Herbicide Resistance. Discussion Topics What is resistance? What causes resistance?

Herbicide Resistance

Discussion Topics

What is resistance?

What causes resistance?

Terminology

Sites of Action

Inhibition of ACCase

Inhibition of ALS

Inhibition of PS II

PS I electron diversion

Inhibition of PPO

Bleaching: inhibition of carotenoid biosynthesis at PDS

Bleaching: inhibition of HPPD

Bleaching: inhibition of carotenoid biosynthesis, unknown target

Inhibition of EPSPS

Inhibition of glutamine synthetase

Microtubule assembly inhibition

Inhibition of long-chain fatty acid synthesis

Inhibition of cell wall synthesis

Inhibition of lipid synthesis; not ACCase inhibition

Synthetic auxins

Inhibition of auxin transport

Unknown

WSSA Code Site of Action

1 Inhibition of ACCase

2 Inhibition of ALS

5 Inhibition of PS II

22 PS I electron diversion

14 Inhibition of PPO

12 Bleaching: inhibition of carotenoid biosynthesis at PDS

27 Bleaching: inhibition of HPPD

13 Bleaching: inhibition of carotenoid biosynthesis, unknown target

9 Inhibition of EPSPS

10 Inhibition of glutamine synthetase

3 Microtubule assembly inhibition

15 Inhibition of long-chain fatty acid synthesis

20 and 21 Inhibition of cell wall synthesis

8 Inhibition of lipid synthesis; not ACCase inhibition

4 Synthetic auxins

19 Inhibition of auxin transport

17 Unknown

From 2011* NC AgChem Manual (>150 entries)

Table 8-11. Herbicide Modes of Action.

Brand names Active ingredient(s) Chemical family

Mode of Action

AAtrex atrazine Triazine 5

Accent nicosulfuron Sulfonylurea 2

Aim carfentrazone Triazolinone 14

Alachlor alachlor Chloroacetamide 15

Alanap naptalam Phthalamate semicarbazone

19

Arrow Clethodim Cyclohexadione 1

Atrazine atrazine Triazine 5

Assure II quizalofop Aryloxyphenoxy-propionate

1

Axiom flufenacet + metribuzin

Oxyacetamide + triazinone

15 + 5

Backdraft Glyphosate + imazaquin

Glycine + imidazolinone

9 + 2

* Revised annually.

Mode of Action Codes

1. ACCase inhibition

2. ALS inhibition

3. Microtubule assembly inhibition

4. Synthetic auxin

5. PS II inhibition, not groups 6 or 7

6. PS II inhibition, not groups 5 or 7

7. PS II inhibition, not groups 5 or 6

8. Lipid synthesis inhibition, not ACCase

inhibition

9. EPSP synthase inhibition

10.Glutamine synthase inhibition

12.Carotenoid biosynthesis inhibition at

PDS

13.Carotenoid biosynthesis inhibition,

unknown target

14.PPO inhibition

15.Inhibition very long-chain fatty acids

17.Unknown MOA

19.Auxin transport inhibition

22.PS I electron diversion

27.Inhibition of HPPD

Herbicide Resistance Defined (WSSA definition)

Inherited ability of a biotype* of a weed to

survive and reproduce following exposure to a

dose of herbicide normally lethal to the wild

type.

*Biotype is a subset of the population having some genetically controlled characteristic not

common to the population as a whole

Herbicide Resistance Defined (WSSA definition)

Inherited ability of a biotype of a weed to

survive and reproduce following exposure

to a dose of herbicide normally lethal to the

wild type.

Herbicide Resistance vs Tolerance

Resistance: herbicide used to kill that weed; it no

longer does; we have selected for

resistance.

Example: Hoelon and ryegrass

Tolerance: the herbicide never did kill that species.

Example: 2,4-D and ryegrass

Cause of Herbicide Resistance

• Herbicides do not create resistance.

• Herbicides can select for resistant individuals already in the population.

