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Insects harmful to ornamentals

Ornamental plants are primarily grown for their beauty either for screening, accent, specimen, color, or any other aesthetic reasons. They are typically no taller than 20', but this is a somewhat arbitrary definition. There are a number of companies that treat ornamental plants, but don't maintain the expensive equipment required to reach above that 20' limitation. Trees falling into that category would require an arborist.

Feeding by insects and mites can reduce the aesthetic beauty of landscape trees and woody ornamentals. In some cases, plants can be severely weaken or killed, damage by other pests can cause aesthetic injury. When damaging pests are present, the application of appropriate control measures can help to reduce damage while having little impact on beneficial species and posing minimum risk to humans and pets. This fact sheet covers alternative control measures that are available. Any pesticide must be used according to label directions, it can cause harm if not used properly.

Establishing new landscapes

When establishing new landscapes, select low maintenance, environmentally adopted, pest free species. Euonymus and Virginia pines are good examples of plants that will be pest infested unless continually treated with insecticides.

Once established, practice sound horticultural methods to reduce plant stress and maintain vigor (don't under-or over-fertilize). Plants in good condition will be less attractive to pests and can better tolerate damage. Lush growth caused by over fertilization can make plants more attractive to certain pests such as aphids.

Because the ornamental landscape is composed of a combination of different species and varieties of plants, designing a single management program for the entire landscape is extremely difficult. Each species has its own requirements for maintaining plant health, and each has its own level of tolerance to insect damage before its health and/or aesthetic value is threatened.

First, determine your goals for management. Decide what level(s) of damage can be tolerated prior to taking action to suppress pest populations. In general, little or no damage can be tolerated on valued plants in prominent positions in the landscape, whereas plants in a landscape maintenance program can sustain some damage from pests before their health and/or aesthetic value becomes impaired.

  1. Pest suppression tactics are best implemented when the pests causing damage first appear.

  2. Take action during the most vulnerable life stage(s) of the pests.

  3. Monitor pest populations using

    • visual inspections of randomly selected sets of leaves,

    • the beat method where pests are dislodged from their host plants by beating plant parts on a piece of paper (this method is great for detecting mites, thrips and scale crawlers),

    • using yellow sticky traps to attract winged aphids, thrips, whiteflies, fungus gnats and shore flies (this method is best suited to the greenhouse),

    • Black light traps and

    • pheromone traps.

  4. Remember that the presence of the pest is not justification for treatment. Inspect plants to determine that the pest is beginning to cause a sufficient amount of plant damage prior to treatment.

For some pests, notably scale, aphids and phylloxera, management begins during the winter when dormant oil is applied prior to the swelling of the buds. On evergreen plants, use a lighter (summer) oil or check the label to ensure that application of the oil will not result in plant injury (phytotoxicity).

Selection of pesticides for the suppression pests on ornamental plants is extremely important since some species/ varieties/cultivars are extremely sensitive to them. Follow label directions and use only on plants listed. If the label is general (i.e. "use on ornamentals") always test pesticides on a few of the plants and observe any reactions that may develop prior to treating all the plants.

Practice good sanitation in the landscape, removing dead limbs, dead leaves (particularly those harboring insect-caused galls), and remove hiding places for "trash pests" such as millipedes, sowbugs, pillbugs, snails and slugs. During the "off season", repair and maintain equipment and update your pesticide product label and material safety data sheet file by contacting chemical company representatives or attending trade shows. Don't depend solely on your memory to remember label instructions and rates. Labels change over time.


Harmful landscape insects