Potatoes
7. External Defects

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External defects are defects which can be detected externally. However, cutting may be required to determine the extent of the injury.

7.1 Air Cracks (C)

Air cracks sometimes occur during harvest or packing, or after packing if the packages are too tight, overfilled, or roughly handled.

They may appear as fresh, longitudinal cracks and are scored if they materially or seriously affect the appearance of the potato.

For more information, please refer to visual aid POT-2, (06/96).

POT-2, (06/96) (CFIA)
Air Cracks – maximum allowed for Canada number one and Canada number two potatoes. Description follows.
Description for image – POT-2, (06/96) (CFIA)

Air cracks are scored when:

A) Canada No. 1

  1. the air crack(s) exceed ⅓ the length/diameter of the potato (whichever is greater) in the aggregate; or
  2. the damage cannot be removed without the loss of more than 5% of the weight of the potato.

B) Canada No. 2

  1. the air crack(s) exceed ¾ the length/diameter of the potato (whichever is greater) in the aggregate; or
  2. the damage cannot be removed without the loss of more than 10% of the weight of the potato.

7.2 Bruises (C) and (P)

Bruises on potatoes generally manifest as one of two kinds: shatter bruises or pressure bruises. Bruises from rough handling that produces areas of cracked, shattered skin, or severe breaks to the flesh are considered shatter bruises. These nearly always result in damage to the underlying tissue. Areas that are flattened or depressed due to pressure at points of contact with adjacent potatoes or the floor are considered to be pressure bruises.

Shatter Bruises

The term "shatter bruises" is used to describe recent injury to a potato from rough handling. In some lots, almost invisible bruising or shattering is followed by extensive rot.

For more information, please refer to visual aid POT-3 (06/96) (CFIA), and photos 97-99 (USDA).

POT-3 (06/96) (CFIA)
Bruises – maximum allowed for Canada number one and Canada number two potatoes
Description for image – POT-3 (06/96) (CFIA)

Damage by shatter bruises is scored when:

A) Canada No. 1

  1. affects more than 5% of the surface area in the aggregate; or
  2. the injury to the surface area cannot be removed without a loss of more than 5% of the weight of the potato; or
  3. materially affects the appearance of the potato.

B) Canada No. 2

  1. affects more than 10% of the surface area in the aggregate; or
  2. the injury to the surface area cannot be removed without a loss of more than 10% of the weight of the potato; or
  3. seriously affects the appearance of the potato.

Note: Shatter bruises should be scored as a condition defect at destination if there is reason to suspect the damage occurred subsequent to grading and packing. They should be reported as; "Shattering".

If the inspector suspects the damage occurred at shipping point, then the defect should be reported as "shattered" and scored as a grade defect. All bruises at shipping point are considered to be grade defects.

Pressure Bruises

Pressure bruises develop in storage on some tubers late in the season. There appears to be a relation between maturity, storage conditions, and pressure bruises. This defect is more often the result of pressure bruises at point of contact with adjacent potatoes or the floor. In most instances, there will be no discolouration of the underlying flesh at time of packing, however, grayish to black discolouration may develop in this tissue, to a considerable depth, upon arrival in the market. It is impossible to predict whether discolouration will occur, or how extensive it will be, from the appearance of the flattened or depressed areas.

Damage by pressure bruises is scored when:

A) Canada No. 1

  1. affects more than 5% of the surface area in the aggregate; or
  2. the injury to the surface area cannot be removed without a loss of more than 5% of the weight of the potato; or
  3. materially affects the appearance of the potato (as determined by the following table A).

B) Canada No. 2

  1. affects more than 10% of the surface area in the aggregate; or
  2. the injury to the surface area cannot be removed without a loss of more than 10% of the weight of the potato; or
  3. seriously affects the appearance of the potato (as determined by the following table B).

All pressure bruises may be lumped under one defect heading, however, if reported as such, the inspector must use the general terms to identify the type of pressure bruises (e.g. generally flattened and depressed, few sunken and discoloured). If reported separately, the use of the general terms is not required.

The following tables should be used as guides when scoring pressure bruises to determine if they materially or seriously affect the appearance. Descriptions of the different types of pressure bruises are as follows:

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.

Visual Aids Refer to photo 137 (USDA).

Sunken Discoloured Areas (C)

These areas vary in size and are sunken in comparison with the adjacent surface. They are darker than the skin colour of the potato and vary in their degree of darkness from light brown to dark brown to black.

Visual Aids Refer to photo 138 (USDA).

Sunken Discoloured Sticky Areas (C)

Discolouration 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.

