Cultivar selection, seed and planting material

Given the narrow range of permitted measures and plant protection products in organic farming, one of the most effective strategies to combat diseases and pests is the cultivation of resistant varieties. Of course, there are no resistant varieties of all species nor those that would be resistant to all pathogens of one species. However, resistant varieties should be sown/planted whenever possible, and they should be preferred even at the cost of compromising with some other important economic characteristics. There are two main reasons for this. Less susceptible varieties are less likely to be infected than susceptible ones and can be grown in the presence of certain pathogens without major damage. The population of pathogens will be reduced by their cultivation, which will allow the cultivation of somewhat more susceptible varieties after a few vegetations. It is also appropriate to simultaneously grow more varieties of different resistance, which is closer to the traditional method of cultivation where the planting material was not so genetically uniform. In this way, less susceptible plants will not develop symptoms or will have fewer symptoms, and part of the spores will retain on them instead of susceptible plants. However, the cultivation of resistant varieties leads to the adaptation of pathogens by the development of new strains that can overcome resistance. Therefore, growing resistant and less resistant varieties together will slow down the appearance of such strains.

One of the strategic controls for diseases and pests in the soil is grafting on resistant rootstocks, for which a good example is the grafting of grapevine on Phylloxera-resistant rootstock.

Planting/sowing healthy planting material is one of the standard phytosanitary measures in modern agriculture. It has additional importance in organic production. Infected planting material brings the source of infection and weed seeds into the crop plantation and allows the development of diseases and weeds early in the growing season when the young plants are especially susceptible which can cause serious damage. These pests are regularly well adapted to a particular species, while some new diseases, pests or weeds that were not present before and to which the producers are not accustomed can be introduced to the farm through infected material.