Botanical Forensics: Determining the 'Cause of Death' in Garden Plants

Botanical forensics is not an exact science, at least not for the average gardener. When a garden plant suddenly dies, many gardeners are left in wonder, with endless questions as to the plant's demise. In order to determine its cause of death, you may have to do a bit of 'digging' and investigating; just as any detective must do while working on a case, especially if the death appears questionable. Law enforcement uses forensic evidence to help solve cases. Botanical forensics is no different, other than the fact that your resources may be limited. There are many reasons for sudden plant death. Since this is rarely due to 'natural' causes, you'll have to consider all of the likely suspects. Pests, like insects and animals, are common. A disease caused from a fungus, bacteria, or virus is another possibility. Extreme or adverse environmental conditions, chemicals, and even unintentional sabotage can all lead to a plant's downfall.

Generally, with botanical forensics, the first question relates to the health of our soil. Most gardeners know healthy soil is vital for healthy plants. Unhealthy or unfavorable soil can be toxic to plants. Obtaining a soil sample and having it analyzed would then be the next logical step in determining the cause of death. Usually your local Extension office can test the quality of your soil. If the test suggest something other than the soil, further investigation will be required. Nutrient deficiencies, as well as unsuitable soil, can sometimes contribute to the demise of a plant but is oftentimes not the sole factor of its death. Instead, these weaken the plant, leaving it susceptible to pests and diseases. A weak plant is also more vulnerable to adverse weather conditions, like drought. When the death is not directly related to soil or nutrient deficiencies, you should consider other possible suspects in the case.

Since there are a number of possible suspects, use all available botanical forensic resources to determine whether the cause of death can be attributed to a living or nonliving agent. Living agents include insects, animals, and diseases. Nonliving agents can be linked to poor soil, environmental elements, and chemicals. This may not give you the exact cause of death but will at least narrow down the list. For instance, if your soil sample was not a factor in the death of the plant, you can cross this nonliving agent off the list. Carefully examine the scene of the crime, or garden. There may be important clues and other evidence within the surrounding area. Every garden plant has its own growing requirements, and many share similar growing conditions. Placing a plant in an unfavorable site can lead to stress, making it vulnerable to lurking predators. Becoming familiar with every plant in the garden beforehand is, of course, the smart thing to do; however, it's just as important after the fact, especially the victim plant. Go over all common problems associated with the plant. Check for specific symptoms or evidence such as yellow leaves, wilting, bite marks, rotted stems, etc. Since many problems share the same symptoms, don't rely on these alone to give you the cause of death. Botanical evidence can certainly lead you down the right path, but common knowledge, and in some cases, the use of an expert may be required as well.

If the cause of death is due to a living agent, such as an insect or fungus, then the plant damage should be limited to that particular species or at least one that is closely related. Insects, for the most part, will leave evidence of their existence at the scene of the crime or on the victim plant itself. This may be in the form of cast skins, webbing, chewing marks, or visible insect trails. The location and type of feeding damage (such as chewing or sucking) are important clues in determining the perpetrator responsible. For example, nematode damage is usually seen at the base of the plant with visible 'galls' present. Caterpillars and cankerworms often devour entire leaves, while beetles and grasshoppers leave scattered holes within the leaf foliage. Slugs, thrips, and beetle larvae can 'skeletonize' leaves. Slugs and snails also leave behind a visible silvery slime trail. Sucking insects, like aphids, kill a plant by sucking out its sap while injecting toxic substances during feeding. As many insects grow, they shed or molt, leaving cast skins as evidence. Determining the cause of death by insect may be as simple as a visit to the local library. Researching native insects and their favorite plant foods, along with the thorough inspection of the victim plant may be the only botanical forensics evidence you need in order to close the case.

Animal pests can be responsible for the death of plants from time to time. Most often, this can be attributed to rodents like rabbits, squirrels, and chipmunks. The plant will show signs of chewing or teeth marks. Rabbit damage is identified by a clean, angled cut no more than two and a half foot above the ground. They may also uproot young seedlings and strip the bark from young trees and shrubs. Gophers bite plants from underneath making it appear as though they wither and die for no apparent reason. Thorough inspection of plant roots will usually be required. Squirrels rarely cause significant damage to plants, but will strip bark from trees to find the sweet sap inside. They will also eat many garden bulbs, as will chipmunks. You may even find animal tracks left behind in the garden. Learn about local wildlife creatures and their favorite plants to determine if they are responsible.

Fungal or bacterial killers may be more difficult to determine, but their symptoms are sometimes quite distinctive. For instance, the most distinguishing clue of a fungal agent may take the form of fruiting bodies. The texture is often dry and papery. Fungal leaf spots are generally round and discolored, like purple or yellow, whereas bacterial leaf spots may be more angular and uniform in color. Bacterial infections may also consist of a slime-like texture accompanied by a rotten odor. Viruses are a different matter all together. Viral infected plants may become disfigured, stunted, and lose color due to loss of chlorophyll production. However, unlike fungal or bacterial infections, viruses don't usually cause death. Most viruses require their host plant to live in order for them to survive as well. Again, performing research into the different types of plant diseases that commonly affect your garden plants, especially the one in question, is important in determining the cause of death.

Nonliving agents are oftentimes the result of environmental or mechanical factors. These are also important considerations in determining the cause of death. Physical damage is often the result of environmental extremes. Plants respond adversely to extreme changes in weather, such as sudden wind gusts. Close examination should point out broken roots or stems as well as bruised, punctured, or damaged leaves. (These physical signs may also be apparent from unintentional sabotage from children or pets.) Changes in light may result in reduced growth and leaf drop. Changes in temperature may result in overly dry or waterlogged plant roots. Chemical pesticides and fertilizers can also lead to plant failure. They can pollute the soil as well, leading to sudden plant death later down the road. Of course, if you do not use these chemicals in the garden, you can safely rule them out as possible suspects. However, you should be aware that wind or rain can carry these harmful chemicals from place to place. Therefore, you may want to pay close attention to nearby neighbors. Ask them if chemicals are used in their lawn or garden.

After the sudden death of a plant, the use of botanical forensics may be necessary in determining the cause. Generally, this entails close examination of the victim garden plant and the surrounding crime scene. You may need to perform extensive research if you're unfamiliar with common problems or visible signs to look for. You may be required to send in soil or even plant samples to be tested at your local Extension office or similar organization. Most of the time, the answers you seek will be right in front of you; however, when all else fails, seek an expert for advice.