Integrated Pest Management of Sunflower Insects
This is the last in a series of articles addressing the Integrated Pest Management (IPM) of insects in sunflower.
Writings of the Chinese, Greeks and Romans indicate that the use of chemicals, usually referred to as insecticides or pesticides (from the Latin word meaning “to kill”) for the management of insects dates back about 3,000 years. However, the modern use of insecticides in the United States began in 1867 when Paris Green (an arsenic compound) was first applied for outbreaks of the Colorado potato beetle.
The earliest chemical pesticides were inorganic compounds (such as sulfur, arsenic or copper) or products derived from plants (e.g., nicotine, pyrethrum, rotenone). Since the 1939 discovery of the insecticidal value of DDT, thousands of other synthetic organic chemicals have been produced. These products are mostly modifications of petroleum-based molecules and kill the insects through contact, inhalation or ingestion. Some newer products — called “insect growth regulators” — are synthetic insect hormones which act by interfering or disrupting the normal growth, development or reproduction of the pest. “Microbial pesticides” are products containing insect pathogenic organisms; and although they constitute a form of biological control, they can be applied like a chemical pesticide.
Insecticides usually are considered the first line of defense against insect pests. They have been widely used because they often provide rapid and effective control of a variety of pest organisms. Pesticides also are relatively easy to use, predictable, can be adapted to a variety of situations, quickly reduce large insect populations, and usually have an immediate effect.
The use of insecticides has increased the yield, quality and efficiency of plant production — and, consequently, has increased the stability of the agricultural sector. Pesticides also have had a positive impact on human health through the destruction of insect vectors of disease organisms. The need for and use of insecticides will undoubtedly continue for the foreseeable future.
The decision to employ insecticides to manage an insect problem in sunflower or any other crop should depend upon an overall assessment of the situation. The principle to follow is that all possible techniques or combinations of methods should be considered. The use of a pesticide is justified only when the expected loss without treatment exceeds the cost of treatments.
Sole reliance on chemicals for pest control does have a number of downsides — among them: pest resistance, resurgence, outbreaks of secondary pests, environmental contamination, destruction of beneficial pests and the expense of the pesticides.
• Reliance on chemical control can foster the development of pesticide resistance in important pest species. This encourages an increase in dosage and the number of pesticide applications, which can then magnify the resistance and also have adverse effects on beneficial organisms (pollinators, predators and parasites).
• Pests may also resurge, because when numbers are lowered, there is less competi-tion for food, thereby allowing maximum reproduction of the insects. In addition, the destruction of predators and parasitoids results in surviving pests being able to breed without restraint from natural enemies.
• A secondary pest outbreak may occur when a pest’s natural enemies — which were not the target of the application — are destroyed. The second species, released from the pressure imposed by its enemies, may then increase to damaging numbers and require further insecticidal treatments.
• Because they are basically poisons, pesticides can result in hazards to humans, wildlife and/or the environment. Though some insecticides break down quickly in the environment, others may persist for days or even weeks. This may prolong the destruction of the pests, but it also may destroy nontarget organisms and become a source of contamination.
• If pesticides eliminate natural enemies, pest populations may increase and emigrate to surrounding habitats, possibly damaging crops at considerable distances from the site of the application.
• The expense of pesticides and their application is an important problem associated with excessive reliance upon chemical pest management. This problem often can be addressed by recognizing that many crops can tolerate substantial damage without economic loss; and that scheduled applications can be replaced with applica-tions based on population assessment.
The amount and frequency of pesticide use on our crops has been, to a large extent, determined by the general public. The public has been conditioned to demand food products which are totally devoid of blemishes or damage caused by pests. In many cases, the marks are only superficial and do not actually reduce the quality of the product; but producers have been led to expect that there should be an absence of all pests — a situation frequently not required in order to prevent economic loss.
Recent years have witnessed a greater interest in organic foods and crops grown without the the use of pesticides. This change in the public’s expectations has been coupled with the realization that reliance on a single-component management system (e.g., insecticides) is often inefficient.
The proper use of insecticides in a sunflower — or any other — crop pest management program relies on knowledge of the pest and the properties of insecticides themselves. With fundamental information about the biology of the pest, chemical applications can be aimed at a weak point in the insect’s life cycle. For example, treatment is geared toward management of the adult stage of the red sunflower seed weevil and sunflower stem weevil; toward the larval stage of the banded sunflower moth; and toward both the adult and larval stages of the sunflower beetle.
Timing of application is based on the plant stage as well. Also, pesticides should be used only when the population has reached or exceeded economic thresholds. Economic thresholds have been established for most major pests of sunflower.
The selective use of insecticides can be a tool to curb the number of pest organisms while having a minimal impact on all other components of the environment. There are pesticides which are physiologically selective, meaning they have a narrow spectrum of activity and affect only certain specific groups of insect (e.g., moth larvae) or mite pests. However, most currently used insecticides for sunflower pests are toxic to natural enemies and pollinators.
Pesticides also can be ecologically selective when the actual application of the chemical is manipulated to minimize the exposure of nontarget organisms while killing the pest. This method includes the use of different pesticide formulations and the altering of the timing of application, method of application and the treatment’s spatial distribution. It exploits the differ-ences in the biology between pollinators and natural enemies and the pest, and it requires knowledge about the pest’s life history, movement and spatial distribution.
Treatment of sunflower fields should occur when activity of the natural enemies and pollinators is at a minimum, such as early morning or late in the day. Also, applications may be made to only a portion of the crop. Since pests and natural enemies differ in their patterns of movement, spot treatments or stratified applications may be made within a field or crop. Examples would include treatment of field perimeters, strips or selected plots, or the use of trap crops that are treated separately. Trap cropping has shown potential for management of the red sunflower seed weevil.
Timing pesticide applications to take advantage of differences in pest-natural enemy biology has probably been the single most common and effective means used to achieve ecological selectivity. Using baits and seed treatments can drastically decrease pesticide residues in the environment while concentrating chemicals where they are effective and selective. The use of granular materials also may control pests selectively while conserving natural enemies through spatial separation of the pesticide and natural enemy of the pest.
The successful use of pesticides with other management tactics (noted in earlier articles) in a successful sunflower IPM program is dependent upon knowledge of the cropping system and the biology, ecology, and behavior of pests and their natural enemies. The best approach to managing sunflower insect pests is a combination of tactics, including: (1) detailed monitoring of life history and population dynamics of pests and natural enemies; (2) use of resistant plant varieties, if available; (3) crop rotation; (4) altering of planting dates; (5) employment of selective pesticides; (6) use of the least-disruptive formulation of the pesticide; (7) application only when absolutely necessary and based on established economic thresholds; and (8) correct timing for maximum effectiveness against the pest and at the least-injurious time for pollinators and natural enemies.
Integrated pest management is a dynamic and evolving process. Specific management strategies vary from year to year and region to region, depending on the species present and population numbers.
As new IPM approaches develop, they should be analyzed and incorporated into the local cropping system if appropriate. Consideration also should be given to how these techniques or approaches fit into the goals of sustainable agriculture: environ-mentally sound, socially acceptable and economically viable.
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