Disclaimer
The information below is for educational purposes only. I would like to clarify that the recommendations below do not constitute professional advice for you or your garden. We recommend consulting a specialist for both your healthcare and plant health needs. I have incorporated affiliate links to products and services that I discovered to be useful. Please refer to the complete disclosure provided here.
Why should gardeners care about plant diseases?
Pests, diseases, or injuries destroy about half of the produce in the world. This can happen in the growing, transporting, or storing phases. Knowing about insects, plant diseases, and weeds can help gardeners avoid and solve plant problems.
What is the S.A.P. Method?
When I was training to be a healthcare provider, we used tricks like mnemonics and acronyms to help us remember anatomy and pathophysiology. SOAP is an effective tool to help healthcare professionals identify, treat, and document patients’ care goals. It stands for subjective, aim, assessment, and plan. Using similar techniques to identify plant diseases, I came up with SAP, which stands for symptom story, assessment, and plan of action.
Let me address prevention briefly before I proceed any further.
How can gardeners prevent plant diseases?
The medical model embraces the slogan “prevention is better than cure.” Preventative interventions reduce risks and threats to health. The medical model has three levels of prevention and education is at the core of all of them.
Primary prevention includes measures that prevent disease and injury before its onset. This can involve passing laws that promote healthy habits and prohibit harmful products and behaviors. Examples of these are laws mandating the wearing of seat belts and car seats. Immunization against infectious diseases is also a primary health initiative.
Secondary prevention is about an early diagnosis of disease for subsets that are at high risk of disease and injury. Breast self-examinations, for example, are essential for women to help early detection of breast cancer. Other screenings, like colonoscopies and yearly health checkups, are examples of secondary prevention.
Tertiary prevention aims to prevent further damage after identifying and treating the disease. Examples include support groups and cardiovascular rehabilitation for people who had a stroke or heart disease.
I realize that as gardeners; we are stewards of the soil. The soil matters in producing a healthy plant. A healthy plant is the best and first defense against disease and injury.
The success of a garden largely depends on the site preparation and plant selection. Site preparation involves ensuring that the soil is properly conditioned and amended to support healthy plant growth. This can include actions such as removing weeds, amending the soil, and adding organic matter. Proper site preparation also takes into account factors such as the amount of sunlight and drainage in the area.
Careful plant selection is equally important. Choosing plants that are well-suited to the site conditions and climate can help prevent disease and pest problems. It is essential to consider the plant’s growth habit, size, and maintenance requirements, as well as its compatibility with other plants in the area. Selecting plants that are native to the region can also help ensure their success.
By paying attention to site preparation and plant selection, gardeners and landscapers can avoid many common plant problems and create a healthy, thriving landscape.
What does a healthy plant need?
To ensure that your plants remain healthy, it’s important to understand the typical growth process and expectations of each plant variety, whether it’s an herb, vegetable, fruit, or flower. Each plant has its unique characteristics for survival, and knowing them can help you care for them properly.
SWALE is an acronym that stands for the key components that gardeners should be aware of for each plant at every stage, from seedling to maturity. When it comes to growing plants, several factors need to be considered to ensure their healthy growth. These factors include soil, water, air, light, and enrichment.
Here are some tips that can help you with each of these factors:
– Soil: Observe the soil structure, color, texture, pH, and organisms through observation or professional tests.
– Water: Conduct a water analysis to test alkalinity, pH, and hardiness. You should also consider the best way to water your plants and how to avoid water stress.
– Air: If you are starting seeds indoors, make sure you allow for proper circulation. Also, consider how air pollution is affecting your plants.
– Light: Depending on how you start your plants, consider the type of light they need. Find out if they can tolerate shade or if they need full sun. You should also check if there are nearby plants that are shading your plant and blocking its light requirements.
– Enrichment: Plants need fertilization, pruning, and mulching. Figure out what your plant needs and how to best support it. Improper fertilization, pruning, and mulching practices can adversely affect plant growth.
How do plant diseases occur?
Understanding critical principles for maintaining healthy plants and preventing diseases is crucial for accurately diagnosing plant diseases.
