Identifying Garden Pests and Diseases

Plants get sick. Pests, bacteria, viruses and fungus abound. But they can be controlled. Identifying garden pests and diseases is your first step to a healthy garden--and a happier gardener.

Where do you begin? With a three step approach similar to a human patient triage protocol that requires investigation, analysis and then action.

Step One: Assess the Problem

Since a plant cannot tell us what ails it, we must rely entirely on observation to narrow our diagnosis. Start with the general and work toward the specific. In a notebook or on a spreadsheet, enter what you feel is wrong. For example, “small spider like mite creatures on leaves,” “chew marks on leaves or stems” or “white powdery substance on leaves along with slow growth.” This last entry is actually two observations, so separate them. Also note the name and species of the plant.

Record keeping is important. As you investigate the web resources in this area, you will find many categorized by plant name and species. So when you plant, start a simple journal. Private investigators and doctors keep notes, so when identifying garden pests and diseases, you should too.

The environment in which the plant lives can provide important clues. Note the soil type and pH, planting depth and spacing, sun exposure, watering schedule and feeding history and prunings. If you consult with a gardening expert, a recent photo of the plant, its name and its history is key to obtaining accurate advice.

Step Two: Analysis

This is where your record keeping comes in handy, since you will make notes as you narrow your diagnosis from general observations to specific causes and then treatments. Through this learning process you will adapt your gardening to avoid future problems.

Your local agriculture extension office is a wonderful informational resource. Except for nominal fees for soil testing and the like, they are essentially free. They are backed by the ongoing research of plant pathologists and master gardeners, so the information is current. There is virtually no risk of a profit-motivated bias which may influence a commercial outlet. And they are familiar with your particular micro climate and plant types, making them local experts in identifying garden pests and pathogens.

If your area does not support an office, look to one nearby. You may even look to better organized sites in other states so long as the plant types they reference are the same.

By way of example, read the Plant Disease Facts publication from the Penn State cooperative extension (a PDF file), which mentions that sand, soil and peat are likely to carry soil borne pathogens, but vermiculite, perlite and hydrogels are not. If your soil is already possibly contaminated, either heat or chemicals can provide a remedy. Since any chemical treatment will impact your plants, read a soil solarization how-to article on heating soil to eradicate pathogens.

Notice that the end of the Penn State article has a “Greenhouse Assessment Worksheet” so you can develop and follow best practices while providing a framework for solving problems. This is where you can use science in support of craft and art to make a complete gardening experience.

Step Three: Your Action Plan

Obviously there are preventative maintenance measures you can take which avoid problems. The Penn State article, above, lists several less obvious standards you can adopt--such as disinfecting tools between the planting or pruning of different species. Or the Alabama extension's practice of solar heating soil each year to reduce disease and pests while improving yields.

Specific actions you take to eradicate a garden pest or disease can be organic, chemical or a combination of the two. Consider, for example, the possible pathogens to an African violet. Scroll to that category and open the PDF file.

The plant’s known diseases are categorized into type, symptoms, cause and management. Photos are available to assist in identifying garden pests and diseases, and the active ingredients and trade names of chemical treatments are provided.

Pay close attention to the chemicals table and the key that follows it. Note that the author lists various chemical trade names you might see on a garden store shelf organized into distinct “FRAC Groups.” Within each group each chemical will have the same mode of action, i.e., the active ingredient is the same. This allows you to choose which you may wish to use based on price or whether the chemical is possibly at higher risk to the development of resistance.

Once you have identified the disease or pest affecting your plant and chosen how to manage it, follow the application guidelines for the method chosen. Make notes of what you apply, where and how you apply it, and the timing of the results. Be specific.

To repeat a favorite dish, you follow the recipe. Successfully identifying garden pests and diseases, and managing them, requires the same skills. In the process you become a better gardener and enjoy the best your plants have to offer.

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