Harvest Operations

Tuber bulking vs vine kill timingEquipment operationCrop maturityVine killingBruise susceptibility

Potato Growth Stages

Physical Maturity (Skin set)

Methods to measure skin set

Torque

High

Low

High Low

Skinning damage

Water loss from a potato in storage98% through skin

2% through lenticels

Increases water loss by

3 to 5 fold

Days After Planting

60 74 88 102 116 130 144 158 172

Red

ucin

g S

ugar

s (m

g/g

dry

wt)

0

3

6

9

12

15

18

21

24

Spe

cific

Gra

vity

1.050

1.055

1.060

1.065

1.070

1.075

1.080

1.085

1.090

1.095Bud

Stem

Sp gravity

Reducing Sugars

R2= 0.84**

Changes in tuber composition with maturity

Physiological Maturity = 145 DAP

Knowles et. al., WSU, Pullman

Physiological Maturity (chemical maturity)

Defined as the average of date when:Maximum yieldMaximum specific gravityMinimum sucroseMinimum reducing sugars

Physiological Maturity DatesDays after planting

Cultivar Max Yield Max SG Min Sucrose Min Sugars DAP to PM

Ranger 160 146 130 130 142

Burbank 156 145 142 145 147

Umatilla 144 158 161 155 155

Alpine 169 153 155 143 155

Clearwater 175 175 130 135 154

Trailblazer 175 160 136 142 153

* All cultivars reached maturity between 2800 and 3000 degree days

130 DAP 145 DAP 160 DAP 175 DAP200

300

400

500

600

700

800

900

0

2

4

6

8

10

12

14

16

18

Trailblazer-Yield/vine wt.

cwt/ac vine wt. (lbs)

cwt/

ac

lbs/

5 pl

ants

130 145 160 1751.0550

1.0650

1.0750

1.0850

1.0950

1.1050

1.1150

-0.04

0.00

0.04

0.08

0.12

0.16

0.20

0.24

Trailblazer

Spec. Gravities

Days After Planting

Spec

ific G

ravi

ties

Redu

cing

Sug

ars

Phys. Maturity- (153DAP)

Harvest Time (days after planting)

155 169 174 179 185 193

Per

cent

Sug

ar E

nds

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0 Ranger Russet2005

R2= 0.96**

n = 7

Sugar Ends can Increase With Increasing Maturity of Ranger Russet

Courtesy Mel Martin, J.R. Simplot Co.

Crop MaturityFactors that influence crop maturity:

Variety (Determinate vs indeterminate)Emergence dateNitrogen fertilization IrrigationDisease pressure

Crop Maturity

Important reasons for correct maturity :Simplify vine killingMinimize harvest damageMaximize tuber solidsMinimize tuber sugarsMaximize storability

Vine Killing

Reasons:

Regulate maturityPrepare tubers for handlingControl tuber sizeCoordinate harvest with appropriate season

(need to balance equipment capabilities with climatic conditions)

One main focus of harvest management is bruise reduction - Estimated to cost the US potato industry $298 million annually (1996) - Processing contract incentives - Rejections at market (5% internal defects) - Storage losses (Shrink and rot) - Losses in productivity (processing and fresh pack)

Black spot bruise (a chemical reaction) occurs just beneath the vascular ring (not visible), and skin is not broken.

Shatter bruise breaks the skin, and is a physical damage.

Chemistry of Black Spot Bruise

Brook, R.C. 1996. Potato Bruising. National Potato Anti-bruise Committee

• Tyrosine (a substrate) and polyphenol oxidase (PPO - an enzyme) mix within a cell when cell membranes are damaged

• Oxidation (addition of oxygen) occurs forming intermediate compounds

• End result is melanin (black, gray, or brown color)

• Process takes 12 to 72 hours, depending on temperature

0 10 20 30 40 500

10

20

30

40

50

60

70

SusceptibleResistant

Variation from optimum operation (%)

% Bruise

Source: Thornton et al., 1973

Effect of tuber susceptibility and harvester operation on bruise damage

Tuber Physical Properties Affecting Bruise

• Tuber Sizeo Large tubers > damage small tuberso Small radius (end) > damage large

radius• Cell Sizeo Large cells > damage than small cellso Growth conditions play large roll in cell

size• AgeoBlackspot increases with vine maturity oTubers less susceptible after one month

curing – tubers can withstand 30-80% more impact

Brook, R.C. 1996. Potato Bruising. National Potato Anti-bruise Committee

Tuber Susceptibility to Black Spot Bruise

Brook, R.C. 1996. Potato Bruising. National Potato Anti-bruise Committee

Mineral Nutrition· N and P do not directly affect susceptibility.· Indirectly – deficiency results in earlier

senescence and more mature tubers.· Indirectly – high specific gravity > blackspot

than low specific gravity (N and P both affect specific gravity).

