Herbicide Resistant Weeds and Their Management Eric P. Prostko and A. Stanley Culpepper Extension Weed Specialists The University of Georgia - PowerPoint PPT Presentation

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Herbicide Resistant Weeds and Their Management Eric P. Prostko and A. Stanley Culpepper Extension Weed Specialists The University of Georgia

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Title: Herbicide Resistant Weeds and Their Management Eric P. Prostko and A. Stanley Culpepper Extension Weed Specialists The University of Georgia


1
Herbicide Resistant Weeds and Their
ManagementEric P. Prostko and A. Stanley
CulpepperExtension Weed SpecialistsThe
University of Georgia
Updated October 2005
2
Herbicide ResistanceDefinition
  • inherited ability of a weed or crop biotype to
  • survive a herbicide application to which the
  • original population was susceptible.

Biotype a group of plants within a species that
has biological traits that are not common to the
population as a whole.
3
Herbicide Resistance
  • cross resistance
  • weed biotype that has gained resistance to
    more than 1 herbicide with the same mode of
    action. Same or different families.
  • multiple resistance
  • weed biotype that has developed tolerance to
    more than one herbicide brought about by
    different selection pressures (different modes of
    action).

4
Why Are Plants Resistant to Herbicides?
  • altered site of action
  • enhanced metabolism
  • sequestration

5
Altered Site of Action
Source J.L. Gunsolus. Herbicide Resistant
Weeds. 1998. North Central Region Extension
Publication 468.
6
Herbicide Resistance
  • How does it occur?

7
Herbicide Resistant WeedsSelection Pressure
Source J.L. Gunsolus. Herbicide Resistant
Weeds. 1998. North Central Region Extension
Publication 468.
8
Herbicide ResistanceAround the World
  • 304 Resistant Biotypes
  • 182 Species (109 dicots and 73 monocots)
  • over 270,000 fields

Source Heap, I. The International Survey of
Herbicide Resistant Weeds. Online. Internet.
October 20, 2005 .
9
The Beginning of Weed Resistance
  • 1968 (Washington)
  • nursery crops
  • common groundsel
  • atrazine
  • simazine

Photo The Missouri Flora Web-Site
10
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11
Weed Characteristics That Favor Resistance
  • reproductive capability
  • seed dispersal mechanisms

12
Worldwide
Source Dr. Ian Heap (www.weedscience.com)
13
Average Number of Seed Produced per Plant
peanut - 175 cotton - 250 corn - 800
Top 4 Herbicide Resistant Weeds in US
14
Herbicide Characteristics That Influence Weed
Resistance
  • herbicides with a single site of action
  • herbicides used multiple times during the
    growing season
  • herbicides used for consecutive growing seasons
  • herbicides used without other control strategies
  • repeated use of a product for more than 2 years
    could develop a herbicide resistance problem!!

15
Herbicide Resistant WeedsBy Mode of Action
16
Commonly Used ALS Herbicides
  • Accent
  • Ally
  • Beacon
  • Cadre
  • Classic
  • Envoke
  • Exceed
  • Express
  • Harmony Extra
  • Peak
  • Permit
  • Pursuit
  • Python
  • Scepter
  • Staple
  • Strongarm

17
Herbicide Resistance in Georgia
18
Other Counties in Georgia with ALS-Resistant
Palmer Amaranth
  • Tested by BASF in 2005
  • Colquitt
  • Cook
  • Mitchell
  • 175 locations were also sampled by UGA weed
    scientists in 2005




19
Glyphosate Resistance Around the World (8 species)
  • rigid ryegrass (1996)
  • goosegrass (1997)
  • horseweed (2000)
  • Italian ryegrass (2001)
  • hairy fleabane (2003)
  • buckhorn plantain (2003)
  • common ragweed (2004)
  • Palmer amaranth (2005)

20
Glyphosate Resistant Horseweed 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
21
Other Weeds in the U.S. that have Developed
Resistance to Glyphosate
Palmer amaranth (GA-2005)
Italian ryegrass (OR-2004)
SWSS
SWSS
Common ragweed (MO-2004)
USDA
L. Hall - UGA
Rigid ryegrass (CA-1998)
22
U.S. Acres Treated with Glyphosate1996-2003
Source USDA - National Agricultural Statistics
Service Agricultural Chemical Usage Reports
23
Herbicide Resistance Should 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.

24
MSMA Resistant Cocklebur in NC (Dr. Alan York
NCSU))
25
Causes of Herbicide Failures
  • weed size
  • moisture
  • temperature
  • humidity
  • rate
  • application method
  • calibration
  • others

All possible reasons for poor performance should
be investigated before considering the
possibility of resistance!!!
26
Herbicide Resistant WeedsStrategies 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

27
How long does resistance last in absence of
further selection pressure?
  • 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) 11369-372.
28
Does the use of reduced rates influence the rate
of 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

29
More Information About Herbicide Resistance
  • UGA Weed Science Web-Site
  • http//gaweed.com
  • International Survey of Resistant Weeds
  • http//www.weedscience.org/in.asp
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