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Issue No. 2, Article 4/April 6, 2012

Multiple vs. Effective Modes of Action

The continuing and expanding challenges imposed on agronomic cropping systems by weed populations resistant to various herbicides has led to renewed interest in using multiple modes of herbicide action for weed management. Indeed, articles about multiple modes of action and advertisements for products containing them populate much of farm media. But simply because a herbicide premix or tank-mix combination contains more than one herbicide mode of action doesn't mean that each component in the premix or tank-mix will necessarily be effective against the target weed species of greatest concern.

There are many instances when multiple modes of action and effective modes of action are not synonymous. A few examples will help illustrate the distinction between the two and how factors such as weed species, herbicide application timing, and herbicide resistance profile influence whether multiple-mode-of-action products contain multiple effective modes of action.

Giant ragweed, a large-seeded summer annual broadleaf weed species, can be particularly difficult to control with a single herbicide. Its extended germination and emergence characteristics often require farmers to use more than one herbicide or multiple applications to provide adequate control. Resistance to herbicides is known to exist in Illinois giant ragweed populations, but it is not as common or widespread as resistance in other weed species.

As a proactive practice to reduce the selection for herbicide resistance in giant ragweed, a farmer decides to use a soil-residual herbicide that contains multiple modes of action. Many premixes are available (see Tables 2 and 3 for lists of products for corn and soybean, respectively) that contain two or more active ingredients, but to effectively reduce the selection intensity for resistance to any particular herbicide active ingredient, each component of the premix or tank-mix should have similar efficacy against the target weed species; each component should also demonstrate similar soil persistence. So despite the many soil-applied herbicide premixes commercially available, few satisfy the criteria described when giant ragweed is the target species.

Table 2. Corn herbicide premixes.

Herbicide

Components (ai/gal or lb)

If you apply/A:

You have applied (ai):

Product equivalents are:

