A Quick Course In Plant Diagnostics

Estimated read time: 6-7 minutes

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With all of the many pleasures of gardening, it is easy to think we are in charge. However, plants are always at the mercy of Mother Nature and there are always potential problems. With this in mind, read on for a quick course in plant diagnostics.

The "art" of diagnosis is not always easy. Diagnosing a problem is an orderly thinking process proceeding from recognition of a problem through a solution. Your challenge is to gather clues, ask good questions, and make accurate observations of your plants and what is happening to them.

Remember that many potential pests and problems can harm your plants. Possible pest problems include insects and other creepy, crawly creatures like mites, slugs and snails and crustaceans. Animals, like rodents, deer, birds and even dogs and cats can damage plants.

Diseases include pathogenic problems caused by living organisms like fungi, bacteria, and viruses and nematodes. It includes nonpathogenic problems like environmental problems, nutritional problems, water problems temperature extremes and many other physical maladies.

To successfully diagnose a plant problem, follow these steps. If you do not know enough to complete the process, get help from one of the sources listed.

1. Identify the plant correctly. If possible, find the scientific name of the plant because the same common names are frequently used for distinctly different plant species. For example, there are many different species of pine trees each with different plant diseases unique to that species. Spruces, pines firs and junipers are all erroneously called pine trees but each kind of tree has separate, distinct problems.

2. Determine what problems are likely to occur on your plant. One good reference is the Ortho Problem

Solver available as a reference at many libraries and most local nurseries or check http://www.ortho.com for an online reference.

3. Compare the affected plant with nearby healthy plants to make certain there is a problem. Sometimes normal plants are mistaken to have problems. For example, conspicuous fuzz that is confused with fungus mycelium covers the leaves of a healthy sycamore.

4. Next, determine the distribution of the problem within the garden. Is more than one plant species affected? If so, climate, chemicals, or other cultural factors likely caused the problem.

If the condition is uniformly distributed in a low spot in the garden or at the edge of a planting, suspect a soil or water factor or toxic chemical. Parasitic diseases and insects progress with time and rarely infect 100% of the plants in an area.

When the problem affects all of the plants in a particular area, the cause of the problem is probably a deficiency or excess of a soil nutrient or problems or drought, frost or hail; or a toxic chemical such as herbicide or air pollution.

Plant pathogens rarely cause a condition to appear suddenly. They usually begin at one point and spread slowly to other plants. If the symptoms show up "overnight" or in one or two days, suspect a climatic factor or toxic chemical.

5. Look at the growing history. Have you grown the same plants there year after year? Were there problems growing other species of plants in the same location? Have herbicides or other chemicals been used in the area? Look at the weather history and determine if there have been any unusually cold, hot or wet climatic conditions in the past.

Unfortunately, overwatering is a major problem and kills many more plants than drought. For best plant growth keep the soil moist but never wet and make certain that the soil drains properly.

Chronically wet soils promote root rot. Many above?ground symptoms indicate root rot. Small, yellow or wilting leaves, poor terminal growth or little fruit or flower production often indicate root rot caused by wet soil and the attendant soil-borne pathogens.

Most fatal plant diseases in Utah are caused by soil?borne pathogens. Look for dead roots or dead areas in the bark. Healthy roots are white or cream colored. If the insides are brown or black, the plant likely has root rot.

6. Pathogenic diseases are caused by fungi, bacteria, viruses, mycoplasmas and other organisms. For these diseases to cause problems, you must have the disease organism, a susceptible host and the right environment. These diseases are best controlled by changing the environment. In our area, this is best done by controlling irrigation.

7. Nonpathogenic diseases are not caused by pathogenic organisms. These are environmental problems including temperature extremes, water excesses or deficiencies, nutrient problems or mechanical damage. Fungicides or other chemicals never control these diseases.

8. Insects and related pests fall into two major categories. They either chew your plants or suck out the juices. It seems like these pests would be easy to diagnose, but pests are often carefully hidden or they may feed only at night.

Sometimes insect damage is confused with other problems. While most insects are specific to one kind of plant, grasshoppers and many others feed on many types of crops.

9. Other pests include slugs and snails, mites and other related creatures. Each kind of pest requires specific controls or environmental changes. Determine what controls are best for your problems. Note that spiders never feed on plants and only poisonous spiders need controls.

One excellent resource to help you with the many problems that affect your plants is the diagnostic clinics done at Utah State University Extension Service Offices along the Wasatch Front. Extension Agents and Master Gardeners will examine your plants or the pests that are bothering your plants and recommend a solution.

Counties along the Wasatch front hold clinics each week during the summer. Quality plant specimens are vital. Enough representative material is needed to determine the problems. Include root, stems, and leaves of the infected plant, if possible.

In most cases, the best diagnosis is made when you include healthy tissue and the tissue that is dying. Dead grass and dead branches are usually not going to give many clues as too what is causing the problem.

Make certain that the sample arrives in good shape by bringing the sample to the clinics on the appointed day.

For more information on the times and dates of the diagnostic clinics, contact the USU Extension office in your county. These are listed in the phone directory or available online at http://extension.usu.edu/coop/regions/index.htm

Most plant problems are preventable by paying attention to what is happening with the plants. Solve problems when they first appear, not when they have destroyed your plants.

Most plant pests have alternative or nonchemical methods to control them. Spraying often kills the predatory insects and makes the problem worse. Always correctly identify the problem and look at all of the possible solutions.