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In a time when we all seek advice from experts, it is not only important to know what plants you have, but also to understand the nomenclature of symptoms caused by insect and disease problems. “I’ve got this thing on my wacha-ma-call-it” won’t get you very far with a Google search or in person. We need to know how to describe the “things” that we find on our plant material so a proper diagnosis and treatment can follow.
There are several different scenarios that can threaten our garden landscape. Non-living, non-infectious diseases or “disorders” are linked to environmental circumstances. A late spring freeze, flood or drought conditions, or excessive heat are all factors in causing non-infectious disorders that effect plant material adversely. These types of disorders can lead to infectious disease or insect infestation. Plant pathogens must be able to “enter” the plant and non-living diseases often open the plant up to living diseases. This is why I have reiterated the importance of pruning away dead, diseased or injured wood, especially trees. Do not make it easier for infectious diseases to live off your landscape plants.
Living, or infectious, diseases involve parasitic plants, bacteria, fungi, viruses or nematodes. For example, white pine decline and white pine root decline (take note of the difference). White pine decline is a non-living, non-infectious disorder caused by environmental circumstances that weaken the tree and cause eventual death. On the other hand, white pine root decline is a living, infectious disease caused by nematodes in the soil that slowly attack the root system. You will notice a white film at the base of the pine’s trunk when it is suffering from white pine root decline. In one circumstance, you could replace the diseased white pine, however, in the latter circumstance, the soil is infected, so it is likely that a second white pine in the same location would see the same outcome: the same gradual decline and eventual death of the tree.
Plant disease and pest diagnosticians at Purdue University define the following common symptoms that plague our landscape plants. Recognizing these as symptoms of a greater problem will help us stop the spread of infectious diseases and treat our plants in a more timely fashion.
Leaf spots are small, discolored areas on the plant’s foliage. Rosarians are quite familiar with leaf spot on their roses.
Blight causes larger, dead areas on leaves, shoots, or flowers of a plant.
Stunting is the abnormally small growth of a plant or plant part.
Chlorosis is when normally green tissues appear yellowish-green in color.
Marginal necrosis is a symptom where the edges, or margins, of a plant’s leaves turn brown due to dead tissue. Houseplants suffer from this during the winter months due to the low humidity in our homes.
Distortion is the twisting or abnormal formation of leaves and new shoots. Aphids, mites and thrips cause this to happen to new daylily growth if the plant is infected.
Wilt, of course, is the flaccid, limp condition of leaves or non-woody shoots. Wilt generally occurs from insufficient water, but can also be brought on by too much water or living diseases. The dreaded clematis wilt is caused by nematodes.
Cankers are localized, often sunken, dead areas on a twig branch or stem.
Gall is an abnormal swelling of a portion of a branch, root, or bud.
And, witch’s broom is the symptom where twig growth appears distorted and stunted forming a broom-like mass of twigs. Once witch’s broom has appeared the plant should be “shovel-pruned.” That’s right, dig it up and throw it out because witch’s broom is caused by a fungus that has no known control and it will spread to other susceptible plants.
As the various, and sometimes inevitable, plant problems present themselves during the new year, these terms should help us describe, determine and treat what crosses our garden path.