SOAa

Basis 75WDG

rimsulfuron = 0.50 lb
thifensulfuron = 0.25 lb

0.33 oz

rimsulfuron = 0.01 lb
thifensulfuron = 0.005 lb

Resolve 25DF = 0.66 oz
Harmony SG = 0.165 oz

ALS
ALS

Basis Blend 30WSG

rimsulfuron = 0.20 lb
thifensulfuron = 0.10 lb

1.25 oz

rimsulfuron = 0.016 lb
thifensulfuron = 0.008 lb

Resolve 25DF = 1.0 oz
Harmony SG = 0.25 oz

ALS
ALS

Bicep II Magnum 5.5L
Cinch ATZ

S-metolachlor = 2.4 lb
atrazine = 3.1 lb

2.1 qt

S-metolachlor = 1.26 lb
atrazine = 1.63 lb

Dual II Magnum 7.64E  = 1.32 pt
AAtrex 4L = 3.26 pt

VLCFA
PSII

Bicep Lite II Magnum 6L
Cinch ATZ Lite

S-metolachlor = 3.33 lb
atrazine = 2.67 lb

1.5 qt

S-metolachlor = 1.2 lb
atrazine = 1.00 lb

Dual II Magnum 7.64E  = 1.31 pt
AAtrex 4L = 2 pt

VLCA
PSII

Buctril + atrazine 3L

bromoxynil = 1.0 lb
atrazine = 2.0 lb

2 pt

bromoxynil = 0.25 lb
atrazine = 0.5 lb

Buctril 2E = 1 pt
AAtrex 4L = 1 pt

PSII
PSII

Bullet 4CS

alachlor = 2.5 lb
atrazine = 1.5 lb

4 qt

alachlor = 2.5 lb
atrazine = 1.5 lb

Micro-Tech 4CS = 2.5 qt
AAtrex 4L = 1.5 qt

VLCFA
PSII

Callisto Xtra 3.7SC

mesotrione = 0.5 lb
atrazine = 3.2 lb

24 fluid oz

mesotrione = 0.0938 lb
atrazine = 0.6 lb

Callisto 4SC = 3 fluid oz
AAtrex 4L = 1.2 pt

HPPD
PSII

Zemax 3.67SC

S-metolachlor = 3.34 lb
mesotrione = 0.33 lb

2 qt

S-metolachlor = 1.67 lb
mesotrione = 0.165 lb

Dual II Magnum 7.64EC = 1.75 pt
Callisto 4SC = 5.28 fluid oz

VLCFA
HPPD

Capreno 3.45SC

tembotrione = 2.88
thiencarbazone = 0.57

3 fluid oz

tembotrione = 0.067 lb
thiencarbazone = 0.013 lb

Laudis 3.5SC = 2.47 fluid oz
thiencarbazone = 0.013 lb ai

HPPD
ALS

Corvus 2.63SC

isoxaflutole = 1.88 lb
thiencarbazone = 0.75 lb

4.5 fluid oz

isoxaflutole = 0.066 lb
thiencarbazone = 0.026 lb

Balance Flexx 2SC = 4.23 fluid oz
thiencarbazone = 0.026 lb ai

HPPD
ALS

Degree Xtra 4.04CS

acetochlor = 2.7 lb
atrazine = 1.34 lb

3 qt

acetochlor = 2.025 lb
atrazine = 1.00 lb

Degree 3.8CS = 2.13 qt
AAtrex 4L = 1 qt

VLCFA
PSII

Expert 4.88SC

S-metolachlor = 1.74 lb
atrazine = 2.14 lb
glyphosate = 0.74 lb ae

3 qt

S-metolachlor = 1.31 lb
atrazine = 1.61 lb
glyphosate = 0.56 lb ae

Dual II Magnum 7.64EC = 1.37 pt
AAtrex 4L = 3.21 pt
Glyphosate 3L = 1.48 pt

VLCFA
PSII
EPSPS

Field Master 4.06S

acetochlor = 2.0 lb
atrazine = 1.5 lb
glyphosate = 0.56 lb ae

4 qt

acetochlor = 2.0 lb
atrazine = 1.5 lb
glyphosate = 0.56 lb ae

Harness 7E = 2.29 pt
AAtrex 4L = 3 pt
Roundup Ultra 3L = 1.5 pt

VLCFA
PSII
EPSPS

Fierce 78WDG

flumioxazin = 0.335 lb
pyroxasulfone = 0.425 lb

3 oz

flumioxazin = 0.063 lb
pyroxasulfone = 0.079 lb

Valor 51SX = 1.97 oz
Zidua 85WG = 1.5 oz

PPO
VLCFA

FulTime 4CS

acetochlor = 2.4 lb
atrazine = 1.6 lb

4 qt

acetochlor = 2.4 lb
atrazine = 1.6 lb

TopNotch 3.2CS = 3 qt
AAtrex 4L = 1.6 qt

VLCFA
