Ohio State University Extension Bulletin

Agronomic Crops Team On-Farm Research Projects 2000

Special Circular 179-01

Evaluation of Herbicide Programs
Using Roundup Ready Soybeans

Steve Ruhl, Agriculture and Natural Resources Extension Agent
Jeff Stachler, Horticulture and Crop Science Extension Associate

Objective

The adoption of Roundup Ready (RR) soybeans has been rapid. It is reported that 60 percent of the soybeans planted in the United States are RR. There are numerous herbicides that can be used with Roundup to extend the window of application, provide residual control, or improve control of certain weed species. This plot was designed to evaluate several different herbicide combinations with and without Roundup in comparison to a Roundup only program.

Background

Cooperator: Tom Weiler

County: Morrow

Nearest Town: Chesterville

Soil type: Sloan silty clay loam

Drainage: Systematic

Previous Crop: Corn

Tillage: Conventional

Row Spacing: 10 inch

Fertilizer: None

Soil Test: pH = 7.0
P = 23 ppm
K = 154 ppm

Herbicide: See Table

Variety: Pioneer 93B01 RR

Planting Date: May 8, 2000

Planting Rate: 210,000 seeds/A

Harvest Date: October 12, 2000

Methods

The field chosen has moderate to high giant ragweed pressure, moderate giant foxtail pressure, and low to moderate common lambsquarters pressure. Eleven different herbicide treatments and an untreated check were replicated four times in a randomized complete block design. Plot size was 10 feet wide by 40 feet in length. The preemergence herbicides were applied on May 8, 2000; the postemergence herbicides were applied on June 6, 2000; and a second postemergence application of Roundup for one treatment was applied on July 18, 2000. Weed control was visually evaluated on August 17, 2000.

Results

The table on the following page shows the treatments, cost, and weed control for study.

Weed Control^d

Herbicide
Treatment^a,b Rate^b Treat-
ment
Timing^b,c Annual
Grass Common
Lambs-
quarters Giant
Ragweed Herb-
icide
Cost^e Total
Cost^f

% % % $ $/A

Canopy
Roundup Ultra +
AMS 3.0 oz/A
1.5 pt/A
17#/100 gal PRE
POST
POST 99 a 99 a 94 ab 6.75
6.75
0.61 31.99

Domain
Roundup Ultra +
AMS 12.0 oz/A
1.5 pt/A
17#/100 gal PRE
POST
POST 99 a 95 ab 89 ab 8.44
6.75
0.61 33.68

Boundary
Roundup Ultra +
AMS 1.25 pt/A
1.5 pt/A
17#/100 gal PRE
POST
POST 94 b 78 b 86 abc 11.88
6.75
0.61 37.12

Roundup UltraDry +
AMS 1.2 #/A
17#/100 gal POST
POST 97 ab 55 c 90 ab 11.43
0.61 25.92

Roundup Ultra +
AMS
Roundup Ultra +
AMS 1.5 pt/A
17#/100 gal
1.0 qt/A
17#/100 gal POST
POST
POST2
POST2 100 a 100 a 99 a 6.75
0.61
9.0
0.61 34.85

Extreme +
NIS +
AMS 3.0 pt/A
0.125 %v/v
2.5 #/A POST
POST
99 a 87 a 91 ab 11.58
0.19
0.45 26.37

FirstRate +
Roundup Ultra +
0.3 oz/A
1.5 pt/A
17#/100 gal POST
POST
POST 100 a 91 ab 95 ab 6.36
6.75
0.61 27.60

Cobra +
Roundup Ultra +
AMS 8.0 oz/A1.0 qt/A
17#/100 gal POST
POST
POST 99 a 94 ab 92 ab 7.59
9.00
0.61 31.08

Canopy +
Dual II Magnum
FirstRate +
MSO +
UAN 3.0 oz/A
1.67 pt/A
0.3 oz/A
1.2 %v/v
2.5 %v/v PRE
PRE
POST
POST
POST 96 ab 100 a 65 cd 6.75
17.32
6.36
2.88
0.37 41.68

