September 2011
Effects of seed treatment fungicides and seed vigor on cotton
seedling stand and yield in southeastern Arizona in 2009 and
2010
Mary Olsen, Claudia Nischwitz and Randall Norton
Department of Plant Sciences and Safford Agricultural Center
The University of Arizona
Abstract
The effect of seed treatment fungicides on cotton seedling stand establishment,
skips and yield were assessed in field experiments conducted at the Safford
Agricultural Center of the University of Arizona in 2009 and 2010. In 2009,
two field trials were conducted, one inoculated with Rhizoctonia solani, the most
common cause of damping-off or collapse of seedlings in Arizona, and the other
not inoculated. In 2010, the trial was repeated, but the field was not inoculated.
Seed of low and high vigor ST4554 BR2RF was treated (1) as a non-treated
control; or with (2) base fungicide made up of Baytan + Vortex + Allegiance,
(3) base fungicide + Trilex Advanced, (4) base fungicide + Dynasty CST. Seed
vigor was based on cool germination percentage. Efficacy of seed fungicide
treatments were determined by stand count, seed cotton yield and skip indices.
Disease incidence was very low in both years, and effects of fungicide
treatments generally made little or no difference in stand establishment or yield.
Seed vigor was significant in both years. Results indicate that, under low
disease pressure, fungicide seed treatments are marginally effective in
increasing stands in the early season, but these increases are not translated into
increased yield. The most important variable in these experiments was seed
vigor indicating that growers should consider the cool germ percentage of
cotton varieties and seed lots when making planting decisions.
Introduction
Seedling disease of cotton in Arizona is caused primarily by Rhizoctonia solani and to a lesser extent by
Thielaviopsis basicola. Both pathogens are soil borne fungi found throughout all cotton growing areas in Arizona.
They commonly cause root and crown rot resulting in post-emergent damping-off or collapse of seedlings when
plant growth is slowed by low soil temperatures, residual herbicide phytotoxicity, planting too deep, poor seed vigor
or crusting. Fungicide treatment of seed is usually recommended if fields are planted before optimum soil
temperatures are attained and if seed is “irrigated up”. In both cases, soil temperature below that for optimum
germination enhances infections by these soil borne pathogens. The most effective preventions for seedling disease
are planting into soils when temperatures are favorable for fast germination and using high quality seed of vigorous
cotton varieties that have performed well in local variety tests (Norton et al., 2007).
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Materials and Methods
Seed treatment fungicides were tested for efficacy at the Safford Agricultural Center (SAC) of the University of
Arizona in Safford, AZ in 2009 and 2010. In 2009, two trials were conducted, one in which the field was not
inoculated (Trial 1) and another that was inoculated with Rhizoctonia solani at planting (Trial 2). Seed of ST4554
B2RF, a Bollgard II, Roundup Ready Flex variety, of either “low vigor” that had been hot water treated to reduce
germination rate of the seed, or of “high vigor” that was not treated, was supplied by Bayer Crop Science. Seed of
both high and low vigor were not treated with fungicides at all (untreated control) or treated with three different
combinations of fungicides: (1) base fungicide, a combination of Baytan (Triademenol) + Vortex (Ipconazole) +
Allegiance (Metalaxyl), was applied to all fungicide treated seed; (2) base fungicide + Trilex Advanced
(Trifloxystrobin + Metalaxyl + Triademenol); and (3) base fungicide + Dynasty CST (Azoxystrobin + Mefenoxam +
Triademenol).
Seed was planted using a tractor mounted cone planter and packets of pre-counted seed. Each 40 ft section of each
row was planted with 200 seed. Inoculum for 2009 Trial 2 was made in the laboratory by colonization of sterile
barley seed with a pure culture of Rhizoctonia solani isolated from cotton at the SAC in 2008. The colonized seed
was incubated for three weeks at 25o C, dried at room temperature in open trays and partially ground by hand using
a wooden roller. Ground inoculum was added to cotton seed during planting by placing 5 grams inoculum .into each
batch of 200 seed as it was planted.
Seed was planted into moisture on April 16 in both 2009 and 2010 in plots of 4 rows on 38 inch center, 40 ft long.
The fields were flood irrigated after planting on May 25 (2009 trial) or June 3 (2010 trial) and thereafter irrigated
every two weeks until the first week of September. There were four replications of each treatment in a randomized
complete block design. Data was collected in the center two rows of each plot (80 ft total).
Stand counts were made at 29 and 48 (2009) or 29 and 53 (2010) days after planting. The number of plants was
used to calculate percent emergence based on the number of seed that was planted (400 seed/80 ft rows). Field
observations for seedling disease caused by R. solani or T. basicola also were conducted at this time by making
observations of dead/dying seedlings and non-germinated seed. Length and number of skips were recorded to
calculate a skip index. Skips were counted and reported according to previous methods (Colyer and Vernon, 2005).
