Appearance signals sick plants

It would be great if plants in the landscape could tell us what is wrong with them when they get sick, but of course, they can’t.


They do let you know when they are sick because of their appearance – wilted or discolored leaves, leaf spots, dying branches and premature leaf drop are just a few of the common symptoms of plant stress.

Unfortunately, plant problems are not always clear cut and easy to diagnose. They often involve a complex interaction of many factors.

Many times when I talk to homeowners about plant problems, I ask many questions and try to narrow down the potential problems.

Most tree problems result from stress of the root system imposed by such things as drought, root disturbance during construction, changes in grade and drainage, fill dirt of the roots and soil compaction.

When attempting to diagnose a plant illness, make sure you have all the facts. Do not make snap judgments, because the problem you perceive at first glance may not be the direct cause. I don’t know how many times a shrub will have an insect problem, so the owner will spray for them and think they have resolved the issue. But the truth of the matter is the plant is stressed from some other problem and this in turn invites the insects to attack the weakened plant.

Another good example is iron deficiency on azaleas. Iron deficiency is often exhibited by plants that are under moisture stress.

An extremely wet soil literally suffocates the root system. As a result, root-rot organisms attack the damaged roots. The roots lose their ability to absorb nutrients like iron and interveinal chlorosis is exhibited by the leaves. You still see the green veins when this happens. Attempting to cure this problem with liquid iron or iron supplements to the soil is only a short-term solution. The best remedy might be to modify the drainage of the site, cut down on the watering, or to transplant the azaleas to another location that is known to drain well.

The second major cause of plant problems is poor cultural or management practices. We literally love our plants to death by applying luxurious quantities of fertilizer and water, or by spraying routinely, even when there are no pests in the vicinity.

Planting too deeply is another common cultural mistake. When plants are set too deeply in the soil, the lower portion of the root system becomes deprived of oxygen and dies.

The most complex problems to diagnose are those resulting from a combination of environmental factors and poor cultural practices. Placing a shade-loving plant in hot, baking, afternoon sun will result in bleaching or scorching of the foliage. I have watched this happen many times with dogwood trees.

The immediate reaction to these problems for homeowners, and even professionals, is to think the plants are hungry, so a generous amount of fertilizer is thrown right on top of the root ball. This adds insult to injury and the plant eventually dies. Concentrated amounts of fertilizer will literally burn the roots. Remember that when a plant is sick, the last thing you need to do until you figure out the problem is fertilize it.

Another problem I see is people trying to grow a plant out of our horticultural zone. One good example is lilacs, which are 99.9 percent of the time not going to do well here so don’t be surprised when they develop problems.

A magnifying glass is always a good tool to keep nearby. A white piece of paper can also come in handy. You can use these two in combination when looking for insects, because they are not always easy to see. When using the white paper, simply shake the plant over the paper and look for insects moving across the white background. This is particularly useful for insects such as spider mites and thrips.