Weed Control in Soybeans

Commercialization of glyphosate-resistant (Roundup Ready) soybeans introduced a new era in soybean weed control. While this technology made postemergence broad-spectrum weed control with a single non-residual herbicide a reality in some situations, other situations require a tank-mix partner or a two-pass weed control program.

With conventional tillage, it is recommended that glyphosate (Roundup PowerMax, Durango DMA, Touchdown Total, etc.) be applied to glyphosate-resistant soybeans 24 to 30 days after planting. While this works in most situations, less than desirable common lambsquarters control has been reported in some instances. Normal application rates of glyphosate in the field or greenhouse have consistently controlled lambsquarters that is no more than 3 inches tall. Lambsquarters that is greater than 3 inches tall may require increased rates of glyphosate or a tank mix of Harmony SG or of Synchrony XP with glyphosate. Table 6.7.2 provides suggestions on how to improve lambsquarters control with either a one pass or two pass program.

When planting no-tillage glyphosate-resistant soybeans, a burndown herbicide should be used before or at the time of planting if significant weed cover is present. Several options that enhance burndown, provide residual weed control, or control dandelions in no-tillage soybeans can be found in Table 6.7.3. A postemergence application of glyphosate should be made 24 to 30 days after planting.

Because soybeans are sensitive to *atrazine and *†Princep residues, care should be taken the year before planting soybeans to ensure that herbicide carryover will not affect their establishment.

Herbicide resistance management

Herbicide resistance management involves the use of crop rotation and cultivation along with herbicide rotation and/or use of herbicide combinations that include herbicides with different sites of action (how they affect weeds). These practices will help manage existing herbicide resistant weed populations and delay development of new resistant weed populations.

To effectively utilize herbicides with different sites of action, everyone involved in decisions about weed management must have the site of action classification readily available. The Weed Science Society of America (WSSA) has approved a numbering system to classify herbicides by their site of action (Mallory-Smith, C.A. and Retzinger, E.J. 2003. Revised classification of herbicides by site of action for weed resistance management strategies. Weed Technol. 17:605-619). A group number is given to all herbicides with the same site of action. These “GROUP NUMBERS” are included in the “Chemical weed control tables” in each crop section.

