APHIS Factsheet

Plant Protection and Quarantine September 2009

Questions and 

Answers: USDA’s 

Potato Cyst Nematode 

Guidelines and Surveys

Q. Why are potato cyst nematodes a problem? 

A. Potato cyst nematodes—Globodera pallida 

(pale cyst nematode) and G. rostochiensis (golden 

nematode)—have been detected in the United States. 

These microscopic worms are considered invasive 

pests and present a serious threat to domestic and 

international commerce in potatoes and nursery 

stock. G. pallida was found in Idaho in 2006, and G. 

rostochiensis was discovered in New York in 1941 and 

also in the Canadian Provinces of Quebec and Alberta. 

Collectively, the two related nematodes are known as 

potato cyst nematodes or PCN. 

 PCN primarily affects plants within the potato family, including potatoes, tomatoes, eggplants, and some 

weeds. PCN are soil-borne organisms that, instead of 

infesting potato tubers, infest the plant’s feeder roots. 

At the feeder roots, female PCN attach, feed, and 

become sedentary, eventually creating cysts containing 200 to 600 eggs that can remain dormant for up to 

30 years while the eggs inside remain viable. 

 Large numbers of nematodes can cause wilting, 

stunted growth, poor root development, and early plant 

death. If left uncontrolled, PCN can reduce yields up 

to 80 percent in potato fi elds. Even with only minor 

symptoms showing on the foliage, PCN can signifi -

cantly reduce tuber size.

Q. What is the U.S. Department of Agriculture 

(USDA) doing to control these pests? 

A. USDA officials are conducting soil surveys in U.S 

seed potato and commercial potato production fi elds 

to monitor for and respond to detections of PCN. Two 

separate surveys are underway in the United States: 

the PCN National Survey and the Certifi ed Export 

Survey for Canada. Each survey has its own distinct 

purpose and protocol.

 The surveys are based on revised guidelines 

developed with input from the potato industry and 

established jointly by the USDA’s Animal and Plant 

Health Inspection Service (APHIS) and the Canadian 

Food Inspection Agency (CFIA). The guidelines are 

detailed in a document entitled, “Guidelines on 

Surveillance and Phytosanitary Actions for the Potato 

Cyst Nematodes: Globodera rostochiensis and 

Globodera pallida,” which was signed by APHIS and 

CFIA on June 3, 2009. The document lists specifi c 

phytosanitary requirements—including survey activities—for seed potatoes traded between Canada and 

the United States. To read the guideline document 

in its entirety, please visit http://www.aphis.usda.gov/

plant_health/plant_pest_info/nematode/downloads/

potato_guidelines.pdf.

Q. What is the PCN National Survey?

A. The PCN national survey is designed to determine 

the presence or absence of PCN in soil samples collected from all potato-producing States. Beginning in 

2009, the national survey plan is designed to sample 

25 percent of the annual seed potato acreage and 

1 percent of the commercial potato production acreage. In addition, all other land used for seed potato 

research, including land owned by universities, government, or other research organizations, will be surveyed 

in the same manner as the land used for commercial 

and seed potato production. This will help ensure that 

the entire seed potato supply, including seed from 

research trials, variety evaluations, post-harvest evaluations, and farm-saved seed are free from PCN. 

Q. What is the Certifi ed Export Survey for 

Canada?

A. This survey is designed to allow certifi cation of 

potato seed for trade between Canada and the United 

States. These requirements may change as USDA’s 

Plant Protection and Quarantine (PPQ) program 

and other partners continue to evaluate appropriate 

sampling rates. For more information, visit http://www.

aphis.usda.gov/plant_health/plant_pest_info/

nematode/downloads/potato_guidelines.pdf to read the 

guidelines document in its entirety.

Q. Why were the previous PCN guidelines 

changed? 

A. Changes were made to accommodate more recent 

detections and the improved science and technology 

for monitoring and controlling PCN. Because PCN 

had not been detected in seed fi elds in North America 

before November 2007, the previous 2006 guidelines 

document did not include specifi c restrictions for seed 

potato fi elds. APHIS and CFIA initiated changes to 

better safeguard the North American potato industry.