Visual Aids Refer to photo 138 (USDA) for ID only.

Score as "materially affects" when the affected area(s) affects more surface area than allowed as outlined in the following table.

A) Canada No. 1

Potato Diameter
inches
Potato Diameter
mm
Potato Weight
oz
Potato Weight
g
Flattened Depressed Areas (in the aggregate)
Not more than:
Sunken Discoloured Areas (in the aggregate)
Not more than:
Sunken Discoloured Sticky Areas (in the aggregate)
Not more than:
<2 <51 <4 <113 13 mm (½ inch) 10 mm (⅜ inch) mm (¼ inch)
2-2 ½ 51-63 4-6 113-170 26 mm (1 inch) 18 mm (¾ inch) 13 mm (½ inch)
>2 (½ -3 >63-76 >6-8 >170-227 32 mm (1 ¼ inch) 26 mm (1 inch) 18 mm (¾ inch)
>3 -3 ½ >76-89 >8-14 >227-397 39 mm (1 ½ inch) 32 mm (1 ¼ inch) 26 mm (1 inch)
>3 ½-4 >89-101 >14-20 >397-568 44 mm (1 ¾ inch) 39 mm (1 ½ inch) 32 mm (1 ¼ inch)
>4-4 ½ >101-114 >20-28 >568-795 51 mm (2 inch) 44 mm (1 ¾ inch) 39 mm (1 ½ inch)
>4 ½-5 >114-127 >28-36 >795-1022 57 mm (2 ¼ inch) 51 mm (2 inch) 44 mm (1 ¾ inch)
>5 >127 >36 >1022 64 mm (2 ½ inch) 57 mm (2 ¼ inch) 51 mm (2 inch)

Score as "seriously affects" when the affected area(s) affects more surface area than allowed as outlined in the following table.

B) Canada No. 2

Potato Diameter
inches
Potato Diameter
mm
Potato Weight
oz
Potato Weight
g
Flattened Depressed Areas (in the aggregate)
Not more than:
Sunken Discoloured Areas (in the aggregate)
Not more than:
Sunken Discoloured Sticky Areas (in the aggregate)
Not more than:
< 2 < 51 < 4 < 113 26 mm (1 inch) 18 mm (¾ inch) 13 mm (½ inch)
2-2 ½ 51-63 4-6 113-170 39 mm (1 ½ inch) 26 mm (1 inch) 18 mm (¾ inch)
>2 ½-3 >63-76 >6-8 >170-227 44 mm (1 ¾ inch) 32 mm (1 ¼ inch) 26 mm (1 inch)
>3-3 ½ >76-89 >8-14 >227-397 48 mm (1 ⅞ inch) 39 mm (1 ½ inch) 32 mm (1 ¼ inch)
>3 ½-4 >89-101 >14-20 >397-568 51 mm (2 inch) 44 mm (1 ¾ inch) 39 mm (1 ½ inch)
>4-4 ½ >101-114 >20-28 >568-795 57 mm (2 ¼ inch) 51 mm (2 inch) 44 mm (1 ¾ inch)
>4 ½-5 >114-127 >28-36 >795-1022 69 mm (2 ¾ inch) 57 mm (2 ¼ inch) 51 mm (2 inch)
>5 >127 >36 >1022 84 mm (3 ¼ inch) 64 mm (2 ½ inch) 57 mm (2 ¼ inch)

7.3 Cuts / Clipped Ends / Knobs Removed (P)

7.3.1 Cuts

Cuts are areas where some of the flesh of the potato has been exposed. This may occur during harvest, storage or packing. Do not confuse this defect with clipped ends, knobs removed or mechanical damage.

Note: Digger cuts are considered the same as cuts and should be scored under the same heading.

Cuts are to be scored when:

A) Canada No. 1

  1. one (1) smooth cut affects more than 5% of the surface area.

B) Canada No. 2

  1. cut(s) affect more than 10% of the surface area in the aggregate; or
  2. a single cut extends beyond one-half (½) the length of the potato.

7.3.2 Clipped Ends

This defect has been included as a result of the Canada/U.S. potato grade harmonization talks. This is intended for information purposes only and is not to be implemented by Canadian inspection staff.

Do not confuse this defect with knobs removed, mechanical damage or cuts.

7.3.3 Knobs Removed

The two main causes of this defect include knobs breaking off accidentally when they are not well attached to the tuber or trimming of these knobs during the sorting and grading process.