PSII

G-Max Lite 5L

dimethenamid-P = 2.25 lb
atrazine = 2.75 lb

3 pt

dimethenamid-P = 0.844
atrazine = 1.03

Outlook 6EC = 18 fluid oz
AAtrex 4L = 2 pt

VLCFA
PSII

Guardsman Max 5L

dimethenamid-P = 1.7 lb
atrazine = 3.3 lb

4 pt

dimethenamid-P = 0.85 lb
atrazine = 1.65 lb

Outlook 6EC = 18.1 fluid oz
AAtrex 4L = 3.3 pt

VLCFA
PSII

Halex GT 4.39SC

S-metolachlor = 2.09 lb
glyphosate = 2.09 lb ae
mesotrione = 0.209 lb

3.6 pt

S-metolachlor = 0.9405 lb
glyphosate = 0.9405 lb ae
mesotrione = 0.0941 lb

Dual II Magnum 7.64EC = 0.98 pt
Glyphosate 3L = 2.5 pt
Callisto 4SC = 3 fluid oz

VLCFA
EPSPS
HPPD

Harness Xtra 6L

acetochlor = 4.3 lb
atrazine = 1.7 lb

2 qt

acetochlor = 2.15 lb
atrazine = 0.85 lb

Harness 7E = 2.46 pt
AAtrex 4L = 1.7 pt

VLCFA
PSII

Harness Xtra 5.6L

acetochlor = 3.1 lb
atrazine = 2.5 lb

2.5 qt

acetochlor = 1.94 lb
atrazine = 1.56 lb

Harness 7E = 2.21 pt
AAtrex 4L = 3.13 pt

VLCFA
PSII

Hornet WDG 68.5WDG

clopyralid = 0.50 lb ae
flumetsulam = 0.185 lb

3 oz

clopyralid = 0.094 lb ae
flumetsulam = 0.035 lb

Stinger 3S = 4 fluid oz
Python 80WDG = 0.69 oz

PGR
ALS

Keystone 5.25L
Breakfree ATZ

acetochlor = 3 lb
atrazine = 2.25 lb

3 qt

acetochlor = 2.25 lb
atrazine = 1.69 lb

Surpass 6.4EC = 2.81 pt
AAtrex 4L = 3.38 pt

VLCFA
PSII

Keystone LA 5.5L
Breakfree ATZ Lite

acetochlor = 4 lb
atrazine = 1.5 lb

2 qt

acetochlor = 2 lb
atrazine= 0.75 lb

Surpass 6.4EC = 2.5 pt
AAtrex 4L = 1.5 pt

VLCFA
PSII

Lexar 3.7L

S-metolachlor = 1.74 lb
mesotrione = 0.224 lb
atrazine = 1.74 lb

3.5 qt

S-metolachlor = 1.52 lb
mesotrione = 0.196 lb
atrazine = 1.52 lb

Dual II Magnum 7.64EC = 1.6 pt
Callisto 4SC = 6.27 fluid oz
AAtrex 4L = 3 pt

VLCFA
HPPD
PSII

Lightning 70DG

imazethapyr = 0.525 lb
imazapyr = 0.175 lb

1.28 oz

imazethapyr = 0.042 lb
imazapyr = 0.014 lb

Pursuit 70DG = 0.96 oz
Arsenal 2AS = 0.896 fluid oz

ALS
ALS

Lumax 3.95L

S-metolachlor = 2.68 lb
mesotrione = 0.268 lb
atrazine = 1 lb

3 qt

S-metolachlor = 2.01 lb
mesotrione = 0.201 lb
atrazine = 0.75 lb

Dual II Magnum 7.64EC = 2.1 pt
Callisto 4SC = 6.4 fluid oz
AAtrex 4L = 1.5 pt

VLCFA
HPPD
PSII

Marksman 3.2L

dicamba = 1.1 lb ae
atrazine = 2.1 lb

3 pt

dicamba = 0.4125 lb ae
atrazine = 0.7875 lb

Banvel 4S = 0.825 pt
AAtrex 4L = 1.56 pt

PGR
PSII

NorthStar 47.4WDG

primisulfuron = 0.075 lb
dicamba = 0.399 lb ae

5 oz

primisulfuron = 0.023 lb
dicamba = 0.125 lb ae

Beacon 75WDG = 0.50 oz
Banvel 4S = 4 fluid oz

ALS
PGR

Prequel 45WDG

rimsulfuron = 0.15 lb
isoxaflutole = 0.3 lb

1.66 oz

rimsulfuron = 0.0156 lb
isoxaflutole = 0.031 lb

Resolve 25DF = 1 oz
Balance 75WDG = 0.664 oz

ALS
HPPD

Rage D-Tech 4EC

carfentrazone = 0.13 lb
2,4-D = 3.93 lb ae

8 fluid oz

carfentrazone = 0.008 lb
2,4-D = 0.245 lb ae

Aim 1.9EW = 0.55 fluid oz