Canopy
Flexstar +
Select +
MSO +
UAN 3.0 oz/A
1.3 pt/A
8.0 fl. oz/A
1.0 %v/v
2.5 %v/v PRE
POST
POST
POST
POST 100 a 94 ab 74 bcd 6.75
13.00
10.62
2.40
0.37 41.14

Authority 3.0 oz/A PRE 7.05

FirstRate + 0.3 oz/A POST 6.36

Select + 5.0 fl. oz/A POST 99 a 74 bc 61 d 6.64 31.30

MSO + 1.2 %v/v POST 2.88

UAN 2.5 %v/v POST 0.37

LSD (0.05) 4.6 21.4 22.2

^aAll treatments applied at 20 gallons per acre and 30 psi.
^bAbbreviations: AMS = ammonium sulfate, NIS = nonionic surfactant, MSO = methylated seed oil, UAN = urea ammonium nitrate (28% N), oz = ounce, pt = pint, A = acre, # = pound, gal = gallon, qt = quart, % v/v = percent volume to volume, fl. oz = fluid ounces, PRE = preemergence, POST = postemergence.
^cThe PRE treatments were applied on May 8, 2000, and a total of 4.6 inches of rainfall was measured between May 8 to May 31. The POST treatments were applied on June 6, 2000, when the annual grasses were two- to four-inches tall, giant ragweed was 12- to 18-inches tall, and soybeans were at the V-3 stage of growth. The POST2 treatment was applied on July 18, 2000.
^dTreatments means followed by the same letter are not significantly different, and visual evaluation of weed control was done on August 17, 2000.
^eAll herbicide and adjuvant costs listed in the table were the 2000 in-season retail prices.
^fThe total cost includes an application cost of $4.00 per application, and a Roundup Ready Technology Fee of $9.88 per acre if Roundup was applied postemergence.

Summary

Only Roundup Ultra followed by Roundup Ultra and Canopy followed by Roundup Ultra provided greater than 93% control of all three species. All treatments provided excellent giant foxtail control. Most treatments provided good to excellent control of common lambsquarters, except Boundary followed by Roundup Ultra, Roundup UltraDry, and Authority followed by FirstRate plus Select, all of which provided significantly lower control. Most treatments provided good to excellent control of giant ragweed, except Canopy plus Dual II Magnum followed by FirstRate, Canopy followed by Flexstar plus Select, and Authority followed by FirstRate plus Select. The poorer control with the two treatments containing FirstRate may be due to the presence of ALS-resistant giant ragweed. The poorer control with the treatment containing Flexstar was caused by too large of giant ragweed at the time of application. The slightly lower control of giant ragweed for the treatments containing Domain and Boundary may be a result of too large of plants at the time of the postemergence application, since these two products are ineffective in controlling giant ragweed.

The benefit of the preemergence herbicides before Roundup is that the early season weed control helps to reduce weed competition and widen the window for the postemergence application. The benefit of tank-mixing residual herbicides with Roundup is to be able to make applications to small weeds and still provide later season weed control and provide improved control for certain weed species. The total cost per acre ranged from $25.92 to $41.68 per acre. The two-pass Roundup Ultra treatment cost $34.85 per acre.

Acknowledgment

We would like to thank Pioneer for donating the soybeans used in the project and thank Geoff Trainer, Ohio State University senior and Agronomy Team member, for evaluating the weed control.

