Roundheaded appletree borer (Saperda candida) | Biological control

Saperda candida – A dangerous pest for fruit trees

The roundheaded appletree borer (Saperda candida) is a quarantine pest that poses a particular threat to apple and other fruit trees. Originally from North America, it was first discovered in Europe on the island of Fehmarn in 2008. Despite intensive measures, the beetle remains a serious risk to agriculture and nature.

Larva of the round-headed appletree borer (Saperda candida)

Distribution and introduction

Saperda candida is widespread in North America, where it prefers to infest apple trees. In Europe, Fehmarn is the only confirmed location of infestation to date. However, international trade in plant material poses a risk of further introductions. The beetle's larvae develop over two to four years in the wood of their host plants, boring feeding tunnels that cause massive damage to the trees.

Host plants

The beetle infests a variety of deciduous trees, in particular:

Apple (Malus)
Pear (Pyrus)
Cherry and plum (Prunus)
Quince (Cydonia)
Hawthorn (Crataegus)
Rowan and service tree (Sorbus)

These host plants are found in orchards, private gardens and on roadsides. Young and healthy trees are particularly susceptible to infestation.

Damage caused by Saperda candida

The larvae cause severe mechanical damage to trees by feeding on them:

Destruction of the trunk and cambium: This impairs the supply of water and nutrients
Susceptibility to breakage: The feeding tunnels weaken the stability of the trees.
Yield losses: Severely infested trees die. In North America, entire new plantations have been destroyed.

The economic damage is considerable, especially in commercial fruit growing. It is estimated that yield losses can vary between 5% and 100%, depending on the severity of the infestation.

Typical feeding tunnels made by the larvae

Control measures against Saperda candida

Mechanical and official measures

Clearing and destruction of infested trees: Infested and endangered host plants within a radius of up to 200 metres around the infestation site must be felled and the wood destroyed.
Monitoring and control: Regular inspections for signs of infestation such as bore holes and gnaw marks are crucial.

Beneficial nematodes as biological control

In addition to clearing, beneficial nematodes (e.g. Heterorhabditis spp.) can be used around the affected areas. They offer a promising environmentally friendly control method. These tiny threadworms are applied to and around the affected trees, penetrate the beetle larvae and kill them. To protect the nematodes from drying out, the treated trunks can also be wrapped in damp coated painter's fleece with the coating to the outside. Advantages of this method:

Environmentally friendly: No chemical residues.
Specific: Infestation of other organisms is minimised.
Effective: Especially when used early against larval stages.

Painter's fleece protects the nematodes from drying out.

Application of nematodes against the roundheaded appletree borer

The recommended dosage of nematodes is 10 million per tree trunk.

Apply the nematode spray solution (10 million/tree) thoroughly to the lower 30 cm of the tree trunk until dripping wet. Add a wetting agent e.g. nema-viscum in standard concentration to increase the mobility of the nematodes.

Repeat application every 4-6 weeks.

Dosage
Dissolve the package contents in 10 liters of water, depending on size. Rinse packaging thoroughly and stir. Always dissolve the entire package, as nematodes may be unevenly distributed in the carrier material.

Use the entire contents of the pack at once and completely use up the mixed spray liquid. Remove all filters and sieves and use nozzles with a diameter of at least 0.8 mm. Stir during application to prevent the nematodes from settling.

Package size	Mix in	Sufficient for
250 million	50 litres water	20-30 trees
500 million	100 litres water	50 trees

Download application instructions

Nematodes of the species Heterorhabditis bacteriohora

Roundheaded appletree borer