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United States Department of Agriculture

Animal and Plant Health Inspection Service

Plant Protection and Quarantine

Importation, from Mexico into the United States, of 

Potato, Solanum tuberosum, Tubers for Consumption

Risk Management Document

February 16, 2012

United States Department of Agriculture

Animal and Plant Health Inspection Service

Agency Contact: David B. Lamb
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Introduction:

The National Plant Protection Organization (NPPO) of Mexico has requested market access for 

the importation of potatoes for consumption, Solanum tuberosum L., into the United States. A

pathway-initiated risk assessment (PRA) was conducted by APHIS (USDA, 2011). The PRA 

was prepared based on United States Department of Agriculture (USDA)’s Animal and Plant 

Health Inspection Service (APHIS) records of intercepted pests and scientific literature. The 

PRA document entitled, Importation, from Mexico into the United States, of Potato, Solanum 

tuberosum, Tubers Intended for Consumption, A Pathway-Initiated Commodity Risk Assessment

(USDA, 2011) identified one bacterium, four fungi, 2 insects and one nematode that may follow 

the pathway of fresh potatoes for consumption from Mexico into the United States.

Bacteria

Ralstonia solanacearum Race 3 biovar 2 (Smith) Yabuuchi et al. (Burkholderiales: 

Ralstoniaceae)

Fungi 

Rosellinia bunodes (Berk. & Broome) Sacc. (Xylariales: Xylariaceae)

Rosellinia pepo Pat. (Xylariales: Xylariaceae)

Synchytrium endobioticum (Schilb.) Percival (Chytridiales: Synchitriaceae)

Thecaphora solani (Thirum. & M. O’Brien) Mordue (Urocystales: Glomosporiaceae)

Insects

Epicaerus cognatus Sharp (Coleoptera: Curculiondae)

Copitarsia decolora (Guenée) (Lepidoptera: Noctuidae)

Nematodes

Nacobbus aberrans (Thorne) Thorne & Allen (Nematoda: Pratylenchidae)

(The risk assessment also identified Globodera rostochiensis, golden cyst nematode, as a pest of 

quarantine significance that exists in Mexico, and determined that this pest is unlikely to follow the 

pathway only because it is under official control within Mexico. Therefore, this document 

recommends mitigations for Globodera rostochiensis, as well.) 

The bacterium Ralstonia solanacearum Race 3 biovar 2, the fungus Synchytrium endobioticum

(Potato wart disease) and the nematode Nacobbus aberrans were rated High overall pest risk 

potential in the PRA. The fungi Rosellinia bunodes, R. pepo and Thecaphora solani and the 

insects Copitarsia decolara and Epicaerus cognatus were rated Medium overall pest risk potential 

in the PRA. Specific phytosanitary measures beyond port of entry inspection are strongly

recommended for pests with High pest risk potentials, and may be necessary for pests with 

Medium pest risk potential (USDA, 2000).
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Risk Management Measures:

APHIS proposes to import fresh potatoes for consumption from Mexico using risk management 

measures equivalent to the management measures agreed for exportation of United States potatoes 

for consumption to Mexico (USDA, 2010). Potatoes for consumption from Mexico may only be 

imported using all of the following risk management measures:

1. COMMERCIAL CONSIGNMENTS AND FOR CONSUMPTION ONLY.

Potatoes from Mexico will be imported as commercial consignments only; limiting and labeling 

the end use to “consumption only.”

2. CERTIFICATION PROGRAM/USE OF CERTIFIED SEED POTATOES

The potatoes must be produced by a grower who is registered within a certification program 

administered by the NPPO of Mexico. At a minimum, the program must require the producer to 

use only seed that has been certified by the NPPO as free of Ralstonia solanacearum Race 3

biovar 2, Rosellinia bunodes, Rosellinia pepo, Synchytrium endobioticum, and Thecaphora

solani to produce the potatoes. It must also require the potatoes to be produced in an enclosed 

environment, or alternatively, must require the field in which the potatoes are grown to be 

surveyed regularly for quarantine pests and tested for Ralstonia solanacearum Race 3 biovar 2 at 

set intervals. 

3. WASHING, FREEDOM OF SOIL, AND APPLICATION OF SPROUT INHIBITOR

Potatoes must be washed, free of soil and treated with a sprout inhibitor: 

 Potatoes will be treated with a sprout inhibitor on the packing line two weeks after being 

harvested in accordance with label restrictions and correct usage of the product. 

 Potatoes in storage less than three months will be treated with sprout inhibitor in storage 

or on the packing line. 

 Potatoes in storage for three to five months will be treated in storage and again on the 

packing line. 

