ENVIRONMENTAL CONDITIONS AND CULTURAL METHODS IN CONNECTION WITH DISEASE CONTROL IN POT PLANTS
The cultivation of pot plants holds a special place in floriculture. From a phytopathological point of view, it is of great importance that every new generation of a pot plant species should be started in pathogen free soil, and sufficiently hygienically managed, so that the limited amount of soil in the pot may still be free from parasites when the product reaches the consumer.
One should realize, however, that the glasshouse area for pot plant growing is being used very intensively, and that pot plants are often grown for decades in the same houses. These facts make the result of hygienic measures in many cases doubtful, e.g. when plants are grown in layers or when the pots are layed in every year in the same soil.
After the pathogenicity of Nectria radicicola (Cylindrocarpon destructans, Scholten 1964) for Cyclamen had clearly been demonstrated, the use of steam sterilized soil for seed and pricking boxes was introduced in the nurseries. In the first season we observed seed bearing mother plants with sporulating mycelium in their hearts over the tables with seedling boxes. In another case, the young plants in steam sterilized soil were sprayed with water from a ditch in which the neighbour had thrown his diseased plant material. Needless to say that in both cases serious losses had been observed.
A similar situation arose in a nursery where healthy young plants of Anthurium scherzerianum, grown in a fresh peat moss mixture, were placed underneath old flowering plants, the roots of which were infected by Phythium splendens. Placing the pots in the same surface soil of a flat or in peat moss year after year would imply more possibilities for a root infection and a rapid spread of the disease than the modern way of cultivation by placing the pots on tables with a thin layer of sand.
Especially when chemical or physical properties of the soil, e.g. the nutrition level, water content or temperature, are unfavourable, several diseases are strongly promoted. Examples of infections that quickly spread in these circumstances are Phytophthora palmivora in the roots of foliage plants such as Ficus, Scindapsus or Hedera, Phytophthora basal rot of Calceolaria, Senecio (= Cineraria), Sinningia (= Gloxinia), Saintpaulia and others, Fusarium moniliforme in Bromeliads and Helminthosporium cactivorum in cacti.
In cases where sand benches are used, a regular replacement of the sand may be required because of the danger of build up of salts and to