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.

Related resource

Cornell CALS Weed Science website - a website to help you reduce the impact of these unwanted plants in fields, gardens, landscapes and ecosystems.

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Tables

Table 6.7.1: Effectiveness of selected soybean herbicides on annual weeds

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.

Table 6.7.2: Chemical weed control in soybeans

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.
Problem Weed Common lambsquarters One pass 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.
Problem Weed Nutsedge, annual grass and broadleaf weeds	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.