How Big of a Concern is Glyphosate Resistance

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How Big of a Concern is Glyphosate Resistance?
Weeds Managed Research Area
Presented to Illinois Soybean Program Operating
Board and Guests
March 18, 2003
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Glyphosate Usage Is On The Rise

• Introduction of Roundup Ready Soybeans 1996
• Prior to 1996, lt20 of U.S. soybean acres
  received a glyphosate application1
• In 2001, 73 of U.S. soybean acres received an
  application of glyphosate
• Estimated in 2002 over 70 of IL soybean acres
  Roundup Ready
• Expect increases in 2003

1 NASS 2002
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Comparison of Roundup Ready and Conventional
Soybean Varieties
bushel/A
5 locations - 5 varieties (2000/2001), 6
varieties (2002)
No differences in yield
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(No Transcript)
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Concerns with Relying on One Herbicide for Weed
Control

• Weed Species Shifts
• To species that appear to be inherently more
  tolerant to glyphosate
• To species that avoid control through other
  mechanisms (i.e., late emergence)
• Herbicide Resistance
• Herbicide resistance is the inherited ability of
  a plant to survive and reproduce following
  exposure to a class of herbicides normally lethal
  to the wild type

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Illinois Invasive Weed Survey 2002 2003

• Top 6 most common broadleaf weeds in soybean
• Waterhemp 44/41
• Giant ragweed 22/18
• Velvetleaf 15/14
• Common cocklebur 6/4
• Common lambsquarters 4/4
• E.B. Night.(02)/Horseweed(03) 2/4

Percent ranked 1
Ranked among the top 3 weeds in soybean in 1995
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Weed Escapes in Soybeans - 2002 2003

• Top 3 weed escapes in soybeans
• Waterhemp
• Giant ragweed
• Velvetleaf
• Common lambsquarters
• Horseweed (03)

Majority of Escapes due to (03) Late emergence
waterhemp, ragweed, velvetleaf Hard to
control lambsquarters, horseweed
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Weeds Invading Fields, Ditches and Woodlands

• Top 3 weeds invading fields
• Waterhemp
• Giant ragweed
• Common pokeweed
• Top 3 weeds invading ditches
• Giant ragweed
• Common pokeweed
• Poison hemlock
• Top 3 weeds invading woodlands
• Common pokeweed
• Multi-flora rose
• G. ragweed (02)/Poison hemlock (03)

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Herbicide Resistance World-Wide
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New Resistant Weed in Illinois

• Initial reports of PPO-resistant waterhemp were
  in Kansas (2000)
• In 2001, a waterhemp population in W. Illinois
  was not controlled by Cobra
• Greenhouse and field studies were initiated in
  2002 from this population
• In 2002, there were several reports of waterhemp
  in IL resistant to PPO-inhibitors
• Cobra
• Ultra Blazer
• Flexstar

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Greenhouse experiments with suspected-resistant
population
Dose Response Curves with Cobra
Tranel (UI)
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Foliar-applied field experiment with
PPO-resistant IL populationPPO-Inhibitors and
Glyphosate
Control ()
Rate
Hager (UI)
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Injury to PPO-Resistant Waterhemp
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PPO-Resistant Waterhemp in Illinois

• PPO-resistant waterhemp is in Illinois
• Resistance to PPO-inhibitors is specific to
  application timing
• Soil-applied Susceptible
• POST Resistant
• Several soil-applied herbicides are effective in
  controlling this biotype
• Authority, Valor, Sencor, Atrazine, Prowl,
  Command, Dual II Magnum
• Glyphosate is the only effective herbicide POST
  in soybean
• This biotype is resistant to 3-classes of
  chemistry
• PPO Inhibitors POST
• ALS Inhibitors PRE and POST
• PSII Inhibitors (Triazines) POST

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What about Glyphosate (Roundup) Resistance?
Waterhemp Escapes from Glyphosate Applications
Photos courtesy of Dr. Bryan Young - SIU
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Glyphosate Rate Creep?
Commercially recommended rates for control of
6-12 inch tall waterhemp
???
79
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Ounces equivalent of Roundup Original
Compliments of Bryan Young (SIU)
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Waterhemps Response to Glyphosate from IL
Collections over the last 10 years
Control ()
1X rate
Glyphosate lb a.e./A
Steckel and Sprague (UI)
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Status of glyphosate-resistant weeds worldwide1

• Horseweed/marestail (Conyza canadensis)
• Delmarva peninsula 2000
• Tennessee 2001
• Kentucky, Indiana, Ohio - 20022
• Goosegrass (Eleusine indica)
• Malaysia 1997
• Italian ryegrass (Lolium multiflorum)
• Chile 2001
• Rigid ryegrass (Lolium rigidum)
• Australia (Victoria) 1996
• Australia (New South Wales) 1997
• USA (California) 1998
• South Africa 2001
• Wild radish (Raphanus raphanistrum)
• Canada - 20022

1 Heap, I. Nov. 23, 2002. www.weedscience.com 2
Other sources
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Regional Questions on Glyphosate Resistance

• Questions sent out on NCWEEDS list serve
• Three basic questions
• Do you have glyphosate resistant weeds in your
  state?
• If so, what are they?
• How much of a concern is glyphosate resistance in
  your state?
• By you?
• Dealer/applicators?
• Growers?
• Are there current recommendations in your state
  on resistance management or prevention of
  glyphosate-resistant weeds?
• If so, what are these recommendations?

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States that Responded
Responses from 14 states
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Do you have glyphosate-resistant weeds in your
state?

