Plant nutrients are predominantly associated with increasing yield and quality through ensuring no mineral deficiency is restricting growth and development.
However, plant nutrients can also help the plant protect itself from disease. A well balanced nutrition program will ensure that the plants cellular structure is robust and resilient, whilst avoiding excessive of nutrient build up that can also be detrimental to plant health. There are numerous examples of nutrients being cited for their role in plant health, with nitrogen, potassium, manganese, zinc, copper and molybdenum being examples.
Nitrogen deficiency predisposes the plant to take-all infection, whilst the absence of satisfactory potash supply, plants will be poor and stunted, especially in dry seasons. Physiological stress will be more damaging if potash nutrition is limiting - frost damage will be more severe, waterlogged areas will take longer to recover and plants will wilt earlier and remain flaccid for longer under drought conditions.
Crops will be more susceptible to disease and pests especially where nitrogen and potash availability are imbalanced. This will result in weaker, sappier growth which will contain a higher concentration of soluble nitrogen compounds and simple carbohydrates providing a readily available food source for diseases such as the mildews.
Thinner cell walls with less mechanical resistance to predators may also result from potassium shortage. A review of over 1000 cereal trials found that where potash levels were low and out of balance with nitrogen supply, application of potash reduced disease and bacterial infections in over 70% of cases (PDA). Potassium deficiency has also been linked to higher rates of rust infection.
Zinc and Copper
Zinc has been shown to reduce the levels of infection of cereal blight (Rhizoctonia cerealis), whilst copper deficiency leads to male sterility giving blind grain sites that become infected with ergot.
Manganese has been associated with disease control in numerous investigations. It has a direct inhibitory effect on fungi growth, especially powdery mildew, as well as being involved in lignin and suberin production giving plant cells more resistance to infection. There is good evidence to support the effect manganese has on reducing the incidence of take-all infection in wheat.