1. The current state of herbicidal weed control Micheal D. K. Owen Iowa State University Ames, IA 50011 USA mdowen@iastate.eduwww.weeds.iastate.edu

2. Introduction Glyphosate-based weed control systems predominate in soybeans and are increasing in corn Glyphosate-based weed control systems predominate in soybeans and are increasing in corn The benefits of glyphosate are intuitively obvious 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) 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 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 shiftsSelection pressure imposed on weed communities resulting in evolved resistant populations or weed population shifts Application timelinessApplication timeliness What alternatives exist? What alternatives exist?

3. Grower perception is the problem Recent survey conducted by Dr. Bill Johnson (Purdue University) quantifies the extent of the problem (see www.weeds.iastate.edu) Recent survey conducted by Dr. Bill Johnson (Purdue University) quantifies the extent of the problem (see www.weeds.iastate.edu) 90% of soybeans and 30+% of corn are RR ® varieties/hybrids 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 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 Growers (~66%) indicate they are not concerned about changes (current or future) in weeds attributable to glyphosate selection pressure new herbicides will be available soonnew herbicides will be available soon Problem does not exist if it is not on my farmProblem does not exist if it is not on my farm WRONG!!! WRONG!!!

4. Glyphosate stewardship Glyphosate stewardship should be a key consideration in order to preserve the utility of the technology Glyphosate stewardship should be a key consideration in order to preserve the utility of the technology Continuing misperceptions about simplicity of glyphosate Continuing misperceptions about simplicity of glyphosate Flexibility of application timing provides a false sense of securityFlexibility of application timing provides a false sense of security Ability to control larger weeds results in treatment after weeds have reduced potential yieldAbility 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 Increased adoption in corn will result in greater selection pressure resulting in “new” weed management issues Evolution of glyphosate resistant weeds continues to escalate Evolution of glyphosate resistant weeds continues to escalate

5. Glyphosate Stewardship: pollen drift provides a new management “opportunity”

6. Glyphosate stewardship Clean fields do not necessarily equate to good weed management Clean fields do not necessarily equate to good weed management The objective of weed management is to protect crop yield potentialThe objective of weed management is to protect crop yield potential Diversified weed management tactics provide significant benefits to glyphosate-based systems 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 programResidual herbicides applied EPP or PRE are important components of a corn and soybean weed management program Mechanical weed control tactics should be includedMechanical weed control tactics should be included Timely application of tactics is critical for all weed management programs Timely application of tactics is critical for all weed management programs

7. Role of Pre-emergent Herbicides in RR (LL, etc.) Systems Broaden spectrum of control Broaden spectrum of control Improve consistency Improve consistency Protect yields Protect yields Widen application windowWiden application window Reduce selection pressure Reduce selection pressure

8. 2005 Critical Period Studies Three pre treatment Three pre treatment ControlControl Corn: 0.6 or 1.2 qt Harness Xtra 6.0Corn: 0.6 or 1.2 qt Harness Xtra 6.0 Soybean: 1 or 2 qt INTRROSoybean: 1 or 2 qt INTRRO Four post timings Four post timings ControlControl V2V2 V4V4 V6V6

9. 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

10. Relationship Between Weed Biomass and Soybean Yield Loss 2 qt INTRRO Control Data include three preemergence herbicide treatments.

11. Weed Growth Rate vs Yield Loss Rate Weed height Growth Rate (inches/day) Yield Loss/day (%) 2 to 4” 0.40.5 4 to 6” 0.50.8 6 to 8” 0.71.5

12. New products A dearth of “opportunities” A dearth of “opportunities” This represents a partial list of that which is “new” 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 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 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) No “silver bullets” in the foreseeable future (if ever there was a “silver bullet” – see workshop 9)

13. Milestone (aminopyralid) Pastures, CRP, non-crop Pastures, CRP, non-crop Growth regulator – pyridine family Growth regulator – pyridine family Particularly strong on composites (thistles) Particularly strong on composites (thistles) No grazing restrictions (3 day flush out) No grazing restrictions (3 day flush out) Non-volatile Non-volatile

14. Milestone Product Product Rate Lb ai/A Half-Life(days) Milestone 4-7 fl oz 0.06-0.125 Stinger(clopyralid) 0.6 -1.3 pt 0.2-0.440 Tordon (picloram) 1-2 pt (2-4 pt Grazon) 0.25 – 0.5 (0.13-0.27) 90 Banvel 1 pt 0.55