Knobs removed is scored when:

A) Canada No. 1

  1. more than one knob is removed;
  2. the area of one removed knob affects more than 5% of the surface; or
  3. the affected area is rough or jagged.

B) Canada No. 2

  1. affects more than 10% of the surface area in the aggregate; or
  2. the area that is rough or jagged affects more than 5% of the surface area in the aggregate.

Visual Aids Refer to photos 100-101 (USDA)

7.4 Dried Stems (P)

This defect is rather unusual and occurs mostly during seasons of extreme drought when enlarged, tough stems do not readily separate from the tubers.

Dried stems which remain attached to individual potatoes are not scoreable as a defect against either the Canada No. 1 or Canada No. 2 grades.

7.5 Dry Rot (P)

This term is used to describe the dry decomposition usually starting in cuts, bruising or other injuries. It may be moist but not wet. Inspectors should follow the same rule as decay regarding the identification of this disease.

Dry rot is scored when:

A) Canada No. 1

  1. affects the flesh of the potato and cannot be removed without a waste of more than 5% by weight of a potato.

B) Canada No. 2

  1. affects the flesh of the potato and cannot be removed without a waste of more than 10% by weight of a potato.

7.6 Elephant Hide (P)

Elephant hide manifests 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.

Elephant hide is to be scored when:

A) Canada No. 1

  1. affects more than 10% of the surface of the potato.

B) Canada No. 2

  1. affects more than 25% of the surface of the potato.

7.7 Enlarged Lenticels (C) and (P)

Excessive moisture before harvest is the main cause of this disorder. Normally lenticels are inconspicuous on tubers but under high moisture conditions they rise about 1.6 mm (1/16 inch) and form numerous whitish protuberances over the tuber surface. If tubers are held in moist atmospheres, these elevated areas remain whitish, but when the tubers dry, they become skin coloured, open and somewhat depressed. They make excellent openings for micro-organisms, particularly soft rot bacteria.

For more information, please refer to visual aid POT-1, (01/95) (CFIA) and photos 105-107 (USDA).

POT-1, (01/95) (CFIA)
Enlarged lenticels – maximum allowed – equal amount or less allowed on opposite side for Canada number one and Canada number two potatoes. Description follows.
Description for image – POT-1, (01/95) (CFIA)

Enlarged lenticels are scored when:

A) Canada No. 1

  1. it materially affects the appearance.

B) Canada No. 2

  1. it seriously affects the appearance.

7.8 External (Surface) Discolouration (C)

Note: External discolouration, previously specified as "Other Than Healed Over Flesh or Scald", "Healed Over Flesh", and "Scald", has now been grouped into one defect, referred to as External Discolouration.

External discolouration is usually caused by a rapid loss of moisture and oxidation through skinned areas. Although some browning occurs eventually on any injured tissue exposed to the air, it is most serious on skinned potatoes. This type of discolouration is usually only skin deep and rarely affects the flesh of the potato.

Areas that are light tan or lighter in colour and blend with the colour of the tuber should be ignored. These scoring guides are to be used in conjunction with the official USDA visual aids.

Score external discolouration when:

A) Canada No. 1

  1. more than 30% of the surface is affected with light tan or light brown and does not blend; or
  2. more than 15% of the surface is affected with areas darker than light tan or light brown in colour.

B) Canada No. 2

  1. more than 60% of the surface is affected with light tan or light brown and does not blend; or
  2. more than 30% of the surface is affected with areas darker than light tan or light brown in colour.

Visual Aids Refer to photos 108-113 (USDA) and to POT-7, (07/97) (CFIA) and POT-8, (07/97) (CFIA).

POT-7, (07/97) (CFIA)
External discolouration, light tan or light brown that does not blend – maximum allowed for Canada number one and Canada number two potatoes
POT-8, (07/97) (CFIA)
External discolouration, darker than light tan or light brown – maximum allowed for Canada number one or Canada number two potatoes

7.9 Freezing and / Chilling Injuries (C) and (P)

Frozen means that the potato temperature is still below freezing; the potato remains firm without the soft, leaking, wet breakdown associated with tubers that have thawed. Ice crystals will be evident within the tissue.

Freezing injury is the term that refers to potatoes that have been frozen but are not in a frozen state at the time of inspection. Tubers with freezing injury may be firm but show internal discoloration and breakdown of the cells. When ice crystals form in the cells, then thaw, tissue may become soft and watery. A dark line often separates the damaged tissue from healthy tissue. Externally, the potato may appear flabby and darker in appearance. Vascular tissue is very susceptible to low temperatures and may turn black.

