2.3 Control methods (biological, cultural, mechanical, chemical) & resistance management

The IPM toolbox: combining tactics

A defining principle of IPM is that no single tactic is relied upon alone. Instead, the applicator combines several complementary control methods so that pressure on the pest comes from many directions and no one tactic is overused. The recognized categories are cultural, mechanical/physical, biological, chemical, and regulatory (legal) control. In true IPM, chemical control is used as a last resort - only when monitoring shows the pest has reached the economic or action threshold and non-chemical methods cannot hold it below the damaging level.

Cultural control

Cultural controls are changes to the way a crop, landscape, or structure is managed that make the environment less favorable to the pest. Examples include sanitation (removing food, water, harborage, crop residue, and weeds that shelter pests), crop rotation (breaking a pest's life cycle by changing the host planted in a field from year to year), planting resistant varieties, adjusting planting or harvest dates to avoid peak pest periods, proper irrigation and fertilization, and eliminating standing water. Sanitation is often the single most effective and lowest-cost tactic, especially for structural and vertebrate pests.

Mechanical and physical control

Mechanical (physical) controls kill, remove, or block pests directly, or change the physical environment. Examples include traps (snap traps, sticky traps, light traps), barriers and exclusion (screens, door sweeps, caulking gaps, tree wraps, fences), tillage or cultivation to bury or expose weeds and soil insects, hand-removal, mowing, mulching to suppress weeds, and manipulating temperature or humidity (heat treatment, cold storage). These methods are non-toxic and form the backbone of much structural pest control.

Biological control

Biological control uses living natural enemies to suppress pests. The three main types of natural enemies are predators (lady beetles, lacewings, and spiders that each eat many prey), parasitoids (parasitic wasps and flies whose larvae develop in or on a single host and kill it), and pathogens (microorganisms such as the bacterium Bacillus thuringiensis, along with certain fungi and viruses that cause disease in pests). Biological control may mean conserving the natural enemies already present (by avoiding broad-spectrum sprays), releasing purchased beneficials, or importing enemies of an introduced pest. Broad-spectrum insecticides can destroy natural enemies and trigger a resurgence or a secondary pest outbreak, so protecting beneficials is a core IPM goal.

Chemical control

Chemical control - the use of pesticides - acts fast and is sometimes the only option when a pest exceeds its threshold. In IPM it is used judiciously: choose a product effective against the target and least harmful to natural enemies, people, and the environment; spot-treat rather than blanket-treat; time applications to the vulnerable stage; and always follow the label. Chemical control is powerful but carries risks - resistance, non-target effects, pest resurgence, and residues - which is why IPM positions it as one tool among many rather than the automatic first response.

Regulatory (legal) control

Regulatory control is government action to prevent the entry and spread of pests. Quarantines restrict the movement of plants, animals, or materials that could carry a pest into a new area, and inspection and eradication programs stop introduced pests before they establish. Applicators support these programs by reporting suspected new or unusual pests. Many of the most damaging pests are invasive species that arrived from other regions without their natural enemies, so keeping them out through quarantine is far cheaper than fighting an established infestation later.

Pesticide resistance management

Resistance is the inherited ability of a pest population to survive a pesticide dose that once killed it. It develops through natural selection: a few individuals happen to carry genes that let them survive; when the same pesticide - or another pesticide with the same mode of action - is used repeatedly, the susceptible individuals die and the survivors pass their resistance genes to their offspring, until the product no longer works. Resistance is a population trait, not something an individual pest 'acquires' during its life.

To slow resistance, applicators should:

• Rotate modes of action - alternate pesticides from different chemical or mode-of-action groups so survivors of one product are killed by the next; never rely on a single product repeatedly.
• Use IPM to reduce total pesticide use - non-chemical tactics lower the selection pressure that drives resistance.
• Apply only when thresholds are reached, at labeled rates - cutting rates lets more partly resistant individuals survive.
• Spot-treat and preserve refuges of untreated, susceptible pests whose genes dilute the resistant ones.
• Combine tactics and, where appropriate, use tank mixes of different modes of action.

Because resistance can develop in insects, weeds, and plant pathogens alike, mode-of-action rotation and integrated tactics are essential to keep today's pesticides working tomorrow.