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

Updated October 2005

Herbicide ResistanceHerbicide ResistanceDefinitionDefinition

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.

Herbicide ResistanceHerbicide 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).

Why Are Plants Resistant to Why Are Plants Resistant to Herbicides?Herbicides?

altered site of action

enhanced metabolism

sequestration

Altered Site of ActionAltered Site of Action

Source: J.L. Gunsolus. Herbicide Resistant Weeds. 1998.North Central Region Extension Publication 468.

Herbicide ResistanceHerbicide Resistance

How does it occur?

Herbicide Resistant WeedsHerbicide Resistant WeedsSelection PressureSelection Pressure

Source: J.L. Gunsolus. Herbicide Resistant Weeds. 1998.North Central Region Extension Publication 468.

Herbicide ResistanceHerbicide ResistanceAround the WorldAround 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 .

The Beginning of Weed ResistanceThe Beginning of Weed Resistance

1968 (Washington) nursery crops common groundsel atrazine simazine

Photo: The Missouri Flora Web-Site

Weed Characteristics That Weed Characteristics That Favor ResistanceFavor Resistance

reproductive capability

seed dispersal mechanisms

Source: Dr. Ian Heap (www.weedscience.com)

Worldwide

Average Number of Seed Average Number of Seed Produced per PlantProduced per Plant

400,000

40,000 40,000 9,0000

50,000

100,000

150,000

200,000

250,000

300,000

350,000

400,000

450,000

PalmerAmaranth

goosegrass annualbluegrass

commoncocklebur

Top 4 Herbicide Resistant Weeds in US peanut - 175; cotton - 250; corn - 800

Herbicide Characteristics That Herbicide Characteristics That Influence Weed ResistanceInfluence 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!!

Herbicide Resistant WeedsHerbicide Resistant WeedsBy Mode of ActionBy Mode of Action

Commonly Used ALS HerbicidesCommonly Used ALS Herbicides

Accent Ally Beacon Cadre Classic Envoke Exceed Express

Harmony Extra Peak Permit Pursuit Python Scepter Staple Strongarm

Herbicide Resistance in GeorgiaHerbicide Resistance in Georgia

Weed Year Herbicide Location

goosegrass 1992 DNA East GA

Prickly sida 1993 IMI ?

Italian ryegrass

1995 Hoelon Peach Co. Hart Co.

Palmer amaranth

2000 2005

SU/IMI glyphosate

Burke Co. Central GA

Other Counties in Georgia with ALS-Other Counties in Georgia with ALS-Resistant Palmer AmaranthResistant Palmer Amaranth

Tested by BASF in 2005– Colquitt– Cook– Mitchell

175 locations were also sampled by UGA weed scientists in 2005 * * *

Glyphosate Resistance Around the Glyphosate Resistance Around the World (8 species)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)

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

UGA Weed Science Web-Site

* http://gaweed.com

International Survey of Resistant Weeds

* http://www.weedscience.org/in.asp