Salvo 75WDG = 0.664 oz

PPO
PGR

Realm Q

rimsulfuron = 0.075 lb
mesotrione = 0.3125

4 oz

rimsulfuron = 0.0188 lb
mesotrione = 0.0781 lb

Resolve 25DF = 1.2 oz
Callisto 4SC = 2.5 fluid oz

ALS
HPPD

Require Q

rimsulfuron = 0.0625 lb
dicamba = 0.4812 lb

4 oz

rimsulfuron = 0.0156 lb
dicamba = 0.1203 lb

Resolve 25DF = 1 oz
Banvel 4S = 3.85 fluid oz

ALS
PGR

Resolve Q

rimsulfuron = 0.184 lb
thifensulfuron = 0.04 lb

1.25 oz

rimsulfuron = 0.0144 lb
thifensulfuron = 0.0031 lb

Resolve 25DF = 0.92 oz
Harmony SG = 0.10 oz

ALS
ALS

Shotgun 3.25F

atrazine = 2.25 lb
2,4-D = 1 lb ae

2 pt

atrazine = 0.56 lb
2,4-D = 0.25 lb ae

AAtrex 4L = 1.13 pt
Salvo 5E = 0.4 pt

PSII
PGR

Spirit 57WDG

prosulfuron = 0.142 lb
primisulfuron = 0.428 lb

1 oz

prosulfuron = 0.009 lb
primisulfuron = 0.027 lb

Peak 57WDG = 0.25 oz
Beacon 75WDG = 0.57 oz

ALS
ALS

Status 56WDG

diflufenzopyr = 0.16 lb ae
dicamba = 0.4 lb ae

5 oz

diflufenzopyr = 0.05 lb ae
dicamba = 0.125 lb ae

diflufenzopyr = 0.05 lb ae
Clarity 4S = 4 fluid oz

ATI
PGR

Steadfast Q 37.7WDG

nicosulfuron = 0.252 lb
rimsulfuron = 0.125 lb

1.5 oz

nicosulfuron = 0.023 lb
rimsulfuron = 0.012 lb

Accent Q 54.5WDG = 0.694 oz
Resolve 25DF = 0.75 oz

ALS
ALS

Stout 72.5WDG

nicosulfuron = 0.675 lb
thifensulfuron = 0.05 lb

0.5 oz

nicosulfuron = 0.021 lb
thifensulfuron = 0.0015 lb

Accent Q 54.5WDG = 0.619 oz
Harmony SG = 0.05 oz

ALS
ALS

SureStart 4.16SE

acetochlor = 3.75 lb

2 pt

acetochlor = 0.9375 lb

Surpass 6.4EC = 1.17 pt

VLCFA

TripleFLEX

flumetsulam = 0.12 lb
clopyralid = 0.29 lb ae

 

flumetsulam = 0.03 lb
clopyralid = 0.0725 lb ae

Python 80WDG = 0.6 oz
Stinger 3S = 3 fluid oz

ALS
PGR

Verdict 5.57EC

saflufenacil = 0.568 lb
dimethenamid = 5

17 fluid oz

saflufenacil = 0.075 lb
dimethenamid = 0.664

Sharpen 2.85SC = 3.39 fluid oz
Outlook 6EC = 14.17 fluid oz

PPO
VLCFA

Yukon 67.5WDG

halosulfuron = 0.125 lb
dicamba = 0.50 lb ae

4 oz

halosulfuron = 0.03 lb
dicamba = 0.125 lb ae

Permit 75WSG = 0.67 oz
Banvel 4S = 4 fluid oz

ALS
PGR

aSOA (site of action) abbreviations: ALS = acetolactate synthase inhibitors (WSSA group 2); ATI = auxin transport inhibitors (WSSA group 19); EPSPS = enolpyruvyl shikimate-3-phosphate synthase inhibitors (WSSA group 9); HPPD = hydroxyphenyl pyruvate dioxygenase inhibitors/carotenoid synthesis inhibitors (WSSA group 28); PSII = photosystem II inhibitors (WSSA groups 5 and 6); PGR = plant growth regulator/synthetic auxins (WSSA group 4); PPO = protoporphyrinogen oxidase inhibitors (WSSA group 14); VLCFA = very long chain fatty acid synthesis inhibitors (WSSA group 15).

Table 3. Soybean herbicide premixes.

Herbicide

Components
(ai/gal or lb)

If you apply/A:

You have applied (ai)

Product equivalents are:

SOAa

Authority Assist 4SC

sulfentrazone = 3.33 lb
imazethapyr = 0.67 lb

10 fluid oz

sulfentrazone = 0.2602 lb
imazethapyr = 0.0523 lb

Spartan 4F = 8.33 fluid oz
Pursuit 2AS = 3.35 fluid oz

PPO
ALS

Authority First 70DF

sulfentrazone = 0.621 lb
cloransulam = 0.079 lb

6.45 oz

sulfentrazone = 0.25 lb
cloransulam = 0.0318 lb

Authority 75DF = 5.34 oz
FirstRate84WDG = 0.6 oz

PPO
ALS

Authority MTZ 45DF

sulfentrazone = 0.18 lb
metribuzin = 0.27 lb

20 oz

sulfentrazone = 0.225 lb
metribuzin = 0.3375 lb

Authority 75DF = 4.8 oz
Sencor 75DF = 7.2 oz

PPO
PSII

Authority XL 70DG

sulfentrazone = 0.622 lb
chlorimuron = 0.0778

6.5 oz

sulfentrazone = 0.2528 lb
chlormuron = 0.0316 lb

Authority 75DF = 5.39 oz
Classic 25DF = 2.023 oz

PPO
ALS

Boundary 6.5EC

S-metolachlor = 5.25 lb
metribuzin = 1.25 lb

2.4 pt

S-metolachlor = 1.57 lb
metribuzin = 0.375 lb

Dual Magnum 7.62E = 1.65 pt
Sencor 75DF = 8 oz

VLCFA
PSII

Canopy 75DG

metribuzin = 0.643 lb
chlorimuron = 0.107 lb

4 oz

metribuzin = 0.161 lb
chlorimuron = 0.027 lb

Sencor 75DF = 3.43 oz
Classic 25DF = 1.71 oz

PSII
ALS

Canopy EX29.5 WDG

chlorimuron = 0.227 lb
tribenuron = 0.068 lb

1.1 oz

chlorimuron = 0.0156 lb
tribenuron = 0.0047 lb

Classic 25DF = 1 oz
Express SG = 0.15 oz

ALS
ALS

Enlite 47.86DG

chlorimuron = 0.0285 lb
thifensulfuron = 0.088 lb
flumioxazin = 0.3621 lb

2.8 oz

chlorimuron = 0.005 lb
thifensulfuron = 0.0154 lb
flumioxazin = 0.0634 lb

Classic 25DF = 0.319 oz
Harmony SG = 0.492 oz
Valor 51WDG = 1.98 oz

ALS
ALS
PPO

Envive 41.3DG

chlorimuron = 0.092 lb
thifensulfuron = 0.029 lb
flumioxazin = 0.292 lb

3.5 oz

chlorimuron = 0.02 lb
thifensulfuron = 0.006 lb
flumioxazin = 0.064 lb

Classic 25DF = 1.29 oz
Harmony SG = 0.2 oz
Valor 51WDG = 2 oz

ALS
ALS
PPO

Extreme 2.17L

imazethapyr = 0.17 lb
glyphosate = 1.473 lb ae

3 pt

imazethapyr = 0.063 lb
glyphosate = 0.552 lb ae

Pursuit 2AS = 4 fluid oz
Roundup 3L = 1.47 pt

ALS
EPSPS

Flexstar GT 3.31SL

fomesafen = 0.66 lb
glyphosate = 2.63 lb ae

3 pt

fomesafen = 0.2475 lb
glyphosate = 0.986 lb ae

Flexstar 1.88L = 16.85 fluid oz
Touchdown Total 4.17L = 30.27
  fluid oz

PPO
EPSPS

Fusion 2.56E

fluazifop = 2 lb
fenoxaprop = 0.56 lb

8 fluid oz

fluazifop = 0.125 lb
fenoxaprop = 0.035 lb

Fusilade DX 2E = 8 fluid oz
Puma 1EC = 4.48 fluid oz

ACC
ACC

Gangster V&FR
 Co-Pack

flumioxazin = 0.51 lb
cloransulam = 0.84 lb

2 oz +
0.6 oz

flumioxazin = 0.064 lb
cloransulam = 0.032 lb

Valor 51WDG = 2 oz
FirstRate 84WDG = 0.6 oz

PPO
ALS

OpTill 68WDG

saflufenacil = 0.178 lb
imazethapyr = 0.502 lb

2 oz

saflufenacil = 0.022 lb
imazethapyr = 0.063 lb

Sharpen 2.85SC = 1 fluid oz
Pursuit 70DG = 1.43 oz

PPO
ALS

OpTill PRO

saflufenacil = 0.178 lb
imazethapyr = 0.502 lb
dimethenamid = 6 lb

2 oz +
10 fluid oz

saflufenacil = 0.022 lb
imazethapyr = 0.063 lb
dimethenamid = 0.468 lb

Sharpen 2.85SC = 1 fluid oz
Pursuit 70DG = 1.43 oz
Outlook 6EC = 9.98 fluid oz

PPO
ALS
VLCFA

Prefix 5.3EC

S-metolachlor = 4.34 lb
fomesafen  = 0.95 lb

2 pt

S-metolachlor = 1.08 lb
fomesafen  = 0.238 lb

Dual Magnum 7.62EC = 1.14 pt
Reflex 2EC = 0.95 pt

VLCFA
PPO

Rezult B&G
  Co-Pack

bentazon = 5 lb
sethoxydim = 1 lb

1.6 pt +
1.6 pt

bentazon = 1.0 lbs
sethoxydim = 0.20 lb

Basagran 4S = 2 pt
Poast Plus 1E = 1.6 pt

PSII
ACC

Sequence 5.25L

S-metolachlor = 3 lb
glyphosate = 2.25 lb ae

3 pt

S-metolachlor = 1.13 lb
glyphosate = 0.84 lb ae

Dual Magnum 7.62EC = 1.18 pt
Touchdown Total 4.17L = 26
  fluid oz

VLCFA
EPSPS

Sonic 70WDG

sulfentrazone = 0.621 lb
cloransulam = 0.079 lb

6.45 oz

sulfentrazone = 0.25 lb
cloransulam = 0.032 lb

Authority 75DF = 5.34 oz
FirstRate 84WDG = 0.6 oz

PPO
ALS

Storm 4S

bentazon = 2.67 lbs
acifluorfen = 1.33 lb

1.5 pt

bentazon = 0.5 lb
acifluorfen = 0.25 lb

Basagran 4S = 1 pt
Blazer 2S = 1 pt

PSII
PPO

Synchrony XP 28.4DG

chlorimuron = 0.215 lb
thifensulfuron = 0.069 lb

0.75 oz

chlorimuron = 0.01 lb
thifensulfuron = 0.003 lb

Classic 25DF = 0.64 oz
Harmony SG = 0.103 oz

ALS
ALS

