Abiotic Plant Disorders: Symptoms, Signs, and Solutions (E2996)
November 10, 2015
The term “abiotic disorders” refers to a wide array of plant problems. We use the word “abiotic” to indicate that the symptom is not caused by a biological agent such as an insect, mite or pathogen. Abiotic disorders are associated with non-living causal factors such as weather, soils, chemicals, mechanical injuries, cultural practices and, in some cases, a genetic predisposition within the plant itself. Abiotic disorders may be caused by a single extreme environmental event such as one night of severe cold following a warm spell or by a complex of interrelated factors or events. They can also be caused by chronic conditions such as a prolonged drought or plant selection inappropriate for the existing site conditions (e.g., planting an acid-loving species in an alkaline soil).
Abiotic plant problems are sometimes termed “physiological disorders”. This reflects the fact that the injury or symptom we see, such as reduced growth or crown dieback, is ultimately due to the cumulative effects of the causal factors on the physiological processes needed for plant growth and development. When a tree is affected by severe drought, for example, water stress will result in closure of the pores, or stomata, on the leaf. This conserves water in the leaf but also reduces the rate of photosynthesis and the ability of the plant to produce sugars for growth. If the drought stress occurs during hot weather, stomatal closure also limits the cooling effect of transpiration, and leaf scorch may occur. Nutritional imbalances also limit growth by reducing photosynthetic rate and other physiological and metabolic processes. Some plants, such as pin oak, have a limited ability to take up iron under alkaline soil conditions. Iron is essential for synthesis of chlorophyll, so pin oaks on alkaline soils frequently develop severe leaf yellowing or chlorosis and have reduced rates of photosynthesis.
The cumulative and subtle nature of many physiological disorders can often make them difficult to diagnose. An extreme event such as a severe late freeze or a misapplied herbicide is an obvious “smoking gun” to indicate the underlying cause of injury. More often, however, diagnosing abiotic problems requires careful consideration of plant and site factors through a process of elimination to determine the source and potential remedy for the problem.
Abiotic disorders are usually classified by causal factor or symptom. In this bulletin, we will present abiotic disorders whose origins are due to biological/ botanical factors, environmental (climate and weather) conditions, soil conditions, chemical applications, animal damage and cultural practice. We will also provide a framework for diagnosing problems and suggest steps to mitigate abiotic injuries before or after they occur.
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