Pests and diseases

Boxwood can be damaged by several parasites. However, it is not necessary to treat the plant for every infestation. Some pests or diseases are not a threat for the plant, or only to a limited extent.  Some diseases do need a vigorous approach however. The most damaging diseases are stated below.

Current news July 12th 2017 : The first caterpillars of the Box tree moth (2nd generation) have been spotted.  This is the time to handle them, e.g. with biological products like Conserve Garden. More info : see section below “Box tree caterpillar”.

The first symptoms of blight have also been detected. Treating now can prevent much damage : see schedule below.

For every pesticide there is a list of examples of active substances, of which is known that they are effective. Brand names are not mentioned because these can differ per country. Not all products are available or registered in every country and these registrations change on a regular basis. Therefore please check your local registrations. For Belgium : www.fytoweb.be

This section was drawn up on the experience of a professional nursery, complemented with scientific research. Following research institutes cooperated in the investigation :

Harmful diseases of Boxwood

Box tree caterpillar Cydalima perspectalis (syn.Diaphania perspectalis) !

The caterpillars are bright green with a black head. This Asian butterfly can grow as big as 4 cm.  There are two generations in Belgium : April/May and August.

Box tree caterpillar

Box tree caterpillar larva

Damage: the caterpillars can strip a plant bare on a short amount of time. Webs can be found on the damaged plants. There are two periods in which most damage occurs : April/May and August

Treatment: to be treated with a special product against caterpillars (insecticide) based on spinosad (Conserve Garden : biologically based), Bacillus thuriengiensis (biological), lambda-cyhalothrin (Karate Garden) or deltamethrin. It is important to hit the caterpillars well and to repeat a week later in case of new caterpillars.

Important: if the first generation of this exotic species is fought well, much fewer problems will occur in summer.
Treat your plants with preferably organic products !
Plants attacked and eaten will recover and do not have to be removed !

Additional tip : the adult Buxus moths are attracted by artificial light.  Use as less garden lighting as possible if adult moths are flying around.

Boxwood blight Cylindrocladium buxicola = Calonectria pseudonaviculata !

The investation starts with black spots on the leaf. A few days later the affected leaves will fall down en masse and black stripes appear on the young twigs.

Buxus blight

Buxus blight

Damage: large, bald places which can lead to plant death.

Treatment: to be treated with special fungicides as from May. Extra care in warm, moisty periods with heavy rainfall.

Treatment schedule Cylindrocladium and Volutella : Consument België 2017

Time Product Dosage/10 l water Remark
May Ortiva Plus
+ Sporgon Garden
10ml
10 gr
 
June Eminent 7.5 ml max. 3x/year
July Eminent 7.5 ml max. 3x/year
August Eminent 7.5 ml max. 3x/year
September Ortiva Plus
+ Sporgon Garden
10ml
10 gr
 

Copper-based products work preventively but are less efficient. Also please take into account that the phyto legislation changes frequently in Europe and not all products are allowed in every member state.

Detailed article: see pdf document.

Volutella blight Volutella buxi

The damage starts with the leaves turning brown. After that they dry out but stay attached to the plant temporarly. under the leaves there are traces of a pale pink fungus.

Volutella blight

Volutella blight

Damage: Brown, dry leaves and twigs mar the plant. When the damage is severe the plant can die.

Treatment: ! to be treated with specialised fungicides. Extra attention is required after pruning or after frost damage.

For more information: see the pdf document

Mussel scale  Lepidosaphes ulmi !

Dark brown, comma-shaped scale insects (ca.3mm) that usually appear in the centre of the plant on old twigs. When the plant is severely damaged it covers the entire plant.

Oystershell scale

Oystershell scale

Damage: the twigs and leaves turn yellow because of the sucking damage. When the damage is severe, the plant dies.

Treatment: ! To be treated with a specialised insecticide, in mid-May and to be repeated 14 days later. The entire plant needs to be treated with plenty of spray fluid. Example: product based on imidacloprid, spirotetramat, a.o.Winter treatment with mineral oils is also possible.

Boxwood spider mite Eurytetranychus buxi

This tiny spider mite (0.3mm) causes sucking damage to the leaves.

Boxwood spider mite

Boxwood spider mite

Damage: small, silver-coloured stripes and dots on the leaves, usually the old leaves. It is clearly visible inside the plant.

Treatment: ! It needs to be treated with a specialised acaricide starting in May. Spray when the weather is warm. Example: product with the active ingredients tebufenpyrad, bifenazaat, a.o.

Less harmful diseases of Boxwood

Boxwood sucker Psylla buxi

These insects have a length of 3 to 5 mm, their larve are covered with a white waxy coat and they prick and suck out dry young shoots.

Boxwood psyllid

Boxwood psyllid larva

Damage: spoon-shaped curly shoots.

Treatment: It needs specialised insecticide from the start of April, but only when the fleas are present. Example, product with the active ingredients imidacloprid, spirodiclofen, a.o. When the plants are pruned at the end of the year, a part of the damage is removed in a natural way.

Buxus gall mite Aceria unguiculata

These are very small gall mites (0.1mm) that feed on plant sap from the shoots.

Buxus gall mite

Damage: small, misshapen leaves in the shoots that grow tick-set.

Treatment: it needs to be treated with a specialised acaricide if the pest occurs. Spray when the weather is warm. When the plants are pruned, the damaged shoots are removed. Example: product with the active ingredient tebufenpyrad.

Boxwood leaf-mining gall midger Monarthropalpus flavus

They are worm-like larve (ca.3mm) that causes swelling in the leaf. The full-grown insects are short-living, red-coloured gnats that have a length of 2-3mm.

Boxwood leafminer

Boxwood leafminer

Damage: yellow to red leaves with pouch-like galls.

Treatment: It needs to be treated with a specialised insecticide from the start of May. Example: a product with the active ingredient spirotetramat, a.o.

Boxwood rust Puccinia buxi

Small, dark brown pustules of spores appear under the surfaces of the leaves. It occurs mostly in shadowy, wild boxwood populations. It is quite rare in gardens.

Boxwood rust

Boxwood rust

Damage: brown pustules of spores affect the appearance of the plant.

Treatment: If necessary, it should be treated with a specialised fungicide including the active ingredients tetraconazole, tebucanozole + trifloxystrobine

Pythium sp. Pythium species

It is a root disease that usually occurs after a watering problem on parcels that are too wet or when the plants are grown in pots. The plant dies or dies partially and dries up.

Damage: died out, dried up twigs and plants.

Treatment: It needs to be treated with a specialised fungicide including the active ingredients propamocarp, dimethomorf, a.o.

Phytophthora root rot Phytophthora species

It is a root disease that usually occurs after a watering problem on parcels that are too wet or when the plants are grown in pots. The plant dies or dies partially and dries up.

Damage: died out, dried up twigs and plants.

Treatment: It needs to be treated with a specialised fungicide including the active ingredients fosethyl, fenamidone+fosethyl, a.o.

Black root rot Chalara elegans/Thielaviopsis basicola

It is a root disease that usually occurs when plants are grown in pots, probably caused by a watering problem.

Damage: The roots die out and usually have damaged, black connections. The plants weaken and the growth stops.

Treatment: It needs to be treated with a specialised fungicide including the active ingredient thiofanate-methyl, a.o.