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8783. Marschner, H.. 1986. Relationship between mineral nutrition and plant diseases and pests. Chpt. 11. p. 369-390.. IN: Mineral Nutrition of Higher Plants. Academci Press, Orlando. 674 pp..
Although plant resistance to diseases is genetically controlled, it is considerably influenced by environmental factors, including level of plant nutrition from the soil. Excees N appears to lower disease resistance while potassium sufficiency increases resistance. Calcium makes cell walls more resitant to fungal parasite attack. Deficiencies of nutrients which lead to an accumulation of low molecular weight organic substances lower plant resistance. Boron-deficient wheat has a higher infection with powdery mildew. The severity of take-all on wheat is greatly inhibited by lower soil pH, beginning at 6.8. Ammonium-based fertilizers which acidify the rhizosphere can inhibit take-all severity, while nitrate N increases pH and disease problems. Ammonia is toxic to certain Fusarium species and nitrite is toxic to Pythium and Phytophthora. There is often a positive correlation between nitrogen application and pest attack, as young or rapidly growing plants are more susceptible. A large potassium supply often decreases pest attack. If a fertilizer increases the content of soluble organic nitrogen in plants, sucking insects tend to become more of a problem. The physical surface of leaves can be made less attractive to insects by some foliar sprays containing sodium silicate. One experiment with wheat found that without chemcial disease control, rust infection reduced grain yield in all fertilizer N treatments, but the zero N plots yielded the greatest. With fungicide, split N application led to highest yields.