Tables

Effectiveness of selected soybean herbicides on annual weeds
Broadleaf Annual Weeds
Herbicides Common Lambsquarters Wild Mustard Redroot Pigweed Common Ragweed Velvetleaf
Preplant-incorporated
*§Dual II Magnum Poor Poor Good Poor None
Prowl Good Poor Good None Fair
§Python Good Good Good Poor Good
Dimetric DF1 Good1 Good Good1 Good1 Fair
Preemergence
*§Dual II Magnum Poor Poor Good Poor None
FirstRate Good Poor Good Good Good
Lorox Good Good Good Good Fair
§Python Good Good Good Poor Good
Dimetric DF1 Good1 Good Good1 Good1 Fair
Postemergence
Basagran Fair Good Poor Fair Good
Classic Poor Good Good Fair Fair
Cobra Poor -- Good Good Good
FirstRate Poor Fair Poor Excel Good
Harmony SG Good Good Good Poor Poor
*§Pursuit Poor Good Good Fair Good
*Reflex Poor -- Good Good Poor
Resource Poor Fair Poor Fair Excel
Annual Grass Weeds
Herbicides Barnyardgrass Crabgrass Foxtails Fall Panicum Witchgrass
Preplant-incorporated
*§Dual II Magnum Good Good Good Good Good
Prowl Good Good Good Good Good
§Python None None None None None
Dimetric DF Poor Poor Poor Poor Poor
Preemergence
*§Dual II Magnum Excel Excel Excel Excel Excel
FirstRate None None None None None
Lorox Fair Fair Fair Fair Fair
§Python None None None None None
Dimetric DF1 Poor Poor Poor Poor Poor
Postemergence
Basagran None None None None None
Classic Poor Poor Poor Poor Poor
Cobra None None None None None
FirstRate None None None None None
Harmony SG None None None None None
*§Pursuit Good Fair Good Fair --
*Reflex None None None None None
Resource None None None None None
*Restricted-use pesticide; may be purchased and used only by certified applicators or used by someone under the direct supervision of a certified applicator.
§Not for use in Nassau and Suffolk Counties.
1Effectiveness ratings for Dimetric DF are not accurate for triazine-resistant lambsquarters, pigweed, and ragweed.
Glyphosate-resistant (Roundup Ready) soybean varieties
Situation Amount of Product(s)/A Remarks and Limitations
Emerged grass and broadleaf weeds 22 fl. oz. Roundup PowerMax
or 24 fl. oz. Durango DMA
24 fl. oz. Touchdown Total
Group 9 Herbicides: For use with glyphosate-resistant (Roundup Ready) soybeans only. Apply these or other glyphosate products 24-30 days after planting glyphosate-resistant soybeans as a total postemergence control program. If common lambsquarter is 3 in. or taller, use 1.5 times the recommended rate or see below for additional information about this problem weed.
Problem Weed
Common lambsquarters
One pass program
22 fl. oz. Roundup PowerMax
or 24 fl. oz. Durango DMA
24 fl. oz. Touchdown Total + 1/8th oz. Harmony SG
Group 2 and 9: Tank mix Harmony SG with glyphosate and apply 24-30 days after planting glyphosate-resistant soybeans as a total postemergence control program.
3.5-4.5 pt. Flexstar GT 3.5 Group 9 and 14 herbicides: Apply Flexstar GT 3.5 postemergence before lambsquarter is 8 in. tall. Use spray adjuvants according to label. Do not apply Flexstar GT 3.5 to any field more than once every 2 years.
Problem Weed
Common lambsquarters
Two pass program
0.89 oz. §Python WDG Group 2 herbicide: Apply Python WDG preemergence and follow with a postemergence application of glyphosate 24-30 days after planting glyphosate-resistant soybeans.
2 oz. Valor SX Group 14 herbicide: Apply Valor SX preplant or preemergence. Follow with a postemergence application of glyphosate 24-30 days after planting glyphosate-resistant soybeans. Valor SX will provide residual control of many annual broadleaf weeds including common lambsquarters.
2.5 oz. Valor XLT Group 2 and 14 herbicides: Apply Valor XLT preplant or preemergence. Follow with a postemergence application of glyphosate 24-30 days after planting glyphosate-resistant soybeans. Valor XLT will provide residual control of many annual broadleaf weeds including common lambsquarters.
1.5 lb. Lorox DF Group 5 herbicide: Apply preemergence and follow with a postemergence application of glyphosate 24-30 days after planting glyphosate-resistant soybeans.
2.8oz. Enlite Group 2 and 14 herbicides: Apply preemergence and follow with a postemergence application of glyphosate 24-30 days after planting glyphosate-resistant soybeans.
2 oz. *§OpTill Group 2 and 14 herbicides: Apply preplant or preemergence. Do not apply once soybeans have reached the cracking stage or after emergence. Follow with a postemergence application of glyphosate 24-30 days after planting glyphosate-resistant soybeans. *§OpTill will provide residual control of many annual broadleaf weeds including common lambsquarters.
Problem Weed
Quackgrass
22-44 fl. oz. Roundup PowerMax
or 24-48 fl. oz. Durango DMA
24-48 fl. oz. Touchdown Total
Group 9 Herbicides: Apply these or other glyphosate products as preplant foliar sprays in the spring when quackgrass is at least 8 in. tall 4- to 5-leaf stage and actively growing. Delay tillage for at least 3 days after spraying. Low rates should be used only in fields that are to be tilled, using 3-10 gal. of water/A and may not provide long-term control. May also be applied 24-30 days after planting glyphosate-resistant soybeans.