15. Impact 2.8SC (topramezone) Postemergence in field corn, seed corn, popcorn and sweet corn Postemergence in field corn, seed corn, popcorn and sweet corn HPPD inhibitor (bleacher) HPPD inhibitor (bleacher) Broadleaf (3-8”) and grass (3-4”) Broadleaf (3-8”) and grass (3-4”) 0.75 fl oz/A (0.02 lb ai/A) 0.75 fl oz/A (0.02 lb ai/A) MSO or COC +UAN MSO or COC +UAN 0.25 to 1.0 lb atrazine recommended 0.25 to 1.0 lb atrazine recommended

16. Impact 2.8SC One application per year One application per year 45 day harvest restriction 45 day harvest restriction Do not tank mix or use sequential application with isoxaflutole (Balance, etc.) or mesotrione (Callisto, etc.) Do not tank mix or use sequential application with isoxaflutole (Balance, etc.) or mesotrione (Callisto, etc.) Rotation restrictions Rotation restrictions Soybean: North of I-80 18 months South of I-80 9 monthsSoybean: 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) 2EE label: North of I-80 (Except N of 20 and west of US71) 0.5 oz rate allows 9 month soybean replant 0.5 oz rate allows 9 month soybean replant

17. Resolve (rimsulfuron) Component of Steadfast (rim + nicosulfuron) Component of Steadfast (rim + nicosulfuron) Current label: Current label: Postemergence up to 12” or V6, whichever is most restrictivePostemergence up to 12” or V6, whichever is most restrictive PRE label newly availablePRE label newly available 1 oz Resolve = 0.25 oz rimsulfuron 1 oz Resolve = 0.25 oz rimsulfuron 0.75 oz Steadfast = 0.19 oz rimsulfuron 0.75 oz Steadfast = 0.19 oz rimsulfuron Half-life: 2-4 days Half-life: 2-4 days

18. ET Herbicide/Defoliant Likely to be introduced in the Midwest by Ninchino America, Inc. Likely to be introduced in the Midwest by Ninchino America, Inc. A PPO inhibitor to be positioned as an addition to glyphosate in corn A PPO inhibitor to be positioned as an addition to glyphosate in corn Registered in cotton as a defoliant Registered in cotton as a defoliant Inexpensive control of small seeded annual broadleaf weeds (e.g. common waterhemp and common lambsquarters) Inexpensive control of small seeded annual broadleaf weeds (e.g. common waterhemp and common lambsquarters) Injury (cosmetic) to corn a factor Injury (cosmetic) to corn a factor

19. Imperium Pre-mix of EPTC plus acetochlor re- introduced by Gowan Company Pre-mix of EPTC plus acetochlor re- introduced by Gowan Company Previously marketed as Doubleplay Previously marketed as Doubleplay Requires incorporation Requires incorporation Effective on difficult annual grasses (i.e. woolly cupgrass) Effective on difficult annual grasses (i.e. woolly cupgrass)

20. KIH-485 60WG KIH-485 60WG New chemistry! New chemistry! Under development by K-I Chemical USA, Inc. Under development by K-I Chemical USA, Inc. ISU has 4 years experience with the productISU has 4 years experience with the product Investigations in field corn, popcorn, soybeansInvestigations in field corn, popcorn, soybeans EPP, PRE, FallEPP, PRE, Fall Chemistry not released but comparisons made to other chloracetamide products (i.e. Dual MAGNUM) Chemistry not released but comparisons made to other chloracetamide products (i.e. Dual MAGNUM) Broad spectrum control Broad spectrum control Woolly cupgrassWoolly cupgrass ShattercaneShattercane Small-seeded annualsSmall-seeded annuals VelvetleafVelvetleaf Excellent residual activity, very low a.i./acre Excellent residual activity, very low a.i./acre

21. Other Products/Changes Radius (Bayer) flufenacet + isoxaflutole Radius (Bayer) flufenacet + isoxaflutole Significantly higher ratio of fluf:isox than in EpicSignificantly higher ratio of fluf:isox than in Epic Callisto: now cleared for pre and post applications on sweet corn 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 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 Boundary: changed from 7.8EC to 6.5EC Propel (Rosens): new brand of dimethenamid-P Propel (Rosens): new brand of dimethenamid-P

22. Questions?