 Potatoes in storage for more than five months will be treated twice in storage and again 

on the packing line. 

 Final application of sprout inhibitor will be done after the potatoes have been washed and 

soil was eliminated. The packer/shipper must provide the certifying official with credible 

documentation (e.g., grower declaration/records and packing shed records) that 

demonstrates that the potatoes have been correctly treated with sprout inhibitor for each 

required application. 
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4. POTATOES PRODUCED IN NPPO OF MEXICO-APPROVED FACILITIES AND 

TRACEBACK OF POTATOES.

 The NPPO of Mexico will approve the packing sheds used to pack potatoes for export to 

the United States and will assign unique numbers to each packing shed. This will allow 

consignments to be traced back to the packing shed and therefore to the grower, as 

necessary. This number must be shown on all consignment units (bag or box) and will be 

shown on the phytosanitary certificate. 

5. PHYTOSANITARY INSPECTION AND CERTIFICATION STATING FREEDOM OF 

PESTS OF QUARANTINE CONCERN

The phytosanitary inspections will be conducted and phytosanitary certificates issued by the 

NPPO of Mexico.

 Containers (i.e., boxes or bags in the consignment) will be sampled using a biometric 

sampling plan at the packing shed and inspected for external symptoms of the pests of 

quarantine concern to the United States (Copitarsia decolora, Epicaerus cognatus, 

Nacobbus aberrans, Rosellinia bunodes, Rosellinia pepo and Thecaphora solani). 

 A portion of the potatoes from each sample will be cut and examined for internal 

symptoms/signs of Epicaerus cognatus, Nacobbus aberrans, Ralstonia solanacearum 

Race 3 biovar 2, and Thecaphora solani.

 The portion must then be sent to a laboratory that is approved by the NPPO of Mexico for 

testing for Ralstonia solanacearum Race 3 biovar 2. 

 Zero tolerance will be allowed for the pests of quarantine significance to the United 

States listed above.

 Potatoes must show no signs of sprouting. 

 Each phytosanitary certificate will bear the additional declaration stating: 

"This shipment does not come from an area of Mexico regulated by the NPPO of Mexico 

for Globodera rostochiensis, has been produced from certified seed free of Ralstonia 

solanacearum Race 3, Rosellinia bunodes, Rosellinia pepo, Synchytrium endobioticum 

and Thecaptora solani, has been inspected for Copitarsia decolora, Epicaerus cognatus, 

Nacobbus aberrans Ralstonia solanacearum Race 3 biovar 2, Rosellinia bunodes, 

Rosellinia pepo, Synchitrum endobioticum, and Thecaphora solani, has been tested for 

Ralstonia solanacearum Race 3 biovar 2, and based on this inspection and testing, has 

been found free of those pests. “
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6. SEALING OF VEHICLES AT THE POINT OF INSPECTION 

All conveyances with potato consignments will be sealed at the point of inspection and the seal 

number will be noted on the phytosanitary certificate. Seals may not be broken in Mexico except 

as noted in Section 7.

7. BROKEN SEALS 

Actions taken when consignments arrive at the border with broken seals are: 

 If seals are broken enroute and the integrity of the load/consignment has not been 

violated, the normal sampling and inspection regime will be applied. 

 If the integrity of the load is questioned because of broken pallet straps or missing or 

opened boxes, or if the consignment arrives at the border with broken seal but no affidavit 

accompanies the consignment, APHIS will determine the phytosanitary measure 

according to the Procedures specified in the corresponding work plan. 

8. DETECTION OF QUARANTINE PESTS 

If the pests of quarantine concern to the United States are intercepted at the United States ports of 

entry, the consignment will be rejected and the NPPO of Mexico will trace back all interceptions 

to origin via the packing house number assigned. Should a second confirmed interception be

attributed to a single packing facility, the NPPO of Mexico will investigate and take appropriate 

action mutually agreed upon by the NPPO of Mexico and APHIS.

In these cases: 

 Should the NPPO of Mexico investigation require the packing facility to identify the 

suspect grower or growers, the packing facility will be required to do so. If the packing 

facility cannot identify the suspect grower, the packing facility will be suspended from the

export program for the remainder of the season. 

 In such cases where grower identification is required by NPPO of Mexico and is provided 

by the packing facility, the grower will be required to identify the field where the 

intercepted infested/infected potatoes were produced. If the grower is unable to do so, the 

grower will be suspended from the export program for the remainder of the season. 