Resistant individuals initially rare

Initial frequency of resistance: 1 in 100 thousand

1 in 1 million

1 in 10 million

1 weed/4.3 square feet = 10,000 weeds/acre

= 1,000,000 weeds/100 acres

Frequency of 1 in 1 million equal to one resistant

plant per 100 acres

0X 1/4X 1/2X 1X 2X 4X 8X 16X 32X

0X 1/4X 1/2X 1X 2X 4X 8X 16X 32X

0X 1/4X 1/2X 1X 2X 4X 8X 16X 32X Hoelon-susceptible biotype

Hoelon-resistant biotype, Union Co.;Treated with Hoelon Group 1, ACCase inhibitor

Hoelon-resistant biotype, Union Co.; Treated with Axial Group 1, ACCase inhibitor

Example of Cross Resistance

Italian ryegrass

0X 1/4X 1/2X 1X 2X 4X 8X 16X 32X

0X 1/4X 1/2X 1X 2X 4X 8X 16X 32X

0X 1/4X 1/2X 1X 2X 4X 8X 16X 32XHoelon-susceptible biotype

Hoelon-resistant biotypeTreated with Hoelon ACCase inhibitor, Group 1

Hoelon-resistant biotypeTreated with Osprey ALS inhibitor, Group 2

0X 1/4X 1/2X 1X 2X 4X 8X 16X 32X

Example of Multiple Resistance:

Italian Ryegrass

Quiz

Multiple resistance is greater concern

than cross resistance.

Why?

Discussion Topics

What is resistance?

What causes resistance?

What is the extent of resistance?

What species have resistant biotypes?

ACY 2008

0 10 20 30 40 50

No. species with resistant botypes

ALS inhibitors

PS II inhibitors (triazines)

ACCase inhibitors

Glyphosate

DNA’s

Ureas/amides

Auxins

Arsenicals

Thiocarbamates

PPO inhibitors

Carotenoid biosyn. inhibitors

Nitriles

Herbicide Resistance in US by Site of Action*

Paraquat

HPPD inhibitors

*Current as of Dec. 6, 2010

Resistance reported with 14 SOAs and 76 species;

128 species by SOA combinations, due to multiple resistance

0

2

4

6

8

10

12N

o.

resi

stan

t b

ioty

pes

1998 2000 2002 2004 2006 2008 2010

Glyphosate-resistant biotypes in U.S.

0

2

4

6

8

10

12N

o.

resi

stan

t b

ioty

pes

1998 2000 2002 2004 2006 2008 2010

Glyphosate-resistant biotypes in U.S.

Glyphosate-Resistant Weeds in the US

7 Broadleaf weeds 5 Grasses

Palmer amaranth Italian ryegrass

Tall waterhemp Rigid ryegrass

Common ragweed Johnsongrass

Giant ragweed Goosegrass

Hairy fleabane Annual bluegrass

Horseweed

Kochia

Examples of glyphosate multiple resistance in US

Palmer amaranth glyphosate and ALS inhibitors

Horseweed glyphosate and ALS inhibitors

glyphosate and paraquat

Common ragweed glyphosate and ALS inhibitors

Giant ragweed glyphosate and ALS inhibitors

Hairy fleabane glyphosate and paraquat

Tall waterhemp glyphosate, ALS inhibitors, and PPO inhibitors

Glyphosate-

Resistant Weeds

in NC

Discussion Topics

What is resistance?

What causes resistance?

What is the extent of resistance?

What species have resistant biotypes?

Impacts of herbicide resistance?

Impacts of Herbicide ResistanceIncreased cost of weed management; reduced profitabilityIncreased complexity of weed managementFewer herbicide optionsFewer crop optionsCompromise conservation tillage

Impacts of Herbicide Resistance

Increased cost of weed management; reduced profitability

Increased complexity of weed management

Fewer herbicide options

Fewer crop options

Impacts of Herbicide ResistanceIncreased cost of weed management; reduced profitabilityIncreased complexity of weed managementFewer herbicide optionsFewer crop optionsCompromise conservation tillage

Impacts of Herbicide Resistance

Increased cost of weed management; reduced profitability

Increased complexity of weed management

Fewer herbicide options

Fewer crop options

Compromise conservation tillage

Discussion Topics

What is resistance?

What causes resistance?

What is the extent of resistance?

What species have resistant biotypes?

Impacts of herbicide resistance?

Basics of resistance management

How does herbicide resistance develop?

Prerequisites for Resistance

1. At least one resistant plant

must be present

2. Selection pressure must be

put on that resistant plant

Herbicide Resistance Management

The focus must be on

reducing selection pressure.

Diversity in management options reduces

selection pressure on herbicides.

