Pests and diseases

Boxwood can be damaged by several parasites. However, it is not necessary to treat the plant for every parasite. Some pests or diseases are not or little threatening for the plant. Some diseases do need a vigorous approach and are stated with an exclamation mark (!).

Every pest or disease is accompanied with a list of active substances, which are available in Belgium for professional use. Brand names are not mentioned because they can differ per country. Not all products are for sale or labelled for the control of pests and diseases on boxwood -in all countries so it is best to refer to- the chemical regulation of your own country. Before using or even buying chemicals, it is important to read the label; this contains vital information on how to use the product safely and effectively. It is important to use chemicals lawfully.

Belgium: www.fytoweb.be

This section was based on the experience of a professional nursery and supplemented with scientific research. Some information can also be found on the following websites:

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.

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 old leaves. It is very 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.

Buxus gall mite Aceria unguiculata

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

Buxustopmijt

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.

Mussel scale  Lepidosaphes ulmi

These are dark brown, comma-shaped scale insects (ca.3mm) which usually occur in the centre of the plant on old twigs. When the plant is severely damaged it covers the whole 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: ! It needs to be treated with a specialised insecticide, in mid-May and it needs to be repeated 14 days later. The entire plant needs to be treated with plenty of spray fluid. Example: product with the active ingredients imidacloprid, spirotetramat, a.o.Winter treatment with mineral oils is also possible.

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.

Box tree caterpillar Cydalima perspectabilis

They are bright green caterpillar, 4cm long with a black head. They feed on the leaves. This butterfly originates in Asia.

Buxusmot

Buxusmot larva

Damage: The caterpillars can devour a plant in a short period of time. They leave a web on the damaged plants.

Treatment: ! They need to be treated with a specialised insecticide including spinosad, Bacillus thuringiensis, a.o.

Boxwood blight Cylindrocladium buxicola = Cylindrocladium pseudonaviculatum

The damage starts with black spots on the leaf. After a few days these leaves will fall off and black stripes will appear on young twigs.

Buxus blight

Buxus blight

Damage: Big, bare spots that could lead to the plant’s death.

Treatment: ! It needs to be treated with specialised fungicides from the start of May. Pay extra attention in periods of warm weather with a lot of rain.

For more information: see the 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. At the bottom of 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: ! It needs to be treated with specialised fungicides. Extra attention needs to be paid after pruning or after damage from frost.

For more information: see the pdf document

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.