It is always distressing to notice that a plant is damaged or unhealthy looking. Whether house plant, garden plant, tree or shrub, we want to find the safest, most effective ways to fix the situation. Diagnosing the true cause can be tricky. The goal of this article is to provide readers with resources that can help, from providing a basic framework for analysis to identifying causes and remedies.
Diagnosis
The first step in fixing a plant problem is diagnosing it correctly. The cause can be obvious if insects are visible on damaged leaves, for instance. But often the cause is a mystery and requires a diagnostic process to correctly identify it.
Plant problems are divided into living (biotic) and non-living (abiotic) causes. Non-living factors include environmental and human-caused issues such as light, heat, water, chemical, nutrient and physical/mechanical issues. Living factors relate to insect or animal pest problems and fungal, bacterial, and viral diseases. All require observation to identify, and because symptoms can be similar for different problems, a process of elimination may be needed. The Virginia Cooperative Extension (VCE) publication Diagnosing Plant Problems provides a good guide to this diagnostic process.
Nutrient Problems
When there are no clear external symptoms or causes of a plant’s problem, nutrients may be a factor. We recommend soil tests approximately every three years to provide good guidance on any nutrient deficiencies in garden soil. For edible gardens where crops are grown and harvested one or more times per year, amendment and fertilization are important to replace soil elements that are taken up by the previous crop(s). Basic guidance on fertilizers and their application is summarized in the Garden Shed article A Fertilization Primer.
If you suspect that over- or under-fertilization may be an issue, scroll down to the “Essential Nutrients for Plant Growth section of the NC Extension Gardener Handbook for a list of symptoms due to an excess or lack of macro- and micro-nutrients, organized by type of plant.
IPM: Integrated Pest Management
When a problem is determined to be caused by a natural factor like an insect or disease, best practice is to resolve it by following an Integrated Pest Management process. IPM truly advocates management, rather than attempting to obliterate the pest at the outset. It starts with clear identification of the pest, monitoring the pest’s impact, accepting limited damage, taking preventive action where possible, and using chemicals only as a last resort. It acknowledges that chemicals sometimes have a role to play but argues against preemptive, premature, and excessive chemical use. Longer term, it advocates creating a healthy and biodiverse habitat around the gardens to build the population of beneficial insects needed to counter the pest populations. A thorough and easy to understand summary of IPM is presented in the Garden Shed article Integrated Pest Management.
The video IPM Basics from the University of Maryland Extension, featuring Michael J. Raupp, PhD, Professor Emeritus of Entomology and Extension Specialist, provides another concise summary of IPM, including the key steps:
- Build your knowledge base about specific crop and garden pests and the damage they do
- Monitor your plants regularly for visible damage
- Decide on appropriate action
- Intervene appropriately, with chemical use only as a last resort, preferably with substances judged to be minimally harmful and classified as suitable and safe for organic gardening
- Measure success and keep records.
IPM tactics for pest issues on specific fruits are available on the MyIPM app. It is sponsored by the Clemson University Extension in collaboration with six other state extension services to promote IPM in the commercial fruit-growing arena. It is available at no cost from the Apple Store and Google Play.
Insects
Insect damage is a factor in all gardeners’ lives. Whereas in the past, a variety of chemicals were applied to kill off insect pest populations, the results of this practice are now recognized as environmentally damaging. Non-selective insecticides kill beneficial insects as well as pests, devastating insect populations. This, in turn, affects our equally-damaged bird population, which depends on insects for food. Our efforts today are to reduce chemical dependence and create more biodiverse and balanced environments on our properties.
A short video from the University of Georgia Extension titled Garden Insects: Friend or Foe provides a nice summary of IPM as well as common beneficial and pest insects. The Xerces Society offers a video presentation on beneficial insects, titled Your Insect Allies: Meet the Beneficlal Insects Controlling Pests in your Garden. It identifies beneficials and provides a lot of good information on their habits and habitats. It can be helpful in building a diverse ecosystem that attracts and helps beneficials thrive and provide natural pest control.
If you can’t find help in the above sources or want further information, try the Cornell Extension’s Resource Guide for Organic Insect and Disease Management. This is a nearly 200-page reference document aimed at commercial organic growers. It presents information by crop, insect, disease, and approved organic treatments. It also includes many references for folks who want to dive even deeper into the topic.