Problem Weed
Nutsedge
22 fl. oz. Roundup PowerMax
or 24 fl. oz. Durango DMA
24 fl. oz. Touchdown Total + ½ oz. Classic
or 0.375 oz. Synchrony XP
Group 2 Herbicide: Tank-mix glyphosate with Classic or Synchrony XP and apply to nutsedge up to 3 or 6 in. tall respectively. When tank mixing Classic or Synchrony with glyphosate herbicides, it is recommended to add ammonium sulfate (AMS) at 4.25—17 lb./100 gal. of spray mixture.
Problem Weed
Volunteer corn, including Liberty Link, and glyphosate-resistant (Roundup Ready) hybrids
6-8 fl. oz. Fusilade DX
or 5 fl. oz. Assure II/Targa
6-9 fl. oz. Select Max
Group 1 Herbicide: Apply postemergence to actively growing corn. Add crop oil concentrate or nonionic surfactant according to label. These herbicides are effective against volunteer glyphosate-resistant corn. Some can be tank-mixed with the glyphosate application in glyphosate-resistant soybeans.
Conventional soybean varieties
Situation Amount of Product(s)/A Remarks and Limitations
PRE Programs
Annual grass and broadleaf weeds
1.33 pt. *§Dual II Magnum
+ 0.89 oz. §Python WDG
Group 2 and 15 Herbicides: Apply preemergence. §Python WDG will control triazine-resistant lambsquarters and pigweed, and will suppress ragweed. *§Dual II Magnum is not for use in Nassau and Suffolk Counties.
1.33 pt. *§Dual II Magnum
+ 2/3 lb. Dimetric DF
Group 5 and 15 Herbicides: Apply preemergence. Dimetric DF is a triazine herbicide and will not control triazine-resistant lambsquarters and ragweed. *§Dual II Magnum is not for use in Nassau and Suffolk Counties.
1.33 pt. *§Dual II Magnum
+ 2 lb. Lorox DF
Group 7 and 15 Herbicides: Apply preemergence. Lorox will control triazine-resistant lambsquarters, pigweed, and ragweed. *§Dual II Magnum is not for use in Nassau and Suffolk Counties.
Problem Weed
Quackgrass
22-44 fl. oz. Roundup PowerMax
or 24-48 fl. oz. Durango DMA
24-48 fl. oz. Touchdown Total
Group 9 Herbicides: Apply these or other glyphosate products as preplant foliar sprays in the spring when quackgrass is at least 8 in. tall 4- to 5-leaf stage and actively growing. Delay tillage for at least 3 days after spraying. Low rates should be used only in fields that are to be tilled, using 3-10 gal. of water/A and may not provide long-term control. May also be applied 24-30 days after planting glyphosate-resistant soybeans.
Problem Weed
Nutsedge, annual grass and broadleaf weeds
1.33-1.67 pt. *§Dual II Magnum
+ ½-2/3 lb. Dimetric DF
Group 5 and 15 Herbicides: Apply tank mixture preplant and incorporate with a single tillage operation or apply *§ Dual II Magnum preplant-incorporated and follow with a preemergence application of Dimetric DF to control annual broadleaf weeds. Dimetric DF is a triazine herbicide and will not control triazine-resistant lambsquarters and ragweed. *§Dual II Magnum is not for use in Nassau and Suffolk Counties.
1.33-1.67 pt. *§Dual II Magnum
+ 1-1.14 oz. §Python WDG
Group 2 and 15 Herbicides: Apply preplant incorporated withing 14 days before planting. The addition of 4 oz. of Dimetric DF will improve triazine-susceptible common ragweed control. *§Dual II Magnum and §Python are not for use in Nassau and Suffolk Counties.
Problem Weed
Common ragweed
12.5 fl. oz. Cobra
or 1.25 pt. *Reflex
Group 14 Herbicides: Apply postemergence when ragweed has 4 to 6 leaves. Add crop oil concentrate or nonionic surfactant according to label. Do not apply*Reflex to any field more than once every 2 years.
Problem Weed
Annual broadleaf weeds including velvetleaf
1.5—2 pt. Basagran Group 6 Herbicide: Apply postemergence with 1 qt./A of an oil concentrate-surfactant blend when velvetleaf has fewer than 4 leaves. Will not control grasses and redroot pigweed.
Problem Weed
Velvetleaf
4—8 fl. oz. Resource Group 14 Herbicide: Use 4 oz./A for velvetleaf up to 6-leaf stage, 6 oz./A upt to 8-leaf stage, and 8 oz./A up to 10-leaf stage. Apply with 1 pt./A crop oil concentrate.
Problem Weeds
Annual grasses
9—16 fl. oz. *Select Max
or 12 fl. oz. Fusilade DX
or 7—8 fl. oz. Assure II/Targa
1.5 pt. Poast Plus
Group 1 Herbicides: Apply postemergence to actively growing grasses. Add crop oil concentrate or nonionic surfactant according to label.
Problem Weed
Volunteer corn, including Liberty Link, and glyphosate-resistant (Roundup Ready) corn.
6—8 fl. oz. Fusilade DX
or 5 fl. oz. Assure II/Targa
6—9 fl. oz. *Select Max
Group 1 Herbicides: Apply postemergence to actively growing volunteer corn. Add crop oil concentrate or nonionic surfactant according to label. These herbicides are effective against volunteer glyphosate-resistant corn.
Liberty Link soybean varieties
Emerged annual grass and broadleaf weeds 22 fl. oz. §Liberty 280 SL Group 10 Herbicide: For use with Liberty Link soybeans only. Apply postemergence when weeds are 2 to 4 in. tall §Liberty 280 SL must be applied between dawn and 2 hours before sunset with a spray grade AMS (ammonium sulfate) at 3 lb./A.
*Restricted-use pesticide.
§Not for use in Nassau and Suffolk Counties.
Refer to section 6.7.1 for information on herbicide resistance management and site of action groups.