Basic Plant Pathology (Continued)
Abiotic (Noninfectious) Plant Diseases
Abiotic diseases or noninfectious diseases are caused by nonliving agents like weather, soils, chemicals, or mechanical injuries. These commonly occur when plants are grown outside their normal habitat or growing zone or when humans disrupt a plant’s growing environment. They can be caused by a single environmental event such as a late freeze or by a combination of cumulative factors or events.
Diagnosing Abiotic Diseases in Plants
Like viral biotic diseases, abiotic diseases are difficult to diagnose because the same symptoms can be caused by many things. Some of the most common symptoms include stunted growth, reduced vigor and wilting in stems, yellowing and wilting of older leaves, heavy seed production, marginal leaf burn, and smaller than normal leaves.
To accurately diagnose an abiotic disease, you must first know about all the symptoms as well as a timeline when the symptoms appeared and a history of the growing conditions. You will want to observe other plants in the area which are of the same and different species to see if they exhibit similar symptoms. It is best if you can observe the plants in person.
Causes of Abiotic Plant Diseases
There are many causes of abiotic disease. Soil structure determines its ability to hold water, nutrients, and oxygen so that they are available for plant roots. Compaction is the most common soil structure issue and can be caused by heavy traffic from farming or construction equipment, rain, and lack of crop rotation. Compaction reduces pore space between soil particles and leads to runoff reducing the amount of water and oxygen available for absorption.
pH is the measure of H+ ion activity in the soil. Put another way, it measures the relative acidity or alkalinity of the soil with 7 being neutral. Soils with a pH below 7 are acidic while those above 7 are alkaline. In general, a slightly acidic soil pH of 6-7 is preferable for most plants. The pH affects which elements and compounds are available in soil for absorption by plants. Growing plants in soil with the wrong pH can lead to abiotic disease.
Too much of a particular nutrient (especially macronutrients such as nitrogen) can be toxic to plants and lead to abiotic disease. Micronutrient toxicities are common in production systems and greenhouse floriculture. Similarly, nutrient deficiencies can also lead to abiotic disease. Such nutrients can be deficient in plants because either the soil lacks the need plant nutrients. Both toxicities and deficiencies can exist because of poor soil conditions like improper pH levels making nutrients in the soil unavailable for absorption.
Extreme moisture due to excessive rain or irrigation as well as too little water can both lead to plant injury and ultimately abiotic symptoms. Too much water can reduce oxygen available in the soil necessary for the absorption of water and nutrients. Too little water can lead to the plants closing their stomata to conserve water which also reduces its ability to photosynthesize or produce food needed for growth.
Both excessively high and low temperatures can be detrimental. They lead to plant injury which varies in severity based on the plant species, its age, the duration of the extreme temperature event, the time of year, and more. The above the ground portion of plants tend to be affected more by these temperature based events than do the roots because the aboveground biomass experiences wider ranges of air temperatures while the roots are exposed to soil temperatures which are slower to fluctuate.