Root neck and stem rot
The Wurzelhals- and stem rot ( Phoma lingam ) is a fungal infection in plants.
The disease is very difficult to assess in terms of its impact on yield. The variety of symptoms of infection of the Phoma fungus ranges from white spots on the leaves in autumn to constrictions on the root neck (premature death) to more or less dark-edged spots on the stem and later also on the pods. What they have in common is that after the bleaching, numerous small black pycnidia ( spore carriers ) develop in all spots , from which the spores spread further in the stand. The main source of infection for the rapeseed that emerges in autumn are old straw and stubble remains. Since the infection of the rapeseed is possible in autumn from emergence to the beginning of winter, there is still no optimal treatment date for approved fungicides . The autumn infestation is considered to be more dangerous, since infested plants can die prematurely due to premature root neck rot. An infestation after winter is considered to have less of an impact on yield. The assessment of the infestation of Phoma is made even more difficult by the very strong balancing power of the rape plant.
Combat
Combating this disease with tolerant varieties is currently more economically promising than the use of chemicals . Fighting earth fleas and weevils can also be helpful. The position of oilseed rape in the crop rotation is not important for this disease.