Potato Response to Seedpiece Treatment and Cutting Management
K.A. Rykbost and J. Maxwell'
Introduction
1
Weather conditions at planting resulted in potato seedpiece decay and
stand losses in several fields in the Klamath Basin in both 1992 and 1993.
Very thy soil and high soil temperatures in May, 1992 led to seedpiece
dehydration when fresh-cut seed was planted and irrigation was not applied
within two to four days. Stand losses were over 50 percent in several cases.
Cold and wet soil conditions in May, 1993 also produced seedpiece decay
problems in several local fields. In both situations, pre-cut and well suberized
seed would have been less susceptible to these adverse conditions.
Rhizoctonia is a common problem that affects local crops to varying
degrees depending on weather conditions. In the cold and wet spring of
1993, stem and root damage due to Rhizoctonia lesions were common in
potato crops. Black scurf on mature tubers, caused by Rhizoctonia sclerotia,
is commonly observed, even in years when stem and root lesions are absent.
Rhizoctonia can be endemic in soils or introduced on seed. When
Rhicoctonia is present on the seed, seedpiece fungicide treatment may reduce
damage.
Silver scurf is becoming a serious problem for stored potatoes held for
late season fresh market use or seed. Applications of Mertect to tubers going
into storage provided good control of silver scurf in some areas in prior years.
The pathogen has developed resistance to Mertect in some production areas.
Mertect has not been used extensively in the Klamath Basin. It is not known
whether local strains of silver scurf are resistent to Mertect. The fungal
disease that causes silver scurf can be introduced on seed or persist in the soil
from year to year. Fungicidal treatment of infected seed may reduce the
incidence of silver scurf
/ Superintendent/Professor and Biological Sciences Research Technician HI, respectively, Klamath
Experiment Station, Klamath Falls, OR.
Acknowledgment: Partial financial support for this study provided by the CSRS and the Oregon Potato
Commission is gratefully recognized.
Klamath Experiment Station 81
Potato Response to Seedpiece Treatment and Cutting Management
This study was initiated in 1994 to evaluate the effects of several
commercially available seed treatment fungicides on pre-cut and suberized
versus fresh-cut tubers of Russet Norkotah. Russet Norkotah was used
because recent experience in the Klamath Basin suggests it is more susceptible to silver scurf infection than Russet Burbank. The seed lot used exhibited
a minor level ofRhizoctonia black scurf, but no silver scurf infections.
Procedures
Russet Norkotah tubers were hand cut to 1.5 to 2.0 ounces/seedpiece
on May 3 and May 13. Approximately 50 pound samples were treated at
each cutting date with Tops 5.0 at 0.5 lb/cwt, Tops 2.5 - MZ at 1.0 lb/cwt,
TBZ Firbark at 1.0 lb/cwt, or Dithane F45 (1.6 fluid ounces/2.5 gal) - Agrimycin 17 (48 m1/2.5 gal) dip. Tubers were immersed in the dip treatment for
five minutes. Additional samples were left untreated. Both cut and uncut
tubers were stored at approximately 50 °F and 95 percent relative humidity
from May 3 to May 13. Treatments were arranged in a 2 X 5 factorial design
with four replications of single-row, 42-hill plots. Potatoes were planted with
a two-row assisted-feed planter on May 13. Other cultural practices are
described on pages 38 and 39.
Emergence data were recorded 21, 24, 28, and 34 days after planting.
Vines senesced uniformly in all treatments in late August. Potatoes were
harvested with a one-row digger-bagger on September 22. All tubers from
each plot were stored and graded in mid-October. Fifty-tuber subsamples
were saved from one replication of each treatment and evaluated visually for
silver scurf infection in mid-February and mid-March.
Results and
Discussion
Soil conditions were excellent at and after planting. Soil temperatures at
four inches ranged from 50 to 60 °F throughout May. Precipitation recorded
at KES in May included 1.06 inches from May 4 to May 8 and 0.81 inches
from May 15 to May 20. Rapid emergence occurred in this experiment with
little evidence ofRhizoctonia damage to stems or roots. Effects of cutting
time and fungicide treatments on emergence were minor except that the precut untreated control seed was slower to emerge (Table 1). Final stands were
above 90 percent for all treatments.