Plant diseases are the outcome of the constant stresses that plants face. These stresses lead to various symptoms, which in turn affect the growth and reproductive abilities of plants. They serve as helpful clues to identify unhealthy planting practices that make plants vulnerable to diseases. Poor site selection, nutrient imbalance, water stress, improper mulching, irrigation, or pruning practices are some examples of problems that are caused by gardeners.
Understand biotic vs. abiotic causes of disease
There are two types of causes for plant diseases: biotic and abiotic. Biotic causes happen when a pathogen, such as fungi, bacteria, viruses, nematodes, or parasitic higher plants, infects the plant. Other living organisms like insects, mites, and animals can also cause diseases. On the other hand, abiotic causes are non-pathogenic and non-living, which means they do not involve any pathogens. They can cause cosmetic damage or a minor decrease in yield or affect only some plants. These problems are usually not contagious and do not spread from plant to plant.
Abiotic causes can be physical, chemical, or environmental factors that make the plant susceptible to true diseases. Chronic exposure to air pollutants like nitrogen dioxide from auto exhaust can lead to temperature, moisture, and light irregularities, which can create less-than-ideal conditions that make plants susceptible to disease. In these cases, we consider the plants to have an injury, not a disease. An injury can predispose a plant to disease. Other abiotic causes of injury include sulfur dioxide from factories, ground-level ozone from the atmosphere, and nutritional deficiencies.
Understand three factors that lead to true plant disease
According to George McNew, there are three factors that must be in place in order for plant disease to occur. This is often conceptualized as a triangulation of three factors: susceptible host, virulent pathogen, and favorable environment. If any of these components are missing, then a disease will not occur.
Understand the plant disease cycle
Inoculum is the part of a pathogenic organism that causes true diseases or infections. Examples of inoculum include bacterial cells, fungal spores, viral particles, and nematodes. If an inoculum is not contained or treated, it can undergo a cycle wherein it spreads, infects the host plant, produces more inoculum, and survives through growing seasons. The pathogen can spread via a vector, which is an insect, wind, or through infected tools or water.
What are the signs and symptoms of plant disease?
Signs and symptoms are two terms that can be confused. Signs are the physical indications of injury or illness, such as the presence of powdery mildew spores or other pathogens that may manifest in plants as spores, fruiting bodies, bacterial ooze, nematode eggs, or waste. Symptoms, on the other hand, are detectable changes in plant parts that occur as a response to infection or injury. Plants can display abnormal tissue coloration, wilting, tissue death, or other reactions.
Abnormal tissue colors can appear on leaves, stems, or roots and can turn yellow (chlorosis), brown (necrosis), purple, bronze, red, or mottled. Water stress can be caused by too little or too much water, but pathogens can also interfere with the plant’s ability to absorb water.
Tissue death can occur in spots or the entire organ, whether it’s leaves, stems, or roots. As the disease progresses, leaves can be defoliated. An abnormal increase in size or tissue can lead to curling or twisting leaves and galls formation on stems. The opposite can also happen, as the infectious pathogen can take over the host plant tissue.
What questions should gardeners ask to diagnose plant problems?
As a clinician, I follow the OLDCARTS mnemonic to evaluate patients’ presenting symptoms or problems. Let’s take the example of a patient presenting with a rash.
O: Onset: When did the rash begin? Is it a new or recurring issue?
L: Location: Where is the rash located?
D: Duration: How long has the rash been in that location? Does it come and go?
C: Characteristics: What does the rash look like? What does it feel like?
A: Aggravating or alleviating factors: What makes the rash worse or better?
R: Radiating: Has the rash spread to other parts of the body?
T: Timing: Does the rash come and go?
S: Severity: Has the rash spread to other areas of the body and caused secondary issues?
When applying the following mnemonic to diagnose a plant problem, it is best to carefully examine the entire garden area first, and then the affected plant.
O: Observations: What exactly are you observing that appears abnormal?
L: Living factors: Do the symptoms indicate the presence of living factors like pests or pathogens? Are you noticing any leaf spots, discoloration, or wilting?