Weed Management in Cotton: Before RR

1. Conventional tillage

2. PPI and PRE herbicides

3. Early POST or POST-directed herbicides

4. Late POST-directed herbicides

5. Cultivation

Weed Management in Cotton: with RR

1. No-till or strip-till

2. No cultivation

3. No PPI herbicide; little to no PRE

4. Multiple in-crop Roundup applications

5. Very little other chemistry

Herbicide Resistance Management (Reducing selection pressure)

1. Minimize seed bank; avoid seed production

Impact of Crop Rotation and Good Control in Rotational Crop (whole field in soybean in 2009; all treated alike in 2009)

Carthage, NC 2009

Impact of Crop Rotation and Good Control in Rotational Crop (whole field in soybean in 2009; all treated alike in 2009)

Carthage, NC 2009

Soybean2008

Tobacco2008

Herbicide Resistance Management (Reducing selection pressure)

1. Minimize seed bank; avoid seed production

Think whole-farm

Good control in all crops in rotation

Avoid seed production on ditchbanks, turnrows

Avoid seed movement

Herbicide Resistance Management

1. Minimize seed bank

2. Do not depend on a single herbicide (or a single SOA)

a. Multiple SOA’s within a crop, starting with a PRE or Preplant

b. Crop rotation, multiple and different SOA’s

Herbicide Resistance Management (Reducing selection pressure)

Herbicide Resistance Management

1. Minimize seed bank

2. Do not depend on a single herbicide (or SOA)

a.Multiple SOA’s within a crop, starting with a PRE.b.Crop rotation, with different SOA’s

3. Use full rates, including sequentials and tank mixes

Herbicide Resistance Management (Reducing selection pressure)

Herbicide Resistance Management

1. Minimize seed bank

2. Do not depend on a single herbicide (or SOA)

a.Multiple SOA’s within a crop, starting with a PRE.b.Crop rotation, with different SOA’s

3. Use full rates, including sequentials and tank mixes

4. Timely POST application

Herbicide Resistance Management (Reducing selection pressure)

This is not a 4-inch pigweed!

Herbicide Resistance Management

1. Minimize seed bank

2. Do not depend on a single herbicide (or SOA)

a.Multiple SOA’s within a crop, starting with a PRE.b.Crop rotation, with different SOA’s

3. Use full rates, including sequentials and tank mixes

4. Timely POST application

5. Start clean

Herbicide Resistance Management (Reducing selection pressure)

1. Minimize seed bank

2. Do not depend on a single herbicide (or SOA)

a. Multiple SOA’s within a crop, starting with a PRE.b. Crop rotation, with different SOA’s

3. Use full rates, including sequentials and tank mixes

4. Timely POST application

5. Start clean

6. Take advantage of non-chemical, cultural practices where applicable (tillage, narrow rows, planting dates, cover crops, etc.)

Herbicide Resistance Management

&

Discussion Topics

What is resistance?

What causes resistance?

What is the extent of resistance?

What species have resistant biotypes?

Basics of resistance management

Management of glyphosate-resistant weeds in NC

Glyphosate-

Resistant Weeds

in NC

96 oz Weathermax Untreated

Martin Co., NC 2006

Distribution of Glyphosate-Resistant Common Ragweed

Grower Applied Glyphosate; Dead and Live Plants;Union Co., NC. Spring, 2009.

Johnston Co.susceptible

Stanley Co.

Union Co.

Edgecombe Co.susceptible

Glyphosate rates, left to right, where 1X = 860 g/ha or 21.8 fl oz PowerMax

0.063X, 0.125X, 0.25X, 0.5X, 1X, 2X, 4X, 8X

1X

1X

8X

8X

Dec. 2009

Distribution of Glyphosate-Resistant Italian Ryegrass

Burndown for Glyphosate-Resistant Ryegrass

• If you suspect glyphosate resistance:

– Minimum of 2 pt/A Gramoxone applied twice.

– Better control if mixed with a Photosystem II inhibitor:

atrazine for corn; Direx for cotton;

linuron or metribuzin product for soybean

Gramoxone 3 pt Mar. 9 PowerMax 22 oz Mar. 9

Gramoxone 2 pt Mar. 9

Gram 2 pt + atrazine Mar. 24

PowerMax 22 oz Mar. 9

PowerMax 22 oz + atrazine Mar. 24

Untreated

C. Simpson Farm

Apr. 10, 2010

Union County

Glyphosate-Resistant Horseweed

Initially found in 2003; resistant biotype spread quickly beginning in

2008; assume all horseweed in eastern NC is resistant.

Wind-borne seed; easily moves long distances.

