Harvest Operations
Tuber bulking vs vine kill timing
Equipment operation
Crop maturity
Vine killing
Bruise susceptibility
Potato Growth Stages
Physical Maturity
(Skin set)
Methods to measure skin set
High
Torque
Low
Low
High
Skinning damage
Water loss from a potato in storage
98% through skin
2% through lenticels
Increases
water loss by 3
to 5 fold
Changes in tuber composition with maturity
24
1.095
Bud
21
Sp gravity
18
1.085
15
R2= 0.84**
1.080
1.075
12
9
1.090
1.070
Stem
1.065
6
1.060
3
Reducing Sugars
0
1.055
1.050
60
74
88
102 116 130 144 158 172
Days After Planting
Physiological Maturity = 145 DAP
Specific Gravity
Reducing Sugars (mg/g dry wt)
Knowles et. al., WSU, Pullman
Physiological Maturity
(chemical maturity)
Defined as the average of date when:
Maximum yield
Maximum specific gravity
Minimum sucrose
Minimum reducing sugars
Physiological Maturity Dates
Days 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
Trailblazer-Yield/vine wt.
900
18
16
800
14
700
600
10
500
8
6
400
4
300
2
200
0
130 DAP
145 DAP
cwt/ac
160 DAP
vine wt. (lbs)
175 DAP
lbs/5 plants
cwt/ac
12
Trailblazer
1.1150
0.24
Phys. Maturity- (153DAP)
0.20
1.1050
1.0950
0.12
1.0850
0.08
Reducing Sugars
Specific Gravities
0.16
1.0750
0.04
1.0650
0.00
1.0550
-0.04
130
145
160
Days After Planting
Spec. Gravities
Red. Sugars
175
Sugar Ends can Increase With Increasing Maturity of Ranger Russet
4.0
Ranger Russet
2005
Percent Sugar Ends
3.5
3.0
2.5
2.0
R2= 0.96**
1.5
1.0
0.5
n=7
0.0
155
169
174
179
185
193
Harvest Time (days after planting)
Courtesy Mel Martin, J.R. Simplot Co.
Crop Maturity
Factors that influence crop maturity:
 Variety (Determinate vs indeterminate)
 Emergence date
 Nitrogen fertilization
 Irrigation
 Disease pressure
Crop Maturity
Important reasons for correct maturity :
Simplify vine killing
Minimize harvest damage
Maximize tuber solids
Minimize tuber sugars
Maximize storability
Vine Killing
Reasons:
Regulate maturity
Prepare tubers for handling
Control tuber size
Coordinate 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
• 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
Brook, R.C. 1996. Potato Bruising. National Potato Anti-bruise Committee
Effect of tuber susceptibility and
harvester operation on bruise damage
70
60
50
% Bruise
40
30
Susceptible
20
Resistant
10
0
0 10 20 30 40 50
Variation from optimum operation (%)
Source: Thornton et al., 1973
Tuber Physical Properties Affecting Bruise
• Tuber Size
o Large tubers > damage small tubers
o Small radius (end) > damage large radius
• Cell Size
o Large cells > damage than small cells
o Growth conditions play large roll in cell size
• Age
oBlackspot 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
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).
Brook, R.C. 1996. Potato Bruising. National Potato Anti-bruise Committee
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 impact
0 = No
Damage
5 = Most
Damage
Field Maturity as it Relates to Blackspot
Bruising of Russet Burbank Potatoes
Blackspot Severity Group1
Field Maturity (%)2
19933 19943 Mean
Resistant (<2.5)
17
54
36
Mod. Susceptible (2.5 – 3.0)
33
59
46
Susceptible (3.1 – 3.5)
48
61
55
Very Susceptible (>3.5)
59
89
74
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.
Corsini, D., J. Stark, and M. Thornton. 1999. American J of Potato Research. P.221-226.
Specific Gravity as it Relates to Blackspot
Bruising of Russet Burbank Potatoes
Blackspot Severity Group1
Specific Gravity2
Resistant (<2.5)
1.074
Mod. Susceptible (2.5 – 3.0)
1.077
Susceptible (3.1 – 3.5)
1.081
Very Susceptible (>3.5)
1.083
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.
Corsini, D., J. Stark, and M. Thornton. 1999. American J of Potato Research. P.221-226.
Soil Moisture as it Relates to Blackspot
Bruising of Russet Burbank Potatoes
Blackspot Severity Group1
Soil Moisture (%)2
Resistant (<2.5)
51
Mod. Susceptible (2.5 – 3.0)
41
Susceptible (3.1 – 3.5)
33
Very Susceptible (>3.5)
34
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.
Corsini, D., J. Stark, and M. Thornton. 1999. American J of Potato Research. P.221-226.
Factors Increasing Black Spot
Bruise Susceptibility
 More mature vines
Russet Burbank - 70% dead vines
Ranger Russet - 20% dead vines
 Higher specific gravity
Russet Burbank - Above 1.080
Ranger Russet - Above 1.085
 Available soil moisture less than 60%
Management Through Harvest
-Tuber hydration
-Drop height
-Pulp temperature
-Drop surface
Tuber Hydration Level Effect on Black Spot
and Shatter Bruise of Russet Burbank at 42ºF
100
90
% Damage
80
70
60
Black Spot
50
Shatter
40
Total
30
20
10
0
Hydrated (crisp)
Dehydrated (limp)
Tuber Hydration
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
51
4 days before harvest
2
25
8 days before harvest
2
13
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.
Stark, J. C. January 1987. University of Idaho Potato School Proceedings. P 82-83.
Impact of temperature and drop
height on bruise incidence
25
20
15
Drop Height
10
(in)
50 oF
60 oF
5
0
0
-5
20
40
60
80
100
Total Bruise (%)
Hyde, G., R. Bajema and R. Thornton, 1993
Impact of temperature and drop
height on bruise incidence
14
50 oF on coated chain
12
10
8
Drop Height
(in)
6
Steel surface
50 oF
60 oF
4
2
0
0
20
40
60
Total Bruise (%)
80
100
Relationship Between Soil Temperature and
Tuber Bruising During a 24-Hour Period
70
More
% Bruise
65
60
55
50
Soil Temperature
45
Less
MN
4 am
8 am
Noon
4 pm
8 pm
MN
Time of Day
Smittle, D.A., et al. 1974. Harvesting Potatoes with Minimum Damage. Am. Potato J. 51: 153-164.