• At the time of the survey, 100 of participants
  responded No, with some concerns.
• Not that they were aware of
• Not that they would call Resistant
• However, since this survey there has been a
  confirmed glyphosate-resistant weed in some of
  these states

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The Westward Movement of Glyphosate-Resistant
Horseweed
Confirmed cases in Kentucky, Indiana, and
Ohio Variable control in Illinois and Missouri
over the last couple of years
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10 DAT
Roundup UltraMax 104 oz/A
Roundup UltraMax 26 oz/A
Untreated
Ohio Susceptible
Delaware Resistant
Jackson Co., IN 2
Jackson Co., IN 1
Compliments of Bill Johnson (Purdue)
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How much of a concern is glyphosate resistance in
your state? By you?

• Concern is growing in states on the western edge
  of the region with the introduction of more
  glyphosate-resistant crops (i.e., wheat, alfalfa,
  potatoes, sugarbeets, and turfgrass seed)
• More of a concern since there are no new active
  ingredients on the horizon
• Many responses indicated species shifts as more
  of a concern
• Resistance is Inevitable!!

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How much of a concern is glyphosate resistance in
your state? By dealer/applicators?

• Many are concerned but, incentives and product
  guarantees drive the market
• Quick, easy and inexpensive system
• Some confuse poor performance with resistance
  (environment)
• Wait till it happens approach

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How much of a concern is glyphosate resistance in
your state? By growers?

• Many are concerned but, incentives and product
  guarantees drive the market
• Quick, easy and inexpensive system
• Some confuse poor performance with resistance
• Some commodity groups are sponsoring research and
  screening for glyphosate resistance
• Wait till it happens approach

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Are there current recommendations in your state
on resistance management or prevention of
glyphosate-resistant weeds?
Recommendations for resistance management
Recommendations specific to glyphosate
of Responses
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Guidelines on how to minimize the risk of
herbicide-resistant weeds1

• Scout fields prior to the application of any
  herbicide to determine the species and if
  economic levels justify a herbicide application.
• Use alternative weed management practices, such
  as mechanical cultivation, delayed planting, and
  weed-free crop seeds.
• Rotate crops with an accompanying rotation of
  herbicides to avoid using herbicides with the
  same site of action on the same field.
• Limit the number of applications of a single
  herbicide or herbicides with the same site of
  action in a single growing season.

1 WSSA Newsletter 1995, 2321-23.
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Guidelines on how to minimize the risk of
herbicide-resistant weeds (cont.)

• Use mixtures or sequential treatments of
  herbicides that each control the weeds in
  question, but have a different site of action.
• Scout fields after application to detect weed
  escapes or shifts. If a potentially resistant
  weed or weed population has been detected, use
  available control methods to avoid seed
  deposition in the field.
• Clean equipment before leaving fields infested
  with or suspected to have resistant weeds.

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Guidelines on how to minimize the risk of
herbicide-resistant weeds (cont.)

• Use mixtures or sequential treatments of
  herbicides that each control the weeds in
  question, but have a different site of action.
• Scout fields after application to detect weed
  escapes or shifts. If a potentially resistant
  weed or weed population has been detected, use
  available control methods to avoid seed
  deposition in the field.
• Clean equipment before leaving fields infested
  with or suspected to have resistant weeds.

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Recommendations specific to glyphosate

• All recommendations started with the Guidelines
  on how to minimize the risk of herbicide-resistant
  weeds
• Additional recommendations specific to
  glyphostate
• Use of an additional herbicide with another site
  of action in an intensive 2-crop glyphosate
  system
• Emphasis on intensive monitoring for changes

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Additional recommendations specific to glyphosate

• Sequential herbicide programs using a
  soil-applied herbicide with a different site of
  action, specifically for waterhemp and giant
  ragweed
• Spray weeds at the proper time and with the
  proper rate
• Avoid continuous glyphosate-resistant crops
• Advantages and disadvantages of the continued use
  of one herbicide versus rotation of herbicides

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Monsantos weed management recommendations
specific to glyphosate

• The preferred management practice to minimize
  weed shifts and resistance to ensure that
  recommended label rates of glyphosate are applied
  at all times.
• Shaving or reducing glyphosate rates poses the
  most likely opportunity for the development of
  weed biotype and community shifts.
• Tank-mixtures that reduce glyphosate efficacy
  (through antagonism) or which encourage reduced
  glyphosate rates, should be avoided.
• Will continue to endorse glyphosate alone in all
  Roundup Ready crops, but will recommend other
  modes of action where agronomically appropriate
  and for difficult to control weeds.

Presented at the NCWSS Meeting St. Louis 2002
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Syngentas weed management recommendations
specific to glyphosate

• Rotate glyphosate with other herbicides
• No more than 2 applications of glyphosate in a
  field over any 2-year period
• In fields likely to require gt1 application
  in-season, use alternative burndown chemistry
• Rotate Roundup Ready crops with conventional
  crops
• Use full rates of glyphosate to minimize tolerant
  weed escapes
• Dont allow weeds to escape and reproduce

Presented at the NCWSS Meeting St. Louis 2002
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Overall Conclusions

• Glyphosate resistance is a concern
• Potential Problems
• Extensive use of glyphosate
• Potentially a rapid increase in future years
• Fewer active ingredients being introduced in the
  market place
• Potential Solutions
• Overriding theme Use recommended rate at
  appropriate timing
• Continuous use of one herbicide increases the
  selection pressure for herbicide resistance
• Make herbicide selections based on good agronomic
  practices

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ACKNOWLEDGEMENTS

• Illinois Soybean Program Operating Board, and
  USDA-ARS, C-FAR
• Colleagues throughout the North Central Region