Plasmopara petroselini (Oomycetes) was identified on parsley (Petroselinum crispum subsp. crispum cv.Petra) (Apiaceae) in Belgium during the winters of 2001 and 2002. The fungus was present in numerous fields, especially on parsley grown in plastic tunnels. Losses were sometimes dramatic and similar to disease problems in France and Switzerland where 80 and 50 ha, respectively, were found infected (1). Initial symptoms consisted of white spots on the upper leaf surface. As the disease progressed, the spots enlarged, became angular, and turned yellow. At the location of leaf spots, white-to-grayish white mycelium developed on the lower surface of the leaves. Eventually the leaves and leaf stalks rotted. The pathogen was identified at the Centraalbureau voor Schimmelcultures (CBS) (Utrecht, the Netherlands) as the downy mildew organism P. petroselini (= P. umbelliferarum pro parte = P. nivea pro parte = P. crustosa), based on morphological characteristics. Sporangia were papillate, lemon-shaped, almost hyaline, and 9 to 20 μm long, and produced on tree-like sporangiophores (100 to 420 × 6 to 8.5 μm) that were monopodially branched at approximately right angles. The sporangiophores usually bear three sterigma (4 to 19 × 2 to 3 μm) that narrow toward the tip (2). Prophylactic actions are the primary method to prevent the disease. Fungicides based on propamocarb can be used as a curative control method. To our knowledge, this is the first report of P. petroselini on parsley in Belgium.
References: (1) E. Béliard and J. Thibault. Phytoma 554:2, 2002. (2) M. Brandenburger. Page 451 in: Parastische Pilze an Gefässpflanzen in Europa. Fischer Verlag, Stuttgart, Germany, 1985.
