United States

Department of 

Agriculture

Agricultural 

Marketing 

Service

Fruit and 

Vegetable 

Programs

Fresh Products 

Division

Potatoes

Shipping Point and Market 

Inspection Instructions 

April 2012

Shipping Point and Market 

Inspection Instructions for 

Potatoes

These inspection instructions are specifically developed and designed by the Fresh 

Products Division to assist officially licensed inspectors in the interpretation and 

application of the U.S. Standards for Grades of Potatoes, Section 51.1540, and U.S. 

Standards for Grades of Seed Potatoes, Section 51.3000.

These instructions do not establish any substantial rule not legally authorized by the 

official grade standards. This publication supersedes any previously issued inspection 

instructions. 

Refer to General Inspection Instructions for additional information pertaining to date, 

inspection point, carrier, condition of carrier, lading, etc. not covered in these 

instructions. (Reference to "General Inspection Instructions" in all Fresh Product 

Division publications refers to any of or all of the following - General Shipping Point 

Inspection Instructions, General Market Inspection Instructions, or Fresh Fruit and 

Vegetable Certificate Writing Handbooks.)

Any portion of these instructions beginning with a section number such as §51.--- and 

followed with bold print is material copied directly from the U.S. standards. The U.S. 

Standards for Grades of Potatoes and U.S. Standards for Grades of Seed Potatoes are 

printed in the appendix of this instruction. All of the U.S. standards are available on the 

Internet under the USDA homepage.

April 2012

ii

Factors noted with (Q) are considered quality only. Factors noted with (C) are 

considered condition at market. Factors with (Q or C) may be considered as quality 

or condition depending on the circumstances.

TABLE OF CONTENTS

PART 1: SHIPPING POINT AND MARKET INSPECTION INSTRUCTIONS FOR 

FRESH POTATOES ....................................................................................................... 2

GENERAL....................................................................................................................... 2

REPRESENTATIVE SAMPLING.................................................................................... 2

SIZE OF SAMPLES .......................................................................................................... 2

NUMBER OF SAMPLES .................................................................................................... 3

SHIPPING POINT ......................................................................................................... 3

MARKET..................................................................................................................... 3

INSPECTION OF BULK LOADS OR BULK BINS ..................................................................... 4

TOLERANCES................................................................................................................ 4

SUMMARY OF TOLERANCES............................................................................................. 6

APPLICATION OF TOLERANCES................................................................................. 7

SUMMARY OF APPLICATION OF TOLERANCES.................................................................... 8

NOTESHEET AND CERTIFICATE ................................................................................. 9

PRODUCT ...................................................................................................................... 9

NUMBER/TYPE OF CONTAINERS ...................................................................................... 9

BRANDS/MARKINGS...................................................................................................... 10

ORIGIN........................................................................................................................ 10

CONDITION OF PACK ................................................................................................. 10

TEMPERATURE OF PRODUCT .................................................................................. 11

SIZE .............................................................................................................................. 11

REPORTING SIZE.......................................................................................................... 12

SIZE A......................................................................................................................... 13

REPORTING PERCENTAGES OF A SPECIFIED SIZE AND LARGER........................................ 14

CERTIFYING MINIMUM SIZE ........................................................................................... 14

CERTIFYING MAXIMUM SIZE .......................................................................................... 15

REPORTING OVERWEIGHT ............................................................................................ 15

CONTAINERS MARKED TO SIZE OR COUNT ..................................................................... 15

CERTIFYING SIZE WITHOUT REFERENCE TO GRADE ........................................................ 16

USE OF UNDERSIZE AND OVERSIZE WITHIN TOLERANCE.................................................. 16

WHEN UNDERSIZED OR OVERSIZED SPECIMENS ARE ALSO DEFECTIVE ............................ 16
iii

MATURITY AND SKINNING......................................................................................... 17

MATURITY/SKINNING CLASSIFICATION TO BE USED UPON REQUEST.................................. 18

COMBINATION OF INTERNAL AND EXTERNAL DEFECTS ..................................... 19

DEFECTS (QUALITY AND CONDITION)..................................................................... 20

EXTERNAL DEFECTS ................................................................................................. 20

AIR CRACKS (C) .......................................................................................................... 20

BRUISES (Q & C) ......................................................................................................... 21

CLEANESS (Q)............................................................................................................. 22

ADHERING DIRT AND STAINING .................................................................................. 23

LOOSE DIRT, CLODS OF DIRT, ROCKS OR OTHER FOREIGN MATTER............................. 23

CUTS/CLIPPED ENDS (Q).............................................................................................. 24

FIGURES 1, 2, AND 3................................................................................................. 25

CORKY RING SPOT (C)................................................................................................. 29

DRIES STEMS .............................................................................................................. 29

ELEPHANT HIDE (Q)..................................................................................................... 29

ENLARGED LENTICELS (Q & C) ..................................................................................... 30

EXTERNAL SURFACE DISCOLORATION (C)...................................................................... 30

FIRMNESS (C).............................................................................................................. 31

FOLDED ENDS (Q)........................................................................................................ 31

FLATTENED OR DEPRESSED AREAS (C) ......................................................................... 32

FLEA BEETLE (Q)......................................................................................................... 33

FREEZING/FREEZING INJURY (Q & C) ............................................................................ 33

GRASS DAMAGE (Q)..................................................................................................... 34

GREENING (C) ............................................................................................................. 35

GROWTH CRACKS (Q).................................................................................................. 35

GRUB DAMAGE (Q) ...................................................................................................... 36

MECHANICAL DAMAGE (Q)............................................................................................ 36

NEMATODE (ROOT KNOT) (Q) ....................................................................................... 37

PINK EYE (C)............................................................................................................... 37

RHIZOCTONIA (BLACK SCURF) (Q)................................................................................. 38

RODENT AND BIRD DAMAGE (Q).................................................................................... 38

ROUGH RAISED NETTING (Q)........................................................................................ 38

RUSSETING (Q)............................................................................................................ 39

SCAB (Q) .................................................................................................................... 39

PITTED SCAB (Q) ..................................................................................................... 39

RUSSET SCAB (Q).................................................................................................... 40

SURFACE SCAB (Q)...................................................................................................... 40

POWDERY SCAB (Q)................................................................................................. 40

SECOND GROWTH (Q).................................................................................................. 41

SHAPE (Q) .................................................................................................................. 41

SILVER SCURF (C) ....................................................................................................... 42

SIMILAR VARIETAL CHARACTERISTICS (Q)...................................................................... 42

SKIN CHECKS (C)......................................................................................................... 43
iv

SPROUTS (EXTERNAL) (C) ............................................................................................ 43

INDIVIDUAL SAMPLING AND REPORTING REQUIREMENTS FOR SPROUTS ............................ 44

U.S. NO. 1 QUALITY FOR SPROUTS............................................................................ 45

NEW POTATO GROWTH ATTACHED BY FLESHY STEMS (Q) .......................................... 45

SUNBURN (Q) .............................................................................................................. 45

SUNKEN DISCOLORED AREAS (C).................................................................................. 46

SUNKEN DISCOLORED AREAS WITH UNDERLYING FLESH DISCOLORED (C) ....................... 46

SUNKEN DISCOLORED STICKY AREAS (C) ...................................................................... 47

SURFACE CRACKS (Q) ................................................................................................. 47

TUBER MOTH DAMAGE (C)............................................................................................ 48

WIREWORM (Q)........................................................................................................... 48

INTERNAL DEFECTS .................................................................................................. 49

SAMPLING TO DETERMINE THE PRESENCE OF INTERNAL DEFECTS.................................. 50

METHODS OF CUTTING TO DETERMINE INTERNAL DEFECTS ............................................. 51

METHOD OF CUTTING TO DETERMINE EXTERNAL OR INTERNAL WASTE............................. 53

BLACKHEART (C) ......................................................................................................... 53

HEAT OR DROUGHT NECROSIS (Q)................................................................................ 53

HOLLOW HEART OR HOLLOW HEART WITH DISCOLORATION (Q) ...................................... 54

INGROWN SPROUTS (C)................................................................................................ 55

INTERNAL BLACK SPOT (C)........................................................................................... 55

INTERNAL BROWN SPOT (Q) ......................................................................................... 55

INTERNAL MAHOGANY BROWNING (C)............................................................................ 56

INTERNAL PINK TO PURPLE DISCOLORATION (C)............................................................. 56

INTERNAL POTATO NECROSIS (C).................................................................................. 57

LIGHT BROWN DISCOLORATION (BROWN CENTER) (Q) ................................................... 58

NET NECROSIS (C)....................................................................................................... 58

STEM END BROWNING (C)............................................................................................ 59

VASCULAR DISCOLORATION (C) .................................................................................... 59

GUIDE FOR MAXIMUM AREA ALLOWED OF HOLLOW HEART, HOLLOW HEART WITH 

DISCOLORATION, OR LIGHT BROWN DISCOLORATION (BROWN CENTER)........................... 60

DRY ROT, SOFT ROT AND WET BREAKDOWN........................................................ 61

CLASSIFYING AND CERTIFYING ROTS ............................................................................. 61

ALTERNARIA TUBER ROT (EARLY BLIGHT) (C)................................................................ 62

BACTERIAL RING ROT (C)............................................................................................. 62

BLACKLEG TUBER ROT (C) ........................................................................................... 63

BROWN ROT (SOUTHERN BACTERIAL WILT) (C) ............................................................. 63

FUSARIUM TUBER ROT (C)............................................................................................ 64

JELLY END ROT (GLASSY END ROT) (C)........................................................................ 65

LATE BLIGHT TUBER ROT (C)........................................................................................ 65

LEAK (C) ..................................................................................................................... 66

PINK ROT (C) .............................................................................................................. 66

SCLEROTIUM ROT (C)................................................................................................... 66

SLIMY SOFT ROT (C).................................................................................................... 67

WET BREAKDOWN (C).................................................................................................. 67
v

FINGERLING POTATOES ........................................................................................... 68

FRENCH FINGERLING ................................................................................................ 68

PART 2: INSPECTION INSTRUCTIONS FOR SEED POTATOES............................. 69

GENERAL..................................................................................................................... 69

TOLERANCES.............................................................................................................. 70

APPLICATION OF TOLERANCES............................................................................... 70

SIZE .............................................................................................................................. 70

REPORTING BACTERIAL RING ROT......................................................................... 71

APPENDIX I: U.S. GRADE STANDARDS................................................................... 73

UNITED STATES STANDARDS FOR GRADES OF POTATOES ............................................... 73

UNITED STATES STANDARDS FOR GRADES OF SEED POTATOES ...................................... 86

APPENDIX II: PERCENTAGE CHART........................................................................ 91

APPENDIX III: CERTIFICATE EXAMPLES................................................................. 92

EXAMPLE 1: FV-184 NOTESHEET ................................................................................. 92

EXAMPLE 1: FV-184 CERTIFICATE................................................................................ 93

EXAMPLE 2: FV-300 NOTESHEET (FRONT).................................................................... 94

EXAMPLE 2: FV-300 NOTESHEET (BACK)...................................................................... 95

EXAMPLE 2: FV-300 CERTIFICATE................................................................................ 96

EXAMPLE 3: FV-300 NOTESHEET (FRONT).................................................................... 97

EXAMPLE 3: FV-300 NOTESHEET (BACK)...................................................................... 98

EXAMPLE 3: FV-300 CERTIFICATE................................................................................ 99

EXAMPLE 4: FV-300 NOTESHEET (FRONT).................................................................. 100

EXAMPLE 4: FV-300 NOTESHEET (BACK).................................................................... 101

EXAMPLE 4: FV-300 CERTIFICATE.............................................................................. 102

EXAMPLE 5: FV-300 FEIRS CERTIFICATE .................................................................. 103

EXAMPLE 6: FV-300 FEIRS CERTIFICATE .................................................................. 104

2

PART 1: SHIPPING POINT AND MARKET INSPECTION 

INSTRUCTIONS FOR FRESH POTATOES

GENERAL

Fresh potatoes constitute one of the major products certified by the USDA Fresh 

Fruit and Vegetable Inspection Service. Shipments and inspections are made every 

month of the year from one or more producing areas, either as being freshly harvested 

or from storage.

Each inspector should study these instructions and become thoroughly familiar 

with the procedures as outlined herein. A complete knowledge of the requirements of 

the U.S. Standards for Grades of Potatoes is absolutely essential in making 

inspections.

The inspector should have a copy of the U.S. Standards for Grades of 

Potatoes (see Appendix I), "Official Visual Aids for Potatoes" (USDA Visual Aid 

Pot.-L-1 May 1998), and color comparators POT-CC 1 and POT-CC 2 available at 

all times for ready reference.

Additional local instructions and instructions applying to state grades may be 

furnished by your supervisor.

REPRESENTATIVE SAMPLING 

The importance of obtaining representative samples cannot be over 

emphasized. Accurate certification is possible only if the samples examined are truly 

representative of the entire lot or accessible portion. All portions of a lot or load should 

receive the same attention in sampling regardless of the difficulty involved in reaching 

all layers or parts of a lot or load. Anytime the entire lot requested is not accessible for 

sampling, the inspection and certificate must be restricted to the accessible portion.

Size of Samples

§51.1548 Samples for grade and size determination. Individual 

samples shall consist of at least 20 pounds. When individual 

packages contain at least 20 pounds, each individual sample is 

drawn from one package; when packages contain less than 20 

pounds, a sufficient number of adjoining packages are opened to 

provide at least a 20-pound sample. The number of such individual 

samples drawn for grade and size determination will vary with the 

size of the lot.
3

Although the sample size must be at least 20 pounds, larger size samples, such 

as the entire container, may be examined when instructed to do so by the supervisor or 

at applicant’s request. Also, count may be used as the method of determining 

percentages when potatoes are packed for size B or smaller. However, the sample 

size must still be at least 20 pounds.

Whenever defects exceed the sample or lot tolerance in one or more samples, 

examine the entire contents, when practical, of at least one of these samples. Never 

double the sample size to 40 pounds. For example, when the sample or lot tolerance is 

exceeded in a sample packed in a 50 pound carton, run the entire 50 pounds. When 

the sample or lot tolerance is exceeded in a sample from a 2000 pound tote, it is not 

practical to run the entire container; therefore, the sample size remains at 20 pounds.

For potatoes packed in consumer units, a sufficient number of adjoining units are 

opened to provide at least a 20 pound sample. It is not necessary to double the sample 

size of consumer units when the sample or lot tolerance is exceeded.

For sample size and sampling procedure to determine the presence of internal 

defects, please see the Internal Defects Section.

Number of Samples

It is the inspector's responsibility to examine enough samples to ensure an 

accurate picture of the lot.

Shipping Point

At shipping point, the supervisor may issue instructions as to the minimum 

number of samples required for each size lot. The inspector may determine the 

number of samples drawn for each combination of sizes, containers (master or 

individual) and brands, according to the following guidelines:

NUMBER OF CONTAINERS MINIMUM NUMBER OF SAMPLES

 1 – 49

50 – 99

100 – 199

200 – 299

300 – 499

500 – over

2 (1 for on-line)

2

3

4

5

add 1 sample for each additional 100 

containers or portions thereof.

NOTE: All consumer packages not packed in master containers should be sampled on 

a hundredweight basis equivalent to the above chart.

Market

As a general rule, a minimum of 1% of the lot must be examined at the market. 

For lots of less than 300 packages, a minimum of 3 samples must be examined. For 
4

individual lots over 2000 packages, sample at the rate of 2/3 of 1% for each lot. To 

ensure an accurate description of the lot, it is the inspector’s responsibility to examine 

additional representative samples when the quality, condition, or size in samples is 

decidedly different. For example, more samples should be taken when encountering 

irregular amounts of soft rot to ensure that the high sample tolerance allowed for soft rot 

(3 to 6% out of every 10 samples, depending on grade) is not overlooked.

Inspection of Bulk Loads or Bulk Bins

In the case of bulk loads, the entire load will be considered the sample unit. 

When the load is divided into sections and a material difference in quality, condition or 

size exists between the potatoes in the different sections, each section may be treated 

as a separate lot.

The sample unit consists of representative sub-samples, which are randomly 

taken throughout the lot. The sub-samples are individually recorded, as taken, on the 

notesheet. The "Application of Tolerances" does not apply to the individual subsample. Also, do not range the sub-samples on the certificate; average them together 

and state as a percentage. For example, “7% undersize, 4% old cuts, 6% soft rot.”

Potatoes in bulk bins or totes are treated the same as potatoes in sacks, cartons 

and other types of containers and are subject to the "Application of Tolerances." 

Generally, the load is restricted since only the upper 18 inches or 2 feet are accessible.

At shipping point, potatoes are often held in bulk holding bins. The bins may 

hold 100,000 pounds or more of product. Inspectors should not obtain official samples 

of product from these bins when inspecting under marketing orders, military orders, 

USDA purchases or certification for Canadian destinations. It is acceptable to do a 

voluntary quality control inspection on these large bins at applicant's request. The 

“Application of Tolerances” does not apply to individual sub-samples from bulk holding 

bins.

TOLERANCES

§51.1546 Tolerances. To allow for variations incident to proper 

grading and handling in each of the foregoing grades, the following 

tolerances by weight or equivalent basis, are provided as specified.

(a) For defects.

(1) U.S. No. 1

(i) At Shipping Point. A total of 8 percent for potatoes in any lot 

which fail to meet the requirements for the grade: Provided, That 

included in this tolerance not more than the following percentages 

shall be allowed for the defects listed: 
5

(A) 5 percent for external defects;

(B) 5 percent for internal defects; and

(C) Not more than a total of 1 percent for potatoes which are frozen 

or affected by soft rot or wet breakdown. See §51.1547

(ii) En route or at Destination. A total of 10 percent for potatoes in 

any lot which fail to meet the requirements for the grade: Provided, 

That included in this tolerance not more than a total of 8 percent 

shall be allowed for permanent defects: And provided further, the 

following percentages shall be allowed for the defects listed: 

(A) 7 percent for external defects, including therein not more than 5 

percent for permanent defects;

(B) 7 percent for internal defects, including therein not more than 5 

percent for permanent defects; and

(C) Not more than a total of 2 percent for potatoes which are frozen 

or affected by soft rot or wet breakdown. See §51.1547.

(2) U.S. Commercial.

A total of 20 percent for potatoes in any lot which fail to meet the 

requirements for the grade: Provided, That included in this tolerance not 

more than the following percentages shall be allowed for the defects listed:

(i) 10 percent for potatoes which fail to meet the requirements for U.S. No. 2 

grade, including therein not more than:

(ii) 6 percent for external defects;

(iii) 6 percent for internal defects; and

(iv) Not more than a total of 1 percent for potatoes which are frozen or 

affected by soft rot or wet breakdown. See §51.1547.

(3) U.S. No. 2.

(i) At Shipping Point. A total of 10 percent for potatoes in any lot 

which fail to meet the requirements for the grade: Provided, That 

included in this tolerance not more than the following percentages 

shall be allowed for the defects listed: 

(A) 6 percent for external defects;
6

(B) 6 percent for internal defects; and

(C) Not more than a total of 1 percent for potatoes which are frozen 

or affected by soft rot or wet breakdown. See §51.1547.

(ii) En route or at Destination. A total of 12 percent for potatoes in 

any lot which fail to meet the requirements for the grade: Provided, 

That included in this tolerance not more than a total of 10 percent 

shall be allowed for permanent defects: And provided further, the 

following percentages shall be allowed for the defects listed: 

(A) 8 percent for external defects, including therein not more than 6 

percent for permanent defects;

(B) 8 percent for internal defects, including therein not more than 6 

percent for permanent defects; and

(C) Not more than a total of 2 percent for potatoes which are frozen 

or affected by soft rot or wet breakdown. See §51.1547.

(b) For off-size.

(1) Not more than 3 percent of the potatoes in any lot may be smaller than 

the required or specified minimum size except that a tolerance of 5 

percent shall be allowed for potatoes packed to meet a minimum size of 

2-1/4 inches or larger in diameter or 5 ounces or more in weight. In 

addition, not more than 10 percent may be larger than any required or 

specified maximum size. See §51.1547.

Summary of Tolerances

U.S. No. 1 – Shipping Point U.S. No. 1 – En Route or At Destination

Total defects: 8%, including

5% external defects,

5% internal defects, and

Included in external or internal defects: 

1% frozen, soft rot or wet breakdown

Total defects: 10%, including

8% permanent defects,

Included in total defects: 7% external

defects, including 5% permanent 

defects,

Included in total defects: 7% internal

defects, including 5% permanent 

defects, and

Included in external or internal defects: 

2% frozen, soft rot or wet breakdown
7

Summary of Tolerances Continued

U.S. Commercial – Shipping Point / En Route or At Destination

Total defects: 20%, including 10% serious damage,

Included in serious damage:

6% external defects,

6% internal defects, and

Included in external or internal defects: 1% frozen, soft rot or wet breakdown

U.S. No. 2 – Shipping Point U.S. No. 2 – En Route or At Destination

Total defects: 10%, including

6% external defects,

6% internal defects, and

Included in external or internal defects: 

1% frozen, soft rot or wet breakdown

Total defects: 12%, including

10% permanent defects,

Included in total defects: 8% external

defects, including 6% permanent 

defects,

Included in total defects: 8% internal

defects, including 6% permanent 

defects, and

Included in external or internal defects: 

2% frozen, soft rot or wet breakdown

Off-Size (All Grades)

Undersize: 3%, except 5% undersize for 2-1/4 inch or 5 ounce minimum.

