Perennial pest management fundamentals

Perennials continue to be in high demand by consumers that want horticultural plants that last for more than one year. However, perennials are susceptible to insect and mite pests, and because there is a wide diversity of perennials, there is a complex of insect and mite pests that will feed on perennials.

Insect and mite pests that feed on perennials can be grouped based on their feeding behavior, which is associated with the damage that insect and mite pests cause to the leaves, stems, or flowers of perennials. The major feeding behaviors of insect and mite pests that feed on perennials are chewers, suckers, miners, and borers.

The primary insect and mite pests of perennials, based on their feeding behaviors, are listed in Table 1 (page 76).

Management of perennial pests

The management of insect and mite pests of perennials involves implementing cultural control, pesticide (insecticides and miticides), and biological control strategies in a holistic plant protection program.

Cultural control

Remove or prevent the growth of weeds inside and outside greenhouses because weeds may serve as reservoirs or alternate hosts for insect pests including aphids, caterpillars, leafhoppers, mealybugs, thrips, and whiteflies. The presence of weeds in or around the greenhouse may lead to increases in insect pest populations. Furthermore, weeds may harbor diseases such as viruses, which may be transmitted by insects that initially feed on weeds and then feed on perennials. Insects that may transmit viruses from weeds to perennials include aphids, leafhoppers, thrips, and whiteflies.

Practices that may minimize problems with weeds in and around greenhouses include the installation of geotextile fabric barriers, physical removal, mowing, and using herbicides. Regarding the use of herbicides, few pre-emergent herbicides are registered for use inside greenhouses and those that are labeled should only be applied when greenhouses are empty because of the potential for plant damage. In addition, post-emergent herbicides should never be applied inside greenhouses when perennials are present.

All plant and growing medium debris needs to be removed from inside and outside greenhouses because plant and growing medium debris may harbor insect pests, and immediate removal should decrease insect populations; thus preventing insect pests from infesting any perennials.

Maintain plant health as perennials that are properly watered and fertilized may be able to tolerate some insect or mite pest feeding without showing noticeable symptoms. Use well-drained growing media and avoid over-watering perennials to prevent problems with fungus gnats and/or foliar nematodes.

In addition, do not over-fertilize perennials, especially with water-soluble, nitrogen-based fertilizers, which may increase susceptibility to insect and mite pests, such as aphids and the twospotted spider mite (Tetranychus urticae). Moreover, over-fertilizing perennials may stimulate insect and mite pest development and reproduction.

Always use new containers and growing medium and dispose of old stock plants because these may serve as a source of insect and/or mite pests. If need be, remove and dispose of any perennials that are heavily infested with insect or mite pests.

Scout/monitor perennial crops at least once per week visually and/or use yellow sticky cards to detect the presence of insect and mite pest populations. Record when insect and mite pests are present on specific perennials during the growing season.

Pesticides (insecticides and miticides)

There are many pesticides (insecticides and miticides) registered for use against insect and mite pests of perennials. These pesticides may have contact, stomach poison (ingestion), translaminar, or systemic activity.

Microbial insecticides are derived from fungi and/or bacteria and are selective in the types of insects they kill. For example, the bacterium, Bacillus thuringiensis subsp. kurstaki, which is a stomach poison, only has activity on caterpillars. However, the insecticide is not harmful to humans, pollinators, or beneficial insects.

Timing: apply pesticides when the most susceptible life stages (larva, nymph, or adult) of insect or mite pests are present.

Coverage: when applying a pesticide, it is important to obtain thorough coverage of all plant parts including leaves, stems, and flowers. Spray applications must reach leaf undersides because most insect and mite pests feed on the underside of leaves.

Frequency: apply pesticides within timely intervals, which is dependent on the residual activity of a given pesticide. Read the pesticide label carefully for information associated with frequency of application.

Contact your local extension service or university-based entomologist for recommendations on those pesticides that can be used for specific insect and mite pests.

Biological Control

Biological control is a plant protection strategy which entails releasing biological control agents such as parasitoids or predators that will regulate insect or mite pest populations below plant damaging levels. Certain parasitoids will attack aphids, whiteflies, or caterpillars. Predators, in general, will feed on a wide-range of insect and mite pests that feed on perennials.

In addition to parasitoids and predators, entomopathogenic nematodes (Steinernema spp., or Heterorhabditis spp.) can be applied to the growing medium to suppress fungus gnat or black vine weevil (Otiorhynchus sulcatus) larval populations.

Biological control agents can be purchased from biological control suppliers or distributors. It is important to release biological control agents when insect or mite pest populations are low. Furthermore, be sure to assess the quality of the biological control agents to ensure that they are alive before releasing into greenhouses.

In conclusion, it is important to correctly identify insect or mite pests that are feeding on perennials, which will help determine those cultural control, pesticide, and biological control strategies that should be implemented to prevent damage to perennial crops.