Pesticide Use and
Integrated Pest Management

Relatively few pesticides are labeled for use on woody ornamentals. Those currently available should be managed judiciously to retain their efficacy against target pests while preserving the environment and worker safety. One detrimental effect of chemical pesticides that often is not considered is the mortality caused to beneficials and other nontarget organisms such as birds and bees. Beneficials are arthropod predators and parasites that prey on pests and are considered helpful to the grower. The following is a brief discussion of the problems with conserving beneficials when pesticides are used. A table of the registered pesticides and an assessment of their impact on beneficials is also available from the IPM menu.

Many species of beneficial insects and mites occur naturally on woody ornamental plants where they find food, moisture and shelter. Lady beetle larvae and adults are well known predators of aphids and miscellaneous insects and mites, but many species specialize on scales. Green and brown lacewings, primarily the larvae, also feed on aphids and mites as well as other miscellaneous arthropods they contact. Less commonly seen but important predators are the ground beetles, damsel bugs, plant bugs, minute pirate bugs, syrphid fly larvae, thrips, assassin and ambush bugs, and non-webbing spiders. A large number of species of predatory mites also prey on the phytophagous mites associated with ornamental plants. Parasites are represented by many families and species of Hymenoptera (wasps) and Diptera (tachinid flies) that are often very specialized as to the host species they attack. Most species of insects including beneficials are attacked by some species of parasitic Hymenoptera (in this case termed hyperparasites). Populations of Lepidoptera (moths and butterflies), aphids, and scales are often regulated by parasites. Diseases also infect arthropods and are important sources of mortality to pests. Bacillus thuringiensis (BT) is a well known bacterial disease of Lepidoptera with many strains having EPA registration. Insect diseases will not be discussed further but they are often suppressed by fungicides and bactericides targeted to plant diseases. However, microbial pesticides like BT are usually not harmful to beneficials. So called natural or botanical (plant derived) pesticides such as rotenone and pyrethrins may or may not cause mortality to specific beneficials.

Theiling and Croft (1988) developed a computer database and reviewed the literature concerning response by beneficials to pesticides. The following comments were extracted from that work. Generally, insecticides are the most toxic to beneficials, followed by herbicides, acaricides, and fungicides. There is a trend of increasing toxicity to beneficials from older inorganics to the synthetic pyrethroids. Predators are usually less susceptible to pesticides than are parasites, but their response is more variable. Life stages of beneficials differ in their response to pesticides. The more protected egg and pupal stages of predators usually are less susceptible. For parasites the larval and pupal stages are usually less susceptible.

Direct mortality to beneficials is not the only detrimental effect imposed by pesticides. Sublethal effects such as decreased longevity and fecundity, interference with sensory modalities which influence the ability to locate and attack prey, and decreased mobility may also occur. Indirect mortality from starvation by the beneficial can occur when pesticides destroy nearly 100% of the prey. A dramatic decrease in prey populations from a pesticide application may cause surviving beneficials to disperse from the crop in search of new prey.

Management choices concerning pesticides that affect beneficials, and which are under grower control, include the rate, method (type of sprayer, size of area treated), and frequency of application; population level of the pest or damage level to the plant when treated; and selection of which chemicals to apply (formulation, chemical class, activity spectrum, relation to previously used chemicals, residual duration).

Application rate, and thus the residual concentration and duration of the pesticide on the plant, may be reduced when using some chemicals, which will be to the benefit of beneficials. This is directly related to the concentration or dose of the pesticide which is toxic to the pest and beneficials. The toxic dose of a specific pesticide is almost never the same for beneficials and pests; it is usually much lower for beneficials. The degradation or breakdown rate of pesticides is related to their chemistry, climate and weather, and to plant chemistry. Pesticides with acute toxicity but short residual times may cause less mortality to beneficials than those with less toxicity but long residuals. Dursban (chlorpyrifos) has a long residual on most organic substrates, Malathion does not. Use of reduced rates may also help conserve beneficials by allowing the survival of low levels of prey. Continuous availability of food is necessary to prevent dispersal by surviving beneficials after pesticide treatments. Spot treatment of pests is recommended to minimize the area in which beneficials may contact toxic pesticides. The use of an airblast sprayer may not deliver pesticides into the plant interiors allowing untreated refuges for beneficials. Less frequent applications and the acceptance of higher pest populations or damage levels also will decrease the amount of time when pesticides are present to affect beneficials.

Granular systemics are usually less harmful to beneficials than foliar sprays. However, feeding on the nectar of systemically treated plants, which beneficials often do, may be toxic to them.

Proper selection of pesticides is critical in Integrated Pest Management (IPM). Read the Label - The Label Is The Law!

Factors to consider in selecting chemicals are:

Make sure proper safety precautions are taken including personal protective equipment, use of appropriate sites and methods for mixing and loading. Sprayers should be properly calibrated to deliver the correct rate and to provide proper coverage of the target plants. It is advisable to use the lowest recommended rate for safety, environmental and cost considerations, etc., so that the side effects are minimal.

Some species of predators are almost completely tolerant of certain classes of pesticides, as for example green lacewings and pyrethroids. This concept is termed selectivity. Pesticides which are less broad spectrum against pests will generally be less toxic (more selective) to some predators. To delay the onset of the development of resistance to pesticides by pests, it is suggested that the available pesticides be used in a rotation, rather than repeated use of one or a few.

Other nontarget organisms which may be harmed by pesticides include earthworms and fish. Potter (1991) reported that Dursban, Triumph, Sevin, Turcam, and Diazinon significantly reduced earthworm populations two weeks after treatment to lawns. Earthworms are important recyclers of organic matter and aerate the soil. The information concerning fish is muddled by the test methods. However, Crenshaw (1991) reported that most pesticides are extremely toxic to fish in the low parts per billion (ppb) or parts per million (ppm) range. All precautions should be taken to prevent the contamination of water resources with pesticides.

The University of Florida offers two computer-verified training tutorials on pesticide use. Core2:Pesticide Labeling trains users how to read a pesticide label, while Core6:Emergency Response to Harmful Pesticide Effects, Heat Stress and Heat Stroke trains users in how to respond to these dangerous situations. Information on these tutorials is available on the Buggy Software Web site at http://pests.ifas.ufl.edu/software/.