 Where the grower can identify the field where the intercepted infested/infected potatoes 

were produced, the field will be suspended from the export program for the remainder of 

the season. 
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9. OPERATIONAL WORK PLAN

An operational work plan will be establised and agreed upon between APHIS and the NPPO of 

Mexico (SENASICA). 

Evidence for Removal of Pests of Quarantine Concern from the Pathway:

This risk management document has been developed to minimize the risk of introduction of the 

following potato pests of quarantine concern from Mexico into the Unites States: Copitarsia 

decolora, Epicaerus cognatus, Globodera rostochiensis, Nacobbus aberrans, Ralstonia 

solanacearum Race 3 biovar 2, Rosellinia bunodes, Rosellinia pepo, Synchytrium endobioticum

and Thecaphora solani.

Limiting the importation of potatoes to commercial consignments for consumption has two 

mitigating effects. First, requiring commercial grade potatoes ensures a certain level of quality

and cleanliness which results from commercial handling. This is a significant measure for pests 

that affect quality or are associated with contaminants (e.g., soil). Second, limiting and labeling 

the use to “consumption only” helps to prevent potatoes from being diverted to other purposes 

where they are more likely to come into contact with host material (i.e., growing plants) or for 

pests to be able to escape and establish in the United States.

Potatoes from Mexico may not come from areas of Mexico regulated by SENASICA for G. 

rostochiensis. It is unlikely that producers in areas of Mexico regulated by SENASICA for G. 

rostochiensis could meet the provisions of the certification program discussed above. 

Additionally, because G. rostochiensis is soil-borne, post-harvest cleaning would serve as an 

additional mitigation for the pest. However, because G. rostochiensis is under official control in 

Mexico, and a quarantine pest within the United States, in order to preclude the dissemination of 

the pest within both countries through the movement of infested potatoes into the United States, 

APHIS considers such a prohibition to be warranted.

Potatoes from Mexico must be produced only from certified seed potatoes. This measure is 

highly effective in mitigating pest risk because it ensures the absence of specific pests at planting. 

Certified seed potato production is based on a generational process, under official control, in 

which a small quantity of nuclear stock of a variety is increased to commercial quantities over a 

number of generations (Armstrong, 2003). During each generation, there is rigorous inspection 

and testing of the material to ensure that it is pest free. Certification programs require that seed 

potatoes be grown specifically for reproduction in a controlled environment to ensure the reduced

potential for disease introduction. Genetic purity and disease control are maintained through the 

use of laboratory testing, greenhouse techniques and limited generation production. Entry into a 

certification program means the field or lot of potatoes undergoes numerous inspections for 

nematodes, bacterial, viral, and fungal diseases, as well as trueness to type, and adheres to strict 

tolerances. Certification tolerances for potato seed diseases are typically very low. A specific 

generation of seed can only be produced from an earlier, more disease-free generation (Mosley et 

al., 2010). The requirement that all potatoes to be exported to the United States must come from 
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a certification program using certified seed potatoes ensures that pests and pathogens are 

eliminated from consignments entirely, or kept at the lowest possible levels.

All potatoes will be washed and brushed and treated with sprout inhibitor. Washing mitigates 

the pest risks posed by soil contamination, and the application of a sprout inhibitor limits the use 

of potatoes for propagation (NAPPO, 2011; USDA, 2010). Washing potatoes eliminates any

adhering soil. Inspection of consignments and quality standards will prevent soil from being 

exported with potatoes. Any findings of soil contamination would result in suspension of 

packinghouses from the export program. Depending on the particular compound used and the 

dosage applied, sprouting has been reported to be curtailed by about 30-100% (e.g., Thon, 1991; 

Afek et al., 2000). Sprout inhibitors also may be effective in controlling some potato pests (e.g., 

Shelton & Wyman, 1980). Research in Argentina (Cacace et al., 1995) using Isopropyl N-(3-

chlorophenyl) carbamate (Chloropropan) as a potato sprout inhibitor (inhibits sprout 

development by interfering with cell division) showed this sprout inhibitor was highly effective 

in reducing sprouting andweight losses due to sprouting, as well as maintaining the external and 

cooking qualities after three months of application of Chloropropan with no negative characters 

such as peeling or internal sprouting.

Because field inspection is a visual process, some plants may be questionable and need

laboratory verification. Most certification programs require some form of winter grow-out 

testing. For winter tests, a percentage of the tubers for each seed lot are planted and the resultant 

plants are visually examined for pest/disease symptoms (Mosley et al., 2010).

 

Phytosanitary inspections consist of sampling and testing potato tubers during the growing 

season and after harvesting. Sampling and inspection of consignments at United States ports of

entry is useful to verify that phytosanitary certification requirements have been met and the 

consignment is generally free of contaminants. The efficacy of this measure depends on the 

statistical level of sampling and the detection of the pests or articles of concern (e.g., soil).

