La sharka est une maladie épidémique et inguérissable des Prunus, provoquée par le Plum Pox Virus (PPV). C'est la virose la plus grave pouvant infecter les abricotiers, pêchers et pruniers. Elle est transmise par le matériel infecté et par nombre d'espèces de pucerons. L'un des points importants pour protéger la filière consiste à maintenir une production de plants à l'abri des contaminations. Dans ce cadre, cinq huiles minérales ont été éprouvées à 1 et 3 %, sur 3 porte-greffe (2 pêchers et un abricotier) placés en conditions naturelles. L'application des émulsions huileuses n'a pas entraîné de manifestation phytotoxique chez les plantes traitées. En conditions contrôlées, les plantes traitées à l'huile minérale à 1 ou 3 % sont protégées à l'égard du PPV transmis par Myzus persicae, 24 heures après l'application. L'usage d'émulsion huileuse appliquée pendant les périodes à risques constitue un moyen de lutte préventive en pépinière fruitière contre les contaminations du PPV assurées par les pucerons. L'huile minérale préserve l'environnement et semble efficace préventivement contre les acariens sur pêcher. The protecting effect of mineral oil sprays against the dissemination of plum pox virus (PPV) has been investigated in order to propose a field method for protecting the nurseries of susceptible Prunus.
PPV is a virus which is transmitted by more than
20 species of aphids in a non persistent manner.
It has been identified in most ot the european countries in plum, peach and apricot trees. In France, the method of control is based on a production of healthy trees at the nursery level and on a sanitation of infected orchards.
Spraying mineral oils has been extensively used in annual crops for reducing the dissemination of non persistent viruses.
In the case of PPV, experiments have been performed in 1996-97 first, in confined conditions, for establishing the protecting effect against PPV aphid transmission, second, under field conditions, for measuring an eventual toxicity of repeated oil sprays on the growth of Prunus rootstocks as well as an eventual deleterious effect on the healing of grafted variety buds.
Five commercial oil preparations were compared in these experiments.
The results show that spraying young shoots with the mineral oils strongly reduces or annihilates the PPV transmission by aphids. Similarly, no phytotoxicity was observed in 1996 and 1997 on rootstocks grown in open field and ten times sprayed with 1 % or 3 % oils emulsions during the spring and early summer of 1996.
No deleterious effect was observed on the graft healing. However, in order to be significative, this part of the experiment has to be repeated on a larger number of grafted rootstocks.
These results suggest that spraying with mineral oil emulsions could be an interesting way to protect Prunus nurseries against a PPV dissemination when used in association with a suitable geographic isolation.
Complementary experiments could be needed to adapt the spraying frequency at the local level to the seasonal frequency of aphids species known to be able to disseminate the virus.