Diagnosing plant diseases can be difficult and frustrating. Unlike pest problems, most plant diseases are caused by organisms that are difficult to see with the naked eye. However, there are some steps you can take to figure out what is attacking your plant and what to do about it.
Make a List of Symptoms
Some diseases, such as powdery mildew and fire blight, cause obvious symptom patterns. While you may not be able to see the disease causing organism, you can recognize the pattern of symptoms. If you have a plant that is doing poorly, and it does not seem to have any critters eating it, try looking at it from the stand point of listing the symptoms the plant exhibits. If you have roses, are the leaves black? Or do your crape myrtles have a gray powdery stuff all over them?
Research Common Diseases
After you have a list of symptoms, it is time to do a little research. Look on the internet by typing in “plant name diseases”. Look at these problems and try to find one that causes the symptoms you have listed. When you think you have found the right disease, search again under “plant name disease name”.
Finding Science Based Sources
When you get a list of possible sources to read, try to select ones put out by an extension service. These will typically be the most comprehensive and contain the best information. Try to find at least three sources on the problem and read them all. That way if one source is in left field you will not be lead astray.
Take Good Photographs
Take some good photographs of the problem. Make sure you take some where the problem meets healthy tissue, too. Many county Extension services have help desks staffed by master gardeners. You can send in your pictures and they will attempt to diagnosis the problem. They will then tell you what treatments are available for that problem on that plant.
Take A Sample
Some diseases are hard to tell apart. The help desk may recommend you take a sample of the problem and send it to the state pathogen lab. Take the sample on the edge where the healthy and sick parts of the plant meet. Try to get at least a 2 X 2 inch plug of grass, including the roots, or six inches of branch or plant.
Send to Plant Pathogen Lab
The specimen will have to be sent to the Plant Diagnostic Lab in your state. This means it may be a week or two before you have an answer. The good part is that they have the microscopes and other equipment to see things that cannot be seen without special equipment. There may be a charge for this service, but they will chase the problem down until they find out what it is.
Once you get a diagnosis, you will also get treatment recommendations. Sometimes, there is no treatment. Cotton root rot is like that. Sometimes, it is a simple matter of watering differently or using a different fertilizer. Others, there is a treatment such as a fungicide that will make the problem go away, such as with powdery mildew. Following the recommendations closely will yield the best outcome for you and your plants.
Want to learn to garden? My first attempt at gardening ended up in failure. The weeds took over and squeezed the vegetables out. I was very frustrated by this waste of good seed, time, and money. So I became a master gardener and spent a lot of time helping other people avoid or overcome problems in their garden.
In order to help others garden successfully, I have written a book, Vegetable Gardening from the Ground Up, available in an ebook or a paperback from Amazon. It is also in Kindle Unlimited.
