1. Roadmap to Managing Weed Resistance
Tom Peters
Extension Sugarbeet Agronomist
North Dakota State Univ / Univ of Minnesota

2. Waterhemp in soybean field, Renville, County, MN

3. How did we get here? Relied on a single herbicide for weed control
Applied reduced rates to save money
Applied over large weed to save trips

4. Number of unique herbicides used on >5% of the soybean acreage, 1990 to 2006
1996 – launch of RR Soybean
Data from USDA-NAS, Agricultural Chemistry Use
Adapted from a slide used by J Norsworthy, Univ of Arkansas

5. Impact of weed escapes
Will increase the complexity and cost of weed control
Will reduce harvest efficiency
Glyphosate will no longer be a stand-alone ‘systems’ approach….in any crop

6. Weed resistance cannot be prevented But it can be delayed
There is a strategy to slow resistance
Crop rotations / sequences
Manage weeds along field perimeters
Back to the future
Manage weeds to seeds
Equipment cleanout

7. Use at least two and preferably three crops in the sequence; rotate to a different crop each year
Have different planting dates
Have different requirements for fertilizer
Unique tillage needs
Plant residue is managed differently
Unique row spacing
Discuss with landlords and bankers about the necessity for implementing special practices or rotating into other crops
Think strategy. Pick fields or a percent (i.e., 10%) of the operation to be targeted for special treatment

8. Washington County Tunica County Bolivar County Coahoma County
Slide from J Bond, Mississippi State Univ.

9. Perimeter Weed Management

10. Back to the Future Oldies but goodies
Efficacious and inexpensive approaches
Treflan/Sonalan, $8.00/A
Sencor, $5.95/A
Basagran, $13.00/A
Row crop cultivation, $8.88/A
Think Strategy pick fields or a percent (i.e., 10%) of the operation to be targeted for special treatment
Since these materials may not be widely available on short notice, plan ahead, secure supplies early instead of just in time

11. Manage the seed bank…it’s a “Numbers Game”
Minimize "Deposits" and
Maximize "Withdrawals”
Single waterhemp plant in 2011 (Clay County, MN) estimate of the actual seed number per plant = 142,000
Photo from J Bond, Mississippi State Univ

12. It’s a numbers game 1 waterhemp plant/A that produced 142,000 seed
142,000 – 90% loss =
14,200 seed
14,200 – 99% control =
142 plants
142 x 33% female =
47 females/A
47 x 142,000 seed =
6,674,000 seed

13. Be proactive – don’t allow a buildup of weeds
432 waterhemp per square meter
Herman, MN, 2014

14. Equipment cleanout
Clean your tillage and harvest equipment to ensure weed seeds will not be carried between fields
Especially important with crops that utilize a platform header.
Open trap doors and use compressed air to remove seeds
Takes 4 to 5 hours
Don’t have time - - consider harvest order; harvest weedy fields last

15. A diversified approach with emphasis on management of the seed bank account
“If it works, do something different next year”
Steve Powles - Director of the Australian Herbicide Resistance Initiative