Larvae with 3 pairs of legs and yellow-green coloration, followed by reddish-brown coloration and elongation of one pair of legs
- prefers warm, dry conditions, therefore intensive propagation, especially in hot summers
- humid weather and precipitation, on the other hand, have a strong population-reducing effect
damage picture
- streaky lightening on the upper and lower side of the leaf, then clearly visible leaf speckles
- in the case of intensive infestation, encasing young shoots in particular with spider threads
- consequently significant impairment of metabolism and photosynthesis of affected areas
- finally weakening of the plant and thus higher susceptibility to secondary diseases
Spider mite infestation
combat
- in autumn, rapeseed oil-based pesticides to prevent oviposition and hibernation
- appropriate insecticides in the spring
- However, it is not absolutely necessary to remove the shoots if you want to combat the mites in other ways
- natural variant: colonization or favoring of predatory mites
notice: The boxwood spider mite was completely unknown to us until a few years ago. It only found its way to us from its North American homeland around the turn of the millennium. Although they can be counted among the neozoa as immigrants, native predators are of great help in combating them. However, an uninhibited spread as a result of a lack of natural enemies is not to be expected.
boxwood midge
(Monarthropalpus buxi)
Boxwood midge, Monarthropalpus buxi
cause
- Larva of the boxwood midge
- after hatching in early summer about 0.5 millimeters in size, legless with orange colored body
damage picture
- Damage caused by intensive feeding activity by the larvae can usually be seen from August
- bright yellow spots on the upper side of the leaf, bump-like formations on the underside of the leaf
- In the case of intensive infestation, the individual galls merge into large blisters
- severe infestation leads to leaf fall and dried shoots
- consequently significant weakening of the plant
combat
- if the infestation is only slight, remove affected shoots in spring to get rid of the eggs
- in the case of severe infestation, cut back all infested areas immediately after detection