Midwest Weed Resistance
Management Recommendations
Herbicide-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, auxins (2,4-D), ALS, HPPD*, PPO and
PSII inhibitors (*Resistance has only been confirmed in post-emergence applications.)
• 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 (separate male and female plants) increases the
chance 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 rows1
–E
arly-season competition can reduce corn yield up to 15 percent by
the time weeds are just 6 inches tall1
•
•
Giant Ragweed (Ambrosia trifida)
Glyphosate resistance first confirmed in 2004
Germinates late-March through July (wide 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
– 2 weeds/110 sq.ft. can reduce corn yield up to 13 percent 2
•
•
Horseweed/Marestail (Conyza canadensis)
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
• Seeds dispersed widely by wind
• Grows 5 to 6 feet tall
• Can cause yield losses of up to 83 percent in soybean3 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.
3 Biology and Management of Horseweed, Loux, et.al., www.glyphosateweedscrops.org.
1
2
Fight Weed Resistance
•
Consider cultural practices such as crop rotation, cover crops
or tillage, as appropriate, to help control resistant weeds
•
Apply an early post-emergence residual herbicide for continued,
overlapping control
•
Start clean with an effective burndown
•
Remove weed escapes from fields before seed set
•
Apply broad-spectrum, pre-emergence residual herbicides
with multiple modes of action with activity on the same
target weed(s) at or prior to planting on every acre
•
Use full, labeled herbicide rates
•
Create your customized weed resistance management plan at
www.resistancefighter.com
Soybean herbicide recommendations:
Burndown
3 pt/A Gramoxone® SL + 1 pt/A 2,4-D ester + 2 pt/100 gal NIS or 1 gal/100 gal COC
Pre-emergence
Post-emergence
3 pt/A Gramoxone SL + 2 pt/A Prefix®
35 fl oz/A Touchdown Total® + 8.5 to 17 lb/100 gal AMS†
3 pt/A Gramoxone SL + 1.5 to 2 pt/A Boundary
®
or
35 fl oz/A Touchdown Total + 8.5 to 17 lb/100 gal AMS†
2 pt/A Prefix
2.5 pt/A Sequence® + 8.5 to 17 lb/100 gal AMS
or
35 fl oz/A Touchdown Total + 8.5 to 17 lb/100 gal AMS†
3.5 pt/A Flexstar® GT 3.5 + 8.5 to 17 lb/100 gal AMS + 2 to 4 qt/100 gal COC or MSO
1.5 to 2 pt/A Boundary
1 to 1.5 pt/A Flexstar + 8.5 to 17 lb/100 gal AMS or 1 to 2.5% v/v UAN +
2 to 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 herbicide recommendations:
Pre-emergence
Post-emergence
3 pt/A Gramoxone SL + 1 pt/A 2,4-D ester + 3 to 3.5 qt/A Lexar®
or 2.5 to 3 qt/A Lumax® + 2 pt/100 gal NIS
35 fl oz/A Touchdown Total + 8.5 lb/100 gal AMS + 5 oz/A NorthStar® +
1 to 4 pt/A COC + 2 to 4 qt/A UAN
or
35 fl oz/A Touchdown Total + 8.5 lb/100 gal AMS + 5 oz/A NorthStar +
1 to 4 pt/A COC + 2 to 4 qt/A UAN
3 to 3.5 qt/A Lexar or 2.5 to 3 qt/A Lumax
or
1 qt/A Lexar or 1 qt/A Lumax + 35 fl oz/A Touchdown Total +
8.5 lb/100 gal AMS
3 pt/A Gramoxone SL + 1 pt/A 2,4-D ester + 2 to 2.5 qt/A
Lexar or 1.5 to 2 qt/A Lumax + 2 pt/100 gal NIS
or
1 qt/A Lexar + 35 fl oz/A Touchdown Total + 8.5 lb/100 gal AMS
2 to 2.5 qt/A Lexar
or
1 qt/A Lumax + 35 fl oz/A Touchdown Total + 8.5 lb/100 gal AMS
1.5 to 2 qt/A Lumax
or
1.3 to 2.1 qt/A Bicep II Magnum®
1.5 to 1.75 qt/A Lexar or 1.25 to 1.5 qt/A Lumax
3.6 pt/A Halex® GT + 1.5 pt/A AAtrex® + 2 to 4 pt/100 gal NIS +
8.5 to 17 lb/100 gal AMS
1 to 2 pt/A Dual II Magnum®
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, auxins, ALS, HPPD, PPO or PSII inhibitors, Syngenta recommends applying herbicides with alternative
or multiple modes of action to target weeds in the post-emergence application.
For more information, visit www.resistancefighter.com or call Syngenta Customer Center at 1-866-SYNGENT(A) (1-866-796-4386).
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