For additional information, contact:

Steve Ruhl
Ohio State University Extension, Morrow County
871 W. Marion Rd., Suite 102
Mt. Gilead, Ohio 43338
419-947-1070
ruhl.1@osu.edu

Back | Forward | Table of Contents

Weed Control^d
Herbicide Treatment^a,b	Rate^b	Treat- ment Timing^b,c	Annual Grass	Common Lambs- quarters	Giant Ragweed	Herb- icide Cost^e	Total Cost^f
			%	%	%	$	$/A
Canopy Roundup Ultra + AMS	3.0 oz/A 1.5 pt/A 17#/100 gal	PRE POST POST	99 a	99 a	94 ab	6.75 6.75 0.61	31.99
Domain Roundup Ultra + AMS	12.0 oz/A 1.5 pt/A 17#/100 gal	PRE POST POST	99 a	95 ab	89 ab	8.44 6.75 0.61	33.68
Boundary Roundup Ultra + AMS	1.25 pt/A 1.5 pt/A 17#/100 gal	PRE POST POST	94 b	78 b	86 abc	11.88 6.75 0.61	37.12
Roundup UltraDry + AMS	1.2 #/A 17#/100 gal	POST POST	97 ab	55 c	90 ab	11.43 0.61	25.92
Roundup Ultra + AMS Roundup Ultra + AMS	1.5 pt/A 17#/100 gal 1.0 qt/A 17#/100 gal	POST POST POST2 POST2	100 a	100 a	99 a	6.75 0.61 9.0 0.61	34.85
Extreme + NIS + AMS	3.0 pt/A 0.125 %v/v 2.5 #/A	POST POST	99 a	87 a	91 ab	11.58 0.19 0.45	26.37
FirstRate + Roundup Ultra +	0.3 oz/A 1.5 pt/A 17#/100 gal	POST POST POST	100 a	91 ab	95 ab	6.36 6.75 0.61	27.60
Cobra + Roundup Ultra + AMS	8.0 oz/A1.0 qt/A 17#/100 gal	POST POST POST	99 a	94 ab	92 ab	7.59 9.00 0.61	31.08
Canopy + Dual II Magnum FirstRate + MSO + UAN	3.0 oz/A 1.67 pt/A 0.3 oz/A 1.2 %v/v 2.5 %v/v	PRE PRE POST POST POST	96 ab	100 a	65 cd	6.75 17.32 6.36 2.88 0.37	41.68
Canopy Flexstar + Select + MSO + UAN	3.0 oz/A 1.3 pt/A 8.0 fl. oz/A 1.0 %v/v 2.5 %v/v	PRE POST POST POST POST	100 a	94 ab	74 bcd	6.75 13.00 10.62 2.40 0.37	41.14
Authority	3.0 oz/A	PRE				7.05
FirstRate +	0.3 oz/A	POST				6.36
Select +	5.0 fl. oz/A	POST	99 a	74 bc	61 d	6.64	31.30
MSO +	1.2 %v/v	POST				2.88
UAN	2.5 %v/v	POST				0.37

LSD (0.05)			4.6	21.4	22.2
^aAll treatments applied at 20 gallons per acre and 30 psi. ^bAbbreviations: AMS = ammonium sulfate, NIS = nonionic surfactant, MSO = methylated seed oil, UAN = urea ammonium nitrate (28% N), oz = ounce, pt = pint, A = acre, # = pound, gal = gallon, qt = quart, % v/v = percent volume to volume, fl. oz = fluid ounces, PRE = preemergence, POST = postemergence. ^cThe PRE treatments were applied on May 8, 2000, and a total of 4.6 inches of rainfall was measured between May 8 to May 31. The POST treatments were applied on June 6, 2000, when the annual grasses were two- to four-inches tall, giant ragweed was 12- to 18-inches tall, and soybeans were at the V-3 stage of growth. The POST2 treatment was applied on July 18, 2000. ^dTreatments means followed by the same letter are not significantly different, and visual evaluation of weed control was done on August 17, 2000. ^eAll herbicide and adjuvant costs listed in the table were the 2000 in-season retail prices. ^fThe total cost includes an application cost of $4.00 per application, and a Roundup Ready Technology Fee of $9.88 per acre if Roundup was applied postemergence.