The pinewood nematode: a threat to conifers
What is the pinewood nematode?
The pinewood nematode is a microscopic worm that attacks certain conifers, mainly pine trees. Once inside the trees and when conditions are favourable, the nematodes multiply and block the flow of sap. When affected, the trees turn red, lose their needles and can die within a few weeks. Originally from North America, the pinewood nematode spread to Asia before arriving in Europe. It has been present in Portugal since 1999 and has been found in certain areas of Spain since 2008. The first outbreak was detected and confirmed in France on 3 November 2025 in the Landes département. The nematodes spread from tree to tree via insect vectors such as the Monochamus galloprovincialis beetle, which is found in all regions of mainland France. This insect becomes a carrier of the nematode when the beetle larva develops in an infected tree. It then transports the nematodes from one tree to another while feeding or laying eggs.
What is the risk of infestation?
The spread of the pest is mainly due to the transport of wood or plants. Infested wood packaging and bark were first discovered in France in 1992 and have been found repeatedly since 2000.
The Landes is a high-risk area because it has several factors that favour the spread of the parasite: climatic conditions that allow the symptoms of tree decline to manifest, the presence of the insect vector, and a forest area made up of maritime pine species that are susceptible to the nematode.
The risk of the disease spreading from an outbreak is linked to the ability of the insect vector to transmit the nematode from tree to tree and depends on:
- the nature of the products and by-products resulting from forestry exploitation and in particular their dimensions;
- the fate of these materials: storage for varying lengths of time and transport;
- the period considered: during or outside the insect vector’s flying period.
What measures should be taken if an outbreak of pinewood nematode is detected?
If pinewood nematodes are detected, European Union legislation requires that mandatory management measures be implemented. These measures aim to limit the risk of spreading pinewood nematodes and their insect vector. The French Directorate General for Food and its regional delegations coordinate the deployment of the national health emergency plan. Clear-cutting may be carried out around the infested trees, extending up to a radius of 500 metres. Other measures are also organised within a 20-kilometre radius of the outbreak. These include a ban on forestry exploitation and timber transport, coupled with active monitoring of the existing trees.
ANSES’s role in combating the pinewood nematode
National and European Reference Laboratory
The Nematology Unit of ANSES’s Plant Health Laboratory in Rennes is the National and European Reference Laboratory for identification of the pinewood nematode. In this capacity, it has been working for more than 25 years to develop innovative detection methods to ensure enhanced surveillance in France and Europe. Every week, the laboratory supervises or carries out tests on wood samples taken from ports, forests or factories, as well as insect-vector samples.
Three expert appraisals to pre-empt the threat of pinewood nematodes
Following a request by the Ministry of Agriculture, ANSES conducted several expert appraisals to assess the risk of introduction and establishment of the parasite and to recommend wood management measures to be applied in France.
Measures for the transport, storage and treatment of wood or bark susceptible to pinewood nematode if an outbreak of this parasite is declared
Following the devastating forest fires of 2017, under the European regulations, Portugal asked to be able to authorise the removal from the country of symptomatic wood – susceptible trees that had died, were dying, were the casualties of storms or fires, or were contaminated by the pinewood nematode – in the form of chips. This led ANSES to assess the risk of the pinewood nematode and its vector spreading from all materials resulting from wood processing in the forest, from their storage in the forest through to their final processing.
Based on current scientific knowledge, the Agency has determined phytosanitary measures for control or prevention to be applied to the various forest products and by-products according to their fate and the time of year:
- during the flying period of the adult insect vector M. galloprovincialis, from 1 April to 31 October, only shreds and/or chips smaller than 3 x 3 x 3 cm can be left in place without any risk of insect development. Only the chips, being a commercial product, are then transported. If they are stored for less than 48 hours, they do not require treatment in the forest but must then be transported securely to avoid attracting and transporting adult insect vectors. Other wood products, not subject to chipping or shredding in the forest, must be protected in the same way as wood chips, taking into account the storage conditions in the forest, whether short (<48 hours) or long. All wood products stored outside the forest in dedicated sites or industrial processing sites must continue to be protected to prevent the emergence of young adults or infestations by mature adults of M. galloprovincialis;
- outside the flying period of the adult insects, from 1 November to 31 March, no treatment is necessary in the forest, as the wood products and by-products cannot, in principle, attract these insects. Treatments are therefore only to be applied in storage areas or sites if storage lasts beyond the winter period.
There are measures to prevent the key stages in the development of the insect vector that increase the risk of spreading the nematode, i.e. attraction and egg-laying or flight. However, these measures remain experimental or are not authorised in France. Scientific research and/or technological advances are therefore needed to conceive realistic technical solutions at the scale of forest exploitation. These will have to ensure risk-free storage and/or transport of material from tree species susceptible to the pinewood nematode and its insect vector. These could include, for example, the use of insecticide-impregnated protective netting or heat treatment of wood products and by-products.
Species likely to facilitate the multiplication of the pinewood nematode
The Agency also assessed the susceptibility of plant species to the pinewood nematode and its insect vector. The main host plant species for the pinewood nematode belong to the genus Pinus, but the list of susceptible plant species includes other conifers of the genera Abies, Cedrus, Larix, etc. At present, there are no species of pine established in Europe that are resistant to the pinewood nematode, although some are less favourable to its multiplication.
If a nematode outbreak is detected:
- the species on which the nematode can multiply should be eliminated as a priority: maritime pine, Scots pine, black pine, Monterey pine, and probably Aleppo pine and loblolly pine;
- susceptible species should be used to produce wood chips, whose dimensions are all less than 3 cm in size, to prevent them from harbouring larvae of the insect vector.
Management of pine bark potentially contaminated by the pinewood nematode
In 2018, following the discovery of bark from Portugal contaminated by the pinewood nematode and intended for sale in France, ANSES’s expert appraisal focused on managing the risk posed by pine bark susceptible to this parasite.
The Agency concluded that planting young seedlings of susceptible pine – especially maritime pine – in forests increases the risk of the nematode becoming established in France. In addition, the presence of wounds on the roots and their close contact with contaminated compost increase the risk of direct transmission of the nematode.
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