Downy mildew

The downy mildew is a dreaded in agriculture and horticulture in Europe since the mid-19th century plant disease. It was first described in 1878 under the name Plasmodium para. Today it summarizes the different downy mildew species under the order Peronosporales the Eipilze together (these are not phylogenetically to the mushrooms ). In contrast to powdery mildew develops on the lower leaf surface a grayish - bluish fungus lawn.

Infection occurs either as a primary infection in the spring by oospores that can overwinter in the soil or by zoospores, which are formed from the primary infected herds. The motile spores ( zoospores ) penetrate through stomata into host tissue, where they form the mycelium ( hyphae ) between the cells ( intercellular ). Overeating organs ( haustoria ), which are introduced into the living cells, the fungi found in the plant nutrients and thereby damaging them. For reproduction, hyphae grow out through the stomata and forms branched fruiting bodies ( sporangiophores ). The nutrient loss leaves turn yellow and fall off the affected leaves. Downy mildew is spreading especially under moist and warm conditions in the field and in greenhouse cultures.

Great economic importance among the Peronosporales downy mildew of grapevine (Plasmopara viticola ), the late blight of potato (Phytophthora infestans ) and the tobacco blue mold ( Peronospora hyoscyami f.sp.. Tabacina ). Under warm, moist site conditions beet, lettuce, cabbages and roses are also at risk. In the greenhouse, can result in total crop failure downy mildew on cucumbers. Of importance is also the downy mildew in sunflower and hops.

Until the second half of the 20th century only copper connections were to combat downy mildew available. Because of the damage to the soil life when using this heavy metal use has been restricted. In the current crop production systemic fungicides and contact fungicides prophylactically mainly synthetic are used. An effective means is the use of phosphonic acid, which is also permitted in organic farming. A special role in powdery mildew control in agriculture and viticulture plays the plant protection warning service. This is issued by the State Plant protection agencies and scientific institutions during the growing season and gives regional information on when, due to the rainfall and temperature control measures to be taken in field crops.

Moreover done special research efforts on the one hand for the purpose of use of natural materials for triggering of resistance against downy mildew in crops and on the other hand for the purpose of breeding mildew resistant plant varieties.