International Plant Protection Convention2010_EWGSGM_Jun_14

Discussion Paper – Barbara PetersonAgenda: 9.08

Movement of Soil and Growing Media in Association with

Plants in International Trade

DISCUSSION PAPER FOR IPPC SPECIFICATION NO. 43

Submitted by: Barbara Peterson, Canadian Food Inspection Agency

Pest Risk Associated with Soil

Soil and growing media are recognized internationally as high risk pathways for the introduction of plant pests and their vectors. However, several factors make it extremely difficult to adequately assess the risk associated with soil from a particular origin or associated with a particular crop, including:

  1. Many soil-borne organisms have not yet been described and their status as plant pests is unknown.
  1. There is insufficient data on the global distribution of known soil pests and this makes it impossible to evaluate the risk posed by soil movement from any particular country or area. Some soil-borne pests are extremely difficult to survey.
  1. The pest risk associated with soil is dependent on its croppinghistory. For example, soil that has previously been used to grow potatoes is much more likely to contain potato cyst nematodes than soil that has never been used for growing potatoes.
  1. The pest risk may be mitigated depending on the end use of the commodity that the soil is associated with. In general plants for planting pose the highest pest risk, plants for processing provide a relatively moderate level of risk, plants for direct consumption pose a lower risk and processed plant products pose the lowest risk (see ISPM No. 32).
  1. It is difficult to detect pests in soil. Rooted plants that are free from soil and growing media are relatively easy to inspect for signs of quarantine pests including nematodes and other organisms that might be associated with plant roots and soil. However, it is extremely difficult to visually inspect the roots of plants if the plants are rooted in soil or growing media. Laboratory analysis of soil samples is unlikely to be sensitive enough to mitigate the risk of introducing nematodes. A single viable nematode cyst is enough to initiate a population.

CFIA Definitions

Soil and Related Matter – Soil is the loose surface of the earth in which plants grow, in most cases consisting of disintegrated rock with an admixture of organic matter. Related matter is clay, silt, sand, soil minerals, humus, compost, earthworm castings, muck, plant litter and debris, either individually, or in combination.

Peat - The non-viable, incompletely decomposed organic residues of plants, often mosses, accumulated under anaerobic, acidic conditions.

Bare-Rooted Plants - Rooted plants with less growing media adhering to the root system than the amount that can harbour any life stage of a pest or that is sufficient to obscure thetransport of that pest.

Pests Associated with Soil

In Canada, the prototypical example of a soil-borne pest is potato wart disease, caused by Synchitrium endobioticum (Schilb.) Perc., which was discovered in Newfoundland in 1909 (Hampson, 1993). This discovery resulted in the creation of the ‘Destructive Pest and Insect Act’, in May 1910, the precursor to the current Plant Protection Act of 1991.

Bacteria, fungi, viruses, phytoplasmas, nematodes, weeds, insects, mites, arachnids and terrestrial molluscs are readily transported in untreated soil either directly or via their vectors. Moldenke (2000) gives a good summary of the variety and number of arthropod organisms that may be found in soil: “A single square yard of soil will contain 500 to 200,000 individual arthropods, depending upon the soil type, plant community, and management system. Despite these large numbers, the biomass of arthropods in soil is far less than that of protozoa and nematodes.”

Kahn (1989) reviews many plant quarantine processes and mentions that soil is a pathway for many plant bacteria (e.g. Agrobacterium spp., Streptomyces spp., Clostridium spp., Pseudomonasspp., Bacillus spp. etc.), fungi (e.g. the rust fungi Puccinia spp., Phragmidium spp., Uromyces spp. etc.), some viruses (Tobacco Mosaic Virus, and possibly Carnation Mottle Virus and members of the tobamovirus and potexvirus groups), nematodes (approximately 10% of nematodes are plant pathogenic e.g. Globodera spp., Heterodera spp., Trichodorus spp., Radopholus spp., Ditylenchus spp. and Tylenchulus spp. whereas others (Longigorus spp., Xiphenema spp. , Trichodorus spp. and Paratrichodorus spp.) vector viruses), snails (Cornu aspersum, Achatina fulica etc.) and arthropods (beetle Anomala orientalis, fruit flies Dacus cucurbitae and Rhagoletis cerasi, and aphid Viteus vitifoliae etc.). He also mentions weeds; in short – all known groups of plant pests can be carried directly or indirectly in soil.