Q. What protocols in the guidelines document 

changed? 
A. The main changes include:

• The revised guidelines require full fi eld surveys 

with different sample sizes for seed potato acreage 

and samples taken from land used for seed potato 

production. 

• Beginning with the 2009 potato season, all seed 

potato fi elds within U.S. States and Canadian 

Provinces must be surveyed and tested 1 year 

prior to or after planting of the crop. 

• A full fi eld survey and testing at the fi eld of origin 

are required prior to the movement of seed potatoes between the United States and Canada.

• At this time, regulated areas and areas with a 

history of PCN infestation include the Canadian 

Provinces of Alberta, British Columbia, and 

Quebec and the U.S. States of Idaho and New 

York.

Q. What happens if PCN is detected during a 

survey?

A. If PCN is detected in a fi eld, APHIS plant health 

officials will take immediate phytosanitary measures 

to control and prevent the spread of the nematodes to 

noninfested areas. Officials will establish a regulated 

area that is subject to Federal quarantine regulations. 

Investigations of the newly regulated area will help 

determine where the infestation came from, where it 

could possibly spread to, and the extent and range of 

the infested area. No further immediate regulatory 

action will be taken as long as all seed fi elds within the 

State have been identifi ed and surveyed. Any further 

actions will be determined by the results of the local 

investigative surveys.

Q. Section 4.1 of the PCN guidelines call for 

immediate regulatory measures to be implemented 

for new PCN detections. How are newly detected 

infested fi elds regulated?

A. In response to a new discovery of PCN on a site, 

all sample specimens must undergo confi rmation for 

PCN. While awaiting confi rmation, APHIS will initiate immediate phytosanitary measures to prevent 

PCN spread to noninfested areas. These actions will 

include: 

• Restricting the movement of all regulated articles 

from the fi eld where the sample was collected;

• Initiating investigations of any historical movement 

of regulated articles that may have been associated with the fi eld in order to identify other potentially exposed fi elds.

 If the suspect fi eld is confi rmed positive for 

PCN infestation, that fi eld as well as adjacent and 

exposed fi elds will represent the interim regulated 

area(s) and adjacent and exposed fi elds will be targeted for sampling to determine the range and degree 

of infestation (delimiting survey). In cases where the 

PCN infested fi eld was used for seed potato production, information will be collected from the seed lots 

produced on the infested fi eld to fi nd out what fi elds 

the seed potatoes were transported to (trace forward 

investigation). At a minimum, the fi elds planted with 

seed potatoes originating from the last potato crop 

grown on the infested fi eld will need to be part of 

the delimiting survey and are considered exposed to 

possible PCN infestation. Any further actions will be 

determined by the results of the delimiting surveys 

and trace forward information. If the fi eld cannot be 

confi rmed as infested with PCN, no further 

phytosanitary measures are required. 

Q. What are considered regulated articles? 

A. Regulated articles include: nursery stock, bulbs, 

corms, rhizomes, tubers of ornamental plants, grass 

sod (all fi eld grown), potatoes (not for planting), potatoes (for planting and certifi cation), soybeans, peas, 

beans, hay, straw, plant litter, root crops (other than 

potatoes), soil, farm equipment, construction equipment, farm tools, and used containers. Additional 

information about the restrictions for each regulated 

article can be found in Section 5 of the guidelines 

document.

Q. If a State is quarantined for PCN, does this 

restrict the international trade of all regulated 

articles? 

A. Yes. Additional trade restrictions and/or suspension 

of trade activities may occur, depending on the nature 

and scope of the quarantine. The movement of regulated articles is restricted in these cases because PCN 

can be easily spread by these movements. 

Q. Is international trade restricted, if not all of the 

fi elds in a State have been sampled?

A. If PCN is detected within a State that has not sampled all of its fi elds, the entire State is placed under 

quarantine and exports of seed potatoes to Canada 

are restricted until the requirements in Section 4.1 of 

the guidelines documents are met.

Q. Will seed potato farms outside of regulated 

areas have to be surveyed before they can ship to 

Canada? 