Diseases
There are numerous on-line resources to assist in identifying, preventing/reducing, and treating plant afflictions that aren’t insect pest-related. Here are a few:
- A very useful database for identifying and treating disease issues on plants ranging from garden vegetables to trees is the VA Cooperative Extension Plant Problem Image Gallery. It includes name, type, description, and photos of different diseases and disorders for many different plants. Once the problem is identified, treatment options can be found in VCE’s Home Grounds and Animals Pest Management Guide. Definitely worth checking out.
- Plant Diseases and Disorders on the Missouri Botanical Garden (MBG) website defines six types of issues: bacterial, fungal, viral, nematodes, nutritional, and environmental. The site breaks each category down further, illustrates specific problems with photos, and provides sound advice on treatment. The MBG website contains a wealth of information on many gardening topics and is worth getting to know.
- Plant Disease Diagnosis Tips is a video from the University of New Hampshire Extension which presents some helpful information for determining the nature of plant problems.
- A detailed catalog of various diseases and disorders is available in the Diseases and Disorders chapter of the NC State Extension Gardeners Handbook. It provides detailed descriptions of different types of plant problems, many including photos, along with advice on how to deal with them. It is a great resource for gardeners who want to go deeper into understanding their plants.
- A couple of more narrowly-focused sites can help with specific common problems. I have found the Missouri Botanical Garden’s A Visual Guide: Tomato Foliage, Stem and Root Problems to be a helpful resource in diagnosing and treating tomato issues.
- Similarly, the VCE video Downy Mildew on Basil offers help in identifying and dealing with a common problem on this popular herb.
Websites and Apps
A broad-based website titled What’s Wrong With My Plant, is maintained by the University of Minnesota Extension. It includes information on problems affecting fruits, vegetables, lawns, annuals, perennials, shrubs, and trees. It is thorough, easy to use, and supported by a very credible organization.
And, there are apps… My experience with photo-driven apps is pretty mixed. It is easy to get a wrong plant identification and go down the wrong path. So care must be taken to validate results. That said, apps will no doubt become more prevalent in the future, and there is a lot of useful information on some existing products. Please note that all references to commercial products or trade names do NOT imply endorsement by Piedmont Master Gardeners or the Virginia Cooperative Extension or bias against those not mentioned.
VCE recently held a webinar titled There’s An App For That? presented by Pam Bennett, the State Master Gardener Coordinator at the Ohio State University Extension. It covers the selection and use of apps on various gardening topics. Ms. Bennett talks specifically about some available apps that may be worth acquiring. The presentation is about an hour but is a worthwhile time investment for folks who would like some coaching on app selection and use.
Some apps mentioned in the presentation above and noted in other extension-based references I’ve reviewed include:
- 3 inexpensive apps supported by the Purdue University Extension which are reported to be good reference and learning tools are:
- Purdue Perennial Doctor
- Purdue Annual Doctor
- Purdue Tree Doctor
- For vegetables, the free app VegDr was created by the University of Georgia Extension with funding from USDA. It currently covers cucumbers, watermelons, squash, cantaloupe, pumpkin, tomato and pepper plants. Georgia is its research base, but its information has broader geographic applicability.
Other Gardening Apps and Sources
While this article focuses on diagnosing plant problems, I ran into some other gardening and nature-based apps that may be of interest:
- Vtree is a free tree identification app for iPhone and Android, developed by Virginia Tech. It has a huge collection of photos and information on trees from around the world. You can download them all, limit the download to local area trees, or simply download the one you are asking about. The app asks questions to lead the observer to photos of potential answers, and even offers the option of sending a photo to an expert at Tech for an answer.
- IDWeeds is a free app from the University of Missouri that helps identify weeds through a series of questions and then presents photos of possible solutions to the user.
- Picture This is a highly-regarded plant identification app that references thousands of species worldwide. It costs about $30 per year to download.
Finally, if you prefer to do your investigations using the web but get frustrated with all the non-relevant search results you get, read the VCE document The Right Answer: How to Find Unbiased, Research-Based Answers to Horticultural Questions. This publication offers many helpful definitions, hints, and practices that will help narrow and legitimize search results.
In Summary…
The amount of information that is available to us is both amazing and frustrating. The sheer quantity of data and the competition among many sources to climb to the top of search lists can make finding the best answers elusive. I hope the information contained here is helpful in narrowing and shortening your searches. Comments are welcome.
