Herbicide Resistant Herbicide Resistant Weeds and Their Weeds and Their Management Management Eric P. Prostko and A. Stanley Culpepper Eric P. Prostko and A. Stanley Culpepper Extension Weed Specialists Extension Weed Specialists The University of Georgia The University of Georgia Updated October 2005
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Herbicide Resistant Weeds and Their Management Eric P. Prostko and A. Stanley Culpepper Extension Weed Specialists The University of Georgia Updated October.
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Herbicide Resistant Weeds Herbicide Resistant Weeds and Their Managementand Their Management
Eric P. Prostko and A. Stanley CulpepperEric P. Prostko and A. Stanley CulpepperExtension Weed SpecialistsExtension Weed SpecialistsThe University of GeorgiaThe University of Georgia
Glyphosate Resistant Horseweed Glyphosate Resistant Horseweed in US (confirmed in 12 states)in US (confirmed in 12 states) DE (2000) TN (2001) IN (2002) MD (2002) NJ (2002) OH (2002) AK (2003) MS (2003) NC (2003) OH (2003) PA (2003) CA (2005)
Horseweed pictures from SWSS Weed ID Guide
Other Weeds in the U.S. that have Other Weeds in the U.S. that have Developed Resistance to GlyphosateDeveloped Resistance to Glyphosate
Palmer amaranth (GA-2005)
Common ragweed (MO-2004)
Rigid ryegrass (CA-1998)
Italian ryegrass (OR-2004)
SWSS SWSS
L. Hall - UGA USDA
U.S. Acres Treated with GlyphosateU.S. Acres Treated with Glyphosate1996-20031996-2003
4 1325
1428
5
30
46
9
36
62
9
5662
13
57
73
9
58
78
19
69
40
20
40
60
80
100
Corn Cotton Soybean
Crop
% o
f Ac
res
1996 1997 1998 1999 2000 2001 2002 2003
Source: USDA - National Agricultural Statistics Service – Agricultural Chemical Usage Reports
Herbicide Resistance Should Herbicide Resistance Should Only Be Suspected When .……...Only Be Suspected When .……... other causes of herbicide failure have been
ruled out. the same herbicide or herbicides with the same
mode of action have been used year after year. one weed that is normally controlled is not
controlled while other weeds are. healthy weeds are mixed with controlled weeds
(same species) a patch of uncontrolled weed is spreading.
MSMA Resistant Cocklebur in NC(Dr. Alan York – NCSU))
Causes of Herbicide FailuresCauses of Herbicide Failures
weed size** moisture temperature humidity
rate application method calibration others
All possible reasons for poor performance should be investigatedbefore considering the possibility of resistance!!!
Herbicide Resistant WeedsHerbicide Resistant WeedsStrategies for Control/PreventionStrategies for Control/Prevention
proactive vs. reactive utilize other weed control tactics
(cultivation, row patterns, etc.) rotate herbicides with different MOA rotate crops scout fields prevent seed production clean tillage and harvesting equipment
How long does resistance last in How long does resistance last in absence of further selection pressure?absence of further selection pressure?
8781
98
0
25
50
75
100
0 DNA 1 DNA 2+ DNA
DNA'a Applied in 7 years
%
Andrews and Morrison (1997) - Canada
DNA resistant green foxtail
% of resistant seeds after 7 years
initial resistance was at least 90%
Source: Weed Technology (1997): 11:369-372.
Does the use of reduced rates influence the rate of Does the use of reduced rates influence the rate of herbicide resistance development ?herbicide resistance development ?
some say yes, some say no
single dominant gene or multi-genic?
Is level of control is same?
rate vs selection pressure
infrequent use of the lowest rate that provides effective control
More Information About More Information About Herbicide ResistanceHerbicide Resistance