Oversize: 10%

APPLICATION OF TOLERANCES

§51.1547 Application of tolerances. Individual samples shall have 

not more than double the tolerances specified, except that at least 

one defective and one off-size potato may be permitted in any 

sample: Provided, That en route or at destination one-tenth of the 

samples may contain three times the tolerance permitted for 

potatoes which are frozen or affected by soft rot or wet breakdown: 

And provided further, That the averages for the entire lot are within 

the tolerances specified for the grade.
8

Summary of Application of Tolerances

U.S. No. 1 – Shipping Point U.S. No. 1 – En Route or At Destination

Total Defects: 16%, including

10% external defects,

10% internal defects, and

Included in external or internal defects: 

2% frozen, soft rot or wet breakdown

Total defects: 20%, including

16% permanent defects,

Included in total defects: 14% external 

defects, including 10% permanent 

defects,

Included in total defects: 14% internal 

defects, including 10% permanent 

defects, and

Included in external or internal defects: 

4% frozen, soft rot or wet breakdown 

(6% permitted in 1/10 of samples)

U.S. Commercial – Shipping Point / En Route or At Destination

Total defects: 40%, including 20% serious damage, 

Included in serious damage:

12% external defects,

12% internal defects, and

Included in external or internal defects: 2% frozen, soft rot or wet breakdown –

3% permitted in 1/10 of samples en route or at destination

U.S. No. 2 – Shipping Point U.S. No. 2 – En Route or At Destination

Total defects: 20%, including

12% external defects,

12% internal defects, and

Included in external or internal defects: 

2% frozen, soft rot or wet breakdown

Total defects: 24% including

20% permanent defects,

Included in total defects: 16% external 

defects, including 12% permanent 

defects,

Included in total defects: 16% internal 

defects, including 12% permanent 

defects, and

Included in external or internal defects: 

4% frozen, soft rot or wet breakdown

(6% permitted in 1/10 of samples)

Off-Size (All Grades)

Undersize: 6%, except 10% undersize for 2-1/4 inch or 5 ounce minimum

Oversize: 20%

At least one defective and one off-size potato may be permitted in any sample. And provided 

further, That the averages for the entire lot are within the tolerances specified for the grade.
9

NOTESHEET AND CERTIFICATE

Entries on the notesheet and certificate must be kept in a legible and accurate 

manner. It is mandatory that all information appearing on the certificate be supported 

by information on the notesheet. It is the responsibility of the inspector to ensure that 

all information is properly recorded. Notations will be recorded so that anyone familiar 

with inspection procedures can interpret them and write a certificate. Also, notesheets 

and certificates are prima facie evidence and must withstand legal scrutiny.

Detailed instructions pertaining to date, inspection point, place of inspection, type 

of carrier, lading, etc., which are not covered by these instructions may be found in the 

General Inspection Instructions. Additional information and instructions may be given 

by your supervisor.

Product

The common name “Potatoes” will be used to describe this commodity in the 

product heading. Color and/or type shall be used in conjunction with “Potatoes” such 

as “Long White,” “Round Red,” “Round White,” “Russet,” “Other,” or “Mixed.”

The term “Other” is applied to potatoes that have skin and/or flesh colors that 

differ from white flesh potatoes that have white, red, or russet skin. For example,

potatoes having yellow flesh, or having bi-colored skin, or having purple skin and flesh, 

etc., would be described as “Potatoes, Other.” When needed, the potatoes can be 

further described in the “OTHER” or “REMARKS” section, such as “Yellow flesh

potatoes,” “Bi-color red and yellow potatoes,” or “Purple skin and flesh potatoes.”

The term “Mixed” is applied to lots having different types and/or colors of 

potatoes packed in the same container or master container. For Example, consumer 

units with round red, white, and purple potatoes would be described as “Potatoes, 

Mixed.” Again, additional description can be reported in the “OTHER” or “REMARKS” 

section, such as “Round red, white, & purple potatoes mixed in bags.”

Number/Type of Containers

The number of containers will always be reported. In the market and at shipping 

point locations for stationary lot certification, the inspector shall always verify the 

container count provided by the applicant for each lot and report it as the “inspector’s 

count.” If the number of containers available for inspection does not match the 

application, it is the inspector’s responsibility to confirm that the amount presented for 

inspection constitutes the lot. If an accurate count cannot be determined, the inspector 

may report the count at someone else’s authority. However, the reason for doing so 

must be reported on the notesheet (e.g., numerous pallets with mixed product).

At shipping point locations for “days-run” certification, the applicant generally 

provides a manifest for count and it is acceptable to use this for the number of 

containers.
10

Potatoes are packed in many types of containers. They are commonly packed in 

volume filled fiberboard cartons or paper bags holding 50 pounds. Film or mesh 

consumer bags containing 3 to 10 pounds, which are placed in master containers 

netting up to 50 pounds, are popular packs. Potatoes are also packed in burlap sacks 

holding 100 pounds and totes or bins accommodating 1000 to 2000 pounds. Creamers 

and fingerlings may be packed in 3/4, 1, 1.5, 2, 3, 4, or 5 pound clamshells shipped in 

master containers of 6, 8, 10, or 12 packs. Russet baking potatoes may be individually 

wrapped in clear film or foil and packed in cartons holding 15 to 25 pounds. These are 

the major packs and containers currently available, but this is not an exhaustive list, 

since the marketing of potatoes continually evolves.

Brands/Markings

The brand, variety, size, count, grade, weight, point of origin and other important 

information appearing on the container should be reported on the notesheet in the 

“Brands/Markings” section. Only the brand name and other key markings necessary to 

properly identify the lot for certification should appear in this section on the certificate.

Origin

The inspector should not make a positive statement on their own authority, but 

when container markings list the state or country of origin, it should be quoted in the 

appropriate space on the notesheet and the certificate. If origin is not marked, it is the 

inspector’s responsibility to make an effort to obtain this information from the applicant. 

This policy is necessary because some firms may use one mark on the same product 

packed in several states. The inspector can certify only to the marks and has no 

means of verifying in which state or country the potatoes were grown.

CONDITION OF PACK

Potatoes do not have any packing requirements. However, when potatoes are 

packed in containers such as cartons or bins, report the fill on the back of market 

notesheets in the Pack Section using the following terms:

Well filled means the contents are level with top edge of the container.

Fairly well filled means the contents are not in contact with the lid or cover, but 

not more than 1-1/2 inches below the lid or cover.

Slack means the contents are more than 1-1/2 inches below the lid or cover. 

Report the amount of slackness in inches or fractions of inches below the lid.

When potatoes are packed in bags or sacks, do not report pack.
11

TEMPERATURE OF PRODUCT

Inspectors would not normally determine or report temperatures at shipping 

point. However, due to the importance of the pulp temperature of fresh fruits and 

vegetables when in transit or at destination, it is essential that the inspector accurately 

determine and report the temperature or range in temperatures on each lot. Pulp 

temperature should be reported regardless of the location of the product, whether in the 

carrier, warehouse, or stacked on the platform. Pre-cool the thermometer in order to 

obtain true readings and report all temperatures to the nearest whole degree.

A minimum of three temperatures for each lot must be taken and recorded on 

the notesheet. More temperatures must be taken if the lot is abnormally cold, heated, 

or there is a specific request for temperature. The location in the lot and/or load must 

be specified in greater detail when additional temperatures are taken.

SIZE

Size is part of grade and the U.S. grades for potatoes have the following size 

requirements:

U.S. No. 1 – 1-7/8 inches in diameter minimum unless otherwise specified.

U.S. No. 2 – 1-1/2 inches in diameter minimum unless otherwise specified.

§51.1545 Size. The minimum size, or minimum and maximum sizes 

may be specified in connection with the grade in terms of diameter 

or weight of the individual potato, or in accordance with one of the 

size designations in Table I or Table II: Provided, That sizes so 

specified shall not be in conflict with the basic size requirements for 

the grade.

(b) When size is designated as shown in Table II, the corresponding 

weight ranges shall apply. These size designations may be applied 

to potatoes packed in any size container: Provided, that the weight 

ranges are within the limits specified.
12

TABLE I

Size designation

Minimum diameter1 or 

weight

Maximum diameter or 

weight

Inches Ounces Inches Ounces

Creamer......................................

Chef............................................

Size A2........................................

3/4

2-3/4

1-7/8

(3)

8

(3)

1-5/8

4-1/2

(3)

(3)

28

(3)

Size B.......................................... 1-1/2 (3) 2-1/4 (3)

Small........................................... 1-3/4 (3) 2-1/2 6

Medium....................................... 2-1/4 5 3-1/4 10

Large........................................... 3 10 4-1/2 28

1 Diameter means the greatest dimension at right angles to the longitudinal axis, without regard to 

the position of the stem end.

2 In addition to the minimum size specified, a lot of potatoes designated as Size A shall contain at 

least 40 percent of potatoes which are 2-1/2 inches in diameter or larger or 6 ounces in weight or 

larger.

3 No requirement.

TABLE II

[Ounces]

Size designation Minimum weight Maximum weight

Under 50.................................................... 15 .................

50............................................................... 12 19

60............................................................... 10 16

70............................................................... 9 15

80............................................................... 8 13

90............................................................... 7 12

100............................................................. 6 10

110............................................................. 5 9

120............................................................. 4 8

130............................................................. 4 8

140............................................................. 4 8

over 140..................................................... 4 8

Reporting Size

The diameter of a potato is measured by passing the potato through a sizer. 

USDA sizers for potatoes consist of rings with round openings that come in many 

different diameters. For the use of other sizers, such as the square sizers recognized in 

international trade (UNECE Standards), please see the Size Section under Part II: 

Inspection Instructions for Seed Potatoes.
13

When measuring the diameter, drop the potato through the opening so that its 

longitudinal axis is at right angles to the sizer, without regard to the position of the stem 

end.

Minimum and/or maximum sizes may be specified in terms of weight or diameter. 

However, long type potatoes should generally be reported in ounces and round type by 

diameter. Typically when a range of more than 1 inch or 4 ounces is encountered a 

"mostly" statement in addition to minimum and maximum size should be reported. 

However, when reporting size for a size designation in Table I or II, it may not be 

necessary to report a "mostly" statement (see sections Size A and Containers Marked 

to Size or Count).

When describing size by weight, the range and "mostly" statement should be 

shown in ounces, with the exception that "1-7/8 inches in diameter or 4 ounces," "2 

inches in diameter or 4 ounces," etc., may be used to indicate the lower end of the size 

range when these terms are appropriate.

Shipping Point Inspections:

When reporting range of size, use general terms if needed. For example, the lot 

is sized for 2 inch minimum. On the notesheet, the range is 1-3/4 to 2-3/4 inches in 

diameter with an average of 2% less than 2 inches. The size statement on the 

certificate would be “Generally 2 to 2-3/4 inches in diameter, average 2% undersize.”

En Route or Destination Inspections:

When reporting range of size, do not begin the size statement with a general 

term, such as “generally” or “mostly.” Report the entire range. For example, the lot is 

sized for 2 inch minimum. On the notesheet, the range is 1-3/4 to 2-3/4 with an 

average of 2% less than 2 inches. The size statement on the certificate would be “1-3/4 

to 2-3/4 inches in diameter. Undersize within tolerance.” The 2% undersize would not 

be reported on the certificate, unless requested by the applicant, since the lot still meets 

the size requirements. If the undersize is 7% instead of 2%, the lot would fail, and the 

size statement would be “1-3/4 to 2-3/4 inches in diameter.” The 7% undersize would 

be reported in the “AVERAGE DEFECTS” section.

Size A

Specifications for Size A were inserted in the grades to provide a greater range 

in size, versus those potatoes which are only slightly over the minimum size for U.S. 

No. 1 grade. Determination of percentages, by weight, for size A will be made when 

requested by the applicant, when the containers are so marked or when it is a general 

practice to certify on this basis in the area of production.

When certifying on the basis of Size A, it is necessary to clearly indicate whether 

or not 40% by weight are 2-1/2 inches in diameter or larger, or are 6 ounces or larger. 

If the individual potato meets either the minimum diameter or minimum weight, it meets 

the requirements for Size A. In addition, a minimum size larger than 1-7/8 inches may 

be certified, but no lot may be certified as Size A if the minimum size is less than 1-7/8 

inches.
14

The inspector should examine each sample to ensure the lot meets Size A; 

however, not all weights and/or diameters need to be recorded, since an exact lot

percentage for Size A is not required. After recording a sufficient number of weights

and/or diameters, the inspector only needs to check off the remaining samples to show 

that they have been examined to meet Size A. For an example of how to report Size A,

see back of notesheet to Example 3 in Appendix III.

As mentioned, when the stock meets the specifications of Size A, an exact lot 

percentage of 2-1/2 inches or larger, or 6 ounces or larger, as the case may be, need 

not be given unless specifically requested by the applicant. It will be satisfactory to 

report the overall range followed by "40% or more 2-1/2 inches in diameter or larger" or 

"40% or more 6 ounces or larger." When a lot inspected for Size A fails to meet the 

specification, the inspector must report "Fails to meet Size A" except when the applicant

only requested Size A for informational purposes. If Size A was only requested for 

informational purposes and it failed to make the size, do not report “Fails to meet Size 

A.” Instead, report a "mostly" range within the overall range, such as "mostly 5 to 7 

ounces."

Reporting Percentages of a Specified Size and Larger

§ 51.1546 (b) (2) When a percentage of the potatoes is specified to be 

of a certain size and larger, individual samples shall have not less 

than one-half of the percentage specified: Provided, That the 

averages for the entire lot is not less than the percentage specified.

The percentage of a certain size and larger, such as 10 ounces or larger, may be 

determined upon request of the applicant. The U.S. Standards for Grades of Potatoes 

require that when a percentage of a certain size and larger is specified, individual 

samples must contain at least one-half the specified percentage.

In connection with Size A, and in other instances where a percentage of a certain 

size and larger is specified, the specified percentage is a definite requirement. 

However, individual samples may contain as little as 1/2 of the percentage specified, 

provided the average for the lot as a whole is within the percentage specified. For 

example, to meet Size A requirements, individual samples must contain at least 20% 

2-1/2 inches or 6 ounces or larger and the average of all samples cannot be less than 

40% 2-1/2 inches or 6 ounces or larger.

Certifying Minimum Size

The size designations "Chef,” “Medium," and "Large" require that individual 

potatoes be of a certain minimum diameter or weight. If the potato meets either the 

minimum diameter or the minimum weight, it meets the minimum size requirements. In 

determining the percentage of potatoes which are under a minimum diameter, it is 

generally best to first size the potatoes by ring measurement. All of the potatoes under

the required minimum diameter should be weighed. Only potatoes which weigh less 
15

than the required weight are considered undersize. Some marketing agreements 

provide for a minimum diameter or weight.

When the minimum size is specified in the grade, such as 1-7/8 inch for 

U.S. No. 1, it need not be reported in the grade statement. It will only be necessary to 

state the size in connection with the grade when it is "otherwise specified." For 

example, "U.S. No. 1, 2 inch or 4 ounce minimum" or "U.S. No. 1, 2 inch minimum

diameter" or "U.S. No. 1, 100 Size" or "U.S. No. 1, Medium." 

Certifying Maximum Size

In Table I when determining maximum size, individual potatoes cannot exceed 

the maximum diameter or weight requirements. For example, under "Medium," a potato 

larger than 3-1/4 inches in diameter or weighing more than 10.49 ounces is considered 

oversize (see following section).

Reporting Overweight

Potatoes which exceed the specified maximum weight by less than one-half 

ounce will be disregarded. Potatoes, which are one-half ounce or more above the 

maximum weight, will be scored as oversize. This policy applies only to oversize.

Table II provides minimum and maximum weights, in ounces, for the various 

count size designations based on the standard 50-lb. carton. These weight ranges 

apply to potatoes packed in any size container.

Containers Marked to Size or Count

When packages are marked:

"80, "90", "100", etc., or

"80 size," "90 size," "100 size," etc., or

"approx. 80," "approx. 90," "approx. 100," etc.

Report conformity or non-conformity to marked size.

When packages are marked to count or approximate count:

Report range in weight only. Establish minimum and maximum sizes. 

Whenever the word "count" is used on the container do not use the size designations in 

Table II. In either case, count shall be reported only at specific request of the applicant. 

When so requested, report the range in number of potatoes per container and the 

average for the lot.

Do not report conformity or non-conformity with marked count under the grade or 

size headings. Lots which fail to conform to marked size or exceed PACA allowances 

for off-count shall be reported to the PACA Division.

Note: When the request for an inspection is made, the applicant should be 

informed that count will not be reported unless specifically requested.
16

When the lot is marked to denote one of the size designations in Table II, it is not 

necessary to show a range in size unless the lot fails to meet the minimum and/or 

maximum weight requirements for that particular size designation.

For the purpose of determining size, each "size," "approx. size," "count" or 

"approx. count" will be treated separately if more than one is noted. For additional 

instructions on reporting the "count" or "approx. count" refer to the section titled "PACA 

Ruling on Grade and Size and Markings" in General Inspection Instructions.

Certifying Size without Reference to Grade

Upon request, size may be certified without reference to quality and condition 

factors. Size should be reported as usual. The certificate should show the proper 

restriction under “REMARKS,” such as, "Inspection and certificate restricted to size only 

at applicant's request."

Use of Undersize and Oversize within Tolerance

When no sample exceeds the size tolerance, it will be satisfactory to state 

"Undersize (or oversize) within tolerance" or "Meets size as marked." When no sample 

exceeds double the size tolerance and averages within tolerance, the statement 

"Undersize (or oversize) average within tolerance" should be used. The term "off-size" 

may be used when both undersize and oversize are involved. 

When the lot fails to grade either because of the average or because individual 

samples exceed double the size tolerance, report the range, regardless of how narrow it 

may be, and the average in actual figures.

Actual percentages of undersize (or oversize) must be reported in the following 

cases:

 At request of the applicant.

 When determining the percentage of U.S. No. 1 quality.

 When undersize (or oversize) exceeds the tolerance.

When Undersized or Oversized Specimens are Also Defective

Undersize and oversize specimens which are also defective should be scored 

twice; first as off-size, second as a grade defect. This is necessary because the grades 

have separate tolerances for off-size and grade defects.

Generally the percentage of off-size specimens that are also defective will be 

negligible, and will make no material difference in the grade certification. When the 

percentage of off-size specimens, that are also defective, amounts to 1% or more, the 

percentage of defective specimens which are also offsize must be reported.

Report this information in the "OTHER" section on market certificates and in the 

"DESCRIPTION OF PRODUCT" section on shipping point certificates. For example:
17

“2% undersize also included in the 4% quality defects.” Oversize should be treated the 

same way.

MATURITY AND SKINNING

The U.S. Standards for Grades of Potatoes do not have any maturity or skinning 

requirements. However, if the applicant requests maturity, apply the following maturity 

definitions:

§51.1554 Mature. “Mature” means that the skins of the potatoes are 

generally firmly set and not more than 5 percent of the potatoes in the lot 

have more than one-tenth of the skin missing or “feathered.”

§51.1555 Fairly well matured. “Fairly well matured” means that the skins 

of the potatoes are generally fairly set and not more than 10 percent of the 

potatoes in the lot have more than one-fourth of the skin missing or 

“feathered.”

The term “Mature” should be used to describe potatoes which have reached full 

development, are firm, and have a tough and tight skin. The term “Fairly Well Matured” 

has the same definition as “Slightly Skinned” (see below).

Also, if the applicant requests the degree of skinning, apply the following 

skinning definitions:

§51.1549 Skinning. (a) The following definitions provide a basis for 

describing lots of potatoes as to the degree of skinning whenever 

description may be appropriate:

(1) "Practically no skinning" means that not more than 5 percent of 

the potatoes in the lot have more than one-tenth of the skin missing 

or "feathered;"

(2) "Slightly skinned" means that not more than 10 percent of the 

potatoes in the lot have more than one-fourth of the skin missing or 

"feathered;"

(3) "Moderately skinned" means that not more than 10 percent of the 

potatoes in the lot have more than one-half of the skin missing or 

"feathered;" and

(4) "Badly skinned" means that more than 10 percent of the potatoes 

in the lot have more than one-half of the skin missing or "feathered."
18

The degree of skinning on individual potatoes refers to the amount of skin 

missing or “feathered.” Usually the more immature the potatoes, the greater the degree 

of skinning.

The degree of skinning may be reported in general terms unless specifically 

requested to report actual percentages. The term "new potatoes" should not be used.

EXAMPLES:

Slightly to badly, most moderately skinned.

Generally moderately, few badly skinned.

Mostly slightly, some moderately skinned.

Such statements should be based upon a record of skinning for each sample on 

the notesheet as:

SLIGHTLY MODERATELY BADLY

SKINNED SKINNED SKINNED

20% 70% 10%

00% 92% 08%

75% 25% 00%

Visual Aids Refer to photos 23 - 26.

