We routinely look at our plants and crops to see if they are doing well and if they are healthy. When we see signs of stress or disease, are we looking at a biological infestation or not? What we do next depends on the answer to this question.
A plant disease is generally understood to be any ongoing internal process that adversely affects the health and growth of a plant. So, it is therefore possible that a plant disease may not actually involve living parasitic organisms.
A plant that is in decline due to something other than biological infestation (abiotic) would be considered a plant disease. Even in this case, it would not be unusual that a biological disease is indeed present, but that presence is actually due to an abiotic pathological process.
Diseases that are not biological, known as abiotic, are typically the result of reactions and interactions between the plant and its surrounding environment. Extreme heat or drought will bring on many diseased plant symptoms.
Flooding or poor drainage will also do this. These are only a few of the environmental conditions that will begin serious decline of production and plant vigor and health. Most abiotic diseases cause symptoms to develop over specific portions of the plant, or they may often affect the whole plant.
Causes like poor irrigation distribution over the root zone will usually cause a portion of plant, where adequate water is missing, to burn and then decline while the other portions of foliage look fine. Many other causes affect the whole root system and therefore the whole plant is affected.
What are some of the symptoms of abiotic diseases?
Being able to recognize the symptoms of abiotic stress or disease is critical in beginning to resolve the issue. Yellowing across most of the plant foliage is common when the root system has been stressed through this type of action. The yellowing is caused by lack of proper nutrition, which in this case occurs from poor root health.
Wilting of the leaves is generally caused by failure of the roots to take up water. If this condition continues, of course, the plant will eventually die. Though root rot is certainly a frequent culprit here, even this fungal disease may be caused initially by poorly draining or overwatered soil.
Slow growth or smaller than normal leaves are other symptoms that are caused by thin or constrained roots. Most root systems, if placed into the soil too deeply, will struggle to absorb the oxygen needed to allow the plant to respire properly. This, in turn, denies the plant the ability to convert sugars into energy. This is the basic cause behind the slow growth.
Branch dieback will often be the result of stress. Fruit trees are subject to this. There are a number of biological and abiotic causes for this disease. The dieback generally starts at the tips of branches and if the condition is not corrected quickly, it will spread throughout the plant and may eventually kill it. Often, even when the original condition is corrected, branches affected do not recover.
Heavier than normal seed production is another indicator of stress. Plants tend to produce a heavier amount of seed when their health is threatened. The plant, sensing danger, attempts to procreate. There are still other indications of abiotic factors that are involved in damaging plant health.
When an abiotic disease becomes a biological disease
Plant decline from an abiotic cause opens the door for a biological infestation of the plant. Too often, this new biotic infection is the only problem recognized and diagnosed for the plant. The treatment for this infection may seem successful at first, but it does not create a general health to return. The abiotic cause is still in place and the biological disease can return.
Chlorosis in a plant is usually the result of insufficient iron or magnesium in the plant and is often caused by soil pH issues or soil compaction problems that have damaged the root system. This causes the plant to be unable to manufacture carbohydrates during photosynthesis.
This instills a general weakness in the plant. Fruit production, growth, and other processes are also negatively affected. If the gardener simply adds these nutrients to the plant, the symptoms may decrease or disappear, but if the soil or other condition is not remedied, the malnutrition and its symptoms will return. Overwatering or poorly draining soil will initiate these same issues. This wet soil inhibits respiration, so adding nutrients will not help.
To make an accurate and complete diagnosis of what ails a plant, these issues, both biological and abiotic, need to be discovered and addressed in order to achieve successful remediation of the problem.
What types of issues cause abiotic disease?
Soil pH is a big cause of abiotic disease, and nutrient uptakes are severely affected by high soil pH. Iron and manganese will not be taken up in significant amounts by root systems in the presence of a pH over 7.8. Even nitrogen uptake is reduced to half from a pH over 8.0.
It is true that various nutrient extremes or imbalances will initiate disease symptoms in a plant, so improper soil pH is a definite culprit. One way to address this problem is by utilizing chelated nutrients. The coating of any nutrient in this way affords the proper ion exchange to occur, and the plant will uptake that nutrient. This, of course, is not the case with other pH sensitive nutrients that may not be chelated. Adjusting and maintaining soil pH is a superior solution.
Air pollutants are another cause. If the stomata become damaged by smoke and dirt, gas exchange, including absorption of CO2, is restricted. This, in turn, affects vigor and production. Drifting herbicides will often baffle gardeners. Sometimes, a neighbor or hired landscaper sprayed weed killer which was carried by the wind to nearby gardens. Regardless of who applied the herbicide, any plant affected by it will suffer damage and decline or die.
Proper irrigation means applying adequate water at the proper interval. Irrigation is not as easy to get right as some growers may think. The symptoms for drought and flooding appear to be very similar. Yellowing leaves can be caused by either of these.
Flagging or wilting is caused by lack of adequate moisture within the plant. Too much water in the soil can cause the root system to shut down and not take up moisture, resulting in the same wilting appearance or symptom.
Leaf scorch can be caused by biological disease, though it can also be caused by heat or radiation extremes. The best way to diagnose scorching is to identify the plant and review what biological scorch typically looks like. Discover how prone to this disease the species is. Some plants can withstand sustained heat and radiation without scorching while others cannot.
Abiotic disease is a common enemy of the gardener and its cure is usually not immediately obvious. First, a proper diagnosis of what has caused the plant decline is needed. Often, this diagnosis will include multiple causes.
To jump at the first apparent culprit will likely lead to a recurring complication or perhaps not even a temporary remedy. As with so many things in horticulture and agriculture; these are sciences where patience and research will pay handsome dividends.
For additional tips on identifying and controlling abiotic disease, review the reference information and pages for this article.