IPM for Gardeners: A Guide to Integrated Pest Management - Hardcover

As we all know, to maintain healthy landscape plants, it is important to manage pests. Equally true, however, is that effective pest management requires a healthy, vigorous plant. These two points cannot be separated, and both are intimately involved in landscape IPM. Before we can even attempt to manage plant pests, it is essential that we understand something about the needs of the host plant.

It is also important to consider the ultimate goal of pest management in a home landscape. Unlike an agricultural setting, where maximum growth rate and yield are the focus, landscapes are intended to be both useful (provide shade, function, added value) and aesthetically pleasing. The goal is not to obtain bigger and better plants as much as to maintain healthy, vigorous plants that are easy to manage, or what is often called plant health care. Healthy plants are more resistant to attack by insects and diseases, more likely to recover from environmental and other stresses, and better able to withstand injury.

Therefore, it is best to rely on healthy plant growth and development as one deterrent to plant problems. Not surprisingly, IPM is closely tied to plant health.

To discuss plant needs, we need a working understanding of plant growth, differentiation, and development. Plant growth is the irreversible increase in either the mass or size of cells. By definition, true growth occurs only in living organisms. Because growth is quantitative, it is easy to measure. In vegetable production, for example, increases in dry or fresh weight are frequently used to measure growth.

Differentiation refers to differences other than size that occur in the process of cell, tissue, or organ changes as cells multiply. One cell divides to form two cells that may develop into different tissues. For example, general plant cells may give rise to water-conducting vessels, or phloem sieve tubes that move organic matter in the plant, or even epidermal cells. Differentiation is qualitative: Although one can see changes as new tissues emerge and the plant takes form, the changes are difficult to measure.

Development takes into account both growth and differentiation. It represents the sum of all changes that a plant undergoes in life. Because these changes are closely interrelated, "plant growth and development" is generally accepted terminology, even though it is somewhat redundant.

Plant development is not always productive. Plants do not increase in size, shape, and volume without limits. Although plants such as kudzu (Pueraria lobata), tree-of-heaven (Ailanthus altissima), and other weedy ornamentals certainly have a high degree of productive metabolism, these plants do not experience unlimited growth. Even plants that appear to be thriving have nonproductive growth processes at work as well.

Plant growth and development is described in terms of metabolism. Metabolism is the sum of the processes of building up and tearing down the living substance of which cells are composed (the protoplasm). Plant development involves a continual process of metabolism — both anabolic (constructive) and catabolic (destructive). Photosynthesis is anabolic metabolism, but for it to take place, complex molecules must be broken down into simpler parts. If plant energy sources are used, then some catabolic metabolism must occur to attain the necessary components. Stated another way, carbohydrates produced and stored earlier are converted to energy as needed in current processes, but for this anabolic metabolism to occur, tissue must be broken down. Thus catabolic metabolism is a necessary part of growth and development.

When plants are young, there is much more anabolic metabolism than catabolic metabolism, so growth is rapid. When anabolic and catabolic metabolism are equal, growth still occurs, but without a change in size. In this case, growth is mostly involved in tissue repair and maintenance, as one can see on a mature tree when callous tissue forms over a wound or canker. Bonsai trees are grown in trays or small containers with restricted root systems. The roots and stems are pruned to maintain a mature tree that is less than 3 feet tall.

Watering and fertilizing are important in keeping anabolic metabolism slightly greater than catabolic metabolism. When catabolic metabolism exceeds anabolic metabolism, decline and death take place. The dying process in plants may be rapid, as with annual plants, or slow, as with the natural decline of a tree.

Plant growth and development requires the absorption of materials from outside the plant used in combination with materials within the plant. Plants convert these materials to food that they can store or use immediately. Photosynthesis, respiration, and transpiration are the three major functions involved in this process.