Chapter 24

Greenhouse Pesticides

Biorationals

Unlike conventional synthetic pesticides as discussed in the previous section, which are classified on the basis of their chemistry, biorational pesticides are grouped on the basis of some shared characteristics. For example, they pose minimal to no risk to the environment due to their chemical make-up, rapid degradation, or the small amounts required to effect control. Biorational pesticides vary in their toxicity and in their potential ecological impact. Biorationals in general have a narrow target range and a very specific mode of action. They are slow acting, have a relatively critical application times, suppress, rather than eliminate a pest population. In addition, they have limited field persistence and a shorter shelf life than conventional synthetic pesticides and present no residue problems. Biorationals fit well into an integrated pest management strategy, which relies on monitoring for early detection of pests and emphasizes the use of selective products that provide control while preserving the ecological health of the farm and minimizing negative effects on beneficial insects that suppress pests. Biorationals encompass a broad array of pesticides which can be classified as follows: 1) microbials, 2) botanicals, 3) spray oils, 4) insecticidal soaps, 5) minerals, 6) pheromones, and 7) insect growth regulators. A similar term that is used by EPA is “biopesticides” (defined in the following section) and often used interchangeably with the term biorationals. The terms “organic” and “biorational” are partially overlapping categories, each defined by specific criteria that are unique. What is considered “organic” is not well defined.

Biopesticides

Biopesticides, as defined by the Environmental Protection Agency (EPA), are certain types of pesticides derived from such natural materials as animals, plants, bacteria, and certain minerals. Categories of biopesticides include: 1) biochemical pesticides, which are naturally occurring substances that control pests by non-toxic mechanisms, such as sex pheromones that interfere with mating and scented plant extracts that attract insect pests to traps; 2) microbial pesticides, which consist of a microorganism (e.g., a bacterium, fungus, virus or protozoan) as the active ingredient; and 3) Plant-Incorporated-Protectants (PIPs), in which pesticidal substances are produced by crop plants as a result of genetic material being added to the plant (e.g., Bt insecticidal protein). With plant-incorporated protectants, the toxin and its genetic material, but not the plant itself, are regulated by EPA.

Microbials

Microbial pesticides are formulated from living microorganisms or their by-products. They tend to be selective, so specific pests may be controlled with little or no effect on non-target organisms. Microbial insecticides may be derived from bacteria (e.g., Bacillus thuringiensis, spinetoram and spinosad, Chromobacterium subtsugae), viruses (e.g., nuclear polyhedrosis virus of corn earworm) or fungi (e.g., Beauvaria bassiana).

Bacteria

Bacterial biopesticides are the most common form of microbial pesticides. They are typically used as insecticides, although they can be used to control unwanted bacteria, fungi or viruses as well. As an insecticide, they are generally specific to individual species of moths and butterflies, as well as species of beetles, flies, and mosquitoes.

Fungi

Fungal biopesticides can be used to control insects, plant diseases including other fungi or bacteria, nematodes, and weeds. They are often parasitic or produce bioactive metabolites such as enzymes that dissolve plant walls. The mode of action is varied and depends on both the pesticidal fungus and the target pest.

Viruses

Baculoviruses (viral biopesticides) are pathogens that attack insects and other arthropods. All types of baculoviruses must be eaten by the host to produce an infection. The resulting infection is typically fatal to the insect host. Each strain of baculovirus is targeted for a specific insect species.

Botanicals

Bontanicals are extracts and oils are specific chemicals or mixtures of chemical components derived from a plant. Bontanicals are most often used as insecticides, but can also be used as herbicides. The mode of action varies greatly from product to product. Where sex pheromones directly interrupt the reproductive cycle of insects, bontanicals often act less directly and specifically. Some botanical extracts such as floral essences attract insects to traps. Others such as cayenne can be used as deterrents. Others, such as lemongrass oil, strip the waxy coating off leaves of weeds to cause dehydration. Products made from plant extracts and oils can be regulated as biorationals or conventional pesticides depending on their mode of action and level of toxicity.

Spray Oils

Spray oils include certain fractions of petroleum oils (narrow-range oils), which are considered synthetic and allowed for insect and disease control. “Narrow-range oils” are defined as petroleum derivatives—predominately of paraffinic and napthenic fractions. Narrow-range oils are allowed for both dormant and growing season uses for insect or disease control. Allowed oils can also be derived from plant and fish sources.

Insecticidal Soaps

Insecticidal soaps are potassium or ammonium salts extracted from plant or animal lipids (fats). Insecticidal soap products work by disrupting the cuticle (skin) layer and suffocating soft-bodied insects. To be effective, the spray solution must contact and thoroughly cover the targeted pest.

Minerals

Some pesticides made from minerals, mined from the earth and minimally processed such as boron, copper, and sulfur. Elemental sulfur may be used for a broad range of pests in a wide variety of plants.

Insect Pheromones

Insect pheromones are chemicals used by an insect to communicate with other members of the same species. Insect sex pheromones are used in pest management. The insect pheromones themselves do not kill a target pest. When used for pest management, two common uses are to attract an insect to a trap containing a lethal pesticide or to disrupt mating. With mating disruption, proportionately large concentrations of the sex pheromones are present in the air, thus confusing the males and decreasing their success at locating a female with which to mate. Pheromones can also be used to monitor pest populations as part of larger IPM systems, particularly to determine appropriate timing and application of pesticides.

Insect Growth Regulators

Insect growth regulators have proven extremely effective as components in IPM programs for control of insects which have become resistant to standard insecticides. Typically, IGRs are less harmful to the environment and more compatible with pest management systems that include biological controls. They generally don’t affect non-target species—such as humans, birds, fish, or other vertebrates. Insect growth regulators are compounds that mimic the action of hormones to disrupt the molting process and modify growth of insect or mite pests.

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