You Can Be a Plant Doctor

Being a plant doctor is actually similar to being a medical doctor – you get a sick patient, you check for symptoms, you make a diagnosis, and then you prescribe treatment.  The only problem though with being a plant doctor, is that your patients cannot tell you directly what is wrong.  In order to figure out what’s causing a plant to be sick, you need to be inquisitive, open-minded, and very knowledgeable. 

Photo: Correctly diagnosing plant problems takes a thorough, comprehensive approach. 

For simplicity’s sake, plant diagnosticians have broken down the causes of plant problems into two categories – biotic and abiotic agents.  Biotic agents are living organisms (other than people) that cause plant problems, including insects, mites, fungi, bacteria, viruses, mammals, birds, and nematodes.  On the other hand, abiotic agents are non-living things or phenomena that cause plant problems.  Examples include hurricanes, construction damage, damage from a weed-wacker, and saturated soil. 

Correctly diagnosing plant problems is essential to maintaining the health, beauty, and longevity of your landscape.  But correct plant diagnosis can be quite challenging.  First off, there are many, many things that cause plant problems.  You have thousands of insects, diseases, nematodes, environmental factors, and physiological problems that can wreck havoc on your plants.  Just knowing all the potential causes of plant problems is a challenge, let alone correctly identifying them!  Many different factors are often working together to cause a plant problem.  Usually an insect or disease is not working in isolation; it is influenced by the current climate and the past and current health of the plant. 

Photo: Except for exotic pests, insect and disease problems of plants are often secondary causes of plant decline, not primary causes.  This drought and heat-stressed birch tree was predisposed to insect attack by the native bronze birch borer.  Notice the insects' exit holes in the trunk.

Another difficult thing about plant diagnosis is that many causal factors will produce similar-looking symptoms in the plant.  For example, both a drought-stressed tree and a salt-damaged tree will show brown crinkled leaves and leaf drop.  Furthermore, landscapes are variable and diverse.  Hundreds of species are planted in the landscape and each landscape has a different combination of plants.  Also, the planting sites themselves are highly variable, with differing soil, terrain, light exposure, and microclimate. 

Because of the difficulty of diagnosing plant problems, a thorough, comprehensive, step-by-step approach is needed.  Step 1 – Identify the plant.  Central to correct diagnosis is accurately identifying the species and sometimes the cultivar.  This is because you need to know what the cultural requirements, normal appearance, and growth characteristics are of a plant before you can detect that there is a problem.  For example, if a plant is yellow and drooping, you may conclude that it has a nutrient deficiency or is drought-stressed.  But if a Gold Thread Cypress (Chamaecyparis pisifera ‘Filifera Aurea’) is yellow and drooping, there is no problem and it doesn’t need more nitrogen or water. 

Step 2 – Inspect the site.  Look for conditions in the landscape that may lead to plant injury.  There are many questions to ask, including:  What is the slope of the terrain?  What is the soil texture – sandy, loam, clay?  What are the soil pH and nutrient levels?  Is it a well-drained soil?  Is it a compacted soil?  Are there dry or wet areas?  Is it a windy or protected site?  Is it shaded or in full sun?  Is there existing hardscape?  Is there existing vegetation nearby?  Are there animals or pets that access the site?  Is there mulch or grass beneath the plantings?

Photo: Figuring out what type of conditions at the site may lead to plant problems is essential for proper diagnosis.  Poor drainage is a common problem in urban landscapes that have compacted soils. 

Step 3 – Investigate the plant management and site history.  Gather as much information as possible and check your maintenance records if they exist.   Any information may provide you with clues to the problem.  There are many questions to ask here as well, including: When was the problematic plant planted?  What was the season of planting?  How large was it when planted? What type of nursery stock was used?  Were there any previous problems?  What are the current irrigation, fertilization, pest management, and pruning, practices?  Were any herbicides used?  Are there underground utilities?  Was there any recent construction(less than five years ago)?  Were there any recent abnormal weather conditions (less than two years ago)?  Were any deicing salts used?  

Step 4 – Inspect and describe the plant symptoms.  In most cases, you will only see the symptoms of a plant problem.  A symptom is the plant’s response to a disorder resulting in abnormal changes in the growth or appearance of a plant, which may be observed on the leaves, shoots, branches, flowers, trunk, or roots.  The difficulty of plant diagnosis is that symptoms are usually non-specific, meaning that several different disorders can result in the same symptom.  You need to gather more information and make close observations.  Ask, which plant part (roots, flowers, shoots, etc.) is affected and how severely?  Is there leaf chlorosis (yellowing)?  Is there leaf necrosis (browning and death)?  Is there discoloration or distortion?  Is the plant a normal size?  Is the plant wilting?  Are there a lot of dead branches and dieback?  Are there tattered leaves?  Any defoliation?  Is there early fall color?  Is the bark falling off?  Is there any bleeding or localized swelling?  Is there trunk splitting or cracking?  How do the roots look? 

Step 5 – Look for patterns and signs.  The pattern of symptoms throughout the plant and the landscape can sometimes give you a hint as to the problem.  If symptoms are uniformly distributed throughout the plant, it can mean that there is an underlying issue with the root system.  If only one plant is affected it can mean that there is an abiotic problem at that specific micro-site.  If only one species is affected, it can mean that there is a species-specific insect or disease problem.  Also look for signs.  When you actually SEE the presence or activity of an insect or disease, this is called, in very scientific terms, a “sign.”  A sign is direct evidence of an insect or disease.  Examples of signs are: adult insects, eggs, nymphs, larvae, pupae, cocoons, shed insect skins, frass, protective wax, exit holes, and fruiting bodies of a fungus.  These can be collected and sent to a lab for diagnosis.

Step 6 – Inspect the rest of the plant for abnormalities.  It is so easy for us to just think about the above-ground portions of trees and shrubs because that is what is visible to us.  But we really need to examine the roots and soil to get at the underlying cause of many landscape problems.

And lastly, Step 7 – Test likely causes and make a diagnosis.  Take soil, water, and tissue samples if needed and get them tested.  Make sure that your diagnosis is consistent with standard descriptions of the problem.

Diagnosing and correcting plant problems is challenging.  But with a comprehensive approach and practice, you’ll be able to figure out what’s wrong with a sick plant.