Protection methods

- During cultivation

There is no curative control method that can effectively control viruses and in particular the agent of necrotic rings in lettuce ( Lettuce ring necrosis agen t , LRNA) during culture. An infected plant will remain so for its entire life.

During and at the end of cultivation, plant debris , in particular root systems, must be removed from the plots and destroyed, in order to prevent them from being subsequently buried in the soil at the same time as the resting spores. Olpidium virulentus (ex Olpidium brassicae ).


- Next crop

should be Healthy plants planted to avoid introducing LRNA into soils that are still free.

The nursery soil should be disinfected with a fumigant . It will also be beneficial to place the plants produced on tables or on a plastic film in order to avoid contact of the roots formed with the soil.

Eradication of the disease in an affected plot seems as impossible as in the case of Big-vein; the resting spores of the vector fungus probably retaining the ability to transmit the virus for many years. Also, contaminated soil will remain so for a long time. The soil of future salad plots will be well prepared and drained in order to avoid the formation of puddles favorable to the development and dissemination of Olpidium virulentus (ex Olpidium brassicae ). It will be better to plant salads on hillocks. Under shelter, fumigation of the soil may be considered, in order to limit the number of viruliferous resting spores in particular. The effectiveness of this treatment can last 2 years, when it is carried out according to the rules of the art . In Provence, as in Roussillon, it appears that the spread of the disease was directly linked to the gradual abandonment, and soon to be compulsory, of this method of disinfection. experiments Solarization , carried out in the Lyon region, have shown that this method of disinfection has definite effectiveness with regard to this disease. However, the mechanism of action remains unexplained to this day. Remember that solarization is only possible in production areas where the climate and the production calendar allow it.

The search for resistance is made difficult due to the lack of knowledge of the responsible agent and the absence of a detection tool. Only observations made in the field, in heavily contaminated soil, showed differences in sensitivity within the types of lettuce, the batavia iceberg type being the least sensitive to the disease. Lesser sensitivities were observed within the European type batavia genotypes.

The combination of solarization and the use of less sensitive lettuce makes it possible to delay the expression of symptoms; as a result, a greater number of plants remain marketable.