Where a tuber has been exposed to freezing temperatures for a short period of time, superficial damage may occur with the lesions becoming a dry, leathery, chalky white, starchy mass.

Chilling injury may be the result of prolonged exposure to temperatures at or slightly above the freezing point. Affected areas may appear as: darkening or necrosis of the vascular bundles, Mahogany Browning, or internal pink, grey or purple discolouration. See Section 8.4 Internal Discolouration for information on Mahogany Browning.

For both Canada No. 1 and Canada No. 2 grades, if wet, soft, mushy or leaky type of injury is present, score against the tolerance for decay.

Freezing and/or chilling injury is scored when:

A) Canada No. 1

  1. external dry type of freezing and/or chilling injury is present affecting the flesh of the potato and cannot be removed without a loss of more than 5% by weight of the potato (score as dry rot against the general tolerance for External Defects); or
  2. discolouration of the tissue of the potato is present which cannot be removed without a loss of more than 5% by weight of the potato; or there are more than the equivalent of three (3) scattered spots 3 mm (⅛ inch) in diameter on a potato of 63 mm (2 ½ inches) or a weight of 170 g (6 oz).

Correspondingly, lesser or greater affected spots are allowed on smaller or larger potatoes.

B) Canada No. 2

  1. external dry type of freezing and/or chilling injury is present affecting the flesh of the potato and cannot be removed without a loss of more than 10% by weight of the potato (score as dry rot against the general tolerance for External Defects); or
  2. discolouration of the tissue of the potato is present which cannot be removed without a loss of more than 10% by weight of the potato or there are more than the equivalent of six (6) scattered spots 3 mm (⅛ inch) in diameter on a potato of 63 mm (2 ½ inches) or a weight of 170 g (6 oz).

Correspondingly, lesser or greater affected spots are allowed on smaller or larger potatoes.

Note: Discolouration of the flesh of the tuber should be scored on a waste basis if the damage is entirely outside of the vascular bundles, and should be scored on the basis of the equivalent of 3 or 6 scattered spots ⅛ inch in diameter in an individual tuber when the damage is entirely within the vascular ring.

Visual Aids Refer to photos 29-31 (USDA)

It is very important to show the location of the freezing injury both within the package and vehicle. The location of affected specimens generally provides conclusive proof of whether the damage occurred prior to or after loading.

For example:

  1. wet freezing damage found mixed throughout sacks and mixed throughout piling in the vehicle would indicate that freezing had occurred prior to loading (field frost).
  2. wet freezing damage found in specimens and sacks contacting and/or adjacent to the floor, wall and doors of the vehicle would indicate that freezing occurred in transit or after loading into the vehicle.

It would be in order to state on the certificate that the location indicates that freezing damage did or did not occur in the vehicle if the facts bear this out. This statement should not be made on certificates covering lots of produce that have been set aside in vehicles, as these lots are not in the original piling.

Every effort should be made to inspect the complete contents of the vehicle. When the vehicle is fully loaded and the load is in a frozen state, it would be in order to take temperature readings, make note of the piling and location of wet bags (if possible) and leave the load until it has thawed out. Both sound bags and wet bags should be examined and the results and quantity of each shown on the certificate.

7.10 Grass Damage / Wireworm Holes (P)

Grass Damage

Usually grass damage is caused by quack grass. The sharp growing points of the stolons penetrate into or completely through the tubers. There is usually evidence of the weed attached to the potato.

Visual Aids Refer to photo 54 (USDA).

Wireworm Holes

Early injury, when the tubers are small, the larva causes deep, funnel-shaped cavities to be formed as the potatoes mature. Mid-season injury results in the formation of pits 6 to 13 mm (¼ to ½ inch) deep and 1.6 to 3 mm (1/16 to ⅛ inch) in diameter, sometimes lined with discoloured scar tissue. Late injury consists of clean cut round holes, scar tissue is not prominent.

Wireworm holes or grass damage are scored when:

A) Canada No. 1

  1. affect the flesh of the potato and cannot be removed without a waste of more than 5% by weight of the potato.

B) Canada No. 2

  1. Affect the flesh of the potato and cannot be removed without a waste of more than 10% by weight of the potato.

7.11 Greening (C)

Greening tubers are found in many warehouses and stores where they are exposed to artificial light. The disorder is serious because it may cause solanine poisoning. Exposed skin surfaces of the tuber turns greenish or green. Usually the inner flesh becomes yellow or cream-coloured.

The affected area could be located anywhere on the tuber. Usually the green colour found on greening tubers is lighter than that found on sunburn tubers. Do not mistake greening with sunburn. For a description of sunburn, please refer to Section 7.25 of this manual.