Maturity/Skinning Classification to be Used upon Request

In case such a classification is requested, the details should be reported on the 

certificate. Request for classification for maturity or skinning at times may be made by 

buyers who contract to purchase lots of potatoes with a provision that they do not 

exceed a certain degree of skinning. In addition, marketing orders may have maturity 

(skinning) requirements for importing and exporting potatoes in and out of the U.S.

For example, if a buyer contracted to purchase a U.S. No. 1 lot to be not more 

than "moderately skinned" and requested inspection on this basis, and the inspector 

found an average of 15% badly skinned potatoes in the lot, it would fail to meet contract 

specifications. Such a classification should be included as part of the grade statement, 

thus: U.S. No. 1, but fails to meet 'moderately skinned' classification due to percentage 

of badly skinned potatoes. It will be necessary to report in the “Remarks” section of the 

notesheet and certificate “Percentage of skinning determined and reported at 

applicant's request."

Inspectors should remember that the percentages shown in the various 

definitions of maturity and skinning classifications are not tolerances in the sense that 

they are subject to the application of tolerances to individual samples. For example, in 

a lot classified as fairly well matured, 10% may be moderately skinned but there is no 

limitation on the percentage of moderately potatoes in individual samples so long as the 

average does not exceed 10%.
19

COMBINATION OF INTERNAL AND EXTERNAL DEFECTS

Occasionally individual potatoes are encountered that exhibit a combination of 

internal and external defects. The following guidelines should be followed in 

accordance with the circumstances as outlined below:

When cutting for internal defects (20 pounds or entire sample), a potato with an 

external defect is found to have an internal defect, and either defect would be scorable 

by itself, the following will apply:

(1) The potato will be scored against the tolerance most affected. When it 

cannot be determined which tolerance is most affected at the time of running the 

sample, follow the procedures below for:

A. Paper notesheet and certificate: Entries will be made for both defects on 

the notesheet and cross-referenced. Once the inspection is completed, 

the inspector will go back to determine which tolerance, if any has been 

affected the most (if no tolerance has been affected more than another, 

see items 2 and 3 below). Once determined, a line will be drawn through 

the entry that is not being applied and percentages will be determined 

based on the final figures.

B. FEIRS: Entries will be made for both defects on the sample page and 

cross-referenced in the “Sample Remarks” block. For example, since 

one-half pound may be scored both for SDA or IBS, record one-half 

pound to the SDA column and one-half pound to the IBS column. At the 

bottom of the sample page in the “Sample Remarks” block record “1/2 

pound scored both for SDA and IBS. At completion of inspection, amount 

will be removed from the tolerance least affected.” Once the inspection is 

completed, the inspector will go back to determine which tolerance, if any 

has been affected the most (if no tolerance has been affected more than 

another, see items 2 and 3 below). Once determined which defect is 

most affected, go back and remove the amount (i.e. “1⁄2 pound”) recorded

earlier to the tolerance least affected. In the “Explanation” box that pops 

up after changing the amount, write “See Sample Remarks.” Or,

(2) If item 1 above does not apply and one defect is more severe than the other, 

the more severe defect will be scored (soft rot will always be considered as the 

more severe defect). Or,

(3) If item 1 above does not apply and neither defect is more severe, it is at the 

inspector's discretion as to which defect to score. When a potato is affected by 

both internal and external defects and neither defect on its own is scorable (i.e. 

4% waste from a bruise, 4% waste from net necrosis) yet in combination the 

potato is scorable (8% total waste), the inspector should divide the percentage in 

combination as equally as possible between the defects. For example, a sample 

has 2 pounds (4%) damage by bruising and 1 pound (2%) damage by net 

necrosis with 1 pound (2%) damage by a combination of the two. The 2% 
20

combination should be divided, adding one-half pound (1%) to bruising and onehalf pound (1%) to net necrosis.

DEFECTS (QUALITY AND CONDITION)

Statements pertaining to freshness, maturity, shape, color, the amount and type 

of defects, and the amount of decay are shown under the appropriate headings. 

Factors noted with (Q) are considered as QUALITY only. Quality (also referred to as 

“permanent” defects) are defects which do not change during storage or shipment 

(shape, scars, etc.). Factors noted with (C) will be reported as CONDITION on market 

certificates. Condition defects are factors that are subject to change during shipment or 

storage, such as sunken discolored areas, internal black spots, and soft rot. Those 

factors noted with (Q or C) may be considered as QUALITY or CONDITION, 

depending on the circumstances.

The grades specify certain factors that are basic to describing the quality and 

condition of a lot such as "cleanness," "firmness" and "shape." These may be 

described in general terms unless they fall below the requirements of the grade.

All photo visual aids referred to are found in USDA "Official Visual Aids for 

Potatoes" POT-L-1 May 1998. The contents of this booklet should be familiar to all 

graders licensed to inspect potatoes.

EXTERNAL DEFECTS

§51.1564 External defects. “External defects” are defects which can 

be detected externally. However, cutting may be required to 

determine the extent of the injury.

When inspecting potatoes, they cannot be held to the same standard of 

perfection that is required of fruits and many vegetables. It is almost impossible to 

remove all defects by the ordinary process of commercial grading; furthermore, slight 

blemishes do not affect the value of the potatoes as they do in the case of many other 

products. In judging whether a potato is scored or not, consider the appearance factor 

first. If the appearance is not affected, then consider the waste for external defects

(see §51.1564 External defects, Tables III, IV, V, and VI in the standard).

Air Cracks (C)

This defect is characterized by longitudinal cracks, often fresh and without 

apparent connection with mechanical injury. They usually occur during the harvesting 

and packing process, although some may occur after packing in very tight packs or if 

the package is handled roughly.
21

Scoring Guide

Damage:

When removal causes a loss exceeding 5% of the total weight of the potato, or 

When affecting more than 1/3 the length or diameter (whichever is greater) in the 

aggregate.

Serious damage:

When removal causes a loss exceeding 10% of the total weight of the potato, or

When affecting more than 3/4 the length or diameter (whichever is greater) in the 

aggregate.

Visual Aids Refer to photos 94 - 96.

Bruises (Q & C)

Bruises are one of the most common defects found in potatoes. Bruises 

generally show discoloration which may vary as to color but will usually be of a brown, 

gray or black shade. The skin and flesh of the potato may be broken or torn or may 

simply show discoloration. The size and shape of a bruise may vary considerably. 

At shipping point all bruises are considered quality defects. En route or at 

destination inspectors must make the distinction as to whether the bruise is “old” or 

“fresh.” Old bruises are considered quality defects. Fresh bruises are considered 

condition defects. 

When the age of the bruise is not obvious at first, upon cutting into the flesh the 

following characteristics should help in making a determination:

Fresh bruises are typically a shade of pink or a bright shiny gray to jet black in 

color and show no sign of dry or dry starchy flesh.

Old bruises are typically dull gray or light brown and other colors which show a 

dry or starchy appearance in the flesh. Also, old bruises may show a separation or 

some corkiness of the flesh.

A deposit of powdery, discolored starch will frequently be noticed in bruises or 

cuts. Inspectors should be careful not to confuse this starch deposit with Fusarium Rot. 

The difference can be readily noted upon cutting the potato. If the flesh next to the 

deposit is affected, the condition has been caused by some decay. If the flesh is 

sound, it should be considered only as a bruise.

Scoring Guide

Damage:

When removal causes a loss of more than 5% of the total weight of the potato,

or 

When affecting more than 5% of the surface area in the aggregate (i.e. 3/4 inch 

on a 2-1/2 inch or 6 ounce potato).
22

Serious damage:

When removal causes a loss of more than 10% of the total weight of the potato, 

or

When affecting more than 10% of the surface area in the aggregate (i.e. 1-1/4

inches on a 2-1/2 inch or 6 ounce potato).

Visual Aids Refer to photos 97 - 99.

Cleaness (Q)

Few lots that have not been properly washed or brushed will deserve the terms 

“clean” and "bright" but the fact that they have been washed or brushed does not 

necessarily mean they merit such a description. Inspectors must learn the relative 

degrees of cleanness in order to properly describe various lots and should frequently 

check their judgment with their supervisors.

At the request of the applicant it will be permissible to report the percentage of 

U.S. No. 1 quality waiving cleanness requirements on unwashed lots of potatoes. 

Extremely dirty potatoes may mask defects; therefore, if the potatoes fail to meet the 

minimum cleanness requirement of the grade, samples must be washed and reported 

as such under remarks. The percentage of U.S. No. 1 Quality will be reported under 

REMARKS, not under Grade, with the following statement – “At applicant’s request 

inspection based on contract specifications which waive cleanness requirements. Lot 

approximately 80% U.S. No. 1 Quality other than dirt (samples were washed).”

The U.S. Grades for potatoes have the following requirements for cleanness:

U.S. No. 1: Fairly clean.

U.S. Commercial & U.S. No. 2: Free from serious damage caused by dirt or 

other foreign matter.

Definitions:

§51.1552 Clean. "Clean" means that at least 90 percent of the 

potatoes in any lot are practically free from dirt or staining and 

practically no loose dirt or other foreign matter is present in the 

container.

§51.1553 Fairly clean. "Fairly clean" means that at least 90 percent 

of the potatoes in any lot are reasonably free from dirt or staining 

and not more than a slight amount of loose dirt or foreign matter is 

present in the container.

Visual Aids Refer to photos 3 - 10.
23

Adhering Dirt and Staining

Adhering dirt, staining from soft rot or other foreign matter must be considered in 

determining whether or not the potatoes meet the cleanness requirements of the 

specified grade.

Scoring Guide

For the U.S. No. 1 grade, if 90% of the potatoes are fairly clean, the remaining 

10% can be slightly dirty. Individual potatoes which are more than slightly dirty 

(i.e. damage or serious damage by dirt) will be scored against the tolerance for 

grade defects and also included in the 10% allowed for slightly dirty. For 

example, if 3% of the potatoes were damaged by dirt, you could have 7% slightly 

dirty (total of 10%) and still meet the requirements for fairly clean. When 

determining the percentage of U.S. No. 1 quality, deduct only that amount which 

is damaged by dirt or which is in excess of the 10% that is allowed for potatoes 

that are slightly dirty or stained.

In U.S. Commercial and U.S. No. 2 grades any potato which is badly caked with 

dirt or badly stained is a grade defect and must be scored against the tolerance 

for defects. A badly caked potato is one having caked dirt on more than 1/2 of 

the surface or an equivalent amount of dirt in excessively thick chunks on a 

lesser area.

Loose Dirt, Clods of Dirt, Rocks or Other Foreign Matter

When loose dirt or clods of dirt, etc., is a factor in closed containers (bags, 

cartons, etc.,) the entire contents must be used as the sample. As a guide, if more than 

1/10 of the containers in a lot have more than the following amounts of loose dirt, clods, 

etc., the lot cannot be considered as meeting the requirements of fairly clean.

 100 lb. container - 8 oz.

 50 lb. container - 4 oz.

 20 or 25 lb. container - 2 oz.

 Less than 20 lb. container - 1 oz.

When inspecting bulk loads of potatoes loose dirt or clods of dirt, etc., is 

considered a tare and not a grade factor. If it appears that clods or loose dirt will be a 

tare factor, a minimum sub-sample of 25 lbs. should be drawn to ensure that there is at 

least 20 lbs. of potatoes for grade and size determination. The weight of loose dirt, 

clods, etc., will be recorded and subtracted from the total 25 lbs. The percentages for 

defects and size should then be figured based on the total lbs. of potatoes.

FOR EXAMPLE:

Sample Loose Dirt, Clods (Potatoes) Sample Defects

25 lbs. 1 lb. (4%) 24 lbs. 1.5 lbs. (6%)
24

When one percent (1%) or less loose dirt or clods, etc., is found, it should only 

be recorded on the notesheet. However, when more than one percent (1%) is found, it 

should be reported on the certificate. The statement should show the cleanness of the 

potatoes, (adhering dirt), followed by the percentage of loose dirt, clods, etc., in 

parenthesis. For example: "Generally all potatoes are fairly clean, (3% clods of dirt). 

Grade defects within tolerance."

Cuts/Clipped Ends (Q)

Cuts are areas where some flesh of the potato has been exposed. They either 

occur during harvest or when knobs or ends are clipped by grading personnel. Knobs 

removed are usually distinguished by smooth cuts exposing circular or nearly circular 

areas on the sides of potatoes. Cuts are injurious in that they open the way for decay. 

First a determination must be made as to whether the cut is a clipped end, knob 

removed or regular cut. If the inspector is not sure do not consider the cut a knob 

removed. Clipped ends should be obvious.

Scoring Guide

Cuts:

Damage:

When one smooth cut affects more than 5% of the surface area.

Serious damage:

When affecting more than 10% of the surface area in the aggregate or, when a 

single side cut extends beyond 1/2 the length of the potato. 

Clipped Ends:

Damage:

When one smooth cut affects more than 5% of the surface area.

Serious damage:

When potatoes are clipped on both ends, or are clipped on one end and the 

length of the remaining portion is less than 1-1/2 times the greatest diameter of 

the cut, or irregular cuts which seriously affect the appearance of the potato.

The U.S. No. 1 and U.S. Commercial grades permit one smooth cut affecting 5% 

or less of the surface.

In the U.S. No. 2 grade, a long type potato having one clipped end which is fairly 

smooth, must weigh a minimum of 6 ounces and its length must be at least 1-1/2 times 

the largest diameter of the clipped end. Such a clipped potato may have no other defect 

or combination of defects. However, a long type potato with one fairly smooth clipped 

end, weighing more than 6 ounces and having a length more than 1-1/2 times the 

diameter of the clipped area, may be affected by other defects or combination of 
25

defects which do not detract from the appearance to a greater extent than is permitted 

on a U.S. No. 2 potato.

For small long type varieties such as fingerlings, a clipped end will be permitted 

in the U.S. No. 2 grade if the clipped area does not affect more than 10% of the surface 

when fairly smooth, or does not affect more than 5% of the surface when rough.

Knobs Removed: 

Damage:

When more than one knob is removed, or

When affecting more than 5% of the surface area, or

When the affected area is rough or jagged.

Serious damage:

When affecting more than 10% of the surface area in the aggregate, or

When an area that is rough or jagged affects more than 5% of the surface area 

in the aggregate.

Figures 1, 2, and 3

Figures 1, 2 and 3 on the following pages show to what extent a long type potato 

with one clipped end, and with a remaining length twice the largest diameter of the cut 

surface, may be affected by knobs, clipped knobs or growth cracks.

Visual Aids Refer to photos 100 - 101 and Figures 1 - 3.
26

U.S. No. 2 – maximum allowed

Figure 1 showing the extent a long type potato with one clipped end may be affected by

clipped knobs.

(Approximate weight 16 ounces)
27

U.S. No. 2 – maximum allowed

Figure 2 showing the extent a long type potato with one clipped end may be affected by

growth cracks.

(Approximate weight 10 ounces.

Consider this a straight cut)
28

U.S. No. 2 – maximum allowed

Figure 3 showing “average length” on a tuber with a diagonal cut.

(Approximate weight 14 ounces.

When the cut is diagonal, measure the average length of the tuber)
29

Corky Ring Spot (C)

Corky ring spot is caused by tobacco rattle virus which is transmitted by 

soilborne nematodes. Affected potatoes show brown rings, semicircles, loops and 

spots on the surface and similar brown rings, loops and spots in the interior tissues. 

The skin often cracks over some of the brown slightly sunken rings. The surface 

markings can usually be traced to similar markings within the tuber, but many internal 

brown spots and semicircles appear to be independent of the surface lesions. The 

affected tissues are moderately firm and corky. The characteristic ring-like external and 

internal markings of tubers affected with this disease distinguish it from internal brown 

spot and tuber necrosis caused by alfalfa mosaic. Tubers from crops infected with 

corky ring spot may appear healthy when harvested but develop the disease in storage. 

NOTE: Corky ring spot is listed in FEIRS; however, if not absolutely sure of the defect, 

describe it as it appears.

Scoring Guide

Damage:

When removal causes a loss of more than 5% of the total weight of the potato,

or 

When materially affecting the appearance of the potato.

Serious damage:

When removal causes a loss exceeding 10% of the total weight of the potato, or

When seriously affecting the appearance of the potato.

Visual Aids Refer to photos 46 - 47a.

Dries Stems

The presence of dried stems is rather unusual and occurs during seasons of 

extreme drought when enlarged, tough stems do not readily separate from the tubers. 

Dried stems are not to be scored as a defect. However, at applicant’s request, they 

may be described in the “OTHER” section on market certificates and in the 

“DESCRIPTION OF PRODUCTS” or “REMARKS” section on shipping point certificates.

Elephant Hide (Q)

This defect, caused by environmental and physiological means, manifests itself 

as a severe roughened scaling of the skin unlike typical scab infections. The skin often 

appears darker and thicker than normal with deep checking, cracking or scaling.

Scoring Guide

Damage:

When affecting more than 10% of the surface area of the potato.
30

Serious damage:

When affecting more than 25% of the surface area.

Enlarged Lenticels (Q & C)

This injury occurs in some potato growing areas, especially where there are 

heavy soils and when soaking rains occur during or just preceding harvest. The injury 

may be found in either of two forms:

1) Numerous small blister-like areas around some of the enlarged lenticels with 

watery appearing spots slightly affecting the flesh immediately beneath the 

skin.

2) Numerous small, slightly sunken or pitted areas occurring around the lenticels 

which may or may not be enlarged.

It is believed that both conditions are due to excessively wet weather 

immediately before digging. Pitting may be due to the loss of surplus water located 

under the enlarged lenticels. The pitted condition can develop, or at least change, in 

transit, and progress even after arriving at the market.

When lenticels become infected, raised, coalesced, discolored, or have any 

other characteristic, describe accurately on the certificate. At en route or at destination

inspections when lenticels are abnormally large but are not sunken, raised, or 

discolored, etc., report as a quality factor (see visual aid 105).

Scoring Guide

Damage:

When materially detracting from the appearance of the potato.

Serious damage:

When seriously detracting from the appearance of the potato.

Visual Aids Refer to photos 48 - 49 and 105 - 107.

External Surface Discoloration (C)

Discoloration can be caused by numerous reasons. It can be caused by a rapid 

loss of moisture and oxidation, most apparent on skinned potatoes. This type of 

discoloration usually affects only the surface of the tuber.

Discoloration may also be caused by staining and diseases such as Black Dot. 

Black Dot describes a fungus that produces numerous dot-like, black microsclerotia that 

appear on tubers in conjunction with brown to gray surface discoloration. Even though 

it mostly affects the surface, it may penetrate the underlying flesh up to a depth of 1/16

inch. Black Dot is frequently associated with Silver Scurf. When encountering staining 

or diseases like Black Dot, describe the defect and report as discoloration.
31

Scoring Guide

The following scoring guide applies to skinned and/or unskinned surfaces and 

should be used in conjunction with the official visual aids:

Areas that are light tan or lighter in color and blend with the general appearance 

of the potato should be ignored.

Damage:

When affecting more than 30% of the surface by light tan or light brown colors 

which do not blend, or

When affecting more than 15% of the surface by darker than light tan or light 

brown colors.

Serious damage: 

When affecting more than 60% of the surface by light tan or light brown colors 

which do not blend, or

When affecting more than 30% of the surface by darker than light tan or light 

brown colors.

Visual Aids Refer to photos 108 - 113.

Firmness (C)

In the U.S. Commercial and higher grades, potatoes are required to be firm. In 

the latter part of the storage season, sprouting may contribute to shriveling and 

flabbiness.

§51.1551 Firm. "Firm" means that the potato is not shriveled or 

flabby.

Scoring Guide

Damage:

When the potato is more than slightly shriveled or flabby.

Serious damage:

When the potato is excessively shriveled, spongy or flabby.

Visual Aids Refer to photos 1 & 2.

Folded Ends (Q)

Folded end is the term used to describe areas that fold inward on potatoes. These 

areas develop during the growing process and generally occur on the end of the potato.
32

Scoring Guide

Damage:

When materially detracting from the appearance of the potato.

Serious damage:

When seriously detracting from the appearance of the potato.

Visual Aids Refer to photos 114 - 117.

Flattened or Depressed Areas (C)

These flattened or depressed areas are usually not found until after the potatoes 

have been in storage for several months. This defect is most often the result of 

pressure at points of contact with adjacent potatoes or floor.

These areas will exhibit a rubbery feel and a slight wrinkling or a soft elasticity of 

the skin over the flattened area. If these qualities are not present on the flattened or 

depressed areas the potato is more likely to be affected by a shape problem.

Scoring Guide

Flattened or depressed areas may have developed grayish to black discoloration 

of the underlying flesh. If discoloration of the underlying flesh is present and the 

areas affected does not exceed the area allowed then score on a waste basis 

only that tissue affected by discoloration (see section on Bruises).

Score as damage or serious damage when the flattened or depressed area(s) 

covers more surface area than allowed as outlined in the following chart or when 

discoloration of the underlying flesh causes more waste than is permitted by the 

grade (5% or 10%).

