The current state of herbicidal weed control

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

2. Introduction • 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?

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) • 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!!!

4. 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

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

6. 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

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

8. 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

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

11. Weed Growth Rate vsYield Loss Rate

12. 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)

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

14. Milestone

15. 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

16. 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

17. 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

18. 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

19. Imperium • 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)

20. 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

21. 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

22. Questions?