Overview
Chemical and physical phytosanitary treatments that kill or inactivate pests in the consignment.
- Examples include chemical treatments and fumigants, heat or vapour heat treatment, cold storage and irradiation. These are mostly applied post-production.
- Demonstrating treatment efficacy requires quantification of pest mortality in response to the treatment conditions.
- Sometimes commercial practices such cold storage can kill pests within the commodity. These can be considered during pest risk assessment. Treatments are often applied as phytosanitary measures (e.g. ISPM 28).
- Assurance that threshold mortality has been reached can be achieved through monitoring and auditing the treatment facilities and providers, and of treatment parameters being recorded for each consignment.
Evidence to support efficacy
Experimental evidence is required to demonstrate that pest mortality (or inactivation by sterility in the case of low dose irradiation) in response to the treatment conditions will achieve a specified efficacy, or to quantify mortality that may already occur under commercial conditions (such as cold storage). Mortality rates may be expressed as a proportion, percentage or as a probit for insect pests, or the reduction in the number of samples from which the pest can be recovered for pathogens.
Treatment efficacy needs to be demonstrated for the most tolerant life stage/s of the pest that have the potential to be associated with the commodity moving in trade. Where more than one life stage is involved then the most tolerant stage needs to be confirmed with scientific evidence. To determine treatment efficacy under the required effective dose and exposure time, data (e.g. mortality rate with a confidence level) from empirical studies and/or under operational conditions should be presented. For some treatments, additional data may be required, such as dose mapping to validate the use of irradiation across different commodities and facilities.
The environmental conditions under which the treatment is applied may impact treatment efficacy and may need to be tested. For example, environmental conditions relevant to fumigation include concentration of the fumigant gas, and exposure time, temperature, relative humidity, atmospheric composition, and the water content, size and density of the commodity. These therefore need to be controlled and documented (see for example ISPM 43). It may also be valuable to test a range of treatment and environmental conditions to identify the best trade-off between efficacy and commercial practicality of applying the treatment.
Efforts are underway to generate standard treatment schedules that can apply to a range of pests and commodities. These are supported by empirical studies conducted on diverse systems that include the most tolerant pests.
Models that are informed by existing studies can also be used to predict the treatment conditions needed to achieve target mortalities for new pest-commodity combinations. For cold treatments they could also be used to estimate time-dependent mortality under commercial storage and transport conditions.
Applying the measure
How it is used
Treatment options are diverse, but the many constraints in their use mean that there are often limited options for any one commodity, pest type and market combination. Treatment options will differ in efficacy, practicality, cost, and effect on quality of the commodity as well as acceptance by trading partners.
Chemical treatments that are toxic to pests include fumigants, as well as aerosols, dips, dusts, granular treatments, and sprays. For pests within the commodity the chemicals need to penetrate the host commodity. Sometimes the chemical can be applied during production with the goal of reducing infestation rate in the commodity. For example, residual systemic insecticides for the treatment of fruit flies, or granular chemical treatment of potting media for invasive ants. Fumigation, most commonly with methyl bromide, is a widely used insect disinfestation treatment and is relatively inexpensive and easy to implement. However, physical treatments such as cold and heat treatments are expected to increasingly replace many fumigation treatments due to environmental and food safety concerns.
Physical treatments, such as cold and heat treatments (hot water immersion, conventional steam, vapour heat, dry heat, forced hot air, or dielectric heat), act by cooling or heating the commodity beyond the thermal tolerances of the pest for a certain period of time. Irradiation acts by disrupting the cellular activity of an insect pest enough to prevent reproduction. This can present a challenge for pre- or at-the-border inspections as live but sterilised insects may remain in the consignment, even though they will not contribute to establishment risk.
Significant pest mortality can occur in commodities and carriers because of existing production or supply chain practices. For example, cold-sensitive pests can be killed by extended cold storage (including during transit), which is a characteristic of many supply chains to maintain freshness of produce. Furthermore, quarantine pests can be killed by chemical treatments applied to target other pests. The risk reduction potential of these commercial practices can be considered during a pest risk assessment, or applied as a phytosanitary measure.
Use with other measures
Single-point treatments are frequently used as a stand-alone phytosanitary measure where the efficacy is considered to be sufficiently high (commonly set a priori at probit 8.7). Even where treatment efficacy is high, there is often an expectation that pest prevalence in the production system is low through good agricultural practices, such as pest management, pest avoidance, and pest exclusion measures.
Pest exclusion measures may be required after treatment to prevent reinfestation by some pests.
An inspection with remedial action measure (e.g. 600 unit or 2% inspection in the case of horticultural produce) can be used following treatment to provide assurance that infestation rates in the production system are low, and that the treatment has been successfully applied.
Treatments that kill or inactivate pests can be combined with other measures as part of a risk-based approach to pest management. Here, treatment efficacy needs to be sufficient to reduce risks not adequately addressed by other measures, but may not need to reach probit 8.7 efficacy.
Similar measures
Treatments that kill or inactivate pests can also be applied as the remedial action in an inspection with remedial action measure. For example, if pests are detected in a consignment, then the application of a treatment may allow that consignment to still be exported.
Pesticide application can sometimes have the dual purpose of managing pest populations in the field (pest management) and directly reducing infestation rates in the commodity (treatment). For example, some systemic pesticides can both manage fruit fly populations and kill immature life stages in fruit prior to harvest.
Treatment measures reduce risk in the same way as physical processing and disturbance measures by killing pests. However, while treatment measures are specifically designed for pest risk management, physical processing and disturbance measures are typically commercial practices where pest reduction is a secondary outcome rather than the main goal.
Assurance of correct implementation
For phytosanitary treatment measures, approval of treatment facilities may be required, as may registration of treatment providers. These facilities and treatment records may be audited regularly by authorised personnel, with oversight by the NPPO or relevant authority of the exporting jurisdiction. Record-keeping of critical process steps may be required to confirm that the treatment was applied in a way that achieves the required pest mortality rate. Monitoring records may include chemical usage and treatment parameters, such as fumigant gas concentration or air and/or internal product temperature conditions recorded at a specified time interval. Authorised personnel with the appropriate training may need to observe any critical steps in-person to give confidence that the treatment has been applied correctly to all traded items. For example, to observe the application of a chemical treatment, or the setting up of sea containers for on-water cold treatment.