MAXIMUM AREA ALLOWED FOR FLATTENED OR DEPRESSED AREAS

Diameter Weight No. 1

(aggregate area)

No. 2

(aggregate area)

Potato is: Potato is: Not more than: Not more than:

Less than 2 in. Less than 4 oz. 1/2 in. 1 in.

2 to 2-1/2 in. 4 to 6 oz. 1 in. 1-1/2 in.

More than 2-1/2 to 3 in. More than 6 to 8 oz. 1-1/4 in. 1-3/4 in.

More than 3 to 3-1/2 in. More than 8 to 14 oz. 1-1/2 in. 1-7/8 in.

More than 3-1/2 to 4 in. More than 14 to 20 oz. 1-3/4 in. 2 in.

More than 4 to 4-1/2 in. More than 20 to 28 oz. 2 in. 2-1/4 in.

More than 4-1/2 to 5 in. More than 28 to 36 oz. 2-1/4 in. 2-3/4 in.

More than 5 in. More than 36 oz. 2-1/2 in. 3-1/4 in.

Visual Aids Refer to photo 137.
33

Flea Beetle (Q)

This injury is caused by a small insect that feeds on or near the surface, which

usually forms brown splinter-like pegs extending 1/8 to 1/4 inch into the potato.

Scoring Guide

Damage:

When materially detracting from the appearance of the potato, or 

When removal causes a loss exceeding 5% of the total weight of the potato, or

When affecting more than 5% of the surface area in the aggregate.

Serious damage:

When seriously detracting from the appearance of the potato, or

When removal causes a loss exceeding 10% of the total weight of the potato, or

When affecting more than 10% of the surface area in the aggregate.

Visual Aids Refer to photo 50.

Freezing/Freezing Injury (Q & C)

§51.1562 Freezing. “Freezing” means that the potato is frozen or shows 

evidence of having been frozen.

Freezing may occur when temperatures drop below 30.9°F. Inspectors must 

always clearly distinguish between potatoes in a frozen condition and those affected by 

freezing injury. The term “frozen” should only be used when ice crystals are present. 

Use the term “freezing injury” when it is evident that the potatoes are not in a frozen 

condition at the time of inspection.

Symptoms vary greatly. Tissue at the stem end of the tuber is more sensitive to 

freezing than those at the bud end. Cells around the vascular ring are more susceptible 

to freezing than other cells in the potato. Potatoes injured by freezing may be firm but

show internal discoloration near the stem end. Potatoes that were frozen will become 

soft and watery upon thawing (wet breakdown), or, in dry air, become dry, leathery, and 

granular with chalky white masses of starch. Often there is a clear line of demarcation 

between affected flesh and healthy flesh. Field freezing will generally manifest first on 

areas that are sunburned (exposed to the elements) and develop bluish-gray blotches 

beneath the skin along with soft, flabby, watery areas.

To provide a clear picture of the freezing in the lot, it is necessary to search for 

clues as to when and where freezing occurred. For example, freezing scattered 

throughout the load may indicate that it occurred in the field or during storage, whereas 

freezing found only along the floor and sidewall of the railcar or trailer may indicate that 

it occurred in transit.
34

When the location of injury indicates when or where the freezing occurred, report 

the facts. For example: “Freezing injury so located as to indicate it occurred after 

packing, but not in present location” or “Freezing occurred on above mentioned trailer.”

When a freezing pattern is determined within a lot, it is important to provide the 

following information:

 Record pulp temperatures taken at various locations.

 Determine and record extent of injury in load and containers.

 Determine and record degree to which individual specimens are affected.

 Describe the pattern of freezing or freezing injury in clear, concise terms.

 Describe using general terms rather than percentages.

When a freezing pattern is found, the inspector will write a freezing statement 

rather than reporting percentages. When a pattern is not present, the individual tuber 

will be scored using the guide below:

Scoring Guide

Potatoes that are frozen are scored as serious damage against the restricted 

frozen/wet breakdown/soft rot tolerance.

Potatoes showing freezing injury that are soft, wet, and leaking will be reported 

as “Wet breakdown following freezing injury” and scored as serious damage

against the restricted frozen/wet breakdown/soft rot tolerance.

When indentified, potatoes showing dry type freezing injury, found scattered 

throughout the container and load, will be considered a quality factor and scored 

as serious damage against the tolerance for external defects or, when not

visible, internal defects.

Visual Aids Refer to photos 29 - 31.

Grass Damage (Q)

There are several grasses that cause damage to potatoes such as quack, nut 

and wire grass. The damage is caused by the grass roots growing into and even 

through the potatoes. The term "grass damage" should be used in reporting all types 

of this damage.

Scoring Guide

Damage:

When affecting the flesh of the potato and removal causes loss of more than 5% 

of the total weight of the potato.

Serious damage:

When affecting the flesh of the potato and removal causes loss of more than

10% of the total weight of the potato.

Visual Aids Refer to photo 54.
35

Greening (C)

Potatoes exposed to light either before or after harvest gradually turn green at 

the surface due to the development of chlorophyll. Greening that occurs before harvest 

is called sunburn (see Sunburn section). The degree of greening varies according to 

the type (incandescent, fluorescent, sun) and brightness of light, time period, and 

thickness of potato epidermis. Usually immature potatoes green more readily than 

mature ones. Greening caused by artificial light rarely affects the flesh and generally 

does not produce solanine, an alkaloid that is poisonous if taken in sufficient amounts.

Scoring Guide

Damage:

When removal causes a loss exceeding 5% of the total weight of the potato, or

When green color affects more than 25% of the surface area in the aggregate.

Serious damage:

When removal causes a loss exceeding 10% of the total weight of the potato or,

When green color affects more than 50% of the surface area in the aggregate.

Visual aids Refer to photo 55.

Growth Cracks (Q)

Growth cracks may be caused by very rapid growth, as when a rainy period follows a 

long dry spell. Growth cracking usually follows the long axis of the potato and results 

from internal pressure exceeding the tensile strength of surface tissues during tuber 

enlargement.

Scoring Guide

Damage:

When affecting more than 1/2 the length in the aggregate on round varieties, or 

When affecting more than 1/3 the length in the aggregate on long varieties, or

When the depth is greater than outlined in the chart below.

Serious damage:

When affecting more than 3/4 the length of the potato in the aggregate, or

When the depth is greater than outlined in the chart below.
36

DEPTH ALLOWED FOR GROWTH CRACKS

Diameter Weight No. 1 (Depth) No. 2 (Depth)

Potato is: Potato is: Not more than: Not more than:

Less than 2 in. Less than 4 oz. 1/8 in. 1/4 in.

2 to 2-1/2 in. 4 oz. to 6 oz. 1/4 in. 3/8 in.

More than

2-1/2 to 3 in.

More than

6 oz. to 8 oz. 3/8 in. 1/2 in.

More than 3 in. More than 8 oz. 1/2 in. 5/8 in.

Visual Aids Refer to photos 118 - 120.

Grub Damage (Q)

This is a very common insect injury affecting potatoes. Grubs eat away at the 

skin and flesh of the potatoes leaving holes, usually of considerable size.

Scoring Guide

Damage:

When removal causes a loss of more than 5% of the total weight of the potato, 

or

When affecting more than 5% of the surface area (i.e. more than 3/4 inch on a 

2-1/2 inch or 6 ounce potato)

Serious damage:

When removal causes a loss of more than 10% of the total weight of the potato, 

or

When affecting more than 10% of the surface area (i.e. more than 1-1/4 on 2-1/2 

inch or 6 ounce potato)

Visual Aids Refer to photos 56 & 57.

Mechanical Damage (Q)

“Mechanical Damage” is not a fully descriptive term for potatoes and should not

be used on the certificate. Instead, describe the damage caused by harvesting and 

handling in terms of bruises or cuts (see Bruises and Cuts/Clipped Ends sections).
37

Nematode (Root Knot) (Q)

This injury is found in varying amounts in most commercial potato areas in the 

United States. Potatoes with advanced infestation usually have a roughened, irregular, 

bumpy or warty appearance due to the presence of galls on the outer surface. When 

such potatoes are cut, the egg masses are seen in abundance scattered throughout the 

outer tissues with most of them approximately 1/8 to 1/4 inch beneath the skin. To the 

naked eye they appear to be somewhat discolored, slightly water-soaked spots. 

Deposits of eggs in the flesh may hatch out after harvest causing a re-infestation of 

feeding nematodes, which generally are not visible to the unaided eye.

Infestation may sometimes show no external symptoms. When internal injury 

conditions are found without external symptoms, use the same sampling procedure for 

determining percentages as you would for hollow heart and internal discoloration.

Scoring Guide

Damage:

When removal causes a loss of more than 5% of the total weight of the potato.

Serious damage:

When removal causes a loss of more than 10% of the total weight of the potato.

Visual Aids Refer to photo 69.

Pink Eye (C)

Pink eye is characterized by pinkish blotches near the eyes and mostly around 

the blossom end of the tubers due to the pink underlying tissue. The internal tissue is 

firm to corky with pink to reddish-brown color. Black areas and cavities may also occur. 

The discolored tissues around the eyes may turn light brown, become wrinkled and 

cracked. Pink eye may be confused with late blight, but it does not have the brick-red 

granular tissue that is characteristic of blight.

This defect, although rare, is sometimes seen in the markets. If during 

inspection of potatoes this defect is found and is clearly identified as pink eye based on 

photos 72 and 73 of the USDA Official Visual Aids for Potatoes, the potato should be 

reported as pink eye. If the defect cannot be clearly identified as "pink eye" the defect 

should be described. 

Scoring Guide

Damage:

When materially detracting from the appearance of the potato, or 

When removal causes a loss of more than 5% of the total weight of the potato.

Serious damage:

When seriously detracting from the appearance of the potato, or 
38

When removal causes a loss of more than 10% of the total weight of the potato.

Visual Aids Refer to photos 72 - 74.

Rhizoctonia (Black Scurf) (Q)

Rhizoctonia, commonly called black scurf, is present in all potato-growing areas. 

Black or dark brown sclerotia develop on surfaces of mature tubers, which may be flat 

and superficial or large irregular lumps resembling soil that will not wash off. However, 

Rhizoctonia has no relation to cleanliness. Rhizoctonia does not penetrate the tuber 

skin and may be scratched or flicked off with a fingernail.

Scoring Guide

Damage:

When affecting more than 15% of the surface in the aggregate.

Serious damage:

When affecting more than 50% of the surface in the aggregate.

Visual Aids Refer to photos 125 & 126.

Rodent and Bird Damage (Q)

Frequently rodents, such as field mice, gophers and rabbits gnaw into potatoes 

and cause cavities. Generally the cavities made by rodents bear the marks of the teeth 

of the animal in the form of corrugations or ridges. Bird damage, such as is caused by 

chickens or other birds, is easily identified by the pit-like markings lining the cavity.

Scoring Guide

Damage:

When removal causes a loss exceeding 5% of the total weight of the potato, or

When affecting more than 5% of the surface area (i.e. more than 3/4 inch on a 2-

1/2 inch or 6 ounce potato).

Serious damage:

When removal causes a loss exceeding 10% of the total weight of the potato, or

When affecting more than 10% of the surface area (i.e. more than 1-1/4 inch on 

a 2-1/2 inch or 6 ounce potato).

Visual Aids Refer to photo 77.

Rough Raised Netting (Q)

Netting affects the skin of potatoes; it may be fine, raised and/or rough. 

However, netting is only scorable when it is rough and raised.
39

Scoring Guide

Score as damage when netting is rough and raised and more than 50% of the 

surface. Rough raised netting is not scored as serious damage.

Visual Aids Refer to POT-L-1(Official Visual Aids for Potatoes), page 32.

Russeting (Q)

Russeting which occurs naturally on russet varieties, or on some red and white 

varieties, is not scorable. Only score russetting when not characteristic for the variety.

Scoring Guide

Score non-characteristic russeting as damage when affecting more than 50% of 

the surface area in the aggregate. Do not score as serious damage.

Visual Aids Refer to photos 127 & 128.

Scab (Q)

Common scab, of which there are three types – pitted, russet, and surface, and 

powdery scab are both soil inhabiting micro-organisms that have been known to 

mankind since the nineteenth century. Both pathogens are universally distributed over 

the potato growing regions of the world and are often described as fungi. However, 

common scab is more closely related to bacteria and powdery scab is related to the 

slime molds. These diseases invade the surfaces of tubers and the plant responds by 

developing corky scabs. Severe attacks of common scab can occur if the soil is dry 

during early tuber development. Powdery scab is more prevalent under wet conditions. 

Common and powdery scabs do not greatly affect the edible quality, but they are 

commercially important since cosmetic damage lowers the value of the crop.

Different types of scabs may be difficult to distinguish from one another. When 

no definite determination can be made as to the type of scab, or a combination of scabs 

are present, the inspector will identify the defect as “scab” and score it as damage when

materially detracting from the appearance and serious damage when seriously 

detracting from the appearance. When the type of scab can be identified, please see 

the following scoring guides for each type of scab.

Pitted Scab (Q)

Pitted scab is the result of early infections, the uninjured tissues growing up 

around the affected areas causing the pitted depressions. Such pits may be only very 

slight depressions or they may extend into the potato 1/4 inch or more.

Scoring Guide (based on a potato 2-1/2 inches in diameter or 6 ounces in weight)

Damage:

When removal causes a loss exceeding 5% of the total weight of the potato, or
40

When affecting an aggregate area of more than 1/2 inch (correspondingly lesser 

or greater areas in smaller or larger potatoes).

Serious damage:

When removal causes a loss exceeding 10% of the total weight of the potato, or

When affecting an aggregate area of more than 1 inch (correspondingly lesser or 

greater areas in smaller or larger potatoes).

Visual Aids Refer to photos 129 & 130.

Russet Scab (Q)

Russet scab is a roughening, scurfing, or cracking of the tuber skin, sometimes 

occurring in localized areas or sometimes over most of the tuber surface. The affected 

tissues vary from light tan to brown in color, and may consist of a superficial cork-like 

layer or have a cushion-like appearance.

Scoring Guide

Damage:

Smooth and affecting more than 1/3 of the surface area, or

Rough and affecting more than 10% of the surface area.

Serious damage:

Rough and affecting more than 25% of the surface area.

Visual Aids Refer to photos 77a - 77b and 143.

Surface Scab (Q)

Affected areas usually appear as individual circular spots from 1/4 to 3/4 inch in 

diameter which are slightly raised or sunken, rough or corky, and usually darker than 

the normal skin color.

Scoring Guide

Damage:

When affecting more than 5% of the surface area in the aggregate.

Serious damage:

When affecting more than 25% of the surface area in the aggregate.

Visual Aids Refer to photos 78 & 78a.

Powdery Scab (Q)

This disease is characterized by jellylike areas under the skin which evolve into 

spore balls. When mature, these spore balls turn yellow, and then brown to black, and 
41

the epidermis (skin) splits and peels back to expose the dusty spore mass formed 

beneath. Sometimes these pustules enlarge to form cankers in the tuber.

Scoring Guide

Damage:

When affecting more than 5% of the surface area in the aggregate.

Serious damage:

When affecting more than 25% of the surface area in the aggregate.

Second Growth (Q)

Second growths are commonly attributed to high field temperatures and drought. 

It may, however, result from regeneration following any condition causing irregular rates 

of tuber development such as uneven availability of nutrients or moisture, extremes in 

temperature, or vine defoliation from hail or frost. When growing conditions improve, 

resumption of tuber growth becomes evident as second growth.

Scoring Guide

Damage:

When materially detracting from the appearance of the potato.

Serious damage:

When seriously detracting from the appearance of the potato.

Visual Aids Refer to photos 131 - 133.

Shape (Q)

The U.S. Grades for potatoes have the following requirements for shape:

U.S. No. 1 & U.S. Commercial: Fairly well shaped.

U.S. No. 2: Not seriously misshapen.

Definitions:

§51.1556 Well shaped. "Well shaped" means that the potato has the 

normal shape for the variety.

§51.1557 Fairly well shaped. "Fairly well shaped" means that the 

potato is not materially pointed, dumbbell-shaped or otherwise

materially deformed.
42

§51.1558 Seriously misshapen. "Seriously misshapen" means that 

the potato is seriously pointed, dumbbell shaped or otherwise badly 

deformed.

Scoring Guide

Potatoes which are slightly curved, slightly pointed, or slightly dumbbell-shaped 

are considered fairly well shaped and should not be scored. Score as damage

when failing to meet the requirements of fairly well shaped and report as “not 

fairly well shaped.”

When shape seriously detracts from the appearance or materially deforms the 

potato, score as serious damage and report as “seriously misshapen.”

Potatoes that are seriously misshapen because of growth cracks or second 

growth should be scored for those defects.

Visual Aids Refer to photos 14 - 17 and 18 - 22c 

Silver Scurf (C)

This is a fungal disease that primarily affects the skin and therefore affects the 

appearance of the potato. Although potatoes from any growing area may be affected it 

is most often found on potatoes grown in the northern half of the continent and more 

frequently on potatoes that have been in storage. The occurrences of superficial 

brownish spots more or less circular in outline, constitutes the first symptoms. As the 

disease progresses the affected areas becomes silvery brown and may coalesce to 

cover most of the tuber surface. The affected areas may not be as conspicuous on dry 

potatoes, but when the potatoes are wet, the silvery appearance may sometimes be 

more readily seen. In severe cases the entire surface of the tuber may be affected with 

little or no contrast with the natural skin color. In advanced stages of the disease 

affected areas begin to shrivel or wrinkle.

Scoring Guide (Apply to any shade or color of the defect)

Damage:

When affecting more than 50% of the surface area of the potato.

Serious damage:

When wrinkling of the skin affects more than 50% of the surface area.

Visual Aids Refer to photos 81 - 82g.

Similar Varietal Characteristics (Q)

§51.1550 Similar varietal characteristics. "Similar varietal 

characteristics" means that the potatoes in any lot have the same 

general shape, color and character of skin, and color of flesh.
43

All grades require potatoes to be of similar varietal characteristics, except when 

designated as a mixed or specialty pack. When so designated, the similar varietal 

characteristic requirement does not apply. All packages in a lot so designated must 

have more than one type of potato in the package. If an inspector encounters 

packages in a mixed lot that do not contain mixed types, those packages constitute a 

separate lot.

Scoring Guide

When not designated as a mixed or specialty pack, potatoes that are not of 

similar varietal characteristics are reported as “Dissimilar varietal 

characteristics” and scored against the external defect tolerance for the grade

being applied.

Skin Checks (C)

Potatoes harvested during low temperature periods, or stored to minimal 

temperatures, or when tender, are subject to small superficial bruises resembling 

"fingernail cuts." These checks occur during the handling, storage or grading 

operations. They are almost invisible on washed potatoes and appear as small 

dampened spots on dry packed potatoes.

Scoring Guide

Damage:

When materially affecting the appearance of the potato.

Serious damage:

When seriously affecting the appearance of the potato.

Visual Aids Refer to photos 134 & 135.

Sprouts (External) (C)

Sprouts are the result of eyes on the potato that begin to grow. They sometimes 

occur singularly or in clusters. Their length varies according to what stage of growth 

they are in and progress rapidly at non-refrigerated temperatures. Growth generally 

begins opposite the stem end of the potato. Whether scorable or not, the presence of 

sprouts shall always be described and reported on the certificate.

Decayed or slimy sprouts should not be scored unless they exceed the length or 

appearance requirements, but they may be reported at the request of the applicant and 

reported as "not affecting grade."
44

Scoring Guide

Shipping Point:

Damage:

When more than 5% of the potatoes in any lot have any sprout more than 1/4 

inch in length, or

When numerous individual and/or clusters of sprouts materially detract from the 

appearance of the potato.

Serious damage (only score serious damage by sprouts for U.S. 

Commercial and U.S. No. 2 grades):

When more than 10 percent of the potatoes in any lot have any sprout more than 

1/2 inch in length, or

When numerous individual and/or clusters of sprouts seriously detract from the 

appearance of the potato.

En Route or At Destination:

Damage:

When more than 5% of the potatoes in any lot have any sprout more than 1/2 

inch in length, or

When numerous individual and/or clusters of sprouts materially detract from the 

appearance of the potato.

Serious damage (only score serious damage by sprouts for U.S. 

Commercial and U.S. No. 2 grades):

When more than 5% of the potatoes in any lot have any sprout more than 1 inch 

in length, or

When numerous individual and/or clusters of sprouts seriously detract from the 

appearance of the potato.

Visual Aids Refer to photo 136.

Individual Sampling and Reporting Requirements for Sprouts

There is no limitation on the percentage of sprouts in individual samples, 

providing the average does not exceed the allowance for their respective grades. 

When a lot shows sprouts exceeding the requirement for that specific grade, the total 

percentage of scorable sprouts will be reported on the certificate to indicate whether or 

not the lot is damaged or seriously damaged by sprouts. For example, if 8% sprouts 

are scored in a U.S. No. 1 lot, record the percentage in the average defects column. 