Score greening when:

A) Canada No. 1

  1. when removal causes a loss of more than 5% of the total weight of the potato; or
  2. when materially detracting from the appearance of the potato.

Green colour affecting more than 25% of the surface in aggregate is considered materially detracting.

B) Canada No. 2

  1. when removal causes a loss of more than 10% of the total weight of the potato; or
  2. when seriously detracting from the appearance of the potato.

Green colour affecting more than 50% of the surface in aggregate is considered seriously detracting.

Visual aids Refer to photo 55 (USDA).

7.12 Growth Cracks (P)

Growth cracks may be caused by very rapid growth, such as when a rainy period follows a long dry spell. Growth cracks most often occur towards the bud end of the tuber and usually extends lengthwise. The cracks vary in size but usually heal over with no rot following the injury.

Growth cracks are assessed on appearance, not on cut-off waste and are scored when:

A) Canada No. 1

  1. they affect more than ½ the length of the potato in the aggregate on round varieties or more than ⅓ the length in the aggregate on long varieties; or
  2. the depth of growth cracks is greater than the depth allowed in Table 3.

B) Canada No. 2

  1. they affect more than ¾ the length of the potato in the aggregate; or
  2. the depth of growth cracks is greater than the depth allowed in Table 3.

Table 3

Depth allowed for growth cracks
Potato Diameter Weight Depth allowed for Canada No. 1 Depth allowed for Canada No. 2
< 51 mm (2 inches) < 113 g (4 oz) < 3 mm (⅛ inch) < 6 mm (¼ inch)
51-64 mm (2 inches-2 ½ inches) 113-170 g (4-6 oz) mm (¼ inch) 10 mm (⅜ inch)
>64-76 mm (2 ½ inches-3 inches) >170-227 g (6-8 oz) 10 mm (⅜ inch) 13 mm (½ inch)
>76 mm (3 inches) >227 g (8 oz) 13 mm (½ inch) 16 mm (⅝ inch)

7.13 Insect Injury (P)

7.13.1 Flea Beetle Injury

Flea beetle injury may appear as surface injury, internal injury, or both. Surface injury consists of pimple-like eruptions or rough, winding trails about 1.6 mm (1/16 inch) wide and of varying length. These trails are produced by larvae feeding just beneath the epidermis of new tubers. Internal injury consists of single or groups of narrow, brown slivers or feeding tunnels that extend into the tuber for 6 to 19 mm (¼ to ¾ inch). Cracks occur where their tunnels come together.

For more information, please refer to visual aid: POT-6, (06/96), and photo 50 (USDA).

POT-6, (06/96)
Identification – flea beetle. Description follows.
Description for image – POT-6, (06/96)

Flea beetle injury is scored when:

A) Canada No. 1

  1. affects more than 5% of the surface area in the aggregate; or
  2. cannot be removed without the loss of more than 5% of the weight of the potato.

B) Canada No. 2

  1. affects more than 10% of the surface area in the aggregate; or
  2. cannot be removed without the loss of more than 10% of the weight of the potato.

7.13.2 Grub Damage

Grub damage is caused by the larvae of June beetles. Injury consists of small to large feeding cavities 6 to 25 mm (¼ to 1 inch) or more in diameter. The irregular-shaped cavities usually are wider than deep, with characteristic rough ridges inside, half or more of the tuber sometimes being consumed.

Grub damage is scored when:

A) Canada No. 1

  1. affects more than 5% of the surface area in the aggregate; or
  2. cannot be removed without the loss of more than 5% of the weight of the potato.

B) Canada No. 2

  1. affects more than 10% of the surface area in the aggregate; or
  2. cannot be removed without the loss of more than 10% of the weight of the potato.

7.14 Mechanical Damage (P)

Mechanical damage may be used for any defects other than cuts or bruises caused by mechanical means during harvesting, storage or packing and the inspector should describe the type of damage under defect description.

Mechanical damage is scored when:

A) Canada No. 1

  1. the injury is not well healed, rough and exceed an aggregate area of more than 5% of the surface; or
  2. any kind of injury which cannot be removed without wasting more than 5% by weight.

B) Canada No. 2

  1. the injury is not well healed, rough and exceed an aggregate area of more than 10% of the surface; or
  2. any kind of injury which cannot be removed without wasting more than 10% by weight.

