Some plant problems may be obvious, while others are more difficult to determine. Use these questions to help guide your diagnostic process, and take your time considering each question.
Know what plant you're working with before you get started. Different species often have a different set of problems. Understand exactly what plant you're dealing with and any normal characteristics. Be cautious with common names - make sure the plant is properly identified. Use the Plant and Weed Identification resources to help.
Understand what a healthy plant looks like. If a plant is a dwarf variety or naturally variegated, this may impact perceived problems. So may common occurrences, such as color change in the fall or naturally occurring needle drop in the summer. Take the time to understand what is normal for the plant.
Consider what problems this plant may normally have. Though this may create a bias, it could also help rule certain problems out and help direct your inquiry. For example, spotted wing drosophila is a growing problem in soft-bodied fruits. If someone asks about quickly decomposing raspberries, that may lead you to ask further questions related to possible spotted wing drosophila.
Look for signs and symptoms of pests and disease issues. Signs are physical evidence of the pest or disease pathogen, such as insects, fungal spores, or animal poop. Symptoms are the visible effects of pests or diseases on plants, such as holes in leaves, plant wilt, or changes in color and shape.
Learn how to distinguish between various signs and symptoms related to common pest and disease problems in Minnesota.
Take a step back and consider the health of the whole plant. Is the tree in general decline, has the problems been going on for years, or is the plant generally healthy? Learning about the general health of the plant will help you understand the potential impact of the pest or disease issues, such as maple tar spot on a healthy maple tree. Or, it may lead you closer to the potential source of the problem.
Are you on the right track? Consider the signs and symptoms, and use your knowledge to observe the problems. Look at patterns of damage, such as where the symptoms first appeared on the plant, and when. Make sure that you're looking at all potential signs and symptoms, and not focusing on just those that confirm a diagnosis you've already decided upon. Remember: take your time to find the right diagnosis and ask questions.
It's easy to focus on the plant concerns brought to you, but some problems can affect more than just one plant. For example, black sooty mold from magnolia scale is likely more noticeable on plants under the tree. Take some time to understand the conditions of the whole garden.
Site conditions, such as soil characteristics, exposure to sun and rain, construction history, and winter salt treatments can greatly impact the health of plants. Learn about potential exposure to wind, soil acidity issue of plants, and potential stress on root systems from construction, roadwork, or landscaping.
This may be difficult to determine if a gardener only notices a problem when it has greatly progressed, but consider when the problems first appeared if known. Keep in mind that some signs or symptoms may appear well after the damaging pest has moved on.
Considering the horticultural history lends information related to cultural practices that, over time, can greatly impact the health of a plant. For example, the planting depth of woody plants, fertilization and watering practices, mulching, and past pruning can all impact the overall health of a plant.
Weather and the surrounding environment can greatly impact plants, especially in Minnesota. Consider the hardiness of plants after a cold winter, snow cover (or lack thereof) for root protection, and drought conditions in the summer and fall. All of these factors can impact the health of a plant.
Not every pest or disease problem requires a solution. Some pest and disease issues are cosmetic in nature, and won't impact the plant health. This may not be a shared opinion of the plant caretaker, but consider the impacts of your diagnosis before making recommendations, and provide educational information within an Integrated Pest Management lens moving forward.
Next: Learn how to identify signs and symptoms of plant pests and diseases.