However, if 5% sprouts are scored in a U.S. No. 1 lot, the percentage of scorable 

sprouts will not be reported on the certificate unless requested by the applicant. When 

the percentage is requested by the applicant, report the facts in the “OTHER” or 
45

“REMARKS” section. Example: “Scorable sprouts range 2 to 9, average 5%, not 

affecting grade and reported at applicant’s request.”

When the lot fails to grade only account of sprouts, report the fact in the grade 

statement. For example, “Fails to grade U.S. No. 1 account condition (sprouts).”

The presence of sprouts, when not exceeding the length or appearance 

requirements, are always reported on the certificate in the “OTHER” or “REMARKS” 

section using general terms. For example: “Most samples show some to many 

potatoes having barely visible sprouts, some samples show none.”

When sprouts are partly broken, flabby, partially shriveled or dried, but still 

attached to the potato, they will be scored if the sprout exceeds the requirement for the 

specific grade.

U.S. No. 1 Quality for Sprouts

At shipping point it is permissible to determine and certify percentage of U.S. No. 

1 Quality in potatoes that are out of grade on account of sprouts. Inspectors should 

allow 5% sprouts, deducting only that amount in excess of 5% in determining the 

percentage of U.S. No. 1 Quality. For example, in a lot having 10% defects, 15% 

sprouts and no undersize, the percentage of U.S. No. 1 Quality is 80%.

New Potato Growth Attached by Fleshy Stems (Q)

Any new potato development will be scored on the basis of second growth even 

though the new potato is attached by a fleshy stem having the appearance of a sprout. 

Sprout development with no potato development is to be scored the same as sprouts.

Sunburn (Q)

Sunburn is caused by tubers being exposed directly to sunlight when 

insufficiently covered with soil. Often the stem end is affected since it is usually the 

portion of the tuber that is exposed to sunlight. Altitude, intensity of sunlight, and length 

of exposure directly affects the amount of chlorophyll (green) in the skin, but more

importantly affects the development of yellow to green discoloration in the flesh. 

Artificial light rarely discolors the flesh. However, sunlight may cause chlorophyll 

production to penetrate deeply into the tuber causing the affected area to taste bitter. 

In addition, sunlight causes solenoid production, an alkaloid that is poisonous if taken in 

sufficient dosages.

Inspectors should always cut potatoes to determine the amount of waste. Any 

green color or marked yellowing of the flesh is considered objectionable. When in 

doubt as to whether the flesh is green or yellow, compare it with a slice from an 

unaffected potato of the same lot.
46

Scoring Guide

Damage:

When removal causes loss of more than 5% of the total weight of the potato.

Serious damage:

When removal causes loss of more than 10% of the total weight of the potato.

Visual Aids Refer to photos 86 & 87.

Sunken Discolored Areas (C)

These areas vary in size and are sunken in comparison with the adjacent 

surface. They are darker than the skin color of the potato and vary in their degree of 

darkness from light brown to dark brown to black.

Scoring Guide

The amount scorable for sunken discolored areas corresponds directly with the 

size of the potato. Refer to the following chart for the maximum area allowed:

MAXIMUM AREA ALLOWED FOR SUNKEN DISCOLORED AREAS

Diameter Weight No. 1 (aggregate) No. 2 (aggregate)

Potato is: Potato is: Not more than: Not more than:

Less than 2 in. Less than 4 oz. 3/8 in. 3/4 in.

2 to 2-1/2 in. 4 to 6 oz. 3/4 in. 1 in.

More than 2-1/2 to 3 in. More than 6 to 8 oz. 1 in. 1-1/4 in.

More than 3 to 3-1/2 in. More than 8 to 14 oz. 1-1/4 in. 1-1/2 in.

More than 3-1/2 to 4 in. More than 14 to 20 oz. 1-1/2 in. 1-3/4 in.

More than 4 to 4-1/2 in. More than 20 to 28 oz. 1-3/4 in. 2 in.

More than 4-1/2 to 5 in. More than 28 to 36 oz. 2 in. 2-1/4 in.

More than 5 in. More than 36 oz. 2-1/4 in. 2-1/2 in.

Visual Aids Refer to photo 138.

Sunken Discolored Areas with Underlying Flesh Discolored (C)

This defect is most noticeable on storage potatoes and appears to be related to 

bruising and rough handling at time of harvesting or while in storage. In some cases, 

sunken areas alone will not affect the appearance sufficiently to cause damage or 

serious damage and it will be necessary for the inspector to cut to determine if there is 

discoloration of the underlying flesh.
47

Scoring Guide

Damage:

When removal causes a loss of more than 5% of the total weight of the potato.

Serious damage:

When removal causes a loss of more than 10% of the total weight of the potato.

Visual Aids Refer to photo 138 for ID only. Cut to determine underlying discoloration.

Sunken Discolored Sticky Areas (C)

Discoloration of this kind is more serious than the previous types as soft rot may 

often develop in transit. This condition most frequently occurs on skinned areas of 

potatoes which are harvested during extremely hot weather with no protection from the 

sun or wind. Cutting may be done to determine sticky areas.

Scoring Guide

The amount scorable for sunken discolored sticky areas corresponds directly 

with the size of the potato. Refer to the following chart for the maximum area allowed:

MAXIMUM AREA ALLOWED FOR SUNKEN DISCOLORED STICKY AREAS

Diameter Weight No. 1 (aggregate) No. 2 (aggregate)

Potato is: Potato is: Not more than: Not more than:

Less than 2 in. Less than 4 oz. 1/4 in. 1/2 in.

2 to 2-1/2 in. 4 to 6 oz. 1/2 in. 3/4 in.

More than 2-1/2 to 3 in. More than 6 to 8 oz. 3/4 in. 1 in.

More than 3 to 3-1/2 in. More than 8 to 14 oz. 1 in. 1-1/4 in.

More than 3-1/2 to 4 in. More than 14 to 20 oz. 1-1/4 in. 1-1/2 in.

More than 4 to 4-1/2 in. More than 20 to 28 oz. 1-1/2 in. 1-3/4 in.

More than 4-1/2 to 5 in. More than 28 to 36 oz. 1-3/4 in. 2 in.

More than 5 in. More than 36 oz. 2 in. 2-1/4 in.

Visual Aids Refer to photo 138 for ID only.

Surface Cracks (Q)

Surface cracks are the superficial cracking of the skin of some varieties of 

potatoes and should not be confused with russeting. The cracks are generally wider 

and more pronounced than russeting.

These guides are to be used in conjunction with the official visual aids:
48

Scoring Guide

Areas affected by fine net-like cracking should be ignored.

Damage: 

When smooth shallow cracking affects more than 1/3 of the surface, or

When rough deep cracking affects more than 5% of the surface area.

Serious damage: 

When rough deep cracking affects more than 10% of the surface.

Visual Aids Refer to photos 139 - 142.

Tuber Moth Damage (C)

Most tuber moth damage occurs from larvae which hatch out either just prior to 

digging or after the potatoes are harvested. Eggs are deposited by the insect, usually 

at or near the eyes, and are most likely to be found on sunburned areas. The larvae 

hatch out and enter the potato, usually through the eye. They make tunnels at first 

close to the surface, and finally riddle the potatoes with deeply penetrating channels, 

making them unmarketable. Since this defect usually gets drastically worse in transit, 

the marketing quality is materially affected when any evidence is found at shipping 

point.

It is entirely possible that there may be no damage visible upon casual 

observation at shipping point in a lot of potatoes which may show a considerable 

percentage of tuber moth damage upon arrival in receiving markets. At market the 

appearance or waste factors should be used in determining damage.

Scoring Guide

Damage:

When materially detracting from the appearance of the potato, or 

When removal causes loss of more than 5% of the total weight of the potato.

Serious damage:

Whenever live larvae are present, or

When seriously detracting from the appearance of the potato, or

When removal causes loss of more than 10% of the total weight of the potato.

Visual Aids Refer to photos 88 & 89.

Wireworm (Q)

There are several types of wireworm holes that cause damage to potatoes. The 

type of hole will depend to a certain extent on the state of development of the potato at 

the time of the injury. When the injury is fairly fresh, it may appear as a small dirty hole. 
49

If it occurred in the early stage of development of the potato, the hole may be lined with 

new skin growth. All types of worm holes should be reported using the terms "worm 

damage."

Scoring Guide

Damage:

When affecting the flesh of the potato and removal causes loss of more than 5% 

of total weight of potato.

Serious damage:

When affecting the flesh of the potato and removal causes loss of more than

10% of total weight of potato.

Visual Aids Refer to photos 92 & 93.

INTERNAL DEFECTS

§51.1565 Internal defects. “Internal defects” are defects which 

cannot be detected without cutting the potato.

Internal Defects are defects which generally cannot be detected without cutting 

the potato. However, a few factors which affect the vascular bundles or interior portion 

of the potato may be detectable without cutting due to the discolored tissue which is 

apparent through the skin. These defects shall also be considered internal defects.

Both the U.S. and Canada score internal discoloration on the same basis (i.e. 5-

10% or 3-6 spots). The U.S. generally uses the following specific defect name: net 

necrosis, stem end browning, vascular discoloration, internal brown spot, heat or 

drought necrosis, internal black spot, internal mahogany browning and internal pink to 

purple discoloration. Canadian inspectors however, use the term "Internal 

Discoloration" when reporting these defects.

Any defect shall be considered as an internal defect when the interior flesh 

of the potato is affected but there is no apparent damage to the surface area of 

the potato.

When inspecting potatoes, internal defects are as important as external defects, 

but much less apparent; therefore, potatoes must be cut to determine the amount of 

damage and serious damage. All types of internal defects should be judged 

immediately after cutting as the appearance of the flesh of the cut potato may be 

affected by reddish-brown discoloration caused by oxidation.

Color comparator POT-CC-1 is ONLY to be used when scoring light brown 

discoloration associated with hollow heart or brown center as noted in the 

scoring guide for these defects. Use color comparator Pot-CC-2 only for internal 

black spot.
50

Sampling to Determine the Presence of Internal Defects

Sampling to accurately determine the percentage of internal defects is difficult 

and requires the inspector to use good judgment in all circumstances. While inspecting 

each sample the inspector will cut a minimum of five potatoes selected totally at 

random from that sample. An inspector may, at their discretion and judgment, make 

additional cuts on potatoes in the sample to determine if internal defects are present. If 

no scorable defects are found in this sample the inspector will continue to cut a 

minimum of five potatoes per sample.

When any scorable internal defects are found in this preliminary examination, a 

twenty pound sample, which includes potatoes cut in the preliminary examination, will 

be drawn from the sample and cut to determine the percentage of all internal defects in 

that sample. If the original sample is 20 pounds the whole sample is cut. If the original 

sample is larger, only 20 pounds shall be cut for internal defects.

Each sample stands on its own. When a scorable defect is found, the inspector 

must cut 20 pounds; otherwise, the inspector cuts a minimum of five potatoes.

In-Line only: When the internal defects in a 20 pound cut sample cause the lot 

to cease meeting grade (the application of tolerances is exceeded, etc.), the inspector 

must cut 20 pounds of the next sample to ensure that the issue has been corrected and 

that the potatoes being run now meet grade. If the lot meets grade again, the inspector 

can resume cutting a minimum of five potatoes until a scorable defect is found.

All cut samples must be recorded on the notesheet. When no scorable internal 

defects are found, the number of potatoes cut for each sample (i.e. “5”) must be 

recorded in the sample size column on the notesheet. This number indicates that “5” or 

more potatoes were cut, not five or more pounds. It is not necessary to place a “0” next 

to the number of potatoes cut to show that there were no scorable internal defects (if 

the sample size is not 20 pounds, there were no scorable internal defects).

Percentages of scorable internal defects in a sample will be based upon twenty 

pounds.

When specifically requested by an applicant, the entire contents of the container 

may be cut for internal defects. This is only done when any scorable defects are found 

in the initial cut sample. Report in the “REMARKS” section on the certificate and 

notesheet that the “Entire contents cut at applicant’s request.” If requested to cut the 

entire contents, percentages of internal defects are based on the entire container. If a 

lot includes cut samples of varying sizes, separate determination of percentages in 

each sample must be made to accurately determine the average percentage of internal 

defects or if the sample has exceeded the application of tolerances.

This same cutting policy, except for the in-line instructions, will be applied to the 

sub-sample units for bulk loads.
51

Methods of Cutting to Determine Internal Defects

Internal defects, such as internal black spot, vascular browning, fusarium wilt, net 

necrosis, other necrosis, stem end browning, and other types of internal discoloration, 

affecting the vascular ring or occurring between the vascular ring and the skin of the 

potato are scored on a waste basis. Internal defects, such as hollow heart or hollow 

heart with discoloration, light brown discoloration (brown center), internal brown spot 

and similar discoloration (heat necrosis) occurring entirely within the vascular ring are 

considered on the basis of the diameter of the affected area, and in the case of internal 

brown spot and similar discoloration, also considered are the number of spots (see 

illustrations on methods of cutting to determine internal defects).

A thin slice exploratory cut will be made at the stem end of the tuber. If the 

exploratory cut reveals a defect follow the appropriate method of cutting for the type of 

defect found. Also, make a lengthwise cut on the same specimen to ensure that all 

internal defects have been accounted for.

Once preliminary cutting reveals the type of internal defects, one of the following 

methods should be used to determine percentages:

Net Necrosis, Stem End Browning and Other Similar Discoloration:

Clip stem end of tuber.

In cutting to remove waste from net necrosis and other similar discoloration at 

the stem end, inspectors should use a straight cut if the discoloration extends more 

than 1/2 of the circumference around the potato. If the discoloration affects 1/2 or less 

of the circumference around the potato, the cut should be made on that particular side, 

using a curved cut so that an excessive amount of uninjured flesh will not be removed.
52

Internal Brown Spot and Similar Discoloration Occurring Entirely within Vascular

Ring:

A - Potato cut in half-inch slices. B - Slices laid down for examination. 

 Dotted lines indicate location of Consider only spots on upper side.

 internal discolored areas.

As illustrated above, potatoes should be sliced crosswise at intervals of 1/2 inch 

in order to detect any discoloration that is present. Lay all the slices down in one 

direction, only the spots visible on the upper side as shown in the above illustration 

would be considered in determining whether the potato should be scored. Allow the 

equivalent of 3 spots 1/8 inch in diameter in a potato 2-1/2 inches in diameter or 6 

ounces in weight, or corresponding numbers of spots in different size potatoes. Double 

the number of such spots is permitted before scoring as serious damage.

Hollow Heart or Hollow Heart with Discoloration and Light Brown Discoloration

(Brown Center):

Cut tuber lengthwise and parallel to the flat side.

Cavities and light brown discoloration are scored according to the Guide for 

Maximum Area Allowed on various potato sizes (see previous section.) After 

determining the size of the potato use a clear diameter gauge to determine if the potato 

is damaged or seriously damaged. This is done by laying the appropriate circle of the 

area gauge (from chart) over the hollow or brown area of the potato.
53

The best effort should be made to position the gauge so that the majority of the 

defect falls within the circle. 

When every bit of the defect falls within the circle, the potato is not scored. 

When any amount of hollow heart falls outside the circle, the potato is scored. 

When any light brown discoloration, whether present with hollow heart or 

alone (brown center), falls outside the area and is as dark as or darker than the 

color comparator POT-CC-1, the potato is scored.

Visual Aids Refer to photos 122a - 122e.

Method of Cutting to Determine External or Internal Waste

Only a normal amount of uninjured tissue, such as in the ordinary process of 

preparing for use, should be removed when examining an external or internal defect.

When removing shatter bruises or other defects on the side of the potato, as a 

general policy, use a round or curved cut. The degree of curve used will depend to a 

certain extent on the shape of the potato and whether the defect is on the flat or round 

side.

Use a straight cut on stem end defects if the discoloration extends more than 1/2 

of the circumference around the potato. When the discoloration affects 1/2 or less of 

the circumference around the potato, the cut should be made on that particular side, 

using a curved cut so that an excessive amount of uninjured flesh will not be removed.

Blackheart (C)

The presence of blackheart generally occurs when the potatoes are exposed to 

high temperatures with an insufficient air supply. The internal symptoms are a dark 

gray to purplish discoloration which later becomes jet black. The discolored areas are 

usually sharply set off from the healthy tissues. Generally the discoloration is restricted 

to the heart of the potato, but frequently radiates to the exterior as well. 

Scoring Guide

Serious damage:

Potatoes in all grades must be free from any amount of blackheart.

Visual Aids Refer to photos 27 & 28.

Heat or Drought Necrosis (Q)

Heat or drought necrosis causes slate-gray to golden-yellow or brown 

discoloration of the water vessels of the affected tubers. It is most pronounced in the 

vascular system and may occur at either the stem end or the bud end. It also is in the 

tissues between the vascular ring and the tuber surface. Discolored tissue near the 

surface makes the skin appear dark, but generally there are no external symptoms.
54

Scoring Guide 

When occurring outside of the vascular ring:

Damage:

When removal causes loss of more than 5% of the total weight of the potato.

Serious damage:

When removal causes loss of more than 10% of the total weight of the potato.

When occurring entirely within the vascular ring (based on a potato 2-1/2 inches

in diameter or 6 ounces in weight):

Damage:

When more than the equivalent of 3 scattered spots 1/8 inch in diameter

(correspondingly lesser or greater areas in smaller or larger potatoes).

Serious damage:

When more than the equivalent of 6 scattered spots 1/8 inch in diameter 

(correspondingly lesser or greater areas in smaller or larger potatoes).

Hollow Heart or Hollow Heart with Discoloration (Q)

Hollow heart is a condition brought about by too rapid or irregular growth. It 

often occurs during wet seasons in potatoes grown in very fertile or heavily irrigated 

soils. Hollow heart consists of more or less irregular cavities of varying size and is 

usually lined with light brown to brown dead tissues. This defect is usually found, but 

not always, in large, rough, misshapen potatoes.

The area affected is measured with a diameter gauge. The potato is considered 

damaged or seriously damaged when the affected area (with the plastic diameter gauge

laid on it) extends beyond the confines of the appropriate measured circle.

When hollow heart with discoloration is found and no hollow heart falls outside of 

the circle but some discoloration does, the color must be checked against the color 

comparator POT-CC-1. If any color outside of the circle is as dark as or darker than the 

color comparator, the potato is scored. See Guide for Maximum Area Allowed.

Scoring Guide (based on a potato 2-1/2 inches in diameter or 6 ounces in weight)

Damage:

When the area affected is more than that of a circle 1/2 inch in diameter 

(correspondingly lesser or greater areas in smaller or larger potatoes).

Serious damage:

When the area affected is more than that of a circle 3/4 inch in diameter 

(correspondingly lesser or greater areas in smaller or larger potatoes).

Visual Aids Refer to photos 121 - 122e, Color comparator POT-CC-1.
55

Ingrown Sprouts (C)

Ingrown sprouts are sprouts that have actually grown back into the flesh of the 

potato. There is usually obvious indication of some abnormal sprout growth on the 

outside of the tuber which will reveal internal growth upon taking an exploratory cut. 

This defect should be scored against the tolerance for internal defects.

Scoring Guide

Damage:

When removal causes loss of more than 5% of total weight of the potato.

Serious damage:

When removal causes loss of more than 10% of total weight of the potato.

Visual Aids Refer to photos 60 & 61.

Internal Black Spot (C)

The affected areas are usually at or near the surface and more often found at 

the shoulders of the stem end, although they occur on all parts of the potato. In the first 

stages, the areas are light tan or light pink in color, later turning gray and finally dark 

brown or black. At these stages they are internal defects. 

As they dry out, they sink and become leathery, at which time they often become 

external defects scorable as sunken discolored areas (SDA) or SDA with underlying 

flesh discoloration (see section describing this defect.) In some cases, the skin over 

them will have a dull dark appearance.

Scoring Guide

Insignificant light shades or minor spots of discoloration should be 

disregarded.

Damage:

When the spot(s) are darker than the official color chip (POT-CC-2) after 

removing 5 % of the total weight of the potato.

Serious damage:

When the spot(s) are darker than the official color chip (POT-CC-2) after 

removing 10 % of the total weight of the potato. 

Visual Aids POT-CC-2.

Internal Brown Spot (Q)

The discolored and necrotic tissues, light yellowish-brown to dark rusty-brown in 

color, are firm, granular or corky in texture and are irregularly shaped and indefinite in 

outline. The spots usually range from 1/4 to 1/2 inch in diameter. The spots are 
56

scattered irregularly in the central tissue inside of the vascular ring but are often found 

in the region of the vascular ring and occasionally in the tissue between the vascular 

ring and the surface of the potato. Most of the lesions are found near the bud (eye) end 

of the potato and they seldom occur much beyond the middle. Affected tissues have 

not been found at the stem end.

Scoring Guide (based on a potato 2-1/2 inches in diameter or 6 ounces in weight)

See section on Methods of Cutting to Determine Internal Defects.

Damage:

When more than the equivalent of 3 scattered spots 1/8 inch in diameter 

(correspondingly lesser or greater areas in smaller or larger potatoes).

Serious damage:

When more than the equivalent of 6 scattered spots 1/8 inch in diameter 

(correspondingly lesser or greater areas in smaller or larger potatoes).