The skip index was calculated as the sum of skips greater than 12 inches within each of the two 40 ft plot lengths of
each replication of each treatment. Skips were assigned as 0=no skips, 1=skips 12 to 18 inches, 2=skips 18-24,
3=skips 24-36 and 4=skips >36 inches. Plots were harvested in the first week of November in both years, and yield
was reported as pounds of seed cotton in 80 ft of row. Data was subjected to ANOVA and comparison of means
using the least significant difference test (P<0.05).
Results and Discussion
Percent Stand.
2009 trials: Results are shown in Tables 1 and 2. In Trial 1 (non-inoculated) at 29 days after planting, the high vigor
base + Dynasty CST treatment had a significantly higher stand compared to the low and high vigor untreated
controls. After 48 days both the high vigor base + Dynasty CST treatment and the base treatment had a significantly
higher stand than the low vigor control. There were no significant differences among the other treatments. In Trial 2
(inoculated) after 29 days, the high vigor base treatment had a significantly higher stand than the untreated high
vigor control and low vigor treatments. After 48 days the base treatment had a significantly higher stand than all
low vigor treatments, but there were no differences among the high vigor treatments.
2010 trials: Results are shown in Table 3. At 29 days after planting, there were no differences in per cent stand
within low or high vigor seed, but all high vigor seed combined was significantly higher than low vigor. Per cent
stand in the untreated control in the high vigor seed was higher than all treatments in the low vigor seed. At 53 days
after planting, all three treatments of the high vigor seed were significantly higher than the untreated control, but not
different from each other. Stand counts in treatments in the low vigor seed were not significantly different.
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Yield.
2009 trials: Results are shown in Tables 1 and 2. Yield of seed cotton in Trial 1 (non-inoculated) was significantly
lower in the high vigor control compared to the high vigor base +Trilex Advanced and the low vigor base + Dynasty
CST. There was no significant difference among the treatments in Trial 2 (inoculated).
2010 trial: Results are shown in Table 3. There were no significant differences among any of the treatments in yield
of seed cotton.
Skip index and number of skips.
2009 trials: The effect of seed treatments on the skip index, length of skips, and number of skips 48 days after
planting are shown in Tables 4 and 5. In Trial 1, the high vigor base and base + Dynasty CST treatments had
significantly fewer skips than both untreated controls. The only significant difference in the skip index was between
the high vigor base +Trilex Advanced and the low vigor control. In Trial 2, there were no significant differences
among all treatments in total number of skips, average length of skips and the skip index.
2010 trial: The effect of seed treatments on the skip index, length of skips, and number of skips 53 days after
planting are shown in Table 6. High vigor seed was significantly different from low vigor for all treatments
including the untreated control. Within high vigor seed, treatments were not significant, but in the low vigor seed,
the three seed treatments were significantly lower than the untreated control.
Conclusions
In both 2009 and 2010 experiments, disease pressure was very low, even in the inoculated Trial 2 in 2009.
Observations of seed remaining in the ground when stand counts were made indicated that poor germination and not
fungal rots of seeds or seedlings was the major factor in determining stand establishment and skip index. Results
from all experiments indicate that seed vigor was more important than seed fungicide treatments in increasing yield
in these trials. Cotton seedling disease is always a consideration when choosing seed treatments and supplier,
especially in fields with a history of disease. Results from these studies indicate that cool germination percentage
(vigor) given for a particular variety and lot of seed may be a more important consideration. Growers should
consider the cool germ percentage of cotton varieties and seed lots when making planting decisions. This
information is available from the seed supplier.
References cited
Colyer, P. D. and P. R. Vernon. 2005. Impact of stale seedbed production on seedling diseases in
cotton. Plant Dis. 89:744-748.
Norton, E. R., E. L. Hatch and K. F. Ellsworth. 2007. 2007 Arizona Cotton Report. College of
Agriculture and Life Sciences, The University of Arizona.
http://cals.arizona.edu/pubs/crops/az1437/az14371d.pdf
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Table 1. 2009 trials: effect of fungicide seed treatments in Trial 1 (non-inoculated) on stand
establishment as a percentage of the seed planted and yield of seed cotton.
Seed treatment
Vigor Percent stand
Percent stand
Seed cotton
1,3
1,3
fungicide
29 days
48 days
yield2,3
lbs/80 ft row
untreated
base
base +Trilex Advanced
base + Dynasty CST
high
high
high
high
38 bc
51 ab
51 ab
53 a
35 ab
46 a
44 ab
47 a
21 b
24 ab
26 a
24 ab
untreated
low
34 c
32 b
24 ab
base
low
43 abc
38 ab
23 ab
base+ Trilex Adavnced
low
43 abc
40 ab
24 ab
base + Dynasty CST
low
46 abc
42 ab
27 a
1
Percent stand values are the number of plants in 80 ft row divided by number of seed planted
(400 seed).
