im Downer is the Environmental Horticulture Advisor in Ventura County Cooperative Extension
As growers of thousands of ornamentals we understand that minerals absorbed mostly by roots as ions are essential for plant growth and development. Some required in parts per hundred are macro-nutrients while others only required in ppm or ppb are considered micronutrients. As long as enough of the 18 essential minerals are available, plants grow and reproduce in a healthful way. When not enough of one of the essential elements is supplied, a deficiency occurs and plants present symptoms. Mineral nutrient symptoms are considered abiotic disorders. There are however cases where excess or deficiency of elements can be predisposing to disease caused by pathogens. While examples of this are not abundant, some mineral elements do have a role in the development of disease caused by some pathogens.