24/02/2020 2 mins

Pinewood nematode: preventing its introduction and spread in order to protect French pine forests

The pinewood nematode (Bursaphelenchus xylophilus), a microscopic worm responsible for significant dieback in conifers, poses an imminent threat to French forests of maritime pine. It is currently present in Portugal and some parts of Spain, and could potentially contaminate the Landes area of France where the parasite's insect vector is also found. The nematode's spread is mainly due to the transport of contaminated wood packaging and products. Nematode-contaminated bark and packaging was intercepted in France in 2018. This led ANSES to conduct several expert appraisals to assess the risk of entry and spread of the pinewood nematode in France. The Agency summarises its recommendations on the use of wood and bark likely to be affected by this parasite.

The risk of French forests becoming contaminated by the pinewood nematode has increased in recent years, mainly due to rising demand for wood chips and bark and the movement across Europe of huge volumes of contaminated products from Portugal and Spain. In 2018, bark and wood packaging infested with live pinewood nematodes was intercepted in France. Following a request by the Ministry of Agriculture, ANSES conducted several expert appraisals in order to provide guidance on the management measures to be applied to wood products.

Pines are especially susceptible to the nematode through its insect vector

In its first expert appraisal, ANSES stated that the risk of spread from a nematode outbreak was mainly associated with the ability of the insect vector, Monochamus galloprovincialis, to transmit the parasite from tree to tree.

This beetle thrives in particular on nematode-contaminated trees, from which it will itself become contaminated. It may then fly to healthy trees, where it will feed and transmit the parasite. The risk of direct transmission of the nematode from infested bark and packaging was regarded as low due to its limited ability to survive and move, from bark to soil and then within soil.

The Agency also identified the plant species most susceptible to this nematode and its insect vector. These are mainly species of the genus Pinus. At present, there are no species of pine established in Europe that are resistant to the pinewood nematode. Planting young seedlings of susceptible pine – especially maritime pine – in forests therefore increases the risk of the nematode becoming established in France.

Recommendations to prevent the pinewood nematode spreading from the site of an outbreak

Based on current scientific knowledge and the conclusions of its expert appraisal, the Agency has made a series of recommendations on outbreak management, in order to prevent the development of the insect vector and the spread of the nematode.

Main recommendations if a nematode outbreak is detected:

  • remove forest species on which it can multiply: maritime pine, Scots pine, black pine, Monterey pine, and probably Aleppo pine and loblolly pine;
  • for wood chips produced from susceptible species, require all dimensions to be less than 3 cm, as chips smaller than this can no longer harbour larvae of the insect vector;
  • during the adult insect vector’s flying period, implement specific control and prevention measures such as the application of plant protection treatments or the use of insecticide-impregnated netting. Outside this flying period, no treatment is necessary in the forest because the insects are unable to fly to the products and by-products of wood harvesting to lay their eggs.

To learn more about ANSES's work and recommendations on the pinewood nematode, read our article.