Pages 143 to 152 and 153 to 172 Plants grow best within a specified range of environmental conditions. Growing plants outside their optima may cause problems.
Symptoms vary from mild to severe, with the severity dependant on the distance from the optima.
Symptoms are often similar to those cause by viruses, phytoplasmas, and root pathogens, so diagnosis is difficult. Nutrient deficiencies and toxicities cause disease and induce susceptibility to pathogenic diseases. 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.