Research on Potassium and Black Spot Bruise

· Black spot bruise potential decreased with increased potassium application in excess of that needed for optimum yield.

· Shatter bruise increased with more potassium.· For each 100 pounds potassium, specific

gravity decreased 2.5 to 3.5 points.

Porter, Greg and P.C. Ocaya. Bruise susceptibility and potassium uptake of Russet Burbank potatoes in response to varied potash rate and timing. University of Maine. Presentation at 2005 PAA meeting. Calgary.

Two requirements for blackspot bruise:- Susceptibility to impact damage

- Potential to darken after impact0 = No

Damage5 = Most

Damage

Field Maturity as it Relates to Blackspot Bruising of Russet Burbank Potatoes

Blackspot Severity Group1 Field Maturity (%)2

Resistant (<2.5)Mod. Susceptible (2.5 – 3.0)Susceptible (3.1 – 3.5)Very Susceptible (>3.5)

19933

17334859

Corsini, D., J. Stark, and M. Thornton. 1999. American J of Potato Research. P.221-226.

19943

54596189

1. Abrasive peel test ratings where 0 = no blackspot and 5 = most damage.2. Percent dead vines in fields in late August.3. R-square values: 1993 = 0.37; 1994 = 0.21. Both significant at P = 0.01.

Mean36465574

Specific Gravity as it Relates to Blackspot Bruising of Russet Burbank

PotatoesBlackspot Severity Group1 Specific Gravity2Resistant (<2.5)Mod. Susceptible (2.5 – 3.0)Susceptible (3.1 – 3.5)Very Susceptible (>3.5)

Corsini, D., J. Stark, and M. Thornton. 1999. American J of Potato Research. P.221-226.

1.0741.0771.0811.083

1. Abrasive peel test ratings where 0 = no blackspot and 5 = most damage.

2. Average for all fields in the survey within a blackspot severity group, 1994. No relationship between specific gravity and bruise in 1993.

Soil Moisture as it Relates to Blackspot Bruising of Russet Burbank Potatoes

Blackspot Severity Group1 Soil Moisture (%)2

Resistant (<2.5)Mod. Susceptible (2.5 – 3.0)Susceptible (3.1 – 3.5)Very Susceptible (>3.5)

Corsini, D., J. Stark, and M. Thornton. 1999. American J of Potato Research. P.221-226.

51413334

1. Abrasive peel test ratings where 0 = no blackspot and 5 = most damage.

2. Available soil water at time of tuber sampling; average for all fields within a severity group. Data for 1994 only. Little to no differences in percent soil moisture in 1993.

Factors Increasing Black Spot Bruise Susceptibility

· More mature vinesRusset Burbank - 70% dead

vinesRanger Russet - 20% dead

vines· Higher specific gravity

Russet Burbank - Above 1.080Ranger Russet - Above 1.085

· Available soil moisture less than 60%

Management Through Harvest- Tuber hydration- Drop height- Pulp temperature- Drop surface

Series10

10

20

30

40

50

60

70

80

90

100

Black SpotShatterTotal

Tuber HydrationDehydrated (limp) Hydrated (crisp)

% D

amag

eTuber Hydration Level Effect on Black Spot and Shatter Bruise of Russet Burbank at

42ºF

Smittle, D.A., et al. 1974. Harvesting Potatoes with Minimum Damage. Am. Potato J. 51: 153-164.

Influence of Post-Vine-Kill Irrigation on Blackspot Bruise of Lemhi Russet Potatoes

Irrigation Treatment Percent Blackspot

No irrigation 1

4 days before harvest 2

8 days before harvest 2

512513

Stark, J. C. January 1987. University of Idaho Potato School Proceedings. P 82-83.

1. Soil moisture at 50% or less at vine kill.2. No effect of irrigation if soil moisture kept at 65% or above after vine kill.

Impact of temperature and drop height on bruise incidence

0 10 20 30 40 50 60 70 80 90 1000

2

4

6

8

10

12

14

16

18

20

50 oFLinear (50 oF)60 oFLinear (60 oF)

Total Bruise (%)

Drop Height (in)

Hyde, G., R. Bajema and R. Thornton, 1993

Impact of temperature and drop height on bruise incidence

0 10 20 30 40 50 60 70 80 90 1000

2

4

6

8

10

12

14

50 oFLinear (50 oF)60 oFLinear (60 oF)

Total Bruise (%)

Drop Height (in)

50 oF on coated chain

Steel surface

Relationship Between Soil Temperature and Tuber Bruising During a 24-Hour Period

More

Less

% B

ruise

MN 4 am 8 am Noon 4 pm 8 pm MNTime of Day

Smittle, D.A., et al. 1974. Harvesting Potatoes with Minimum Damage. Am. Potato J. 51: 153-164.

7

0

6

5

6

0

5

5

5

0

4

5Te

mpe

ratu

re

(°F)

% Bruise

Soil Temperature