Visual Aids Refer to photos 63 & 64.

Internal Mahogany Browning (C)

This form of low temperature injury is caused by long storage below 38°F, but 

above the freezing point of potatoes. The color of affected tissues may be brown, 

mahogany and various shades of gray. The affected flesh is usually tough, brittle or 

leathery. In northern shipping areas it is usually found in late March through April, 

especially in bins near cold walls where it may extend in as much as two feet.

Scoring Guide

Damage:

When removal causes loss of more than 5% of the total weight of the potato. 

Serious damage:

When removal causes loss of more than 10% of the total weight of the potato.

Visual Aids Refer to photos 67 & 68.

Internal Pink to Purple Discoloration (C)

This discoloration generally affects the vascular ring area and often radiates in 

toward the center of the potato. The color of the affected tissue ranges from pink to 

various shades of purple and may be found throughout the length of the potato. The 

exact cause of this discoloration is unknown. It has been speculated that it is a form of 

reversion (back to a parentage). Another suggested cause is field events such as 

extremes in temperatures or in moisture. 
57

Scoring Guide

When occurring outside of the vascular ring:

Damage:

When removal causes a loss of more than 5% of the total weight of the potato. 

Serious damage:

When removal causes loss of more than 10% of the total weight of the potato.

When occurring entirely within the vascular ring (based on a potato 2-1/2 inches 

in diameter or 6 ounces in weight):

Damage:

When more than the equivalent of 3 scattered spots 1/8 inch in diameter

(corresponding lesser or greater areas in smaller or larger potatoes).

Serious damage:

When more than the equivalent of 6 scattered spots 1/8 inch in diameter

(correspondingly lesser or greater areas in smaller or larger potatoes).

Visual Aids Refer to photo 64a.

Internal Potato Necrosis (C)

Since the cause of this disease is an alfalfa mosaic virus that is transmitted by 

aphids, this defect occurs when potatoes are grown near alfalfa. The first sign of 

internal potato necrosis appears near the stem end. The tissue under the skin 

becomes a rusty-brown color in patches that suggest late blight infections. Later the 

discolored areas enlarge and may extend throughout the potato.

Potato necrosis is present when the potatoes are harvested, but the 

discolorations enlarge and become darker after harvest. Potatoes apparently clean at 

harvest may show discoloration after six weeks storage. Evidently the internal damage 

caused by the virus does not immediately result in visible discoloration, but gradually 

develops the brown color in the field, in storage, or in transit.

There is no definite pattern of internal discoloration; sometimes it is in the form of 

dry, brown blotches in pockets and sometimes in loops and half circles. In suspected 

lots of potatoes, a true estimate of potato necrosis damage can be obtained only by 

cutting. 

Scoring Guide

Damage:

When removal causes loss of more than 5% of the total weight of the potato.

Serious damage:

When removal causes loss of more than 10% of the total weight of the potato.
58

Light Brown Discoloration (Brown Center) (Q)

This is a condition that may develop while tubers are very small. The center of 

the potato shows areas of dead, brown cells. During the growing season these cells 

can split apart and form cavities (hollow heart).

The area affected is measured with a diameter gauge. The potato is considered 

damaged or seriously damaged when the affected area (with the plastic diameter gauge

laid on it) extends beyond the confines of the appropriate measured circle. See Guide 

for Maximum Area Allowed.

Scoring Guide (based on a potato 2-1/2 inches in diameter or 6 ounces in weight)

Shades of color that are as dark as or darker than the official color 

comparator "POT-CC-1" only will be considered in determining affected 

area.

Damage:

When the area affects more than that of a circle 1/2 inch in diameter

(correspondingly lesser or greater areas in smaller or larger potatoes).

Serious damage:

When the area affects more than that of a circle over 3/4 inch in diameter

(correspondingly lesser or greater areas in smaller or larger potatoes).

Visual Aids Refer to photos 123 & 124, Color comparator POT-CC-1.

Net Necrosis (C)

The outstanding characteristic of net necrosis is the presence of a network of 

necrotic strands, brown to brownish-black in color and sometimes extending throughout 

the flesh of the potato.

Net necrosis is usually found developing from the stem end, but it may be found 

on the side or other parts of the potato. Where such is the case, cuts should be made 

on the sides as well as from the ends. In mild cases, the netting may be limited to a 

small portion of the potato, usually at the stem end. In typical cases, it is never 

confined to the vascular ring.

Scoring Guide

Damage:

When removal causes loss of more than 5% of the total weight of the potato. 

Serious damage:

When removal causes loss of more than 10% of the total weight of the potato.

Visual Aids Refer to photos 70 & 71.
59

Stem End Browning (C)

The characteristics of stem end browning are the presence of dark brown to 

black streaks or areas which can be detected by clipping only the stem end. 

Consequently, the value of the potato is not totally destroyed. The discoloration 

generally does not extend to any appreciable depth into the potato, but is rather uniform

near the surface.

In severe cases, it is impossible to identify it from the early stages of net 

necrosis. However, in most cases, the discoloration caused by stem end browning will 

appear more nearly as a solid area while net necrosis appears more often as separate

discolored or dead strands.

Scoring Guide

Damage:

When removal causes loss of more than 5% of the total weight of the potato.

Serious damage:

When removal causes loss of more than 10% of the total weight of the potato.

Visual Aids Refer to photo 85.

Vascular Discoloration (C)

The vascular bundle is typically slightly darker than the natural flesh of the 

potato. However, when the vascular bundle is discolored to a degree that it is distinctly 

darker than the natural flesh of the potato the term vascular discoloration is used. It is 

usually most severe at the stem end. Sudden killing of vines is one of several causes, 

others being verticillium wilt and fusarium wilt. 

Inspectors should not attempt to diagnose either of these wilt diseases, nor use 

these terms on the certificate, but should apply the term "damage by vascular 

discoloration."

Scoring Guide

Damage:

When removal causes loss of more than 5% of the total weight of the potato. 

Serious damage:

When removal causes loss of more than 10% of the total weight of the potato.

Visual Aids Refer to photos 90 & 91.
60

Guide for Maximum Area Allowed of Hollow Heart, Hollow Heart with

Discoloration, or Light Brown Discoloration (Brown Center)

Diameter Weight U.S. No. 1 U.S. No. 2

Potato is: Potato is: Maximum 

Diameter

Maximum 

Diameter

2 in. 4 oz. 3/8 in. 5/8 in.

2-1/2 in. 6 oz. 1/2 in. 3/4 in.

2-3/4 in. 7 oz. 5/8 in. 7/8 in.

3 in. 8 oz. 3/4 in. 1 in.

3-1/4 in. 10 oz. 7/8 in. 1-1/4 in.

3-1/2 in. 14 oz. 1 in. 1-1/2 in.

3-3/4 in. 16 oz. 1-1/8 in. 1-5/8 in.

4 in. 20 oz. 1-1/4 in. 1-7/8 in.

4-1/4 in. 24 oz. 1-3/8 in. 2 in.

4-1/2 in. 28 oz. 1-1/2 in. 2-1/8 in.

1 Note: Correspondingly lesser or greater areas in smaller or larger potatoes.

2 Note: These dimensions are based on area affected not aggregate area.

3 Note: For Light Brown Discoloration (Brown Center) use the shade of color depicted

on POT-CC-1. Shades of color lighter than this shall not be considered in

determining affected area.

4 Note: When determining maximum area allowed use the size column which allows the

greatest area affected (i.e. In the U.S. No. 1 grade a potato 3 inches in diameter,

which weighs 10 ounces is allowed 7/8 inch in diameter area affected.)
61

DRY ROT, SOFT ROT AND WET BREAKDOWN

To make it more convenient, both dry rots and soft rots are discussed under this 

heading. Decays are progressive in nature, and may seriously affect the marketing 

quality of potatoes. All decays should be tabulated separately on the note sheet.

Classifying and Certifying Rots

All rots, regardless of the name or type, should be considered as soft rot when 

the rot is soft, mushy or in a leaky condition. Dry rots, other than late blight, should be 

scored on appearance or waste basis. Do not name decays but classify them as "dry 

rot" or "soft rot." However, proper identification is necessary in order to score 

blackheart, late blight, southern bacterial wilt and ring rot, since these defects are 

listed in the grade sections of the standards.

The application of tolerances states:

§51.1547...That en route or at destination one-tenth of the samples 

may contain three times the tolerance permitted for potatoes which 

are frozen or affected by soft rot or wet breakdown.

The inspector should take additional samples, regardless of the lot size, when 

encountering large amounts of frozen, soft rot or wet breakdown to ensure that the high 

sample allowance stated in the application of tolerances has not been overlooked.

Soft rot is applied to either external or internal tolerances depending if it is an 

external or internal defect. Generally, it is external; however, there are occasions when 

it is internal, such as finding soft rot following blackheart or bacterial ring rot. When soft 

rot is internal, it must be designated as such on the notesheet and certificate and 

applied against the restricted tolerance for internal defects. When soft rot is reported 

as just “soft rot,” it is assumed to be external.

Scenario 1: Based on U.S. No 1 at shipping point.

2% damage by scab (external defect).

3% damage by brown surface discoloration (external defect).

1% soft rot (external defect).

6% checksum.

The lot fails to grade, since the soft rot causes the external defects to exceed the 

restricted tolerance of 5% (5% external + 1% soft rot = 6%).
62

Scenario 2: Based on U.S. No 1 at destination.

2% damage by scab (external defect).

6% damage by internal black spots (internal defect).

2% internal soft rot (internal defect).

10% checksum.

The lot fails to grade, since the internal soft rot causes the internal defects to 

exceed the restricted tolerance of 7% (6% internal + 2% internal soft rot = 8%).

Scenario 3: Based on U.S. No 1 at destination.

1% old cuts (external).

6% damage by net necrosis (internal defect).

2% soft rot (external defect).

9% checksum.

The lot meets the grade since the soft rot does not cause the external defects to 

exceed the 7% tolerance (1% external defect + 2% soft rot = 3%). If the soft rot was 

internal, then the internal defects tolerance would be exceeded and the lot would fail to 

grade (6% internal defects + 2% internal soft rot = 8%).

Alternaria Tuber Rot (Early Blight) (C)

The lesions on the tuber are of irregular size and shape and vary from 1/4 to 1 

inch in diameter. They are brown to purplish-brown, slightly sunken with irregular 

borders and appear somewhat similar to those produced by late blight but are 

shallower.

Alternaria tuber rot is a serious storage and market disease that occurs in 

potatoes harvested during cool, humid weather. The infection opens the way for 

secondary infections by species of fusarium and other organisms. Alternaria tuber rot 

is a form of dry rot.

Scoring Guide

Damage:

When the appearance is materially affected or more than 5% waste.

Serious damage:

When the appearance is seriously affected or more than 10% waste.

Visual Aids Refer to photos 40 & 41.

Bacterial Ring Rot (C)

Potatoes may appear to be healthy or have dark discolorations under the skin at 

the stem end or under the eyes. In some cases, they show a very characteristic 
63

cracking extending only as far as the vascular system. Upon cutting the potato near the 

stem end, in typical cases the vascular ring shows a yellowish-white or light brown 

discoloration. This may involve the entire ring or only isolated portions of it. The 

infected tissue is often crumbly in consistency and may ooze from the freshly cut 

surface if the potato is squeezed. Infected potatoes may be apparently healthy at 

digging time and develop characteristic symptoms in storage.

Bacterial ring rot potatoes are very susceptible to secondary infection, especially 

by soft rot organisms, and potatoes from diseased plants show various stages of decay

up to complete disintegration. With secondary infection, there is often a distinctive 

separation between the portions of the potato inside and outside of the vascular region; 

the outer layer can be broken off like a shell.

Scoring Guide

Serious damage:

All U.S. grades require potatoes to be free from bacterial ring rot. When present 

in any degree, score against the restrictive soft rot tolerance.

Visual Aids Refer to photos 35 & 36.

Blackleg Tuber Rot (C)

This type of decay always enters through the stem end. A mild infection may 

result only in the discoloration of the vascular ring at the stem end. Decayed potatoes 

may be white or only slightly colored and cheesy or buttery in consistency but gradually 

turn black and slimy as the decomposition progresses. In storage it is typical for 

blackleg to be confined to the center of the potato, which becomes hollowed and black 

with a layer of slimy lining. Decomposing parts have a disagreeable odor.

Scoring Guide

Blackleg which has advanced to soft rot should be scored on the basis of 

soft rot. If the discolored tissue is firm and shows no soft rot, score as:

Damage:

When removal causes loss of more than 5% of total weight of the potato.

Serious damage:

When removal causes loss more than 10% of total weight of the potato.

Visual Aids Refer to photos 42 & 43.

Brown Rot (Southern Bacterial Wilt) (C)

The disease occurs in southern districts of the United States. In the earlier 

stages, the potatoes, when cut, show the vascular ring moist and brown with a slight 

exudation from the discolored ring. In many cases, pockets develop, starting in the 

vascular regions and often with droplets of bacterial ooze. The disease is sometimes 

indicated by sunken spots at the stem, or by gray colored spots on the surface. 
64

Frequently there are no external indications, and the presence of the defect may be 

determined only by cutting the potatoes. In the more advanced stages, this disease is 

termed brown rot. In this stage, it is frequently followed by slimy soft rot.

Scoring Guide

Serious damage:

All U.S. grades require potatoes to be free from brown rot. When present in any 

degree, score against the restrictive soft rot tolerance.

Visual Aids Refer to photos 37 & 38.

Fusarium Tuber Rot (C)

This type of decay usually enters through injuries such as cuts and bruises, and 

may occur any place on the potato. The decaying tissues soon become sunken and 

the skin will have a wrinkled appearance. The color of the affected tissues varies from 

light to dark brown or even black. A distinct open cavity and/or masses of whitish mold 

are the two conclusive indicators of fusarium infection.

Do not confuse infections of multi-colored starchy molds with fusarium tuber rot. 

These starchy molds, commonly misidentified as fusarium, often appear either alone or 

in conjunction with fusarium as they also enter the potato through injuries, cuts and 

bruises. The rot may be dry and brittle, wet and jelly-like or even mushy and leaky.

Fusarium tuber rot is usually dry at low temperatures and wet at high 

temperatures. It is never slimy even when wet and never has a bad odor unless 

accompanied by other fungi or bacteria.

Sometimes the center of the decayed area is dry with margins being moist, but 

not moist enough to spot a container or wet adjacent potatoes, in which case it should 

be classed as moist type. If the entire decayed area is so dry that no moisture appears 

when squeezed, or is only moist as described above it should be reported as "dry rot."

Scoring Guide

Wet Type:

Serious damage:

Score against the soft rot tolerance in all grades regardless of the affected area 

when the affected area is wet and mushy. Report as “soft rot.”

Moist and Dry Types:

Damage:

When more than 5% waste. Report as “dry rot.”

Serious damage:

When more than 10% waste. Report as “dry rot.”

Visual Aids Refer to photos 51 - 52b.
65

Jelly End Rot (Glassy End Rot) (C)

Jelly end rot is identified by its jelly like, watery consistency occurring at the stem 

end of the potato, second growth knobs or pointed ends. This disorder is caused by 

conditions that interfere with the deposition of starch in the growing tissues. There is 

some evidence that fluctuations in moisture supply during the growing season may be 

responsible. Jelly end rot often dries leaving a shriveled flaky area.

Scoring Guide

Dry or Moist Stage:

Any yellowish flesh discoloration or translucence due to jelly end rot will 

be included in the waste cut.

Damage:

When materially affecting the appearance of the potato, or 

When removal causes loss of more than 5% of the total weight of the potato.

Serious Damage:

When seriously affecting the appearance of the potato, or 

When removal causes loss of more than 10% of the total weight of the potato.

Mushy or Leaky Stage:

Serious damage:

Score any amount as soft rot.

Visual Aids Refer to photo 53.

Late Blight Tuber Rot (C)

When not complicated by secondary organisms, the decay is reddish-brown or 

purplish-brown in color and spreads irregularly from the surface through the flesh, like 

the diffusion of a brown stain.

Under storage conditions, the disease is typically a dry rot, forming irregular 

sunken patches which, under conditions favorable to their development, such as high 

humidity and temperature, may involve the entire potato. These patches are usually 

quite firm, unless secondarily affected by other parasites. Frequently, they have a 

metallic tinge, especially on the border of healthy tissue. This defect can be detected 

by making thin cuts on the exterior of the potatoes.

Scoring Guide

Serious damage:

All U.S. grades require potatoes to be free from late blight tuber rot. When 

present in any degree, score against the restrictive soft rot tolerance.

Visual Aids Refer to photos 32 - 34.
66

Leak (C)

Infection usually takes place through cuts or bruises. The skin may show a 

brownish, somewhat water-soaked discoloration. The enlarging lesions are frequently 

sharply defined by a dark brown boundary line. The most characteristic symptom is the 

extremely watery nature of the affected tissue. The water is held by the tissues until 

pressure is applied, causing the skin to brake and release a yellowish or brownish 

liquid.

Scoring Guide

Serious damage:

When present in any degree, score against the restrictive soft rot tolerance.

Visual Aids Refer to photos 65 & 66.

Pink Rot (C)

Pink rot occurs chiefly in cool, wet, poorly drained soils. External symptoms occur 

usually at the stem end, however at times the eyes and lenticels are infected. In whiteskin potatoes the infected area turns dark brown, whereas in red-skin potatoes the first 

symptom is fading red. Blotchy purplish or black discoloration develops around the 

eyes and lenticels. Rotted tubers feel spongy or rubbery and the skin is easily sloughed 

off. When squeezed, droplets of liquid come from eyes and lenticels.

Scoring Guide

Serious damage:

When present in any degree, score against the restrictive soft rot tolerance 

Visual Aids Refer to photos 75 & 76.

Sclerotium Rot (C)

This rot is usually found in the early southern crop of potatoes. It seems to be 

associated with dirty potatoes, which, in all probability, were wet when dug and packed. 

This disease is marked by a watery, soft, mushy, odorless, and often colorless condition

of the affected tissue. The lesions at times are yellowish to light brown and may appear 

as small, slightly sunken spots with brown margins. The consistency is granular-wet to 

watery, rather than slimy, and the soft, decaying tissue can easily be separated from 

the healthy tissue. As the disease develops, a rather fine, silky, white mycelium grows 

radially from a given point and forms fans closely appressed over the surface of the 

lesions and adjacent healthy tissues.

Scoring Guide

Serious damage:

When present in any degree, score against the restrictive soft rot tolerance.
67

There are instances when Sclerotium Rot causes dry pitted areas, which are 

judged on the same basis as pitted Scab (appearance/waste).

Visual Aids Refer to photos 79 & 80.

Slimy Soft Rot (C)

Slimy soft rots of potatoes are quite common and may be either of primary or 

secondary nature. The decaying parts turn into a stringy slime with a repulsive odor. 

As a secondary infection, it may follow other diseases or injuries, especially late blight 

tuber rot and scald or freezing injury.

Scoring Guide

Serious damage:

When present in any degree, score against the restrictive soft rot tolerance.

Visual Aids Refer to photo 39.

Wet Breakdown (C)

Potatoes that are frozen will exhibit ice crystal formation within the tissues (see 

section on Freezing/Freezing Injury). Upon thawing, potatoes will exhibit a wet leaking

condition known as wet breakdown.

Scoring Guide

Serious damage:

All potatoes with any amount of wet breakdown are scored against the restrictive

tolerance for freezing, soft rot and wet breakdown.

Visual Aids Refer to photo 31.
68

Fingerling Potatoes

Fingerlings are small thin-skinned potatoes. There are several varieties of 

fingerling potatoes including French, Russian, Austrian, and American. These varieties 

can be red-skinned, tan-skinned, or purple-skinned.

The U.S. Standards for Grades of Potatoes can be applied to fingerling varieties 

when performing the inspection. However, in the U.S. No.1 grade the minimum size is 

1-7/8 inches unless otherwise specified. Generally fingerlings will not meet the size 

requirement for the grade; therefore the applicant may specify the size. For example, 

the applicant may specify “U.S. No. 1, 1 inch minimum diameter. If the applicant does 

not specify size, the lot can still be certified using the standard but may or may not meet 

grade due to size.

Visual Aids Refer to POT.-L-1 (Official Visual Aids for Potatoes), page 31.

French Fingerling

French Fingerling is a variety of fingerling potatoes that are small finger shaped tubers. 

These potatoes have shallow eyes, red smooth skin and a red-yellow swirl colored 

flesh. When cut across, the potatoes show an internal ring of pink, which is 

characteristic for the variety and is not scorable as a defect.
69

PART 2: INSPECTION INSTRUCTIONS FOR

SEED POTATOES

GENERAL

The standards apply to potatoes positively identified as certified seed of one 

variety by the State of origin. They do not supplement any State seed grade or 

regulation. Potatoes sold for seed purposes that are not positively identified by 

tags, seals, container markings or some other suitable means of identification 

cannot be certified as meeting the requirements of the U.S. No. 1 Seed grade.

In order to properly handle requests for certification on the basis of State grades 

or regulations, each office should have copies of State grades and regulations. If there 

is a question as to the seed grade requirements, the inspection should be based on the 

U.S. Standards for Grades of Seed Potatoes. Statements or tags or other means of 

identification of the lot should be reported.

