Midwest Weed Resistance
Recommendations
Glyphosate-Resistant Weeds
Waterhemp (Amaranthus tuberculatus (syn. rudis))
History of developing herbicide resistance quickly
Glyphosate resistance first confirmed in 2005
– Populations have also been confirmed with multiple resistance
to combinations of glyphosate, ALS, PPO and PSII inhibitors.
• Germinates mid-May through July
• Can grow as much as 1 inch per day to an average height of 4 to 5 feet
• Dioecious species has separate male and female plants, increasing the
chances that resistant genetics are passed on to the next generation
– 1 female plant can produce 500,000 to 1 million seeds
• Heavy infestations of waterhemp:
–S
eason-long competition can reduce soybean yield up to 44 percent
in 30-inch rows and 37 percent in 7.5-inch rows*
–E
arly-season competition can reduce corn yield up to 15 percent by
the time weeds are just 6 inches tall*
•
•
Giant Ragweed (Ambrosia trifida)
Glyphosate resistance first confirmed in 2004
Germinates spring through July (expanded window)
• Pollen transfer between plants can increase the chances that resistant
genetics are passed on each year
• Found in patches, since its large seeds are not highly mobile
• Grows 1 to 5 feet tall, but can reach heights of 17 feet
• Season-long giant ragweed competition:
– 1 weed/110 sq.ft. can reduce soybean yield up to 50 percent**
– 2 weeds/110 sq.ft. can reduce corn yield up to 13 percent**
•
•
Horseweed/Marestail (Conyza canadensis)
Most commonly known as marestail
• First glyphosate-resistant weed in U.S. row crops, confirmed in 2000
• Often an early sign of increasing weed control problems with glyphosate
• Germinates in fall, spring and summer
• Produces up to 200,000 seeds/plant
• Grows up to 5 or 6 feet tall
• Can cause yield losses of up to 83 percent in soybean*** if left uncontrolled.
•
*Biology and Management of Waterhemp, Nordby, et.al., www.glyphosateweedscrops.org.
**Biology and Management of Giant Ragweed, Johnson, et.al., www.glyphosateweedscrops.org.
***Biology and Management of Horseweed, Loux, et.al., www.glyphosateweedscrops.org.
Fight Glyphosate Resistance
Management practices:
Apply broad-spectrum pre-emergence residual herbicides with
multiple modes of action at or prior to planting on every acre
• Use full, labeled herbicide rates
• Create your customized weed resistance management plan at
www.resistancefighter.com
•
Consider cultural practices such as crop rotation,
cover crops or tillage as appropriate to help control
resistant weeds
• Start clean with an effective burndown
•
Soybean recommendations:
Burndown
3 pt/A Gramoxone Inteon® herbicide + 1 pt/A 2,4-D ester + 2 pt/100 gal NIS or 1 gal/100 gal COC
Pre-emerge
Post-emerge
3 pt/A Gramoxone Inteon + 2 pt/A Prefix® herbicide
32 oz/A Touchdown Total® herbicide + 8.5-17 lb/100 gal AMS†
3 pt/A Gramoxone Inteon + 1.5-2 pt/A Boundary® herbicide
or
32 oz/A Touchdown Total + 8.5-17 lb/100 gal AMS†
2 pt/A Prefix
2.5 pt/A Sequence® herbicide + 8.5-17 lb/100 gal AMS
or
32 oz/A Touchdown Total + 8.5-17 lb/100 gal AMS†
3.5 pt/A Flexstar® GT 3.5 herbicide + 8.5-17 lb/100 gal AMS +
2-4 qt/100 gal COC or MSO
1.5-2 pt/A Boundary
1-1.5 pt/A Flexstar + 8.5-17 lb/100 gal AMS or 1-2.5% v/v UAN +
2-4 qt/100 gal COC or MSO
Refer to Prefix, Flexstar and Flexstar GT 3.5 labels for the maximum rate of fomesafen that may be applied per acre per year or in alternate years.
Corn recommendations:
Pre-emerge
Post-emerge
3 pt/A Gramoxone Inteon + 1 pt/A 2,4-D ester + 3-3.5 qt/A Lexar®
or 2.5-3 qt/A Lumax® herbicides + 2 pt/100 gal NIS
32 oz/A Touchdown Total + 8.5 lb/100 gal AMS + 5 oz/A NorthStar®
herbicide + 1-4 pt/A COC + 2-4 qt/A UAN
or
32 oz/A Touchdown Total + 8.5 lb/100 gal AMS + 5 oz/A NorthStar +
1-4 pt/A COC + 2-4 qt/A UAN
3-3.5 qt/A Lexar or 2.5-3 qt/A Lumax
or
1 qt/A Lexar or 1 qt/A Lumax + 32 oz/A Touchdown Total +
8.5 lb/100 gal AMS
3 pt/A Gramoxone Inteon + 1 pt/A 2,4-D ester + 2-2.5 qt/A
Lexar or 1.5-2 qt/A Lumax + 2 pt/100 gal NIS
or
1 qt/A Lexar + 32 oz/A Touchdown Total + 8.5 lb/100 gal AMS
2-2.5 qt/A Lexar
or
1 qt/A Lumax + 32 oz/A Touchdown Total + 8.5 lb/100 gal AMS
1.5-2 qt/A Lumax
or
1.3-2.1 qt/A Bicep II Magnum® herbicide
1.5-1.75 qt/A Lexar or 1.25-1.5 qt/A Lumax
3.6 pt/A Halex® GT + 1.5 pt/A AAtrex® herbicides +
2-4 pt/100 gal NIS + 8.5-17 lb/100 gal AMS
1-2 pt/A Dual II Magnum® herbicide
Herbicide rates will vary based on soil type, geography, complete weed spectrum and other factors.
†
If you suspect you have other weed populations with increased tolerance or resistance to glyphosate, Syngenta recommends you do not apply glyphosate alone in the post-emerge application.
For more information, visit www.farmassist.com or call Syngenta Customer Center at 1-866-SYNGENT(A) (1-866-796-4386).
©2011 Syngenta Crop Protection, LLC, 410 Swing Road, Greensboro, NC 27409. Important: Always read and follow label instructions before buying or using Syngenta
products. The instructions contain important conditions of sale, including limitations of warranty and remedy. AAtrex, Bicep II Magnum, Gramoxone Inteon, Lexar
and Lumax are Restricted Use Pesticides. Flexstar GT 3.5 is not currently registered for sale or use in all states. Please check with your state and local extension
service before buying or using this product. AAtrex®, Bicep II Magnum®, Boundary®, Dual II Magnum®, Flexstar®, Gramoxone Inteon®, Halex®, Lexar®, Lumax®, NorthStar®,
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