82 Klamath Experiment Station
Potato Response to Seedpiece Treatment and Cutting Management
Cutting time did not affect yield, tuber size distribution, or grade (Table
2). Yield differences between fungicide treatments were statistically significant
for 8- to 12-ounce No.ls, total No.ls, No.2s, and total yield. The Tops 5.0
treatment was among the lowest in each of these parameters. Tops 2.5 - MZ
and TBZ - Firbark treatments produced among the highest yields. Intermediate yields were observed for control and dip treatments. Rhizoctonia black
scurf was observed to a minor extent on tubers from all treatments. Differences were not sufficient to make visual ratings of infection levels.
Fifty tubers from each treatment were scored for visual symptoms of
silver scurf under a magnifying lamp on February 16 and March 20 (Table 3).
With no replication, data must be interpreted with caution. There may have
been some suppression of silver scurf by both Tops 2.5 - MZ and TBZ Firbark treatments. Suberizing seed may have slightly reduced infection
levels.
9
Klamath Experiment Station 83
Potato Response to Seedpiece Treatment and Cutting Management
Table 1.
Effect of cutting time and fungicide treatments on emergence ofRusset Norkotah potatoes
at Klamath Falls, OR, 1994.
Cutting
time
Fungicide
treatment
nt
May 3
Control
Tops 5.0
Tops 2.5 - MZ
TBZ-Firbark
Dip
10
25
26
19
17
37
71
58
55
50
64
90
85
81
80
81
96
94
93
95
May 13
Control
Tops 5.0
Tops 2.5-MZ
TBZ-Firbark
Dip
22
29
26
21
22
68
63
58
56
54
89
88
78
90
81
94
96
91
98
93
19
24
54
60
80
85
92
94
16
27
23
20
20
53
67
58
56
52
77
89
82
86
81
88
96
93
96
94
June 3
Percent emergence
June 6 June 10 June 16
Treatment main effects:
Cutting time:
May 3
May 13
Fungicide:
Control
Tops 5.0
Tops 2.5-MZ
TBZ-Firbark
Dip
9
84 Klamath Experiment Station
Potato Response to Seedpiece Treatment and Cutting Management
Table 2.
Effect of cutting time and fungicide treatment on yield and grade of Russet Norkotah
potatoes at Klamath Falls, OR, 1994.
Cutting
time
Fungicide
treatment
Yield U.S. No. 1s
4-8 oz 8-12 oz >12 oz Total
Bs
Yield
No. 2s Culls
Total
cwtlA
May 3
Control
Tops 5.0
Tops 2.5 - MZ
TBZ-Firbark
Dip
179
225
212
195
199
146
162
150
170
164
88
50
82
77
55
413
436
444
441
417
68
61
64
64
77
35
22
37
31
25
6
0
4
1
3
522
520
549
536
521
May 13
Control
Tops 5.0
Tops 2.5-MZ
TBZ-Firbark
Dip
198
178
197
217
197
161
137
171
180
156
65
68
74
64
73
424
382
442
460
425
83
93
64
62
74
21
29
43
29
41
3
1
3
1
2
530
504
551
552
541
Cutting time:
May 3
May 13
202
197
158
161
70
69
430
427
67
75
30
32
3
2
529
536
LSD (0.05)
NS
NS
NS
NS
NS
NS
NS
NS
188
201
205
206
198
154
149
160
175
160
76
59
78
71
64
418
409
443
451
421
75
77
64
63
75
28
26
40
30
33
5
1
4
1
2
526
512
550
544
531
NS
25
NS
39
NS
12
NS
34
12
15
41
9
27
36
177
6
Treatment main effects:
Fungicide:
Control
Tops 5.0
Tops 2.5-MZ
TBZ-Firbark
Dip
LSD (0.05)
CV (%)
Klamath Experiment Station 85
Potato Response to Seedpiece Treatment and Cutting Management
Table 3.
Effect of cutting time and fungicides on incidence of silver scurf in Russet Norkotah
potatoes in Klamath Falls, OR, 1994.
Cutting
time
Fungicide
treatment
May 3
Control
Tops 5.0
Tops 2.5 - MZ
TBZ-Firbark
Dip
34
28
20
16
18
48
50
30
34
28
May 13
Control
Tops 5.0
Tops 2.5-MZ
TBZ-Firbark
Dip
48
44
26
14
44
68
60
36
18
74
23
35
38
51
41
36
23
15
31
58
55
33
26
51
Silver scurf infection
February 16
March 20
)
Treatment main effects:
Cutting time:
May 3
May 13
Fungicide:
Control
Tops 5.0
Tops 2.5-MZ
TBZ-Firbark
Dip
1/
86
•
Percent of tubers with any visual symptoms of silver scurf,
Klamath Experiment Station