Sampling and inspection procedures are the same as for the "fresh standards." 

However, scoring guides and tolerances must be followed in accordance with the U.S. 

Standards for Grades of Seed Potatoes.

Whenever possible the inspection should be made with non-infected equipment. 

The applicant should be advised that inspectors are not equipped to clean and sterilize 

their equipment and that clean equipment or cleaning facilities should be furnished by 

the applicant.
70

TOLERANCES

FOR DEFECTS:

10% Serious Damage Hollow Heart

10% Damage Soil

5% Serious Damage Vascular Ring Discoloration

11% Remaining Requirements of the Grade, Including

6% External Defects

5% Internal Defects, Including

0% Bacterial Ring Rot

2% Serious Damage Fusarium (Dry/Moist)

1% Late Blight

0% Nematode or Tuber Moth Injury

.25% Variety Mixture

.50% (SPI) Frozen, Soft Rot, Wet Breakdown

1% (MKT) Frozen, Soft Rot, Wet Breakdown

FOR OFF-SIZE:

5% UNDERSIZE

10% OVERSIZE

APPLICATION OF TOLERANCES

Individual samples cannot exceed double the tolerance specified, except that at 

least one defective and one off-size potato may be permitted in any sample, provided 

the lot averages within tolerance.

En route/at destination: 10 percent of the samples may contain three times the 

tolerance permitted for potatoes which are frozen or affected by soft rot or wet 

breakdown: And provided further, That the averages for the entire lot are within the 

tolerances specified for the grade.

SIZE

When measuring diameter on seed potatoes, the inspector must confirm that the 

seed potatoes meet the minimum/maximum diameters for the U.S. grades using round 

sizers. During this process the industry may request that the potatoes also be sized 
71

using internationally recognized (UNECE Standards) square sizers. Square sizers are 

usually applied to determine the percent of potatoes less than 28 mm.

On the notesheet, keep columns for all sizes being determined by round and 

square sizers. Write the U.S. grade statement, determined from the round sizers, in the 

“GRADE” section. Report the size determined by the square sizers in the “OTHER” or 

“REMARKS” section. For example: GRADE: “U.S. No., 1-3/4 inch minimum diameter.” 

OTHER or REMARKS: “Applicant specified 1-3/4 inch minimum diameter. Also meets

contract specifications of 28 mm minimum diameter, determined with square sizers and 

reported at applicant’s request.”

When measuring the diameter, drop the potato through the round or square 

opening so that its longitudinal axis is at right angles to the sizer, without regard to the 

position of the stem end.

The U.S. Standards for Grades of Seed Potatoes have the following size 

requirements:

MINIMUM SIZE: Unless otherwise specified, the minimum diameter will not be 

less than 1-1/2 inches.

MAXIMUM SIZE: Unless otherwise specified, the maximum size will not exceed 

3-1/4 inches in diameter or 12 ounces in weight.

When determining maximum size, individual potatoes cannot exceed the 

maximum diameter or weight requirements. Therefore, a potato larger than 3-1/4 

inches in diameter or weighing more than 12.49 ounces is considered oversize unless a 

larger diameter or weight is specified in connection with the grade. When State 

certified seed tags are printed "U.S. No. 1 Seed Potatoes" only, the total of maximum

diameter and maximum weight will be added together to compute oversize. For 

example, a lot showing 8% of potatoes over 3-1/4 inches in diameter and 5% over 

12.49 ounces (the two added together exceeds the 10% tolerance for oversize) will be 

certified as “Failing to grade U.S. No. 1 Seed Potatoes account oversize.”

REPORTING BACTERIAL RING ROT

Bacterial ring rot is a very serious disease in seed potatoes. Many growers 

refuse to plant a lot of seed in which even a single specimen of ring rot is found. 

Therefore, it is very important that the diagnosis of this disease in seed potatoes be 

correct. An inspection certificate which shows bacterial ring rot when the cause of the 

disease is common slimy soft rot, wilt or early stages of blackleg may cause a serious 

and unwarranted loss to the shipper. Whenever a soft rot is found in a lot of seed 

potatoes, it should be reported only as soft rot even though the inspector believes it 

may be bacterial ring rot, unless representative samples have been diagnosed as such 

by a Federal or State pathologist.

An applicant may request that seed potato inspections show factors such as 

scab, net necrosis, stem end browning and Rhizoctonia which are not severe enough to 
72

score against the U.S. No. 1 grade. This can be reported followed with the statement 

"not affecting grade, reported at applicant's request."

Since freedom from inheritable diseases is one of the most important factors in 

determining quality of seed potatoes, no statement should be made as to the quality or 

fitness of the stock for seed purposes.

FOR DEFECT SCORING GUIDELINES AND DEFINITIONS, REFER TO THE U.S 

STANDARDS FOR GRADES OF SEED POTATOES IN APPENDIX I.
73

APPENDIX I: U.S. Grade Standards

United States Standards for Grades of Potatoes1

Effective June 3, 2011

Grades 

51.1540 [Reserved].

51.1541 U.S. No. 1.

51.1542 U.S. Commercial.

51.1543 U.S. No. 2.

51.1544 [Reserved].

Size

51.1545 Size.

Tolerances

51.1546 Tolerances.

Application of Tolerances

51.1547 Application of tolerances.

Samples for Grade and Size Determination

51.1548 Samples for grade and size determination.

Skinning

51.1549 Skinning.

Definitions

51.1550 Similar varietal characteristics.

51.1551 Firm.

51.1552 Clean.

51.1553 Fairly clean.

51.1554 Mature.

51.1555 Fairly well matured.

51.1556 Well shaped.

51.1557 Fairly well shaped.

51.1558 Seriously misshapen.

51.1559 [Removed and Reserved].

51.1560 Damage.

51.1561 Serious damage.

51.1562 Freezing.

51.1563 Soft rot or wet breakdown.

51.1564 External defects.

51.1565 Internal defects.

Metric Conversion Table

51.1566 Metric conversion table.

Grades

§51.1540 [Reserved].

§51.1541 U.S. No. 1. 

"U.S. No. 1" consists of potatoes which meet the following requirements: 

(a) Similar varietal characteristics, except when designated as a mixed or specialty pack; 

 1 Packing of the product in conformity with requirements of these standards shall not excuse failure to comply with the provisions of 

the Federal Food and Drug Cosmetic Act or with applicable State laws and regulations.
74

(b) Firm; 

(c) Fairly clean;2

(d) Fairly well shaped; 

 

(e) Free from: 

(1) Freezing; 

(2) Blackheart; 

(3) Late blight, southern bacterial wilt and ring rot; and, 

(4) Soft rot and wet breakdown. 

(f) Free from damage by any other cause. See §§51.1564 and 51.1565. 

(g) Size. Not less than 1-7/8 inches in diameter, unless otherwise specified in connection with the grade. 

(h) For tolerances see §51.1546. 

§51.1542 U.S. Commercial. 

"U.S. Commercial" consists of potatoes which meet the requirements of U.S. No. 1 grade except for the 

following: 

(a) Free from serious damage caused by: 

(1) Dirt or other foreign matter; 

(2) Russet scab; and, 

(3) Rhizoctonia. 

(b) Increased tolerances for defects specified in §51.1546. 

§51.1543 U.S. No. 2. 

"U.S. No. 2" consists of potatoes which meet the following requirements: 

(a) Similar varietal characteristics, except when designated as a mixed or specialty pack; 

(b) Not seriously misshapen; 

(c) Free from: 

(1) Freezing; 

(2) Blackheart;

(3) Late blight, southern bacterial wilt and ring rot; and, 

(4) Soft rot and wet breakdown. 

(d) Free from serious damage by any other cause. See §§51.1564 and 51.1565. 

(e) Size. Not less than 1-1/2 inches in diameter, unless otherwise specified in connection with the grade. 

(f) For tolerances see §51.1546. 

§51.1544 [Reserved].

Size 

§51.1545 Size. 

(a) The minimum size, or minimum and maximum sizes may be specified in connection with the grade in 

terms of diameter or weight of the individual potato, or in accordance with one of the size designations in 

Table I or Table II: Provided, That sizes so specified shall not be in conflict with the basic size 

requirements for the grade. 

(b) When size is designated as shown in Table II, the corresponding weight ranges shall apply. These 

size designations may be applied to potatoes packed in any size container: Provided, that the weight 

ranges are within the limits specified.

 2

Potatoes in containers bearing official State Seed Certification Tags and Seals are not required to be fairly clean but shall be free 

from damage by dirt.
75

Table I

Size designation

Minimum

diameter1 or

weight

Maximum

diameter1 or

weight

Inches Ounces Inches Ounces

Creamer................ 3/4 (

3

) 1-5/8 (

3

)

Chef.................. 2-3/4 8 4-1/2 28

Size A2................. 1-7/8 (

3

) (

3

) (

3

)

Size B.................. 1-1/2 (

3

) 2-1/4 (

3

)

Small................... 1-3/4 (

3

) 2-1/2 6

Medium.................. 2-1/4 5 3-1/4 10

Large................... 3 10 4-1/2 28

1

Diameter means the greatest dimension at right angles to the longitudinal axis, without regard to the position of the stem end.

2

In addition to the minimum size specified, a lot of potatoes designated as Size A shall contain at least 40 percent of potatoes 

which are 2-1/2 inches in diameter or larger or 6 ounces in weight or larger. 3

No requirement.

Table II

[Ounces]

Size designation

Minimum

weight

Maximum

weight

Under 50....................... 15 ...........

50............................. 12 19

60............................. 10 16

70............................. 9 15

80............................. 8 13

90............................. 7 12

100............................ 6 10

110............................ 5 9

120............................ 4 8

130............................ 4 8

140............................ 4 8

Over 140....................... 4 8

Tolerances 

§51.1546 Tolerances. 

To allow for variations incident to proper grading and handling in each of the foregoing grades, the 

following tolerances by weight or equivalent basis, are provided as specified.
76

(a) For defects – (1) U.S. No. 1. (i) At Shipping Point: A total of 8 percent for potatoes in any lot which 

fail to meet the requirements for the grade: Provided, That included in this tolerance not more than the 

following percentages shall be allowed for the defects listed: 

(A) 5 percent for external defects;

(B) 5 percent for internal defects; and

(C) Not more than a total of 1 percent for potatoes which are frozen or affected by soft rot or wet 

breakdown. See §51.1547.

(ii) En route or at Destination: A total of 10 percent for potatoes in any lot which fail to meet the 

requirements for the grade: Provided, That included in this tolerance not more than a total of 8 percent 

shall be allowed for permanent defects: And provided further, the following percentages shall be allowed 

for the defects listed: 

(A) 7 percent for external defects, including therein not more than 5 percent for permanent external 

defects;

(B) 7 percent for internal defects, including therein not more than 5 percent for permanent internal defects;

and

(C) Not more than a total of 2 percent for potatoes which are frozen or affected by soft rot or wet 

breakdown. See §51.1547. 

(2) U.S. Commercial: A total of 20 percent for potatoes in any lot which fail to meet the requirements for 

the grade: Provided, That included in this tolerance not more than the following percentages shall be 

allowed for the defects listed: 

(i) 10 percent for potatoes which fail to meet the requirements for U.S. No. 2 grade, including therein not 

more than: 

(ii) 6 percent for external defects; 

(iii) 6 percent for internal defects; and

(iv) Not more than a total of 1 percent for potatoes which are frozen or affected by soft rot or wet 

breakdown. See §51.1547. 

(3) U.S. No.2. (i) At Shipping Point: A total of 10 percent for potatoes in any lot which fail to meet the 

requirements for the grade: Provided, That included in this tolerance not more than the following 

percentages shall be allowed for the defects listed: 

(A) 6 percent for external defects;

(B) 6 percent for internal defects; and

(C) Not more than a total of 1 percent for potatoes which are frozen or affected by soft rot or wet 

breakdown. See §51.1547.

(ii) En route or at Destination: A total of 12 percent for potatoes in any lot which fail to meet the 

requirements for the grade: Provided, That included in this tolerance not more than a total of 10 percent 

shall be allowed for permanent defects: And provided further, the following percentages shall be 

allowed for the defects listed: 

(A) 8 percent for external defects, including therein not more than 6 percent for permanent external 

defects; 

(B) 8 percent for internal defects, including therein not more than 6 percent for permanent internal defects;

and

(C) Not more than a total of 2 percent for potatoes which are frozen or affected by soft rot or wet 

breakdown. See §51.1547.

(b) For off-size. (1) Not more than 3 percent of the potatoes in any lot may be smaller than the required 

or specified minimum size except that a tolerance of 5 percent shall be allowed for potatoes packed to 

meet a minimum size of 2-1/4 inches or larger in diameter or 5 ounces or more in weight. In addition, not 

more than 10 percent may be larger than any required or specified maximum size. See §51.1547. 

(2) When a percentage of the potatoes is specified to be of a certain size and larger, individual samples 

shall have not less than one-half of the percentage specified: Provided, That the average for the entire lot 

is not less than the percentage specified. 

Application of Tolerances 

§51.1547 Application of tolerances. 
77

Individual samples shall have not more than double the tolerances specified, except that at least one 

defective and one off-size potato may be permitted in any sample: Provided, That en route or at 

destination one-tenth of the samples may contain three times the tolerance permitted for potatoes which 

are frozen or affected by soft rot or wet breakdown. And provided further, That the averages for the 

entire lot are within the tolerances specified for the grade.

Samples for Grade and Size Determination 

§51.1548 Samples for grade and size determination. 

Individual samples shall consist of at least 20 pounds. When individual packages contain at least 20 

pounds, each individual sample is drawn from one package; when packages contain less than 20 pounds, 

a sufficient number of adjoining packages are opened to provide at least a 20-pound sample. The 

number of such individual samples drawn for grade and size determination will vary with the size of the lot. 

Skinning 

§51.1549 Skinning. 

(a) The following definitions provide a basis for describing lots of potatoes as to the degree of skinning 

whenever description may be appropriate: 

(1) "Practically no skinning" means that not more than 5 percent of the potatoes in the lot have more than 

one-tenth of the skin missing or "feathered;" 

(2) "Slightly skinned" means that not more than 10 percent of the potatoes in the lot have more than onefourth of the skin missing or "feathered;" 

(3) "Moderately skinned" means that not more than 10 percent of the potatoes in the lot have more than 

one-half of the skin missing or "feathered;" and 

(4) "Badly skinned" means that more than 10 percent of the potatoes in the lot have more than one-half of 

the skin missing or "feathered."

Definitions 

§51.1550 Similar varietal characteristics. 

"Similar varietal characteristics" means that the potatoes in any lot have the same general shape, color 

and character of skin, and color of flesh. 

§51.1551 Firm. 

"Firm" means that the potato is not shriveled or flabby. 

§51.1552 Clean.

"Clean" means that at least 90 percent of the potatoes in any lot are practically free from dirt or staining 

and practically no loose dirt or other foreign matter is present in the container. 

§51.1553 Fairly clean. 

"Fairly clean" means that at least 90 percent of the potatoes in any lot are reasonably free from dirt or 

staining and not more than a slight amount of loose dirt or foreign matter is present in the container. 

§51.1554 Mature. 

"Mature" means that the skins of the potatoes are generally firmly set and not more than 5 percent of the 

potatoes in the lot have more than one-tenth of the skin missing or "feathered." 

§51.1555 Fairly well matured. 

"Fairly well matured" means that the skins of the potatoes are generally fairly firmly set and not more than 

10 percent of the potatoes in the lot have more than one-fourth of the skin missing or "feathered." 

§51.1556 Well shaped. 

"Well shaped" means that the potato has the normal shape for the variety. 

§51.1557 Fairly well shaped. 

"Fairly well shaped" means that the potato is not materially pointed, dumbbell-shaped or otherwise 

materially deformed. 

§51.1558 Seriously misshapen. 

"Seriously misshapen" means that the potato is seriously pointed, dumbbell-shaped or otherwise badly 

deformed. 

§51.1559 [Removed and Reserved]. 

§51.1560 Damage. 

"Damage" means any defect, or any combination of defects, which materially detracts from the edible or 

marketing quality, or the internal or external appearance of the potato, or any external defect which cannot 
78

be removed without a loss of more than 5 percent of the total weight of the potato. See Tables III, IV, V, 

VI in §51.1564 and Table VII in §51.1565. 

§51.1561 Serious damage. 

"Serious damage" means any defect, or any combination of defects, which seriously detracts from the 

edible or marketing quality, or the internal or external appearance of the potato, or any external defect 

which cannot be removed without a loss of more than 10 percent of the total weight of the potato. See 

Tables III, IV, V, VI in §51.1564 and Table VII in §51.1565. 

§51.1562 Freezing. 

"Freezing" means that the potato is frozen or shows evidence of having been frozen. 

§51.1563 Soft rot or wet breakdown.

"Soft rot or wet breakdown" means any soft, mushy, or leaky condition of the tissue such as slimy soft rot, 

leak, or wet breakdown following freezing injury.

§51.1564 External defects.

"External defects" are defects which can be detected externally. However, cutting may be required to 

determine the extent of the injury. Some external defects are listed in Table III, IV, V, and VI.
79

Table III - External Defects

Defects Damage Serious Damage1

Air Cracks When removal causes a loss of more than 5 

percent of the total weight of the potato or 

when the air crack(s) affects more than 1/3 the 

length or diameter of the potato (whichever is 

greater) in the aggregate. 

When removal causes a loss of more 

than 10 percent of the total weight of the 

potato or when the air crack(s) affects 

more than 3/4 the length or diameter of 

the potato (whichever is greater) in the 

aggregate.

Artificial Coloring When unsightly or when concealing any defect 

causing damage or when penetrating the flesh 

and removal causes loss of more than 5 

percent of total weight of potato.

When concealing a serious defect or 

when penetrating into the flesh and 

removal causes loss of more than 10 

percent of total weight of potato.

Bruises (Not including pressure 

bruise and sunken discolored 

areas)

When removal causes a loss of more than 5 

percent of the total weight of the potato or 

when the area affected is more than 5 percent 

of the surface in the aggregate (i.e. 3/4 inch on 

a 2-1/2 inch or 6 oz. potato). Correspondingly 

lesser or greater areas in smaller or larger 

potatoes.

When removal causes a loss of more 

than 10 percent of the total weight of the 

potato or when the area affected is more 

than 10 percent of the surface in the 

aggregate (i.e. 1-1/4 inches on a 2-1/2 

inch or 6 oz. potato). Correspondingly 

lesser or greater areas in smaller or 

larger potatoes.

Cuts When one smooth cut affects more than 5 

percent of the surface area.

Cut(s) that affect more than 10 percent 

of the surface area in the aggregate or 

when a single side cut extends beyond 

1/2 the length of the potato.

Dirt When materially detracting from the 

appearance of the potato.

When seriously detracting from the 

appearance of the potato.

Elephant Hide When affecting over 10 percent of the surface 

area of the potato. 

When affecting over 25 percent of the 

surface area.

Enlarged Lenticels When materially detracting from the 

appearance of the potato.

When seriously detracting from the 

appearance of the potato.

External Discoloration (Areas that 

are light tan or lighter in color and 

blends should be ignored.)

When more than 30 percent of the surface is 

affected by light tan or light brown colors which 

do not blend or when more than 15 percent of 

the surface is affected by colors darker than 

light tan or light brown. 

When more than 60 percent of the 

surface is affected by light tan or light 

brown colors which do not blend or when 

more than 30 percent of the surface is 

affected by colors darker than light tan or 

light brown. 
80

Defects Damage Serious Damage1

Flattened or Depressed 

Areas/Pressure Bruises

When removal of underlying discolored flesh 

causes a loss of more than 5 percent of the 

total weight of the potato or when the flattened 

or depressed area(s) covers more surface 

area than allowed in Table IV. (See Table IV.)

When removal of underlying discolored 

flesh causes a loss of more than 10 

percent of the weight of the potato or

when the flattened depressed area(s) 

covers more surface area than allowed 

in the Table IV. (See Table IV.) 

Flea Beetle Injury When materially detracting from the 

appearance or when removal causes a loss of 

more than 5 percent of the total weight of the 

potato or when the area affected is more than 

5 percent of the surface in the aggregate.

When seriously detracting from the 

appearance of the potato or when 

removal causes a loss of more than 10 

percent of the weight of the potato or 

when the area affected is more than 10 

percent of the surface in the aggregate.

Greening When removal causes a loss of more than 5 

percent of the total weight of the potato or 

when green color affects more than 25 percent 

of the surface in the aggregate. 

When removal causes a loss of more 

than 10 percent of the weight of the 

potato or when green color affects more 

than 50 percent of the surface in the 

aggregate.

Growth Cracks When the growth crack(s) affects more than 

1/2 the length of the potato in the aggregate 

on round varieties or more than 1/3 the length 

in the aggregate on long varieties; or, when 

the depth is greater than that as outlined in 

Table V. (See Table V.)

When the growth crack(s) affects more 

than 3/4 the length of the potato in the 

aggregate or when the depth is greater 

than that as outlined in Table V. 

(See Table V.)

