79
Effects of Seed Piece Treatment on Performance
of A74212-1
K.A. Rykbost', J. Maxwell' and D, Beck'
INTRODUCTION
In commercial and research experience A74212-1 has frequently encountered stand problems due to seed piece decay. Fusarium dry rot in
seed is common, particularly in tubers over 10 ounces in size. Comparisons of several different seed lots and several seed treatment materials
in 1988 were inconclusive as soil conditions were favorable and seed
decay did not occur, even in untreated seed highly infected with
fusarium dry rot.
This experiment was conducted to continue the search for control
options to address what has been a serious problem with A74212-1 in
commercial production. Several new or experimental formulations of
fungicides were included in the study.
PROCEDURES
The seed source used was obtained from a grower whose seed has
experienced stand problems in previous years. Fusarium dry rot was
present in a significant percentage of tubers, but not as extensively
as in seed used in 1988 experiments.
One batch of seed was hand cut, treated with TOPS 2.5 D immediately,
and stored at 50 ° F and high relative humidity for 10 days prior to
planting. The remaining treatments were batch applied to fresh-cut seed
and planted on the same day, May 24. Plots were two rows, 30-feet long,
arranged with four replications in a randomized complete block design.
Seed was spaced at 8.7 inches in 32-inch rows. Fertilizer included 600
lbs/A of 16-16-16 banded at planting and 50 lbs N/A applied as solution
32 on June 6.
Vines were desiccated with diquat at 1.5 pints/A on September 12 and
potatoes were harvested on October 6. All tubers from both rows of each
plot were weighed in the field. Approximately 60-pound samples were
stored and graded in early November.
1/ Superintendent/Associate Professor and Biological Sciences Research
Technician, respectively, Klamath Experiment Station.
2/ Associate Professor, Klamath County Extension Service.
80
RESULTS AND DISCUSSION
Several small commercial fields planted locally with the same seed
source during the first week of May experienced severe seed breakdown
problems. In each case the seed was cut, treated with TOPS2.5 D, and
planted within one day of cutting time. Within a few days after planting 0.4 inches of rainfall was followed by two days with minimum air
temperatures of 30 ° and 27 ° F. Two weeks after planting a majority of
seed pieces were breaking down or had already disintegrated. A sample
of decaying seed was assayed. The only organism isolated was Geotricum
candidum, a saprophytic organism of opportunity. By early June remaining seed pieces healed and a stand of 50 to 60 percent developed into a
fair crop.
In the experimental field the crop was planted in moist soil one day
after a 0.38-inch rain. Emergence was quite slow and final stands were
less than 85 percent for all lots planted freshly cut (Table 1). Crop
vigor was generally poor. In part this was due to high salt content in
the soil and heavy weed competition from nightshade, which was not
adequately controlled with herbicides.
Ridomil-treated seed experienced minor phytotoxic injury which plants
recovered from eventually, but at the expense of some yield reduction.
In both 1988 and 1989 the TOPS - Rovral treatment delayed emergence and
reduced final stands slightly. This product reduced yield slightly in
1988 but not in 1989. The combination of TOPS - NAA severely delayed
emergence and reduced final stand and yield.
TOPS 2.5 D alone produced the highest yield of US No. l's for seed
cut and planted immediately. A further yield increase was observed when
a ten-day suberization period was allowed after cutting and treating.
Pre-cutting and suberizing seed prior to planting did not improve performance of five seed lots in a 1988 experiment. The results of this
trial and the observations of a seed grower with several years of
experience with A74212-1 suggest that this practice may be beneficial in
situations where adverse soil conditions occur soon after planting.
SUMMARY AND CONCLUSIONS
The results of this experiment suggest that the TOPS 2.5 D fungicide
was superior to other products tested and that pre-cutting and suberizing seed was beneficial. The TOPS - Rovral combination increased tuber
size slightly due to reduced stands. TOPS-NAA produced several undesirable effects and should be avoided. Ridomil alone reduced yields
slightly, a result that has been observed elsewhere.
For three consecutive years serious seed decay has occurred in one or
more commercial fields of A74212-1 in the Klamath Basin. Susceptibility
to tuber damage at harvest and the development of fusarium dry rot in
storage undoubtedly contributes to this problem. Commercial experience
with A74212-1 and research with this and other selections suggest a
81
number of control strategies to improve seed quality, including: 1)
control of tuber size in seed crops; 2) a minimum delay of three weeks
between topkilling and harvest; 3) careful handling at harvest and
storage loading; and 4) use of a fungicide at storage loading. For seed
lots with the potential for seed decay problems the following practices
may reduce the severity of damage: 1) pre-cutting and suberizing seed
for a minimum of 10 days prior to planting; 2) avoid planting too early
and exposing the crop to cold, wet soil conditions; 3) seed treatment
with an effective fungicide; and 4) cutting seed to provide large,
blocky pieces with a minimum of cut surface area; 5) increasing seeding
rate to compensate for loss of stand.
Table 1.
Effects of seed treatment on A74212-1, Klamath Experiment Station,
1989.
Seed
Treatment
4-6oz
Yield US No l's
6-10oz >10oz Total
cwt/A
B's
Yield
No 2's Total
Emergence
6/20 6/28
%- -
Control
Gypsom
TOPS 2.5 D
Ridomil-Mancozeb
Ridomil-Mertect
74
54
61
56
65
111
106
113
106
102
80
114
142
142
118
265
274
316
304
285
47
47
37
43
46
16
12
8
11
17
364
364
374
384
363
65
64
64
59
69
81
80
81
80
82
TOPS-Rizolex
TOPS-Rovral
TOPS-NAA
Ridomil
TOPS 2.5 D-PreCut
67
49
40
52
97
107
94
47
96
131
123
131
110
93
125
297
274
197
240
353
49
36
15
39
63
20
14
18
10
26
407
359
279
307
460
72
54
25
56
72
83
69
47
78
89
Avg.
CV (%)
LSD(.05)_
61
40
36
101
41
61
118
45
NS
280
31
127
42
29
18
15
78
17
366
28
151
60
77