Arthropod presence on a valuable plant does not necessarily mean that an effort should be made to eliminate it. If the plants are in nursery production and if the organism is an acknowledged pest species, then it should be controlled as soon as it becomes vulnerable to an efficient control tactic. However, the arthropod might be a beneficial species or a pest species at a low enough density on a landscape plant that control is not necessary. Several factors are considered sequentially to determine the need for indirect or direct action.
The first step when an arthropod is detected is to determine its identity. Many insects found on landscape plants are transients or beneficials, part of the natural community that helps keep pest species at low levels. It is extremely important to conserve beneficial arthropods like ladybird beetles, green lacewings, and parasitic wasps, by using pesticides only when they are needed. County agents, extension specialists located at land grant universities, and landscape maintenance personnel can help identify common arthropods, both pests and non-pests.
Once an insect or mite has been identified as a pest species, its biology and seasonal life history can be obtained to determine how and where it feeds, damage symptoms, number of generations it completes each year, the kinds of plants it infests, stage(s) and time(s) when it is vulnerable to control tactics, and current control options. All of this information is then used to determine the best strategy for dealing with the pest. (see INSECT & MITE MANAGEMENT ALTERNATIVES - The Control Options)
Until a certain number of insects is present on a plant, control measures are not needed. It's not always easy to know when there are enough insects present to justify control measures. One thousand caterpillars eating leaves might completely defoliate a tree in two weeks, whereas that same number of aphids would hardly be noted. Yet 1,000 aphids today may become 100,000 in a month. This may be more than a plant could tolerate.
It is especially difficult to say how many insects should be present on ornamental plants before we should spray. Plants established and growing well in the landscape may be able to tolerate more pests than poorly growing plants. Likewise, some home owners expect no pests while others don't even notice anything until extreme damage has already been done. Of course, nurseries are a different problem. State and federal regulations, as well as purchaser demands, require that plant stock for sale be "pest free." This places rather difficult standards for the final product to be sold. Experience tells us that certain pests must be controlled at the first sign of their presence because they will likely increase in numbers and cause considerable damage. With some pests and on certain plants, we will want to watch the infestation closely and treat only if the injury gets progressively worse.
In some cases, doing nothing is the best course of action because predators, parasites, and other factors take over and the pests soon disappear. Most established deciduous trees can be completely defoliated without any apparent permanent harm to them, but defoliation may weaken younger or newly transplanted trees and most shrubs until they die or become susceptible and attractive to other injurious pests.
Doing nothing may result in the beauty of a plant being destroyed or a pest becoming numerous enough to make a general nuisance of itself. In the case of a heavy borer or scale infestation, doing nothing could result in the death of a plant, regardless of its age or size.
The cost of having a tree or shrub sprayed one or more times may help a person to make up his/her mind quickly about what to do. It often requires at least two applications of an insecticide/miticide to clean up an infestation. Small trees and shrubs can be sprayed by the homeowner at much less expense. Tall trees may require a sprayer capable of developing as much as 500 pounds of pressure to force the spray to the top of the trees. This undoubtedly must be done by a commercial operator.
From what we have said so far, you probably realize that a person confronted with a pest problem may need some help to know just how serious the problem is and what needs to be done about it.
The Ohio State University Extension has offices throughout the state. In these offices, personnel are available to help you with your pest problems. Take the specimen to your local county OSU Extension office where they can determine if the sample needs to be submitted to The Plant and Pest Diagnostic Clinic in Columbus, OH. Be sure to provide as much information about the problem as possible. This helps specialists evaluate the problem and prescribe a recommendation.
The Plant and Pest Diagnostic Clinic charges a nominal fee for specimen identification. Your county office has proper forms and fee schedules.
Because the number and kinds of ornamental pests vary from year to year and even from month to month in any one year, you never know what pest problems you can expect or how severe they will be. So to prevent a pest from slipping in and becoming established on a plant without being noticed, visually inspect plants at least two or three times during the growing season. This may only involve a general inspection of the plants to see that there isn't a loss of color or that the leaves are not being eaten. Turn over a few leaves to see if there are any pests on them. Remember, some insects feed only at night and hide during the daytime. Early detection of a pest provides time to get the problem corrected before the plant suffers permanent injury.
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Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
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