7.15 Nematode Damage (P)

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 laying nematodes are seen in abundance scattered throughout the outer tissues with most of them approximately 3 mm to 6 mm (⅛ to ¼ inch) beneath the skin. To the naked eye, they appear to be somewhat discoloured, slightly water-soaked spots. As deposits of eggs in the flesh sometimes hatch out and the nematode starts feeding after the potato has been harvested, infestation may sometimes show no external symptoms.

Nematode damage is scored when:

A) Canada No. 1

  1. the affected area cannot be removed without wasting more than 5% of the weight of the potato.

B) Canada No. 2

  1. the affected area cannot be removed without wasting more than 10% of the weight of the potato.

Visual Aids Refer to photo 69, 69a and 69b (USDA).

7.16 Rhizoctonia (P)

Rhizoctonia or black scurf on the tuber is identified by the presence of hard, black or dark brown bodies called sclerotia resting on the surface of the tubers. Frequently it is called "the dirt that will not wash off". The sclerotia will vary in size from small specks to large masses nearly 25 mm (1 inch) across. Frequently, the fungus is confined to mild to severe netting or scurf, and often, even in extreme cases, only a portion of the tuber is affected.

Rhizoctonia is scored when:

A) Canada No. 1

  1. damage that exceeds an aggregate area of more than 5% of the surface.

B) Canada No. 2

  1. damage exceeds an aggregate area of more than 25% of the surface.

7.17 Rodent and Bird Damage (P)

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 forms 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.

Rodent and bird damage is scored when:

A) Canada No. 1

  1. affecting more than 5% of the surface area; or
  2. causing more than 5% waste

B) Canada No. 2

  1. affecting more than 10% of the surface area; or
  2. causing more than 10% waste

7.18 Russetting (P)

The exact cause of russetting on non russet type potatoes is unknown. Other than affecting the outward appearance and marketability of the affected potato, it does not lead to decay in storage or in transit.

There are two types of russetting that may occur, either smooth or rough. Smooth russetting may appear as streaked, patchy or solid and is smooth to touch. Rough russetting will be considered as rough when the potatoes show rough skin with minor shallow splitting.

For more information, please refer to visual aid POT-4, (06/96) (CFIA) (top two pictures only).

POT-4, (06/96) (CFIA)
Russeting – maximum allowed for Canada number one potatoes and Canada number two potatoes. Description follows.
Description for image – POT-4, (06/96) (CFIA)

Russetting that is not characteristic of the variety is scored when:

A) Canada No. 1

  1. more than 50% of the surface area in the aggregate is affected.

B) Canada No. 2

  1. not scoreable.

7.19 Scab (P)

Scab of potatoes is caused by two very different of organisms; one fungal; one bacterial. Scab lesions may appear as purplish-brown sunken areas, pitted areas, raised pustules, raised corky rough areas, or nearly smooth lesions blending with the skin of the tuber.

For the purposes of scoring scab, however, regardless of the causal agent, the defect is assessed in terms of the symptoms observed, which would be: a) Pitted Scab; b) Russet Scab; or c) Surface Scab. All scab may be lumped under one defect heading, however if reported as such, the inspector must use the general terms to identify the type of scab, i.e. generally pitted scab; few russet scab. If reported separately, the use of the general terms is not required.

7.19.1 Pitted Scab

Pitted scab is generally the result of early infection with the uninjured tissues growing up around the affected areas. The resulting pitted depression may be relatively shallow or may extend ¼ inch or more into the tuber flesh.

Score pitted scab:

A) Canada No. 1

  1. when removal causes a loss of more than 5% of the total weight of the potato; or
  2. when materially detracting from the appearance.

When scab affects an aggregate area of more than 12 mm (3 ½ inch) on a potato that has a diameter 63 mm (2 ½ inches) or a weight of 170 g (6 oz) that is considered materially detracting from the appearance.

B) Canada No. 2

  1. when removal causes a loss of more than 10% of the total weight of the potato; or
  2. when seriously detracting from the appearance.

When scab affects an aggregate area of more than 25 mm (1 inch) on a potato that has a diameter 63 mm (2 ½ inches) or a weight of 170 g (6 oz) that is considered seriously detracting from the appearance.

Visual Aids Refer to photos 129 & 130 (USDA).

7.19.2 Russet Scab

Russet scab is a roughening, scurfing or cracking of the tuber skin. The affected tissues vary from light tan to brown colour. Russet scab may occur in localized areas or in large areas on the skin of a potato. The scab will appear as smooth, rough or may be cracked.

Smooth russetting means net-like, streaked, patchy or solid, readily apparent but smooth to touch.

