January 24, 2017
Weed Resistance Series
As Resistant Weeds Spread,
the Challenges Increase
"Two things are happening at the same time in local corn and soybean fields in the Federated service area," said Kevin Carlson, Federated's senior agronomist, "the spread of waterhemp, and the development of herbicide-resistant biotypes. Both are very problematic for our growers."
The issue of herbicide resistance in waterhemp can be narrowed down to two main challenges.

Challenge #1: Waterhemp has spread significantly in the last several years, caused by waterhemp seeds being moved by equipment, birds, wind, and other environmental factors, all of which are very difficult to control. How can anyone keep the seeds out of a combine, or geese out of the fields?
Challenge #2: Once waterhemp is introduced into a field, controlling it becomes an issue because, according to Carlson, "most often it is already a herbicide-resistant biotype of some kind." And, if it is not, he added, "it will quickly become resistant to one in particular: glyphosate (Round Up®)."
To address these challenges and start to take control of waterhemp, growers need to think differently, first about the weed's characteristics, and secondly about the nature of the biotypes that have become resistant and how to select the right herbicides.
Waterhemp is a dioecious species, and thus cross pollination must occur to make seed (male plants + female plants = mixing of the gene pool.) Also, female
waterhemp seeds
plants are capable of producing large amounts of seed  (photo at right shows small but prolific waterhemp seeds).
Other Midwest states have been dealing with the waterhemp issue longer than Minnesota and Wisconsin; Illinois has documented waterhemp to be resistant to six different site-of-action (see article below) classes of herbicides to date.
  1. ALS (e.g., Pursuit)
  2. Triazines (e.g., Sencor)
  3. PPO inhibitors (e.g., Flexstar)
  4. Glyphosate (e.g., Roundup)
  5. HPPD inhibitors (e.g., Callisto)
  6. Auxinic herbicides (e.g., 2,4-D)
Choosing the right herbicide, or combination of herbicides, becomes increasingly complex with one additional factor, according to Carlson: "These six different herbicide resistances that are known in waterhemp can also be stacked in the biotypes that become resistant." In other words, a grower could conceivably spray all six herbicides in a field at the same time in a tank-mix and not kill some or all of the population of waterhemp in a field.
Thus, said Carlson, "It comes down to management. Herbicide management." And it is no simple task.
Federated Agronomists are ready to help growers face the challenge of waterhemp and other herbicide resistant weeds. Call with your questions and concerns. Also watch for more information on this important topic at the Soybean Grower Workshops (see dates at right), and in upcoming Agronomy Updates.
new soybean plant
Multiple Modes of Action 
Fight Herbicide Resistance
Herbicide-resistant weeds often bring conversations around to modes or sites of action. The mode of action is "the way in which a herbicide controls susceptible plants," while the site of action is "the specific biochemical site that is affected by the herbi­cide."* These two terms are often used interchangeably.
John Swanson, Federated agronomist at the Ogilvie location, recently attended a presentation by Kevin Bradley of the University of Missouri. Discussing modes (and/or sites) of action, Bradley tried "to help those of us in Minnesota and Wisconsin to avoid the situation . . . in Missouri," said Swanson. Herbicide resistant waterhemp and Palmer Amaranth are taking root in an extremely high percentage of their acres.
Bradly reported that Missouri growers are seeing resistance to two modes of action, and they have as high as five modes of resistance in one weed species. What can Minnesota growers learn from them? Swanson outlined several facts, based on Bradley's presentation.
  • Continue -- or increase -- use of pre-emerge programs.
    • There is currently no resistance to Group 15 herbicides. Weeds that don't germinate and emerge are significantly less likely to become resistant to herbicides.
  • Rotate modes of action, but more importantly, mix modes of action.
    • According to Bradley, using multiple modes of action in tank mixes during a single crop year has been more effective than merely rotating modes of action.
    • The more modes being applied, the better the chance of killing weeds and not allowing a resistant population to survive and/or explode.
  • Layer residual products.
    • Missouri growers have found major success with residual products because hard-to-control weeds can germinate for long periods of time (the trait that makes them hard to control).
    • It is important to lay down a pre-emerge herbicide as part of a base program, but then add a residual product with a post application "to continue to help prevent these weeds from germinating later in the season, when we can't go back and spray," said Swanson (Dual® is a good example).
"We have some very hard-to-control and resistant weeds coming our way," said Swanson, "and we need to learn from others and not make the same mistakes they did." Following these basic guidelines will set Minnesota and Wisconsin growers on the right path.
Contact your Federated Agronomist to further discuss modes of action and application programs for 2017.
*See this link for a more complete discussion of the terms, as defined by Dr. Joe Armstrong of the University of Oklahoma Cooperative Extension Service. 
In This Issue
Quick Links
Corn Grower Workshops Dates Set
Federated's 2017 Corn Grower Workshops will focus on the theme, Corn Economics and Agronomics. All meetings start at 10 a.m. and conclude with a free lunch. Watch for your invitation in the mail. Plan to attend one of these valuable workshops. 

RSVP to the Federated location nearest you.
Monday, Feb. 20, Osceola

Tuesday, Feb. 21, Rush City

Wednesday, Feb. 22, Ogilvie

Thursday, Feb. 23, Albertville

Friday, Feb. 24, Isanti
Staunch II™ 
Pre-Emerge Herbicide Option
As the need for pre-emerge herbicides resurges, Federated recommends Staunch II™, a private label version of Dow's Surestart II®. With the active ingredients acetochlor (with a safener), flumetesulum, and clopyralid, Staunch II can be applied pre-plant, pre-emerge, and early post, and offers an excellent value in the fight against common weeds in Minnesota, including
foxtails, crabgrass, barnyard grass, yellow nutsedge, pigweed, waterhemp,
nightshade, annual morning glory, and common ragweed.
The common use rate on field and silage corn in the Federated service area is 1.5-2.0 pt./ac.
Staunch II is one strong option for growers wanting to include pre-emerge herbicides in their crop management plan. Talk to your local Federated Agronomist to determine which product fits your needs. 
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