Agrochemicals can interfere in the cycle of nature destroying normal saprophytes which are enemies of harmful pathogenic agents. Competition of nutrients Saprophytic bacteria can multiply within an half hour. Pathogen mould need days to multiply being so in disadvantage on regard of nutritional resources. Interfering in the natural environment may destroy useful saprophytes boosting pathogens. Virus with mycopathogenic activity.
Some virus act toxic on pathogenic moulds.
The protection of the natural environment is therefore important. Modern agricultural techniques should protect the complex interaction of th different biological systems. Hyperparasites A parasite with phytopathologic activities may be invaded on its turn, by other parasites ,like nematodes, bacteria and bacteriophages. Parasitic plants can be halfparasites having well developed leaves. Full parasites have underdeveloped or no leaves at all.