Examples of Regulated Soil-Borne Pests forCanada

Apple maggot, Rhagoletis pomonella (Walsh)

Blueberry maggot Rhagoletis mendax Curran

Columbia root-knot nematode, Meloidogyne chitwoodi (Golden, O’Bannon, Santo and Finley)

European brown garden snail, Cornu aspersum

Golden nematode, Globodera rostochiensis (Wollenweber) Behrens

Japanese beetle, Popillia japonica Newman

Pale cyst nematode, Globodera pallida (Stone) Behrens

Potato wart, Synchytrium endobioticum Schlib. (Percival)

Soybean cyst nematode, Heterodera glycines (Ichinoe)

Sudden Oak Death Disease, Phythophthora ramorum (Werres et al.)

Potato Rot Nematode, Ditylenchus destructor (Thorne)

Dwarf Bunt, Tilletia controversa (J. G. Kuhn)

Brown Rot of Potatoes, Ralstonia solanacearum; Race 3 (Smith) Yabuuci et al.

CFIA Import Requirements Related to Soil and Growing Media

Canada prohibits the importation of all soil and related matter from off-continent. This prohibition applies to bulk soil, as well as, to soil associated with plants, roots crops, machinery, equipment and other things. Bulk peat isallowed entry to Canada, provided it is mined from non-agricultural areas, is free from soil and related matter and has not been previously used for growing, rooting or packing plant and plant material.

Plants rooted in soil-free growing media are also prohibited entry to Canadaunless they originate from a pre-approved Production Facility and meet the requirements of the Canadian Growing Media Program (CGMP). Most propagative plant material, therefore, enters Canada as either unrooted cuttings, or rooted plants free of all soil and growing media.

The CGMP is a clean stock program that takes a systems approach to ensuring freedom from quarantine pests (ISPM 14). The CGMP requires the use of clean water and clean, soil-free growing media. The plants must also be grown in a greenhouse in a manner that avoids contamination from the floor or structure of the production facility. Measures to prevent the entry and establishment of plant pests in growing media and to eliminate plant pests on the foliage and in the production facility must be in place. These procedures apply not only to the plants intended for export to Canada under the CGMP, but also to the propagative stock materials being used for the production of those plants.

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Non-compliance

The risk of contamination with soil depends to a large degree on the morphology of the root system and the type of soil in which the plants were grown. Even when plants are imported rooted in artificial growing media or bare-rooted, there is a risk of soil contamination. Plants with fibrous or complex, high density root systems are more likely to hide these materials. CFIA does not have a tolerance for soil. A thin film of soil on the surface of the roots is acceptable provided it appears to be the result of dirty wash water. Plants from off-continent that are found to be contaminated with growing media, soil or related matter are refused entry to Canada, returned to origin, or disposed of at the importer's expense.CFIA does not allow plants to be washed in Canada.

Facilities that export plants under the CGMP, but which do not consistently meet the phytosanitary standards and/or that violate any phytosanitary requirement are suspended from the program.

References:

Hampson, MC. 1993. History, biology and control of potato wart disease in Canada. Canadian Journal of Plant Pathology 15:223-316.

Kahn RP. 1989. Plant Protection and Quarantine. Volume 1 Biological Concepts. Boca Raton, Florida: CRC Press, Inc.

Moldenke AR. 2000. Chapter 7: Arthropods. In: The Soil Biology Primer (Tugel A, Lewandowski A, Happe-von Arb D, eds). Ankeny, Iowa: Soil and Water Conservation Society.

Canadian Food Inspection Agency. D-96-20: Canadian Growing Media Program, prior approval process and import requirements for plants rooted in approved media.

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