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 March 28th 2018 : The first caterpillars of the Box tree moth 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”.

 

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.