PH plays a major role, because as pH increases some elements become less available, while others can become toxic. In high pH soils, iron and zinc become deficient. When mobile elements such as N, P, K, Na, Mg, Cl, S become deficient, the symptoms show up in older leaves, while deficiencies of immobile elements such as boron, iron, and Ca show up in younger leaves. Nutrient problems can be diagnosed by soil testing, tissue testing, and symptoms. The environment has pronounced effects on plants disease by effecting pathogens and plants.
Plants grown outside of their optimum are more susceptible to disease.
A pathogens ability to cause disease depends on its optimum environmental conditions. Some fungi grow better at cooler temperatures, others at hot temperatures. Moisture has a significant effect on the germination and penetration of fungal spores and a role in dissemination of pathogens. It influences disease development, ex. Some pathogens prefer higher moisture, others lower moisture.