ROBERT L. WICK
Abiotic means nonliving, and abiotic agents are not transmissible or infectious. Abiotic causes of plant diseases include nutrient deficiency and toxicity, chemical injury, environmental constraints, air pollution, and genetic abnormalities. Nutrient deficiencies most often occur when elements needed in large amounts (S, P, Mg, Ca, K, N) are deficient in the soil. Deficiencies of nitrogen and phosphorus are common in agricultural crops, and that is why fertilizers are applied. When nitrogen is low, chlorophyll production is reduced and the plants become yellow. Calcium is important for cell wall development; when deficient, growing parts such as buds and fruit may develop abnormally. In some cases there are sufficient nutrients present in the soil but unfavorable pH, or imbalance between soil elements, makes them unavailable to the plant.
Nutrient toxicities usually occur when elements needed in small amounts are overly abundant (Mo, Cu, Zn, Mn, B, Fe, Cl). This may result from natural sources, soil pollution, or deliberate addition of trace elements to the soil. In some cases the pH of the soil solution results in the plant taking up excessive quantities of trace elements. For example, when the pH is low, manganese and iron are released into the soil solution. Geraniums and marigolds develop stippled necrotic foliage when they take up excessive amounts of iron and manganese. There are several resources available for diagnosing nutrient disorders of plants (1-3).
Additional toxins include herbicides and other pesticides (3-5). Injury to sensitive nontarget plants occurs when herbicides drift through the air or are carried by water to where it was not intended. Some pesticide formulations injure sensitive plants, and mixtures of pesticides can result in unexpected injury.
The most common environmental constraints are too little or too much moisture, temperature, or sunlight. Hail, lightning, and excessive wind can also injure plants. The soil environment can also have a profound effect on plant health. Poorly drained soils can remain excessively wet; water displaces oxygen in the soil and roots suffer. Soil texture, structure, pH, and organic and mineral composition are very important to plant growth and health.
Air pollution can be from natural causes such as volcanic gases or artificial such as ozone and acid rain. Air pollution can cause visible symptoms or reduce crop yield without other evidence of disease. Other pollutants to air and water can result from accidental chemical spills.
1. W.F. Bennett, Nutrient Deficiencies and Toxicities in Crop Plants, APS Press, St. Paul, Minn., 1993.
2. C. Bould, E.J. Hewitt, and P. Needham, Diagnosis of Mineral Disorders in Plants: Principles, vol. 1, Ministry of Agriculture Fisheries and Food/Agricultural Research Council, Her Majesty's Stationery Office, London, 1983.
3. M.C. Shurtleff and C.W. Averre, The Plant Disease Clinic and Field Diagnosis of Abiotic Diseases, APS Press, St. Paul, Minn., 1997.
4. Diagnosis of Herbicide Damage to Crops, Chemical Publishing, New York, 1981.
5. J.F. Derr and B.L. Appleton, Herbicide Injury to Trees and Shrubs: A Pictorial Guide to Symptom Diagnosis, Blue Crab Press, Virginia Beach, Va., 1988.
This Web site Copyright ® 2000 John Wiley & Sons, Inc. All rights reserved.