Thursday, February 7, 2008

Landscape - What Causes Landscape Plant Failures

It is common to see plants fail in the landscape. Most failures are due to stress factors with diseases being a secondary cause most of the time. The following is a short article on what causes plant failures in the landscape.

Plant failures are common in the landscape. Some occur soon after planting, while others develop over time. "What causes plant failures in the landscape?" is a question that homeowners, landscapers, contractors and educators frequently ask. Answers to this question will help not only to diagnose, but also to prevent similar problems in the future.

In Delaware, analysis of plant disease samples received from the local landscape industry and homeowners reveals that environmental stresses and/or improper cultural practices are the primary causes of plant failure in the landscape. The majority of plant failures occur soon after planting. The transition from container-growth, under controlled conditions in a nursery, to the landscape can be very difficult. If an appropriate planting site and proper cultural conditions are not provided, the plant will not establish adequately, and is likely to die. Frequently, insufficient irrigation during the establishment period is a major cause of plant failure. However, too much water due to severe weather, watering too frequently, or poor soil drainage may also cause plants to die or become diseased. Salinity of the soil and the quality of well water used for irrigation are other common concerns in the eastern part of the mid-Atlantic region.

Actual plant pathogens are generally a secondary cause of plant failure or decline in the landscape. Plant pathogens may include fungi, viruses, bacteria or nematodes with most problems caused by fungi. Disease development of this type also is subject to weather conditions and cultural practices. Commercial nurseries maintain healthy plants with regular fungicide programs. However, after transplanting into the landscape, unprotected plants may become diseased. Disease can develop soon after planting or develop after a year or more, depending on the plant, the type of pathogen, and environmental stress.

A less common cause of plant failure is insect damage. Sometimes it is difficult to distinguish disease symptoms from insect damage. It is also difficult to make a disease diagnosis on an unknown or new plant species. Landscape plant species are very diverse, and if the normal appearance of a plant is not known, diagnosis may not be possible. Other signs and symptoms that are often confused with diseases include normal leaf variegation, corky ridges on stems, lack of flowers, and normal leaf senescence and drop, particularly associated with the springtime leaf senescence of broadleaf evergreens or fall needle senescence of conifers.

The first steps in attempting to diagnose a plant problem are to determine (i) what the plant is, (ii) what it is supposed to look like, and (iii) what environmental conditions it requires.
Keeping this information in mind should help you to learn what to look for in diagnosing plant problems. Characteristics of the plant, environmental conditions, and cultural practices utilized should be the first things to determine, followed by observation of signs and symptoms of plant pathogens.

Extracted from "A Guide to Diagnosing Diseases of Landscape Plants" Author: Chuan Hong, Extension Specialist; Tom Banko, Associate Professor; and Marcia Stefani, Research Specialist; Virginia Tech

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