PB1623-Decision Making Handbook for Insect & Mite Pests of Ornamental Plants

Attractive, vital landscape plants contribute significantly to real estate values. On the other hand, poorly maintained landscapes may become a liability, especially if trees or their parts fall and cause property or bodily injury. This realization, coupled with increased leisure time to enjoy our yards and more discretionary income for landscaping and landscape maintenance, has contributed to dramatic increases in the demand for nursery products and competent service personnel. At the same time, concerns for environmental quality and safe use of pesticides require that plant health care activities, including pest control, provide quality plants without creating adverse side effects. This is the challenge for anyone dealing with plant propagation, production or maintenance.

The nursery industry produces a diverse array of plant materials for landscape use. In many cases, these plants are native to North America and are not seriously damaged by insects or mites on native sites. However, when these same plants are grown under nursery conditions or in a landscape, native arthropods sometimes become pests. Although we do not know precisely why this occurs, it is undoubtedly related to site factors that create instability in plant-insect relationships. Either the effectiveness of natural enemies, including other arthropods and microorganisms, that normally minimize reproductive success is reduced, or the plants become stressed so they are more attractive or susceptible to opportunistic colonizers. Perhaps both regulating mechanisms commonly break down when plants are grown on non-native sites, especially under stressful conditions like those found in the urban forest.

Of course, many pests that damage landscape plants were introduced in the absence of natural enemies that normally limit their exploitation. Japanese beetle, black vine weevil and gypsy moth are examples of exotic insects that have become extremely common and damaging in North America. Although major efforts have been made to introduce parasites and predators of some introduced pests, they must usually be controlled with pesticidal sprays when their density threatens plant vitality. In any case, potentially damaging arthropods are common on landscape plants.

Since most of us take plants for granted or at least fail to inspect them periodically, insects and mites commonly cause damage before their presence is detected. This chronic lack of vigilance often results in plant damage and causes unnecessary use of large amounts of pesticides. Scheduled plant inspections and use of spot-spraying to control small but building infestations of pest species are superior ways to minimize damage from arthropods.

This publication has been prepared to inform users about the insect and mite pests that commonly attack landscape plants, when these pests are most vulnerable to control measures and currently available control options. The following narrative is included to help plant producers and landscape management practitioners understand the basic principles involved in making responsible and effective pest control decisions.