Valor XLT 40.3WDG

flumioxazin = 0.3 lb
chlorimuron = 0.103 lb

2.5 oz

flumioxazin = 0.047
chlorimuron = 0.016 lb

Valor 51WDG = 1.47 oz
Classic 25DF = 1 oz

PPO
ALS

aSOA (site of action) abbreviations: ACC = aCCase inhibitors (WSSA group 1); ALS = acetolactate synthase inhibitors (WSSA group 2); EPSPS = enolpyruvyl shikimate-3-phosphate synthase inhibitors (WSSA group 9); PSII = photosystem II inhibitors (WSSA groups 5 and 6); PPO = protoporphyrinogen oxidase inhibitors (WSSA group 14); VLCFA = cery long chain fatty acid synthesis inhibitors (WSSA group 15).

Waterhemp, a small-seeded summer annual broadleaf weed species, has become one of the most problematic species the state's farmers contend with each season. Evolution of herbicide resistance in many Illinois waterhemp populations has greatly reduced the number of herbicide options that remain viable to control this species. Aside from herbicide resistance, the application timing of a herbicide premix or tank-mix can influence the effectiveness of each component active ingredient. For example, if a farmer decides to apply Harness Xtra (or any other premix of a chloroacetamide and atrazine) before waterhemp seed has germinated, each component of the premix (acetochlor and atrazine) would provide effective residual control of waterhemp. However, if some unforeseen circumstance kept the Harness Xtra from being applied until after waterhemp had emerged, only one component of the premix (atrazine) would effectively control the emerged waterhemp plants. Similarly, a tank-mix of a chloroaceta¬mide herbicide and glyphosate applied after waterhemp emergence does not contain more than one effective mode of action to control emerged waterhemp, nor does it contain more than one effective mode of action for soil-residual control of later-germinating waterhemp.

Illinois waterhemp populations have evolved resistance to herbicides from at least five herbicide site-of-action families, including inhibitors of acetolactate synthase (ALS), photosystem II (PSII), protoporphyrinogen oxidase (PPO), enolpyruvyl shikimate-3-phosphate (EPSPS), and hydroxyphenyl pyruvate dioxygenase (HPPD). While not every individual waterhemp plant is resistant to one or more herbicides, most field-level waterhemp populations contain one or more types of herbicide resistance.

Perhaps even more daunting is the occurrence of multiple herbicide resistances within individual plants or fields. Waterhemp plants and populations demonstrating multiple herbicide resistance are becoming increasingly common, can be more difficult to manage, and greatly reduce the number of herbicide modes of action effective for their control. For example, resistance to ALS-inhibiting herbicides in Illinois waterhemp populations is the norm rather than the exception. Resistance to ALS inhibitors is often "stacked" with resistance to herbicides from other mode-of-action families. Soil- and foliar-applied herbicide premixes containing various ALS-inhibiting herbicides are numerous (see Tables 2 and 3), and while many of these products do in fact contain multiple modes of action, the ALS inhibitor component would provide no effective control of ALS-resistant plants. In a postemergence scenario, applying a premix or tank-mix of a diphenylether (PPO inhibitor) and glyphosate (EPSPS inhibitor) would provide two effective modes of action against sensitive waterhemp, one effective mode of action against waterhemp resistant to either PPO inhibitors or glyphosate, and no effective modes of action against waterhemp resistant to both PPO inhibitors and glyphosate.

In summary, using herbicides from multiple mode-of-action groups may help reduce the selection intensity for resistance to any particular herbicide active ingredient. However, many factors determine the effectiveness of each active ingredient of a premix or tank-mix against the weed species of greatest concern.--Aaron Hager

Author:
Aaron Hager

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