Problem in no-till. Postemergence options limited. Focus on good burndown program. Photo by R. Hayes

Burndown Program for

Glyphosate-Resistant Horseweed

Two components of burndown program:

1. Something to kill emerged horseweed

2. Something to give residual control

0

5

10

15

20

25

30

35

40

% e

mer

gen

ce

Sept Oct Nov Dec Jan Feb Mar Apr May June July Aug

Burndown Programs for

Glyphosate-Resistant Horseweed

Two components of burndown program:

1. Something to kill emerged horseweed*

2. Something to give residual control

Programs:Glyphosate + Clarity (1/2 pt)** + residual herbicide

Glyphosate + 2,4-D (2 pt)** + residual herbicide

*Best if applied while weed still in rosette state

__________________________________

** Waiting intervals required

Edgecombe Co., 2008

GR Horseweed

Roundup at burndown

Roundup + 2 pt 2,4-D

+ 2 oz Valor

at burndown

In-Crop Control of Glyphosate-Resistant Horseweed

Cotton: Ignite under hood (any variety)Ignite overtop tolerant variety

Corn: Dicamba or 2,4-DIgnite on LL hybrid

Soybean: FirstRate, horseweed < 6 inches

Ignite overtop LL variety

Glyphosate-Resistant Palmer Amaranth

• Found in NC in 2005; now common • Spreading rapidly

- Equipment- Pollen flow

• Best to assume it is all glyphosate-resistant• ALS resistance also common in Palmer

amaranth; multiple resistance in some populations

GR Palmer amaranth distribution

Palmer amaranth sampling, fall 2010

Palmer present

No Palmer found

Not surveyed

What Makes Palmer Amaranth Such a Bad Weed?

• Heat and drought tolerant

• High photosynthetic capacity

• Rapid growth; large stature

• Very prolific

• Resistance trait transferred via pollen

4” in 52 hrs

Can have thousands of seed 99% control is a disaster

per square yard in seed bank;

hundreds emerge per square yard

Untreated Atrazine-based program

GR Palmer Amaranth Control in RR CottonSoutheast US Recommendations

• Avoid cotton in badly infested fields; rotate out of

cotton for a year or more and strive for good control

in rotational crop; reduce seed bank

Palmer Amaranth Programs for Corn

POST

PRE RR Corn LL Corn Conventional

Bicep Halex GT + atrazine Ignite + atrazine Capreno + atrazine

Guardsman Max Roundup + atrazine Clarity + atrazine

Harness ExtraRoundup + Dual II

Magnum* Laudis + atrazine

Lariat Roundup + Warrant*

Lexar Roundup + Clarity

*No activity on emerged glyphosate-resistant weeds.

Palmer Amaranth Programs for Soybeans

PPO PRE’s Non-PPO PRE’s POST

Authority MTZ + grass herbicide

Boundary Roundup + Blazer

Envive + ProwlCanopy +

grass herbicideRoundup + Cobra

Prefix* Roundup + Flexstar*

Valor + Prowl R’up + Harmony SG**

Roundup + Prefix*

Roundup + Pursuit**

*Contains fomesafen. Only one application per year.

**ALS inhibitor.

Glyphosate-resistant Palmer amaranth, Wayne Co., NC 2008;

PRE herbicide followed by timely glyphosate tank mix

GR Palmer Amaranth Control in RR CottonSoutheast US Recommendations

• Avoid cotton in badly infested fields

• Aggressive Preplant and/or PRE herbicide program.

Get it PRE or you don’t get it. No salvage POST

options in RR or conventional cotton.

Hedging Against Lack of Timely Rain on PRE Herbicides:Palmer Amaranth in Cotton or Soybeans

• In conventional tillage, incorporate a yellow herbicide.

• In no-till cotton or no-till full-season soybeans, put residual with

preplant burndown. Paraquat if needed at planting.

• In double-crop soybeans, pray for rain.

Preplant/PRE herbicides for Palmer amaranthin Cotton

Preplant PPI no-till conv. till PRE

Valor Treflan Cotoran Diuron + Staple

Direx Prowl Diuron Reflex + Staple

Reflex Reflex + Cotoran

Staple Reflex + diuron

Prowl Prowl + Reflex

Prowl + Cotoran

Prowl + diuron

• Avoid cotton in badly infested fields

• Aggressive Preplant and/or PRE herbicide

program.

