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The current state of herbicidal weed control. Micheal D. K. Owen Iowa State University Ames, IA 50011 USA [email protected] Introduction. Glyphosate-based weed control systems predominate in soybeans and are increasing in corn

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the current state of herbicidal weed control

The current state of herbicidal weed control

Micheal D. K. Owen

Iowa State UniversityAmes, IA 50011 USA

[email protected]

  • Glyphosate-based weed control systems predominate in soybeans and are increasing in corn
  • The benefits of glyphosate are intuitively obvious
  • Pseudo-benefits of glyphosate-based systems reflect incorrect assumptions by growers (i.e. simplicity and cost compared to “conventional” systems)
  • Risks of glyphosate-based systems are no different than with other herbicide systems
    • Selection pressure imposed on weed communities resulting in evolved resistant populations or weed population shifts
    • Application timeliness
  • What alternatives exist?
grower perception is the problem
Grower perception is the problem
  • Recent survey conducted by Dr. Bill Johnson (Purdue University) quantifies the extent of the problem (see
  • 90% of soybeans and 30+% of corn are RR® varieties/hybrids
  • Multiple applications of glyphosate yearly imposes selection pressure on weeds resulting in evolved resistance or weed population shifts
  • Growers (~66%) indicate they are not concerned about changes (current or future) in weeds attributable to glyphosate selection pressure
    • new herbicides will be available soon
    • Problem does not exist if it is not on my farm
  • WRONG!!!
glyphosate stewardship
Glyphosate stewardship
  • Glyphosate stewardship should be a key consideration in order to preserve the utility of the technology
  • Continuing misperceptions about simplicity of glyphosate
    • Flexibility of application timing provides a false sense of security
    • Ability to control larger weeds results in treatment after weeds have reduced potential yield
  • Increased adoption in corn will result in greater selection pressure resulting in “new” weed management issues
  • Evolution of glyphosate resistant weeds continues to escalate
glyphosate stewardship6
Glyphosate stewardship
  • Clean fields do not necessarily equate to good weed management
    • The objective of weed management is to protect crop yield potential
  • Diversified weed management tactics provide significant benefits to glyphosate-based systems
    • Residual herbicides applied EPP or PRE are important components of a corn and soybean weed management program
    • Mechanical weed control tactics should be included
  • Timely application of tactics is critical for all weed management programs
role of pre emergent herbicides in rr ll etc systems
Role of Pre-emergent Herbicides inRR (LL, etc.) Systems
  • Broaden spectrum of control
  • Improve consistency
  • Protect yields
    • Widen application window
  • Reduce selection pressure
2005 critical period studies
2005 Critical Period Studies
  • Three pre treatment
    • Control
    • Corn: 0.6 or 1.2 qt Harness Xtra 6.0
    • Soybean: 1 or 2 qt INTRRO
  • Four post timings
    • Control
    • V2
    • V4
    • V6
effect of preemergence harness xtra 6 0 and int rr o in weed density at v6 application
Effect of preemergence Harness Xtra 6.0 and INTRRO in weed density at V6 application

Harness Xtra: Low = 0.6 qt, High = 1.2 qt

INTRRO: Low = 1 qt, High = 2 qt

relationship between weed biomass and soybean yield loss
2 qt INTRRORelationship Between Weed Biomassand Soybean Yield Loss


Data include three preemergence herbicide treatments.

new products
New products
  • A dearth of “opportunities”
  • This represents a partial list of that which is “new”
  • Many “new” companies taking an increasingly active role in re-introducing old products or marketing generic versions of existing herbicides
  • In corn and soybeans, still some discovery activity by the major companies
  • No “silver bullets” in the foreseeable future (if ever there was a “silver bullet” – see workshop 9)
milestone aminopyralid
Milestone (aminopyralid)
  • Pastures, CRP, non-crop
  • Growth regulator – pyridine family
  • Particularly strong on composites (thistles)
  • No grazing restrictions (3 day flush out)
  • Non-volatile
impact 2 8sc topramezone
Impact 2.8SC(topramezone)
  • Postemergence in field corn, seed corn, popcorn and sweet corn
  • HPPD inhibitor (bleacher)
  • Broadleaf (3-8”) and grass (3-4”)
  • 0.75 fl oz/A (0.02 lb ai/A)
  • MSO or COC +UAN
  • 0.25 to 1.0 lb atrazine recommended
impact 2 8sc
Impact 2.8SC
  • One application per year
  • 45 day harvest restriction
  • Do not tank mix or use sequential application with isoxaflutole (Balance, etc.) or mesotrione (Callisto, etc.)
  • Rotation restrictions
    • Soybean: North of I-80 18 months South of I-80 9 months
      • 2EE label: North of I-80 (Except N of 20 and west of US71)

0.5 oz rate allows 9 month soybean replant

resolve rimsulfuron
  • Component of Steadfast (rim + nicosulfuron)
  • Current label:
    • Postemergence up to 12” or V6, whichever is most restrictive
    • PRE label newly available
  • 1 oz Resolve = 0.25 oz rimsulfuron
  • 0.75 oz Steadfast = 0.19 oz rimsulfuron
  • Half-life: 2-4 days
et herbicide defoliant
ET Herbicide/Defoliant
  • Likely to be introduced in the Midwest by Ninchino America, Inc.
  • A PPO inhibitor to be positioned as an addition to glyphosate in corn
  • Registered in cotton as a defoliant
  • Inexpensive control of small seeded annual broadleaf weeds (e.g. common waterhemp and common lambsquarters)
  • Injury (cosmetic) to corn a factor
  • Pre-mix of EPTC plus acetochlor re-introduced by Gowan Company
  • Previously marketed as Doubleplay
  • Requires incorporation
  • Effective on difficult annual grasses (i.e. woolly cupgrass)
kih 485 60wg
KIH-485 60WG
  • New chemistry!
  • Under development by K-I Chemical USA, Inc.
    • ISU has 4 years experience with the product
    • Investigations in field corn, popcorn, soybeans
    • EPP, PRE, Fall
  • Chemistry not released but comparisons made to other chloracetamide products (i.e. Dual MAGNUM)
  • Broad spectrum control
    • Woolly cupgrass
    • Shattercane
    • Small-seeded annuals
    • Velvetleaf
  • Excellent residual activity, very low a.i./acre
other products changes
Other Products/Changes
  • Radius (Bayer) flufenacet + isoxaflutole
    • Significantly higher ratio of fluf:isox than in Epic
  • Callisto: now cleared for pre and post applications on sweet corn
  • Select Max: no additives required with ‘loaded’ glyphosate; greater adjuvant flexibility with other posts; 1 lb/gal EC rather than 2 lb/gal
  • Boundary: changed from 7.8EC to 6.5EC
  • Propel (Rosens): new brand of dimethenamid-P