Malheur Experiment Station
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Information for Sustainable Agriculture
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ROTATIONAL RESPONSE OF ALFALFA AND SUGAR BEET TO CLARION™ AND STEADFAST™ HERBICIDES
Corey V. Ransom, Charles A. Rice, and Joey K. Ishida
Malheur Experiment Station
Oregon State University
Ontario, OR, 2003
Introduction
Informed herbicide selection in diverse crop rotations is crucial to
avoid adverse effects on future crops from herbicide carryover.
Sulfonylurea herbicides are some of the most effective and low-use rate
herbicides available. However, the rotational restrictions can be
as long as 26 months for selected crops. One such herbicide is
Steadfast 75 WDG which is a premix of the sulfonylurea herbicides
nicosulfuron and rimsulfuron at a 2:1 ratio. Steadfast provides
selective postemergence (POST) grass and broadleaf weed control in
field corn. Steadfast has a rotational restriction of 12 months
for alfalfa and 10-18 months, depending on soil pH, for sugar
beet. A newly registered product, Clarion 75 WDG (formerly
DPX-79406) also consists of nicosulfuron and rimsulfuron but in a 1:1
ratio. The reduced amount of nicosulfuron in Clarion compared to
Steadfast may potentially decrease the rotational restrictions for
sugar beet and alfalfa. A field trial was conducted to evaluate
the rotational tolerance of alfalfa and sugar beet to Clarion and
Steadfast herbicides.
Materials and Methods
Clarion and Steadfast were applied postemergence (POST) to field corn
on May 29, 2002 preceding alfalfa and sugar beet establishment in the
spring of 2003. Clarion was applied at the labeled rate of 0.375
oz ai/acre and at twice the labeled rate at 0.75 oz ai/acre.
Steadfast also was applied at 1x and 2x rates of 0.56 and 1.12 oz
ai/acre, respectively. Steadfast and Clarion were applied to corn
plots measuring 20 by 30 ft. Treatments were arranged in a
randomized complete block design with four replicates. Plot size
for the rotational crops measured 10 by 30 ft with half of the original
20 by 30 ft plots planted to alfalfa and the other half to sugar beet
in 2003. Following corn harvest the trial area was roto-tilled on
October 28 and bedded on 22-inch rows on November 7, 2002.
Alfalfa (var. Surpass) was seeded at a rate of 20 lb/acre on April 30,
2003 (11 months after treatment [MAT]). Sugar beets (var.
Hilleshog PM 21) were planted on April 30, 2003 (11 MAT) at a 2-inch
seed spacing (~142,000 seeds/acre). After sugar beet planting,
the trial was corrugated and Counter 20 CR was applied in a
7-inch band over the row at a rate of 6 oz/1,000 ft of row. Temik
15G was applied on June 2 for sugar beet root maggot control at a rate
of 9.5 oz/1,000 ft of row. Plots were sidedressed with 176 lb
nitrogen, 96 lb phosphate, 100 lb potash, 38 lb sulfates, 62 lb
elemental sulfur, 2 lb zinc, and 1 lb/acre of boron on June 3,
2003. Sugar beets were thinned to an 8-inch plant spacing
(~35,640 plants/acre) on June 10, 2003. The soil was an Owyhee
silt loam with a sand, silt, and clay content of 19, 63, and 18
percent, respectively. A soil test determined a pH of 8.0, cation
exchange capacity of 12, and an organic matter content of 1.8
percent. Weeds were controlled in both the alfalfa and sugar beet
plots using hand labor.