• Dual Magnum or Warrant early POST

• Residual lay-by

GR Palmer Amaranth Control in RR CottonSoutheast US Recommendations

Weed control with

glufosinate-based systems

Weed Management in Glufosinate-Tolerant Cotton• Weaknesses of Ignite: grasses, pigweed sp., nutsedge, perennials

• Ignite not as effective as glyphosate on grasses, perennialweeds, or glyphosate-susceptible Palmer, but it will control glyphosate-resistant Palmer if properly timed

Left: 29 oz Ignite Right: 22 oz Powermax

GR Palmer amaranth,14 days after treatment

• Timing is critical!! 3 to 4 inches for consistent Palmer control.

• Use additional chemistry, similar to RR program

Better control, Ignite timing somewhat less critical Absolutely must avoid Ignite resistance

Strong PRE and/or preplant program for residual control

Dual or Warrant POST for additional residual control

Residual lay-by

Weed Management in Glufosinate-Tolerant Cotton

1. Minimize seed bank

2. Do not depend on a single herbicide (or SOA)

a. Multiple SOA’s within a crop, starting with a PRE.b. Crop rotation, with different SOA’s

3. Use full rates, including sequentials and tank mixes

4. Timely POST application

5. Start clean

6. Take advantage of non-chemical, cultural practices where applicable (tillage, narrow rows, planting dates, cover crops, etc.)

Herbicide Resistance ManagementHerbicide Resistance Management (Reducing selection pressure)

Harrington Seed DestructorRay Harrington

Western Australia

No Deep Tillage Deep Turn

No Herbicide Treatment

Number of Palmer Amaranth Plants During Early Season. Macon Co., Georgia 2008.*

0

20

40

60

80

100

81 b

No deep turn

No Cover

Deep turn

No cover

Rye 7 foot when killed, rolled, planted.

Deep turn 12 inch in previous fall.

Herbicide program: Direx + Reflex + Staple PRE; RU + Parrlay POST, Direx + MSMA at layby.

per

cen

t

63 c

80 b

98 a

GR Palmer amaranth control at harvest with Roundup-based systems. Macon Co., GA 2009.

No deep turn

Rye Cover

Deep turn

Rye Cover

0

700

1400

2100

1627 b

No deep turn

No Cover

Deep turn

No cover

Rye 7 foot when killed, rolled, planted.

Deep turn 12 inch in previous fall.

Herbicide program: Direx + Reflex + Staple PRE; RU + Parrlay POST, Direx + MSMA at layby.

1298 d1524 bc

2078 a

Seed cotton yield (lb/A) with Roundup-based systems. Macon Co., GA 2009.

No deep turn

Rye Cover

Deep turn

Rye Cover

Staple + Reflex + Direx PRE

Roundup WMax + Parrlay POST

Direx + MSMA Layby

No deep tillageNo cover crop

Deep tillageNo cover crop

Palmer amaranth response to deep tillage. Macon County, GA. 2009.

Staple + Reflex + Direx PRE

Roundup WMax + Parrlay POST

Direx + MSMA Layby

No deep tillageNo cover crop

No deep tillageRye cover crop

Palmer amaranth response to cover crops. Macon County, GA. 2009.

Staple + Reflex + Direx PRE

Roundup WMax + Parrlay POST

Direx + MSMA Layby

No deep tillageNo cover crop

Deep tillageRye cover crop

Palmer amaranth response to deep tillage and cover crops. Macon County, GA. 2009.

Seed concentrated on surface in no-till system.

Palmer amaranth seed will not emerge from deeper than about 1 inch.

Seed viability reduced 80% 30 months after burial.

Fall plowing every 3 to 5 years, followed by cover crop established in same fall, then no-till for 3 to 5 years.

Staple + Reflex + Direx PRE

Roundup WMax + Parrlay POST

Direx + MSMA Layby

No deep tillageNo cover crop

Palmer amaranth response to deep tillage and cover crops. Macon County, GA. 2009.

Staple + Reflex + Direx PRE

Ignite + Parrlay POST

Direx + MSMA Layby

No deep tillageNo cover crop

Percent reduction in Palmer emergence by cover crops without herbicides. GA and NC. 2007. 42 DAP.*

0

20

40

60

80

100

59,895 lb/A 66,429 lb/A 68,607 lb/A 96,921 lb/A

*Compared to the no cover conventionally tilled system.

38 b

53 ab40 b

57 a

wheat biomass rye biomass