Containers (i.e., boxes or bags in the consignment) will be sampled using a biometric sampling 

plan at the packing shed and inspected for external symptoms of the pests of quarantine concern 

to the United States. During the external inspection, the potatoes will be examined for lesions, 

galls, and necrotic rings or spots on the surface of the tubers. The confidence level and percent 

infestion the inspection will detect can be established based on a hypergeometric distribution.

Consignments will be inspected and certified by the NPPO of Mexico or their designate to be 

free of pests of quarantine concern. A portion of the potatoes from each sample will be cut and 

examined for internal symptoms of Epicaerus cognatus, Nacobbus aberrans, Ralstonia 

solanacearum Race 3 biovar 2, and Thecaphora solani, and will also be tested for Ralstonia 

solanacearum Race 3 biovar 2. This will also be the basis of the Phytosanitary certificate and the 

additional declaration. Consignments must be sealed at point of inspection. 

If any pest is found during inspection upon entry into the United States, then the field where the 

potatoes were produced will be suspended from the export program for the remainder of the 

growing season. If the packinghouses or the grower cannot trace back the production to a field 
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then the packinghouse or the grower will be suspended for the remainder of the season. This 

ensures that any problem fields (or growers or packinghouses) will be removed from the program 

until the cause of the failure can be eliminated. It will also maintain an incentive to ensure that 

records are kept so that traceback can occur. Sprout inhibitors are applied to all fresh potatoes 

prior to export to the United States. These applications will limit the misuse of fresh potatoes 

and prevent plant growth and spread of any pathogens (NAPPO, 2011; USDA, 2010).

Potatoes will be produced under an operational workplan agreed to by the NPPO of Mexico and

APHIS. This workplan can be revised at any time to deal with unexpected pest problems.

Specific mitagations for pests/diseases of quarantine concern:

(a) Bacterium:

Ralstonia solanacearum infected tubers exhibit conspicuous symptoms and may include brown 

rot caused by breakdown of infected vascular bundles (EPPO, 2006). The Ralstonia 

solanacearum of concern is Race 3, biovar 2, which is a select agent of quarantine concern for 

the the United States. Ralstonia solanacearum Race 3 biovar 2 was eradicated from the United 

States. None of the interceptions from Mexico have ever been identified to Race. 

(b) Fungi:

Synchytrium endobioticum (Potato wart disease) causes dark brown warty cauliflower-like galls 

(corrugated surfaces) of infected tubers which decay to release golden-brown resting spores. 

Galls appear at stem bases, stolon tips and tuber eyes. Tubers may be disfigured or completely

replaced by galls. Tubers in storage may develop galls after harvest. The fungus could be 

introduced via infected soil or plant tissues. Local spore dispersal was reported by water and 

wind as a limited pathway for distribution. Resting spores can remain viable for decades. 

Introduction into soil not only renders the crop unsuitable, but the soil itself cannot be used for 

further crop production due to the longevity of the fungus (CABI. 2012d; Walker, 1983).

Rosellinia bunodes induces wilt and death of the whole plant or individual stems. At the potato 

plant’s collar, the mycelial sheet is at first cream-white shading to purplish black, extending 

above the soil surface in moist conditions. The fungus produces thick and irregular knots on root

surfaces, where black mycelial strands are firmly applied (Sivanesan & Holliday, 1972).

Rosellinia pepo (black root rot) spreads rapidly from organic debris left on crop surfaces after 

harvest. Removal and burning of infected material followed by changes in land use to cultivation 

of resistant crops is effective field management (CABI. 2012b). On bulbs and roots, the grayish 

cobweb-like mycelia become black and coalesce into woolly or felt-like masses, usually visible 

to the naked eye (Booth & Holliday, 1972; CABI. 2012b). Plant aerial symptoms may be visible 

at the base of stems, with pale-gray to black mycelia (CABI. 2012b). 

Thecaphora solani (potato smut) is transmited by infested tubers and is soil borne. Infections 

start in meristematic regions in young shoots, the underground portion of stems and eventually in 

tubers. Resultant galls increase in size throughout the growing season (Mordue, 1988). Infested 
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tubers are misshapen or have warty hard swellings on the surface; brown-black specks (spore 

sori) 1-4 mm diameter can be seen in the flesh (CABI. 2012c).

