14. Evolution of Herbicide Rates
Full label rate Acetochlor Flumetsulam Clopyralid
Pre RR 3 pts Harness +
5 oz Hornet
2.6 lbs 0.9 oz 2.5 oz
Post RR 2 pts SureStart 36% 50% 50%
Post RRv2.0 3 pts SureStart 54% 75% 75%
April May June July
Waterhemp emergence
#emerged/week
%herbicideremaining
15. Keys to Resistant
Weed Management
• Cultural practices
– Manipulation of cropping conditions to
reduce the density and competitiveness of
weeds
or
16. Effects of Cultural Practices
in Nebraska Wheat Fields
Row Direction
0
10
20
30
40
LQ Pig Grass
E-W N-S
Drill Type
0
2
4
6
Fox Kochia Stinkgrass 8 Others
Disk Hoe
Wicks et al. 2003. Weed Technol.
20. • Row spacing
• Planting rate
• Planting date
• Variety characteristics
Cultural Practices For
An Herbicide Era
21. Herbicide Resistance
• Weeds adapt to all tactics, all herbicides
• The greater the reliance on a tactic, the
greater the speed of adaption
• Integrated management programs
needed to stay ahead of evolution