Grub Damage When removal causes a loss of more than 5 

percent of the total weight of the potato or 

when affecting more than 5 percent of the 

surface area (i.e. more than 3/4 inch on a 2-

1/2 inch or 6 ounce potato). Correspondingly 

lesser or greater areas in smaller or larger 

potatoes.

When removal causes a loss of more 

than 10 percent of the total weight of the 

potato or when affecting more than 10 

percent of the surface area (i.e. more 

than 1-1/4 inch on a 2-1/2 inch or 6 

ounce potato). Correspondingly lesser 

or greater areas in smaller or larger 

potatoes.

Insects or Worms (See Serious Damage.) When present inside the potato.

Nematode (Root Knot) When removal causes loss of more than 5 

percent of total weight of potato. 

When removal causes loss of more than 

10 percent of total weight of potato. 

Rhizoctonia When affecting more than 15 percent of the 

surface in the aggregate. 

When affecting more than 50 percent of 

the surface in the aggregate. 
81

Defects Damage Serious Damage1

Rodent or Bird Damage When removal causes a loss of more than 5 

percent of the total weight of the potato or 

when affecting more than 5 percent of the 

surface area (i.e. more than 3/4 inch on a 2-

1/2 inch or 6 ounce potato). Correspondingly 

lesser or greater areas in smaller or larger 

potatoes.

When removal causes a loss of more 

than 10 percent of the total weight of the 

potato or when affecting more than 10 

percent of the surface area (i.e. more

than 1-1/4 inch on a 2-1/2 inch or 6 

ounce potato). Correspondingly lesser 

or greater areas in smaller or larger 

potatoes.

Russeting (On Non Russet Type) When more than 50 percent of the surface is 

affected in the aggregate. 

N/A

Scab, Pitted When removal causes a loss of more than 5 

percent of the total weight of the potato or 

when scab affects an aggregate area of more 

than 1/2 inch. (Based on a potato 2-1/2 inches 

in diameter or 6 oz. in weight.) 

Correspondingly lesser or greater areas in 

smaller or larger potatoes.

When the removal causes a loss of 

more than 10 percent of the total weight 

of the potato or when scab affects an 

aggregate area of more than 1 inch. 

(Based on a potato 2-1/2 inches in 

diameter or 6 oz. in weight.) 

Correspondingly lesser or greater areas 

in smaller or larger potatoes.

Scab, Russet Smooth and affecting more than 1/3 of the 

surface or rough russet scab which affects 

more than 10 percent of the surface in the 

aggregate.

Rough and affecting more than 25 

percent of the surface in the aggregate.

Scab, Surface When more than 5 percent of the surface in 

the aggregate is affected.

When more than 25 percent of the 

surface in the aggregate is affected.

Second Growth When materially detracting from the 

appearance of the potato.

When seriously detracting from the 

appearance of the potato.

Silver Scurf When affecting more than 50 percent of the 

surface area of the potato.

When its severity causes a wrinkling of 

the skin over more than 50 percent of 

the surface.

Sprouts When more than 5 percent of the potatoes in a 

lot may have any sprout not more than 1/4 

inch in length at shipping point; more than 1/2 

in length at destination; or have numerous 

individual and/or clusters of sprouts which 

materially detract from the appearance of the 

potato.

When more than 10 percent of the 

potatoes in any sprout more than 1/2 

inch in length at shipping point; more 

than 1 inch in length at destination; or 

have numerous individual and/or clusters

of sprouts which seriously detract from 

the appearance of the potato. Serious 

damage by sprouts shall only be scored 

against the U.S. Commercial and U.S. 

No. 2 grades.

Sunburn When removal causes loss of more than 5 

percent of total weight of potato.

When removal causes loss of more than 

10 percent of total weight of potato.
82

Defect Damage Serious Damage1

Sunken Discolored Areas SEE TABLE VI SEE TABLE VI

Surface Cracks (Areas affected by 

fine net-like cracking should be 

ignored.)

When smooth shallow cracking affects more 

than 1/3 of the surface or when rough deep 

cracking affects more than 5 percent of the 

surface.

When rough deep cracking affects more 

than 10 percent of the surface.

Wireworm or Grass Damage When affecting the flesh of the potato and 

removal causes loss of more than 5 percent of 

total weight of potato.

When affecting the flesh of the potato 

and removal causes loss of more than 

10 percent of total weight of potato.

1

The following defects are considered serious damage when present in any degree: 1. Freezing. 2. Late blight. 3. Ring rot. 

4. Southern bacterial wilt. 5. Soft rot. 6. Wet breakdown.

Table IV

Flattened or Depressed Areas - Pressure Bruises Maximum Area Allowed

Diameter Weight

No. 1

(aggregate area)

No. 2

(aggregate area)

Potato is: Potato is: Not more than: Not more than:

Less than 2 in. Less than 4 oz. 1/2 in. 1 in.

2 to 2-1/2 in. 4 to 6 oz. 1 in. 1-1/2 in.

More than 2-1/2 to 3 in. More than 6 to 8 oz. 1-1/4 in. 1-3/4 in.

More than 3 to 3-1/2 in. More than 8 to 14 oz. 1-1/2 in. 1-7/8 in.

More than 3-1/2 to 4 in. More than 14 to 20 oz. 1-3/4 in. 2 in.

More than 4 to 4-1/2 in. More than 20 to 28 oz. 2 in. 2-1/4 in.

More than 4-1/2 to 5 in. More than 28 to 36 oz. 2-1/4 in. 2-3/4 in.

More than 5 in. More than 36 oz. 2-1/2 in. 3-1/4 in.

Table V

Depth Allowed For Growth Cracks

Diameter Weight

No. 1 

(Depth)

No. 2 

(Depth)

Potato is: Potato is: Not more than: Not more than:

Less than 2 in. Less than 4 oz. 1/8 in. 1/4 in.

2 to 2-1/2 in. 4 oz. to 6 oz. 1/4in. 3/8 in.

More than 2-1/2 to 3 in. More than 6 oz. to 8 oz. 3/8 in. 1/2 in.

More than 3 in. More than 8 oz. 1/2 in. 5/8 in.
83

Table VI

Sunken Discolored Areas Maximum Area Allowed

Diameter Weight 

No. 1

(aggregate area)

No. 2

(aggregate area)

Potato is: Potato is: Not more than: Not more than:

Less than 2 in. Less than 4 oz. 3/8 in. 3/4 in.

2 to 2-1/2 in. 4 to 6 oz. 3/4 in. 1 in.

More than 2-1/2 to 3 in. More than 6 to 8 oz. 1 in. 1-1/4 in.

More than 3 to 3-1/2 in. More than 8 to 14 oz. 1-1/4 in. 1-1/2 in.

More than 3-1/2 to 4 in. More than 14 to 20 oz. 1-1/2 in. 1-3/4 in.

More than 4 to 4-1/2 in. More than 20 to 28 oz. 1-3/4 in. 2 in.

More than 4-1/2 to 5 in. More than 28 to 36 oz. 2 in. 2-1/4 in.

More than 5 in. More than 36 oz. 2-1/4 in. 2-1/2 in.
84

§51.1565 Internal defects.

"Internal defects" are defects which cannot be detected without cutting the potato. Some internal defects 

are listed in Table VII. 

Table VII -- Internal Defects

Defects

Damage

Maximum Allowed

Serious Damage

Maximum Allowed

Occurring outside of or not entirely confined to the vascular ring

Ingrown Sprouts, Internal Black Spot, 

Internal Discoloration, Vascular 

Browning, Fusarium Wilt, Net Necrosis, 

Other Necrosis, Stem End Browning

5% waste 10% waste

Internal Black Spot. When the spot(s) are darker than the 

official color chip (POT-CC-2) after 

removing 5 percent of the total weight of 

the potato.

When the spot(s) are darker than the 

official color chip (POT-CC-2) after 

removing 10 percent of the total weight 

of the potato.

Occurring entirely within the vascular ring

Hollow Heart or Hollow Heart with 

Discoloration

Area affected not to exceed that of a 

circle 1/2 inch in diameter in a potato 2-

1/2 inches in diameter or 6 ounces in 

weight.1

Area affected not to exceed that of a 

circle 3/4 inch in diameter in a potato 2-

1/2 inches in diameter or 6 ounces in 

weight.

1

Light Brown Discoloration

(Brown Center)

Area affected not to exceed that of a 

circle 1/2 inch in diameter in a potato 2-

1/2 inches in diameter or 6 ounces in 

weight.

1

Area affected not to exceed that of a 

circle 3/4 inch in diameter in a potato 2-

1/2 inches in diameter or 6 ounces in 

weight.

1

Internal Brown Spot and Similar 

Discoloration (Heat Necrosis)

Not more than the equivalent of 3 

scattered spots 1/8 inch in diameter in a 

potato 2-1/2 inches in diameter or 6 

ounces in weight.

1

Not more than the equivalent of 6 

scattered spots 1/8 inch in diameter in a 

potato 2-1/2 inches in diameter or 6 

ounces in weight.

1

1

Note: Correspondingly lesser or greater areas in smaller or larger potatoes.
85

Metric Conversion Table

§51.1566 Metric conversion table.

Ounces Grams

1 equals...............................................28.35

4 equals.............................................113.40

5 equals.............................................141.75

6 equals.............................................170.10

7 equals.............................................198.45

8 equals.............................................226.80

9 equals.............................................255.15

10 equals...........................................283.50

12 equals...........................................340.20

14 equals...........................................396.90

16 equals...........................................453.60

18 equals...........................................510.30

19 equals...........................................538.60

20 equals...........................................567.00

Inches Millimeters (mm)

1/8 equals..............................................3.2

1/4 equals..............................................6.4

1/2 equals............................................12.7

3/4 equals............................................19.1

1 equals...............................................25.4

1-1/2 equals.........................................38.1

2 equals...............................................50.8

2-1/2 equals.........................................63.5

3 equals...............................................76.2

3-1/2 equals.........................................88.9

4 equals.............................................101.6

4-1/2 equals.......................................114.3
86

United States Standards for Grades of Seed Potatoes

Effective March 6, 1987

51.3000 General.

51.3001 Grade.

51.3002 Tolerances.

51.3003 Application of tolerances.

51.3004 Samples for grade and size determination.

51.3005 Definitions.

51.3006 Classification of defects.

§51.3000 General.

Compliance with the provisions of these standards shall not excuse failure to comply with provisions of 

applicable Federal or State Laws.

§51.3001 Grade.

"U.S. No. 1 Seed Potatoes" consist of unwashed potatoes identified as certified seed by the state of origin 

by blue tags fixed to the containers or official State or Federal State certificates accompanying bulk loads, 

which identify the variety, size, class, crop year, and grower or shipper of the potatoes, and the State 

certification agency. These potatoes must meet the following requirements: 

(a) Fairly well shaped. 

(b) Free from: 

(1) Freezing injury; 

(2) Blackheart; 

(3) Late Blight Tuber Rot; 

(4) Nematode or Tuber Moth injury; 

(5) Bacterial Ring Rot; 

(6) Soft rot or wet breakdown; and, 

(7) Fresh cuts or fresh broken-off second growth. 

(c) Free from serious damage caused by: 

(1) Hollow Heart; and, 

(2) Vascular ring discoloration. 

(d) Free from damage by soil and any other cause. (See §51.3005 - 06). 

(e) Size: 

(1) Minimum diameter, unless otherwise specified, shall not be less than 1-1/2 inches (38.1 mm) in 

diameter; 

(2) Maximum size, unless otherwise specified, shall not exceed 3-1/4 inches (82.6 mm) in diameter or 12 

ounces (340.20 g) in weight. 

(f) Tolerances. (See §51.3002).

§51.3002 Tolerances.

In order to allow for variations incident to proper grading and handling in the foregoing grade, the following 

tolerances, by weight, are provided as specified.

(a) For defects:

(1) 10 percent for potatoes in any lot which are seriously damaged by hollow heart;

(2) 10 percent for potatoes in any lot which are damaged by soil;

(3) 5 percent for potatoes in any lot which are seriously damaged by vascular ring discoloration;

(4) 11 percent for potatoes which fail to meet the remaining requirements of the grade including therein 

not more than 6 percent for external defects and not more than 5 percent for internal defects: Provided, 

that included in these tolerances not more than the following percentages shall be allowed for the defects 

listed:
87

 Percent

Bacterial Ring Rot .................................................................................................. 0.00

Serious damage by dry or moist type Fusarium Tuber Rot.................................... 2.00

Late Blight Tuber Rot ............................................................................................. 1.00

Nematode or Tuber Moth injury.............................................................................. 0.00

Varietal mixture ...................................................................................................... 0.25

Frozen, soft rot or wet breakdown.......................................................................... 0.50

Provided, that en route or at destination, an additional 0.50 percent, or a total of 1 percent, shall be 

allowed for potatoes which are frozen or affected by soft rot or wet breakdown.

(b) For off-size:

(1) For undersize: 5 percent for potatoes in any lot which fail to meet the required or specified minimum 

size.

(2) For oversize: 10 percent for potatoes in any lot which fail to meet the required or specified maximum 

size.

§51.3003 Application of tolerances.

Individual samples (See §51.3004) shall not have more than double the tolerances specified, except that 

at least one defective and one off-size potato may be permitted in any sample; Provided, that en route or 

at destination, one-tenth of the samples may contain three times the tolerance permitted for potatoes 

which are frozen or affected by soft rot or wet breakdown; and provided further, that the averages for the 

entire lot are within the tolerances specified for the grade.

§51.3004 Samples for grade and size determination.

Individual samples shall consist of at least 20 pounds (9.06 kg). The number of such individual samples 

drawn for grade and size determination will vary with the size of the lot.

§51.3005 Definitions.

(a)"Fairly well shaped" means that the potato is not materially pointed, dumbbell-shaped or otherwise 

materially deformed. 

(b)"Nematode or Tuber Moth injury" means the presence of, or any evidence of, Nematode or Tuber Moth.

(c) Soil:

(1)"Fairly clean" means that at least 90 percent of the potatoes in the lot have no more than 10 percent of 

the surface covered with caked soil.

(2)"Damage by soil" means that caked soil covers more than 25 percent of a potato's surface.

(3)"Loose soil" -- A lot of seed potatoes is not considered damaged by the presence of loose soil, clods, 

rocks, vines, and foreign material, but such will be considered a tare factor if the following allowances are 

exceeded:

8 ounces (226.80 g) in a 100 pound (45.3 kg) container.

4 ounces (113.40 g) in a 50 pound (22.65 kg) container.

2 ounces (56.70 g) in a 25 pound (11.33 kg) container or less.

1 percent in a bulk load.

(d) "Shriveling" -- Damage by shriveling means that the individual potato is more than moderately 

shriveled, spongy or flabby.

(e) "Freezing injury" means that the potato is frozen or shows evidence of having been frozen.

(f) "Soft rot or wet breakdown" means any soft, mushy or leaky condition of the tissue.

(g) "Zero Tolerance" (0.00) means none found during the normal inspecting procedures. Certification of a 

lot is not a guarantee that the lot inspected is free of a zero tolerance disease or injury.

(h) "Damage" means any defect or any combination of defects which materially detracts from the internal 

or external appearance of the potato, or any external or internal defect which cannot be removed without a 

loss of more than 5 percent of the total weight of the potato (See §51.3006).

(i) "Serious damage" means any defect or any combination of defects which seriously detracts from the 

internal or external appearance of the potato, or any internal or external defect which cannot be removed 

without a loss of more than 10 percent of the total weight of the potato (See §51.3006).

(j) "External defects" are defects which can be detected by examining the surface of the potato. Cutting 

may be required to determine the extent of the injury (See §51.3006, Table I).
88

(k) "Internal defects" are defects which cannot be detected without cutting the potato (See §51.3006, 

Table II).

(l) "Permanent defects" are defects which are not subject to change during storage or shipment.

(m) "Condition defects" are defects which may develop or change during storage or shipment.

§51.3006 Classification of defects.

(a) Brown discoloration following skinning, dried stems, flattened depressed areas (showing no underlying 

flesh discoloration), greening, skin checks and sunburn do not affect seed quality and shall not be scored 

against the grade.
89

(b) Table I – External Defects.

X-indicates method of scoring unless otherwise noted.

Defect

Damage

When materially detracting

from the appearance of the

potato

or When removal causes a loss of

more than 5 percent of the total

weight of the potato.

Air cracks................................................ ..................................................... X

Bruises.................................................... ..................................................... X

Cuts and broken-off second growth 

(healed)................................................... X................................................... X

Elephant hide (scaling)............................ X...................................................

Enlarged, discolored or sunken 

lenticels................................................... X...................................................

Folded ends............................................ X...................................................

Second growth........................................ X...................................................

Shriveling................................................ When more than moderately 

shriveled, spongy, or flabby.

Sprouts...................................................

When more than 20 percent of 

the potatoes in any lot have any 

sprout more than 1 inch (25.4 

mm) in length.

Surface cracking..................................... X................................................... X

Flea Beatle injury.................................... X................................................... X

Grub damage.......................................... X................................................... X

Rodent and/or bird damage..................... X................................................... X

Wireworm or grass damage....................

Any hole more than 3/4 inch (19.1 

mm) long or when the aggregate 

length of all holes is more than 1-

1/4 inches (31.mm)1

.

Dry rots................................................... ..................................................... X

Rhizoctonia............................................. X...................................................

Scab, pitted............................................ X................................................... X

Scab, russet............................................ When affecting more than 1/3 of 

the surface.............

Scab, surface.......................................... When affecting more than 5 

percent of the surface

Silver Scurf............................................. When affecting more than 25 

percent of the surface........

Growth cracks......................................... When seriously detracting from 

the appearance......

Pressure bruises and sunken areas-with 

underlying flesh discolored..................... .....................................................

When removal causes a loss of more 

than 10 percent of the total weight.

1

Definitions of damage and serious damage are based on potatoes that are 2-1/2 inches (63.5 mm) in diameter or 6 ounces

(170.10 g) in weight. Correspondingly lesser or greater areas are permitted on smaller or larger potatoes.
90

(c) Table II- Internal Defects.

Defect

Damage

When materially detracting from 

the appearance of the potato. or

When removal causes a loss of

more than 5 percent of the total

weight of the potato.

Ingrown sprouts...................................... ....................................................... X

Internal discoloration occurring interior

to the vascular ring (such as, Internal 

Brown Spot, Mahogany Browning and 

Heat Necrosis.).

When more than the equivalent of 

three scattered light brown spots 

1/8 inch (3.2 mm) in diameter1

All other internal discoloration 

excluding discoloration confined to the 

vascular ring........................................... ...................................................... X

1

Definitions of damage and serious damage are based on potatoes that are 2-1/2 inches (63.5 mm) in diameter or 6 ounces

(170.10 g) in weight. Correspondingly lesser or greater areas are permitted on smaller or larger potatoes.

Defect

Serious damage

When seriously detracting from 

the appearance of the potato. or

When removal causes a loss of

more than 10 percent of the total 

weight of the potato.

Internal Discoloration confined to the 

vascular ring........................................... ............................................ X

Hollow Heart or Hollow Heart with 

discoloration...........................................

When affected area exceeds that 

of a circle 3/4 inch (19.1 mm) in 

diameter.1

1

Definitions of damage and serious damage are based on potatoes that are 2-1/2 inches (63.5 mm) in diameter or 6 ounces

(170.10 g) in weight. Corresponding lesser or greater areas are permitted on smaller or larger potatoes.
91

APPENDIX II: PERCENTAGE CHART

20 LB. SAMPLE 50 LB. SAMPLE

 .25 = 1% .50 = 1%

 .50 = 3% 1.00 = 2%

 .75 = 4% 1.50 = 3%

1.00 = 5% 2.00 = 4%

1.25 = 6% 2.50 = 5%

1.50 = 8% 3.00 = 6%

1.75 = 9% 3.50 = 7%

2.00 = 10% 4.00 = 8%

2.25 = 11% 4.50 = 9%

2.50 = 13% 5.00 = 10%

2.75 = 14% 5.50 = 11%

3.00 = 15% 6.00 = 12%

3.25 = 16% 6.50 = 13%

4.00 = 20% 7.00 = 14%

7.50 = 15%

8.00 = 16%

8.50 = 17%

9.00 = 18%

9.50 = 19%

 10.00 = 20%

________________________________________________________________

25 lb. sample - each 1/4 lb. equals 1%

50 lb. sample - each 1/2 lb. equals 1%

Remember to round up or round down wherever necessary.
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APPENDIX III: CERTIFICATE EXAMPLES

Example 1: FV-184 Notesheet
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Example 1: FV-184 Certificate
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Example 2: FV-300 Notesheet (Front)
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Example 2: FV-300 Notesheet (Back)
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Example 2: FV-300 Certificate
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Example 3: FV-300 Notesheet (Front)
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Example 3: FV-300 Notesheet (Back)
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Example 3: FV-300 Certificate
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Example 4: FV-300 Notesheet (Front)
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Example 4: FV-300 Notesheet (Back)
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Example 4: FV-300 Certificate
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Example 5: FV-300 FEIRS Certificate
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Example 6: FV-300 FEIRS Certificate