Rough russetting means bark-like, pebbly or thick, not blending with the skin of the tuber. It has more of a coarse sand paper feel when lightly brushed over the affected area.

Score russet scab when it:

A) Canada No. 1

  1. smooth – affects more than ⅓ of the surface area; or
  2. rough – affects more than 10% of the surface area in aggregate.

B) Canada No. 2

  1. smooth – not scoreable; or
  2. rough – affects more than 25% of the surface area in aggregate.

Visual Aids For more information, please refer to visual aid POT-4, (06/96) (CFIA) (bottom picture only), or to photos 77a, 77b & 143 (USDA).

POT-4, (06/96) (CFIA)
Russet scab (smooth) – maximum allowed for Canada number one potatoes

7.19.3 Surface Scab

The lesions affected by surface scab may be superficial, slightly raised or sunken, rough or corky depending on such factors as the susceptibility of the variety of potato, time of infection of the tubers, environmental conditions, and the aggressiveness of the particular bacterium. Lesions may vary in size and shape from 6 mm (¼ inch) to 18 mm (¾ inch) in diameter, may be few or many scattered over the entire tuber surface, may be highly concentrated in one or more isolated areas of the tuber, or may appear as net-like on a large area of the tuber surface.

Score surface scab when it:

A) Canada No. 1

  1. affects more than 5% of the surface area in the aggregate of an individual potato

B) Canada No. 2

  1. affects more than 25% of the surface area in the aggregate of an individual potato.

Visual Aids For more information, please refer to visual aid POT-6, (06/96) (CFIA) or to photos 78 & 78a (USDA).

POT-6, (06/96) (CFIA)
Identification – flea beetle, surface scab, sunburn

7.20 Shape (P)

See Section 5 for description of shape defects.

7.21 Silver Scurf (C)

Silver scurf is characterized by a gray, smooth, leathery appearance of the skin and is more noticeable when the tubers are wet because of the silvery sheen. This silvery condition is caused by a fungus which penetrates the tubers through the lenticels and epidermis.

The occurrence of superficial brownish spots more or less circular in outline, constitutes the first symptoms. The disease may spread in storage, especially under high humidity and temperatures. As the disease progresses the affected areas become silvery brown and may coalesce to cover most of the tuber surface. In severe cases the entire surface of the tuber may be affected with little or no contrast with the natural skin colour. In advanced stages of the disease affected areas begin to shrivel or wrinkle.

Keep in mind that these guidelines apply to any shade or colour of the defect.

Visual Aids Refer to photos 81-82g (USDA).

Score silver scurf when:

A) Canada No. 1

  1. it affects more than 50% of the surface area of the potato in the aggregate

B) Canada No. 2

  1. its severity causes a wrinkling of the skin over more than 50% of the surface

7.22 Skin Checks or Thumbnail Marks (C)

This disorder is caused by rough handling, excessively dry atmosphere or is associated with sudden changes in temperature. Actually, skin checks appear similar to the injury caused by pressing a thumbnail directly into the tuber. The surface is covered with many crescent-shaped slits which are sometimes confused with symptoms of ring rot. The tubers dry out rapidly and shrivel unless stored in moist conditions.

For more information, please refer to visual aid POT-5, (02/99) (CFIA), or photos 134 & 135 (USDA).

POT-5, (02/99) (CFIA)
Skin checks – maximum allowed for Canada number one and Canada number two potatoes. Description follows.
Description for image – POT-5, (02/99) (CFIA)

Skin checks or thumbnail marks are scored when:

A) Canada No. 1

  1. it materially affects the appearance, edibility or shipping quality of the potatoes.

B) Canada No. 2

  1. it seriously affects the appearance, edibility or shipping quality of the potatoes.

7.23 Skin Spot (P)

Skin spot of potatoes in storage is characterized by purplish-black, slightly raised spots up to 2 mm (approximately 1/16 inch) in diameter, singly or in groups over the surface of the tuber. They may appear either at random over the surface or aggregated around the eyes. Sometimes larger necrotic areas form over the tuber surface. These necrotic areas can be picked out, leaving circular pits of healthy flesh.

Skin spot is scored when:

A) Canada No. 1

  1. purplish-black, slightly raised areas or areas where the damage penetrates the flesh, no matter the colour. Score when affecting more than 5% of the surface area in the aggregate; or
  2. smooth, brown coloured areas which tend to blend into the surface of the tuber, particularly in the case of varieties with a russet skin or where silver scurf is present. Score when affecting more than 25% of the surface area in the aggregate.