D: Distribution of the symptoms: Is it affecting a particular plant or a similar group of plants? How many plants of the affected species are impacted, and what is the extent of the damage? Which parts of the plant are affected, and what is the pattern of damage?
C: Characteristics of this plant: What are the normal characteristics of this plant for this season and weather? How does it typically display these characteristics during the growing season?
A: Abiotic factors: Is the problem due to mechanical, environmental (including weather), or chemical causes?
R: Resources: What diagnostic tools are available to identify this problem? When should you reach out to specialists?
T: Timing: When did the symptoms first appear? Is it sudden or progressive? What time of year did it appear, and did it occur after a scheduled event like fertilization, mulching, or pesticide application?
S: Samples: Are samples needed to confirm the diagnoses? What samples do you need (soil, leaf, etc) and how should I take them?
How to use the S.A.P. method to diagnose plant diseases?
Identifying the problem in a plant is a crucial step in resolving any issue. The first step is to get a detailed symptom story, and this can be done using the following steps:
- Identify the plant’s name and variety.
- Investigate the symptom story using OLDCARTS.
- Review the plant’s growing history using SWALE to consider potential causes.
In the assessment phase, it’s important to identify at least three potential causes for the problem. Number them by probability and reason why you think this is the problem. At this stage, you are trying to define the problem and determine whether it’s a normal variation or a serious issue. It’s important to put this issue in proper perspective relative to the overall plant health and quality. However, plant problems may not affect quality but rather aesthetics, and that needs to be taken into consideration.
The last step is to create a plan of action. Make recommendations as specific as possible and include reevaluation. Keep in mind that sometimes doing nothing is a valid plan, while at other times, removal and replacement of the plant may be necessary.
When action recommendations are addressed, timing is a crucial element along with proper expectation, especially if the problem is severe.
What are the five methods to manage plant diseases?
Managing plant diseases requires a stepwise approach known as integrated pest management. The first option is to select a genetically resistant plant. If that is not possible or desirable, it is essential to regulate your garden practices to ensure healthy plants. This can be done by minimizing or eliminating insect pests, weed seeds, and pathogenic inoculum. It is imperative to use clean tools and equipment, including soil, water, and fertilizer. If any plants or soil are diseased, they must be removed.
If problems persist despite good garden practices, biological control can be used to deal with the issue. Beneficial or antagonistic organisms can be used to kill or suppress plant pests. These organisms can parasitize pests, outcompete them, produce toxins to kill them or change the host plant’s reaction to the pests.
If biological control fails to resolve the issue, chemical application may be necessary. It is vital to identify the disease and confirm it with a specialist before applying any chemicals.
If all treatment measures fail or if the disease is severe, gardeners should quarantine the diseased plant.
References
Boggs, J., Draper, E., Chatfield, J., Williams, S. D., & Boehm, M. J. (2017, February 16). 20 Questions on Plant Diagnosis. Ohioline. Retrieved September 6, 2023, from https://ohioline.osu.edu/factsheet/plpath-gen-3
Kennelly, M., O’Mara, J., Rivard, C., Miller, G. L., & Smith, D. (2012). Introduction to Abiotic Disorders in Plants. American Phytopathological Society. Retrieved September 6, 2023, from https://www.apsnet.org/edcenter/disandpath/abiotic/intro/Pages/Abiotic.aspx
Williams, S. D., & Boehm, M. J. (2017, February 1). Keeping Plants Healthy. Ohioline. Retrieved September 6, 2023, from https://ohioline.osu.edu/factsheet/plpath-gen-4
Williams, S. D., & Boehm, M. J. (2017, February 2). Plants Get Sick Too! Retrieved September 6, 2023, from https://ohioline.osu.edu/factsheet/plpath-gen-1
Williams, S. D., Boehm, M. J., Chatfield, J., Boggs, J., & Draper, E. (2017, February 16). Diagnosing Sick Plants. Ohioline. Retrieved September 6, 2023, from https://ohioline.osu.edu/factsheet/plpath-gen-2