The fungi Rosellinia bunodes, Rosellinia pepo, Synchytrium endobioticum, and Thecaphora 

solani and the bacterium Ralstonia solanacearum Race 3 biovar 2 will be subject to detection 

during field certification inspections and tests and packinghouse inspections and tests. The 

NPPO of Mexico must certify consignment freedom from these fungi, specifically stating this in 

an additional declaration. Potatoes will be cut, inspected, tested, and found free of Ralstonia 

solanacearum Race 3 biovar 2 and Thecaphora solani, which will also be stated in the 

phytosanitary certificate issued by the Mexican NPPO. Sampling of consignments at ports of 

entry can be used to readily detect visible disease symptoms in tubers (Zitter & Loria, 2010). 

Any producers’ fields and any associated packinghouses that ship infected tubers will be 

suspended from the program for the remainder of the season.

(c) Insects:

The two insect pests found by the PRA to follow the pathway of fresh potatoes from Mexico, 

Epicaerus cognatus and Copitarsia decolora, will be removed from the pathway by culling and 

inspection. 

The weevil Epicaerus cognatus is normally found only in non-commercial potatoes because good 

agricultural practices eliminate this pest species. The weevil larvae are internal feeders in the 

tubers and can be identified by holes and waste (frass) (USDA, 1959). If no exit hole is present, 

the feeding damage leaves the tuber soft. These symptoms of damage are readily detected and 

any infested potatoes will be culled or detected by inspections. Potatoes will be cut for internal 

inspection to find Epicaerus cognatus.

Copitarsia decolora is a Lepidoptera that feeds in the larval stage on a wide variety of host 

plants. These pests are often found in weedy fields where they may feed on almost any host plant 

that is present. Damage to potatoes is primarily to the seed potatoes and the stalks of new plant 

growth (Munro, 1968). Damage caused by this insect to the part of the potato tuber that is above 

ground is very obvious and will be removed during normal packing house culling processes to 

produce a quality product. This damage would be very obvious and easily detected during any

phytosanitary inspection, either by the NPPO of Mexico or at the United States port of entry. 

(d) Nematodes:

Nacobbus aberrans produces root galls mainly along the root axis and at the root tips with a 

beaded appearance (CABI. 2012a); mature galls tend to be flat with a rough corky surface and 

bear many lateral roots (Manzanilla Lopez et al., 2002). On heavily infected plants, the 

symptoms above ground include poor growth, stunting and yellowing of leaves. Nacobbus 

aberrans can be carried by potato tubers and in soil as well as in the roots of host plants (Jatala, 

1979). The first step in detection is visual inspection for root or tuber knots. Nematodes have to 

be examined under a microscope to be differentiated from other root-knot nematodes (CABI. 

2012).
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Contaminated soil is the most important means of spread of potato pests such as nematodes 

(Brodie, 1989). Potatoes imported from Mexico must be washed and free of soil to ensure 

freedom of nematodes as well as other pests of quarantine concern. External and internal 

(cutting) inspection will help ensure that the nematode Nacobbus aberrans does not follow the 

pathway of fresh potatoes for consumption from Mexico to the United Stares. 

Conclusion:

The phytosanitary requirements described above for the importation of fresh potatoes for

consumption from Mexico into the United States include commercial consignments only, seed 

potato certification, washing and freedom of soil, external and internal inspections, treatment 

with sprout inhibitors to prevent misdirection of table stock to planting, traceback and suspension 

of problem packinghouses and production sites, sealed consignments, and phytosanitary

certificates with an additional declaration stating freedom of pests of concern.

PPQ finds that when combined, these mitigations will ensure a pest-free system for the 

production of potatoes for consumption because the initial propagules are uncontaminated (use of 

certified seed potatoes), redundant safeguards keep the plants from becoming contaminated 

during production, harvest and transport, and the sprouting capacity will be inhibited. If 

compliance with this program is achieved, then the potatoes produced in Mexico and imported

into the United States will be protected from pest infestation and infection during the entire 

production process and phytosanitary risks will be minimized.

APHIS finds that the safeguards of this risk management document will result in the effective 

removal of the pests of concern identified in the pest risk assessment (USDA, 2011) for the 

importation of fresh table stock potatoes for consumption from Mexico into the United States.

Authors:

José R. Hernández, Ph.D.

Senior Risk Manager – Plant Pathology

Regulations Permits and Manuals

Walter P. Gould, Ph.D.

Senior Risk Manager – Entomology

Regulations Permits and Manuals

Robert L. Griffin

Director Plant Epidemiology and Risk Analysis Laboratory

Center of Plant Health Science and Technology

Richard Zink, Ph.D.

National Weeds Management Laboratory
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Center for Plant Health Science and Technology

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