Sugar beet and alfalfa injury were evaluated throughout the
season. The alfalfa stand was evaluated by counting seedlings
within four, 1-ft² quadrats in each plot on May 29. The
sugar beet stand was evaluated by counting the number of plants within
the entire length of the center two rows in each plot prior to thinning
on May 29 and again prior to harvest on October 7. Sugar beet
yields were determined by harvesting the center two rows of each plot
on October 7. Sugar beet yields were adjusted to account for a 5
percent tare. One sample of 16 beets was taken from each plot for
quality analysis. The samples were coded and sent to Hilleshog
Mono-Hy Research Station in Nyssa, Oregon, to determine beet pulp
sucrose content and purity. Sucrose content and recoverable
sucrose were estimated using empirical equations. Alfalfa yields
were determined by cutting a 3-ft by 26-ft swath from the center of
each plot using a flail mower on July 15 and August 13. Biomass
from the harvest area was weighed to determine the total fresh
weight. A subsample was weighed from each plot and dried in a
forced air dryer at 140°F. Once dry, the sample was removed
and reweighed to determine the percent moisture at the time of
cutting. Alfalfa forage yield was reported based on 12 percent
moisture.
Data were analyzed using analysis of variance procedures and means were
separated using protected LSD at the 95 percent confidence interval (P
= 0.05). The untreated control was not included in the analysis
of variance for crop injury.
Results and Discussion
Injury to seedling alfalfa planted 11 months after POST-applied
Steadfast and Clarion ranged from 20 to 66 percent on May 29, 2003 (365
days after treatment [DAT]) (Table 1). Injury to alfalfa
seedlings consisted of stunting and chlorosis of new growth. The
greatest alfalfa injury was observed with Steadfast at 1.12 oz
ai/acre. Clarion applied at 0.375 oz ai/acre produced
significantly less injury than all other herbicide treatments 365
DAT. Herbicide carryover also resulted in reduced alfalfa
stand. At 365 DAT, all herbicide treatments except Clarion
applied at 0.375 oz ai/acre resulted in a significant alfalfa stand
loss compared to the untreated control. Alfalfa injury on July 1
(397 DAT) was similar with both Clarion treatments and Steadfast at
0.56 oz ai/acre. Injury with Steadfast at 1.12 oz ai/acre was
greater than all other herbicide treatments at 38 percent. Injury
associated with Clarion treatment did not significantly reduce forage
yield on July 15. Herbicide injury resulted in reduced forage
yield on July 15 for both Steadfast treatments. There was no
visually detectable injury to alfalfa regrowth on July 24, 10 days
after the first cutting (data not shown). Yields from the second
cutting on August 20 were similar among all treatments.
Sugar beet injury on May 29, (365 DAT), ranged from 5 to 59 percent
(Table 2). Injury was greater with Steadfast at 1.12 oz ai/acre
than from all other treatments. Sugar beet injury was similar
with the labeled rate of Steadfast (0.56 oz ai/acre) and with Clarion
applied at twice its labeled rate at 0.75 oz ai/acre. Clarion
applied at the labeled rate of 0.375 oz ai/acre injured sugar beet
significantly less than all other herbicide treatments on May 29,
2003. Sugar beet injury on July 1 (397 DAT) was greatest with
Steadfast applied at 1.12 oz ai/acre. All other herbicide
treatments provided similar injury. Sugar beet stand on May 29
(365 DAT) was not different among treatments prior to thinning.
Steadfast applied at 1.12 oz ai/acre was the only treatment that
reduced stand compared to the untreated control prior to harvest on
October 7. There were no significant differences among treatments
with regard to root yield, percent sucrose content, or estimated
recoverable sucrose yields.
Since this trial was conducted, Clarion has been registered for use in
field corn. The label stipulates the same rotational restriction
of 12 months for alfalfa as does the Steadfast label. The
rotational restriction for sugar beet following Steadfast application
is 10 months for soils with pH < 6.5 and 18 months with pH >
6.5. The rotational restriction for sugar beet following Clarion
application is 10 months, regardless of soil pH.