A. Yes. States containing a PCN-regulated area are 

required to survey all seed potato areas. Any potato 

fi elds that produce seed potatoes that are traded 

between Canada and the United States must undergo 

a soil sampling and testing protocol using at least the 

Method B sampling method, as described in Section 

8 of the guidelines document. The movement of seed 

potatoes and other articles with soil presents the 

highest risk for the movement of this pest. 
Q. What are the restrictions for shipping seed 

potatoes to other States?

A. The guidelines document is specifi cally for international trade of seed potatoes between Canada and the 

United States. The regulation of interstate shipments 

is not covered under these guidelines. Contact your 

specifi c State plant regulatory officials for interstate 

requirements. Contact information for all State plant 

regulatory officials is available at 

http://www.nationalplantboard.org/member/index.html

Q. Currently, commercial growers perform surveys 

on a voluntary basis. Is this still the case?

A. Yes. APHIS is committed to working cooperatively 

with potato producers, State plant regulatory officials, 

and others to safeguard the national potato industry. 

Q. How are the surveys paid for? 

A. APHIS funds the PCN National Survey and the 

Certifi ed Export Survey for Canada through cooperative agreements with States. APHIS remains committed to providing all available survey funding in future 

years. For information about PCN funding and survey 

initiatives, please contact your APHIS State plant 

health director (SPHD) or the State plant regulatory 

official (SPRO) for your State.

Q. Is diagnostic support available for this survey?

A. Yes. For information about diagnostic protocols and 

about where to ship suspect samples, please visit the 

APHIS PCN Web site. The address is: 

http://www.aphis.usda.gov/plant_health/plant_pest_

info/index.shtml

Q. Are the results from the 2006 and 2007 surveys 

still valid under the new PCN guidelines? 

A. No. Because PCN was detected in both the United 

States and Canada, both APHIS and CFIA have 

adopted more stringent movement restrictions and 

strengthened survey requirements in order to prevent 

the spread of PCN infestations. 

Q. Why have APHIS and CFIA adopted a full fi eld 

approach for surveys in place of partial or 

perimeter surveys? 

A. Information provided by partial or perimeter sampling is useful but limited. Results from fi elds that are 

fully sampled provide the best and most defi nitive 

survey assessment.

Q. Why is APHIS using a larger sampling size of 

5 pounds (2000cc) per acre for some of its survey 

methods?

A. APHIS and its partners are continuing to evaluate 

and revise sampling sizes used for detection surveys. To date, the best approach to soil sampling is to 

remove and test as much fi eld soil as is economically 

practical. A larger soil sample size, covering as much 

of a fi eld as possible, helps detect small infestations 

that may be present. 

Q. Will this current sampling size change or will 

that be the standard?

A. A science panel comprised of internationally recognized nematologists provided the current recommendations that were accepted by both APHIS and CFIA 

as the standard sampling rate. Based on the panel’s 

recommendations, a 2000cc per acre sampling rate 

was deemed to be the most efficient, effective, and 

practical sampling rate for PCN. Future sampling sizes 

may change depending on the situation. However, 

they will not fall below 5 pounds (2000cc) per acre. 

Q. How were States and the potato industry 

involved in the development of the guidelines 

document?

A. The revised guideline document was developed 

based upon input from APHIS’ State plant health 

directors, State plant regulatory officials and the potato 

industry. The revised guidelines were the result of 

bilateral trade negotiations between the United States 

and Canada. Both countries are committed to keeping 

their respective industries informed about sciencebased risk mitigation approaches to prevent the spread 

of PCN.

Q. What is the National Potato Council’s (NPC) 

position on the bilateral trade agreement and the 

implementation of the revised survey guidelines?

 A. The NPC is supportive of the bilateral trade agreement and the revised survey guidelines because they 

will both safeguard the U.S. potato industry.

Q. Where can I fi nd more information about PCN?

A. For the latest information about PCN, please visit 

the APHIS Web site at http://www.aphis.usda.gov/

plant_health/plant_pest_info/index.shtml

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