15 septembre 1991
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Les données sur la biologie de Sclerotinia trifoliorum et sur l'épidémiologie de la sclérotiniose permettent d'établir des directives pour la lutte, qui doit associer les diverses techniques disponibles pour être pleinement efficace. En raison de la sporulation strictement automnale et du développement hivernal du champignon, les semis non protégés doivent être réalisés au printemps et non en fin d'été, les jeunes plantes étant particulièrement sensibles aux pourritures. Plusieurs fongicides anti-sclerotinia testés en culture grainière, appliqués en novembre, peuvent protéger les cultures des attaques des ascospores, notamment les cultures installées en fin d'été. Ces traitements font l'objet d'avertissements en production grainière. Certaines variétés, tétraploïdes, mais aussi diploïdes, montrent un bon niveau de résistance à la sclérotiniose et une bonne pérennité, surtout si elles sont semées au printemps.
Sclerotinia trifoliorium as a major threat to red clover in France, and in the absence of measures taken to control it, farmers could have to give up growing this crop. The research work carried out in France these 10 years or so on the biology of the fungus and the epidemiology of the disease is given a rapid review. The data collected make it possible to set up rules for the control of clover rot. It is pointed out that the fungus sporulates only in October and November, and develops rot on the leaves and crown in Winter and early Spring, under conditions of continuous moisture and temperatures near 10-15°C. The disease can be highly destructive on young stands sown in Autumn. In the case of Spring sown stands, the progress of the disease during subsequent years depends mainly on the resistance of the cultivar.
It is therefore recommended to sow red clover in Spring, especially if no fungicide is applied. Fungicides have been tested in seed production (carbendazime, procymidone, vinchlozoline, carbendazime+vinchlozoline). All exhibited a good control of the disease if applied in November, especially on the young stands own in Autumn, at 1,5 kg/ha of the commercial product. The forecasting of treatment effects is possible by observing the date of ripening of apothecia formed by sclerotia produced in the laboratory and put in Autumn in the field. A good varietal resistance, but not a total one, can be found in tetraploid varieties (Temara, Tetri, Lossam, Vanessa) and also in diploid ones (Diper, Kuhn, Noe, Albatros, Justin). These varieties have been selected under field conditions, but studies are made nowadays to screen varieties in growth chambers, under artificial contamination with ascospores produced in the laboratory. All the recommended techniques should be associated so as to improve their individual effectiveness.
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