Table 1. Alfalfa injury, stand, and yield in response to Clarion™
and Steadfast™ herbicides applied the previous year to field corn,
Malheur Experiment Station, Oregon State University, Ontario, OR, 2003.
|
|
Alfalfa‡ |
Alfalfa‡ |
Alfalfa‡ |
Alfalfa‡ |
Alfalfa‡ |
|
|
Injury§
|
Injury§ |
Stand
|
Yield¶ |
Yield¶ |
| Treatment* |
Rate†
|
5/29
|
7/1
|
5/29
|
7/15
|
8/13 |
|
oz ai/acre |
%
|
%
|
No/ft2 |
ton/acre |
ton/acre |
Clarion
|
0.375
|
20
|
4
|
47
|
1.54
|
1.82 |
Clarion
|
0.75
|
38
|
9
|
40
|
1.50
|
1.76 |
Steadfast
|
0.56
|
43
|
5
|
37
|
1.40
|
1.72 |
Steadfast
|
1.12
|
66
|
38
|
31
|
1.34
|
1.72 |
Untreated control
|
--
|
--
|
--
|
59
|
1.65
|
1.81 |
LSD(0.05)
|
|
14
|
10
|
18
|
0.17
|
NS |
*Treatments were applied to field corn on May 29, 2002.
†Clarion and Steadast were applied at 1x (0.375 or 0.56 oz ai/acre) and
2x (0.75 or 1.12 oz ai/acre) the labeled rates, respectively.
‡Alfalfa was seeded on April 30, 2002.
§The untreated control was not included in the analysis of variance for alfalfa injury.
¶Alfalfa forage yields were adjusted to a moisture content of 12 percent.
Table 2. Sugar beet injury, stand, and yield in response to
Clarion™ and Steadfast™ herbicides applied the previous year to field
corn, Malheur Experiment Station, Oregon State University, Ontario, OR,
2003.
|
|
Sugar beet‡ |
Sugar beet‡ |
Sugar beet‡ |
Sugar beet‡ |
Sugar beet‡ |
Sugar beet‡ |
Sugar beet‡ |
|
|
Injury
|
Injury |
Stand§
|
Stand§ |
Yield¶ |
Yield¶ |
Yield¶ |
Treatment*
|
Rate†
|
5/29
|
7/1
|
5/29
|
10/7
|
Root
|
Sucrose
|
ERS |
|
oz ai/acre |
% |
% |
No./10' |
No./10' |
ton/acre |
% |
lb/acre |
Clarion
|
0.375
|
5
|
8
|
42.7
|
16.1
|
36.7
|
16.1
|
10,902 |
Clarion
|
0.75
|
25
|
11
|
44.8
|
16.2
|
37.5
|
15.9
|
10,928 |
Steadfast
|
0.56
|
24
|
8
|
39.6
|
16.6
|
36.2
|
16.3
|
10,807 |
Steadfast
|
1.12
|
59
|
24
|
39.0
|
15.2
|
36.9
|
15.9
|
10,759 |
Untreated control
|
--
|
--
|
--
|
43.7
|
17.0
|
35.5
|
16.6
|
10,909 |
LSD (0.05)
|
|
16
|
11
|
NS
|
1.0
|
NS
|
NS
|
NS |
*Treatments were applied to field corn on May 29, 2002.
†Clarion and Steadast were applied at 1x (0.375 or 0.56 oz ai/acre) and
2x (0.75 or 1.12 oz ai/acre) the labeled rates, respectively.
‡Sugar beets were planted April 30 and harvested on October 7,
2003. The untreated control was not included in the analysis of
variance for sugar beet injury.
§Sugar beet stands on May 29 were recorded prior to hand thinning on June 10, 2003.
¶ERS = Estimated recoverable sucrose.
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For
additional information about the Malheur Agricultural Experiment
Station, please send an e-mail request to:
Dr. Clinton C. Shock
Clinton.Shock@oregonstate.edu
Malheur Agricultural Experiment
Station
595 Onion Avenue
Ontario, OR 97914
(541) 889-2174
FAX (541) 889-7831
Last updated
Wednesday July 7, 2004 .
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