Balanced fertility, based on a soil test, can reduce losses due to diseases. Adequate levels of nitrogen, phosphorous, and potassium are necessary to encourage vigorous growth of the wheat plant. Several diseases, particularly take-all and Pythium root rot, are more severe in low fertility fields or fields low in phosphorus.
Adequate levels of nitrogen should be applied to attain top yields. However, excessive nitrogen favors the development of certain diseases, particularly powdery mildew. High nitrogen promotes the development of a dense canopy of succulent leaf tissue. The increased humidity in the canopy favors growth of the powdery mildew fungus, and the nitrogen-rich, succulent leaf tissue is more susceptible to infection. Therefore, the application of nitrogen should be balanced with available phosphorus and potassium.
Research has shown that the form of nitrogen has an effect on certain diseases. Take-all severity is increased by applying nitrate forms of nitrogen as a spring top dress, and its severity can be reduced by using ammonium forms. Therefore, an ammonium form of nitrogen should be used wherever take-all may be a problem.
Soil pH has a varying effect on the severity of some diseases. Cephalosporium stripe is always more severe in soils with lower pH. Take-all, on the other hand, is favored by soils with a pH of 7 or above. Generally, lime should not be applied immediately before planting wheat because of the danger of infection with take-all, except where the lime is applied to correct an abnormally low pH soil. Soil pH should be adjusted to achieve optimum conditions for nutrient uptake by the wheat crop and its rotational crops.