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TRANSCRIPT
Managing Herbicide
ResistanceBob Hartzler
Extension Weed ScienceDepartment of Agronomy
Evolution of Row CropWeed Management
1900 1920 1940 1960 1980 2000 2010
Cultural + Chemical + mechanical mechanical
Chemical
Important Resistant Weeds in Iowa
Decade Herbicides
Weeds
1980’s Triazines Pigweed, lambsquarter
1990’s ALS inhibitors Waterhemp, cocklebur, foxtails, several others
2000’s Glyphosate Waterhemp, horseweed,giant ragweed
PPO inhibitors
Waterhemp
2010’s HPPD inhibitors
Waterhemp
www.weedscience.org
Resistance Mechanisms in Waterhemp
Family Herbicides MechanismTriazines Atrazine,
metribuzinAltered target site,Enhanced metabolism
ALS inhibitors Pursuit, Classic Altered target site
PPO inhibitors Blazer, Cobra, Reflex
Altered target site
Glyphosate Roundup Target site amplification, perhaps others
HPPD inhibitors Callisto, Laudis Unknown
Growth regulators
2,4-D Unknown
Why Waterhemp?
Seed ProductionResistance is a numbers
game
Time of emergence
Soybean Corn
With crop 320,000 48,000
V4 20,000 2,000
‘Standard’ Resistance Management Strategies
• Fundamentals– Start with clean fields– Use weed-free seed– Scout fields– Control weed escapes– Clean equipment between fields
www.monsanto.comwww.resistancefighter.com
‘Standard’ Resistance Management Strategies
• Herbicide management– Rotate crops to allow alternate
herbicides– Use multiple herbicides– Use full rates
www.monsanto.comwww.resistancefighter.com
‘Standard’ Resistance Management Strategies
• Miscellaneous tactics– . . . and add cultural practices– Consider mechanical control– Use cover crops
www.monsanto.comwww.resistancefighter.com
YEAR PRE POST MOA1999 Dual Basagran + atrazine 32000 Prowl Glyphosate 22001 Dual Callisto 22002 Prowl Glyphosate 22003 Dual Accent + atrazine (E-POST)
Callisto + atrazine (L-POST)4
2004 Prowl Glyphosate 22005 Dual Accent + Callisto + atrazine 42006 Prowl Glyphosate 22007 Dual Callisto + atrazine (E-POST)
Impact + atrazine (L-POST)3
2008 Prowl Glyphosate 22009 Dual Callisto + atrazine 3
Keys to Resistant Weed Management
• Know your enemy
• Optimize herbicide effectiveness
Evolution of Herbicide RatesFull label rate Acetochl
orFlumetsulam
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
# e
merg
ed
/week
% h
erb
icid
e r
em
ain
ing
Keys to ResistantWeed Management
• Cultural practices– Manipulation of cropping conditions to
reduce the density and competitiveness of weeds
or
Effects of Cultural Practices in Nebraska
Wheat FieldsRow Direction
LQ Pig Grass0
10
20
30
40
E-W N-S
Drill Type
Fox Kochia Stinkgrass 8 Others0
2
4
6
Disk Hoe
Not
sig
nific
ant
Wicks et al. 2003. Weed Technol.
Value of Cultural Practices
Value of Cultural Practices
Preemergence No Pre Glyphosate at V3 Glyphosate at V3
Value of Cultural Practices
• Row spacing• Planting rate• Planting date• Variety characteristics
Cultural Practices For An Herbicide Era
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
Questions