2
Yield is pounds of seed cotton harvested using standard practices with a 2 row picker.
3
Treatments with the same letter are not significantly different from each other (ANOVA with
P<0.05).
Table 2. 2009 trials: Effect of fungicide seed treatments in Trial 2 (inoculated with Rhizoctonia
solani) on stand establishment as a percentage of the seed planted and yield of seed cotton.
Seed treatment
Vigor Percent stand
Percent stand
Seed cotton
1,3
1,3
fungicide
29 days
48 days
yield2,3
lbs/80 ft row
untreated
base
base +Trilex Advanced
base + Dynasty CST
high
high
high
high
44 bc
54 a
49 ab
50 ab
43 abcd
53 a
48 abc
51 ab
26 a
28 a
26 a
26 a
untreated
low
32 d
31 d
25 a
base
low
39 cd
38 cd
25 a
base+ Trilex Advanced
low
38 cd
38 cd
26 a
base + Dynasty CST
low
43 bc
41 bcd
28 a
1
Percent stand values are the number of plants in 80 ft row divided by number of seed planted
(400 seed).
2
Yield is pounds of seed cotton harvested using standard practices with a 2 row picker.
3
Treatments with the same letter are not significantly different from each other (ANOVA with
P<0.05).
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Table 3. 2010 trials: effect of fungicide seed treatments on stand establishment as a percentage of
the seed planted and yield of seed cotton.
Seed treatment
Vigor
Per cent stand at Stand at
Seed cotton
1,3
1,3
fungicide
29 days
53 days
yield2,3
lbs/80 ft row
untreated
base
base +Trilex Advanced
base + Dynasty CST
high
high
high
high
69 ab
76 a
76 a
76 a
65 bc
74 a
78 a
72 ab
29 a
30 a
29 a
29 a
untreated
low
55 c
54 d
29 a
base
low
58 c
54 d
29 a
base+ Trilex Advanced low
61 bc
60 cd
28 a
base + Dynasty CST
low
63 bc
59 cd
28 a
1
Percent stand values are the number of plants in 80 ft row divided by number of seed planted
(400 seed).
2
Yield is pounds of seed cotton harvested using standard practices with a 2 row mechanical
picker.
3
Treatments with the same letter are not significantly different from each other (ANOVA with
P<0.05). Values are means of 4 replications of each treatment.
Table 4. 2009 trials: effect of seed treatments in Trial 1 (non-inoculated) on the skip index,
length of skips, and number of skips 49 days after planting.
Seed treatment
Vigor
Skip index1,2
Length of Number of
fungicide
(X100)
skips1,2
skips1,2
untreated
base
base +Trilex Advanced
base + Dynasty CST
high
high
high
high
16 ab
9 ab
8b
8 ab
43 ab
22 b
21 b
21 b
11 ab
8c
6 bc
5c
untreated
low
18 a
46 a
11 a
base
low
12 ab
31 ab
8 abc
base+ Trilex Advanced
low
13 ab
33 ab
8 abc
base + Dynasty CST
low
12 ab
32 ab
8 abc
1
Values are means of 4 replications of each treatment.
2
Treatments with the same letter were not significantly different from each other (ANOVA with
P<0.05).
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Table 5. 2009 trials: Effect of seed treatments in Trial 2 (inoculated with Rhizoctonia solani) on
the skip index, length of skips, and number of skips 49 days after planting.
Seed treatment
Vigor
Skip index1,2
Length of Number of
fungicide
(X100)
skips1,2
skips1,2
untreated
base
base +Trilex Advanced
base + Dynasty CST
high
high
high
high
9a
10 a
12 a
8a
24 a
26 a
32 a
23 a
6a
6a
8a
6a
untreated
low
23 a
53 a
12 a
base
low
19 a
49 a
12 a
base+ Trilex Advanced
low
18 a
47 a
11 a
base + Dynasty CST
low
13 a
32 a
8a
1
Values are means of 4 replications of each treatment.
2
Treatments with the same letter were not significantly different from each other (ANOVA with
P<0.05).
Table 6. 2010 trial: effect of seed treatments on the skip index, length of skips, and number of
skips 53 days after planting.
Seed treatment
Vigor
Skip index1
Length
Number
(x100)
skips1
skips1
untreated
base
base +Trilex Advanced
base + Dynasty CST
high
high
high
high
10 cde
7e
7e
10 de
30 cde
18 e
19 e
27 de
8 cde
5e
5e
7 de
untreated
low
25 a
68 a
17 a
base
low
18 b
49 b
12 b
base+ Trilex Advanced low
13 bcd
37 bcd
10 bcd
base + Dynasty CST
low
16 bc
45 bc
12 bc
1
Treatments with the same letter were not significantly different from each other (ANOVA with
P<0.05). Values are means of 4 replications of each treatment.
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