B) Canada No. 2

  1. purplish-black, slightly raised areas which do not penetrate the flesh. Score when affecting more than 25% of the surface area in the aggregate; or
  2. penetrates the flesh and cannot be removed without a waste of more than 5% by weight of the potato; or
  3. skin spot does not affect this grade when smooth, brown coloured areas which tend to blend into the surface of the tuber.

7.24 Sprain (Corky Ring Spot) (C)

This disease in potatoes may also be known as corky ring spot or internal rust spot. Affected tubers show rings, semi-circles or spots on the surface with similar marks on the interior tissues. The tuber skin over some of the brown, sunken rings often cracks. The affected tissues are moderately firm and corky.

Both grades must be free from this disease.

7.25 Sunburn (P)

Sunburned tubers are found in many potato fields. The disorder is serious in table stock, as the tubers may cause solanine poisoning. The skin of the tuber turns as green as the above ground parts of the plant. Typically, the bud end is affected and may involve only one area of the tuber. Usually the inner flesh becomes yellow or cream-coloured.

Sunburn is caused by exposure to sunlight as opposed to greening, which is caused by exposure to light in storage. For a description and tolerance of greening, please refer to Section 7.11 of this manual.

Although sunburn is scored on the waste basis, it is usually possible for experienced inspectors to determine, without cutting, whether individual specimens are scoreable by judging the size of the affected area and the intensity of green colour. Inexperienced inspectors should always cut potatoes to determine the amount of waste. Any amount of green colour of the flesh is scoreable, if over the tolerance allowed. When the inspector is in doubt as to whether the flesh is green or yellow, he should cut an unaffected portion of the potato, preferably on the opposite side of the affected area. If the flesh of the affected area is definitely more greenish than the unaffected area, he scores the greenish part against the waste basis.

For more information, please refer to visual aid POT-6, (06/96) (CFIA) (bottom two pictures only) or photos 86 & 87 (USDA).

POT-6, (06/96) (CFIA)
Identification – sunburn. Description follows.
Description for image – POT-6, (06/96) (CFIA)

Sunburn is scored when:

A) Canada No. 1

  1. removal causes loss of more than 5% of the total weight of the potato *(TM).

B) Canada No. 2

  1. removal causes loss of more than 10% of the total weight of the potato *(TM).

7.26 Sunken Discoloured Areas with Underlying Flesh Discoloured (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 sufficiently materially or seriously affect the appearance and it will be necessary for the inspector to cut to determine if there is discolouration of the underlying flesh.

Score sunken discoloured areas with underlying flesh discoloured when:

A) Canada No. 1

  1. removal causes a loss of more than 5% of the total weight of the potato.

B) Canada No. 2

  1. removal causes a loss of more than 10% of the total weight of the potato.

Visual Aids Refer to photo 138 (USDA) for ID only. Cutting must be done to determine underlying flesh discolouration.

7.27 Surface Cracks (P)

Surface cracks are the superficial cracking of the skin of some varieties of potatoes and should not be confused with russetting. The cracks are generally wider and more pronounced than russetting.

Score this defect when:

A) Canada No. 1

  1. fine, net-like cracking – not scoreable; or
  2. smooth, shallow cracking affecting more than ⅓ of the surface area; or
  3. rough, deep cracking affecting more than 5% of the surface area.

B) Canada No. 2

  1. fine, net-like cracking – not scoreable; or
  2. smooth, shallow cracking – not scoreable; or
  3. rough, deep cracking affecting more than 10% of the surface area.

7.28 Tuber Moth Damage (C)

Score this defect when:

A) Canada No. 1

  1. any live larvae is present; or
  2. when materially detracting from the appearance of the potato; or
  3. the affected area cannot be removed without the loss of more than 5% of the weight of the potato.

B) Canada No. 2

  1. any live larvae is present; or
  2. when seriously detracting from the appearance of the potato; or
  3. the affected area cannot be removed without the loss of more than 10% of the weight of the potato.

Visual Aids: Refer to photos 88 & 89 (USDA).

7.29 Other External Defects

Other external defects which are not described in Sections 7.1 to 7.28 are scored as free from any injury or defect or a combination thereof that:

A) Canada No. 1

  1. affects the flesh of the potato and cannot be removed without a loss of more than 5% of the weight of a potato; or
  2. materially affects the appearance, edibility or shipping quality of the potatoes.

B) Canada No. 2

  1. affects the flesh of the potato and cannot be removed without a loss of more than 10% of the weight of a potato; or
  2. seriously affects the appearance, edibility or shipping quality of the potatoes.
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