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Group Title: Bulletin
Title: Turf herbicide families and their characteristics
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Title: Turf herbicide families and their characteristics
Series Title: Bulletin
Physical Description: 42 p. : ; 28 cm.
Language: English
Creator: McCarty, L. B ( Lambert Blanchard ), 1958-
Colvin, Daniel Lamar, 1959-
Florida Cooperative Extension Service
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
Place of Publication: Gainesville
Publication Date: 1993
 Subjects
Subject: Herbicides   ( lcsh )
Turf management   ( lcsh )
Turfgrasses -- Weed control   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
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Bibliography: Includes bibliographical references (p. 37).
Statement of Responsibility: L.B. McCarty and D.L. Colvin.
General Note: Cover title.
General Note: "August 1993."
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Full Text


-' UNIVERSITY OF

FLORIDA
Florida Cooperative Extension Service


Turf Herbicide Families and Their Characteristics


Bulletin 280
August 1993


L. B. McCarty and D. L. Colvin


The Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research,
educational information and other services only to individuals and institutions that function without regard to race, color, sex, age, handicap,
or national origin. For information on obtaining other extension publications, contact your county Cooperative Extension Service office.
Florida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida / John T. Woeste, Dean






TABLE OF CONTENTS


Introduction ..................................................................... 1

Herbicide properties ........ .. ..................................................... 1

Herbicides and herbicide families .................. ................................... 3

Acetanilides ............................ .......... ..................... .......... 3

A m ides ........................................................................ 5

Aryl-oxy phenoxy ....................... .. ........................................ 7

Benzoic Acids ....................................................................... 8

Bipyridyllums ........................................................ ............ 9

Carbamates (Phenyl) and carbanilates ............................... ............................. 11

Cyclohexendiones ......................................................... ....... 12

Dinitroanilines ................................................ ......................13

Diphenyl-ethers ..................................................................15

Imidazolinones ...................................................................16

Nitriles (Benzonitriles) ..............................................................18

Organic arsenicals ................................................................. 19

Phenoxies .................... ....................... .... .... .... ............ 21

Phthalic acids ....................................................................24

Pyridines and picolinic acids ...................... ................................... 25

Substituted ureas ...................................... .. ......................... ....... 27

Sulfonamides ........ .............................................................29

Sulfonylureas .......................................... ..........................30

Triazines ........................................................................ 31

Unclassified herbicides .......................................... ...... ............. 33

References and further reading ...................................................... 37

Appendix Cross-reference of herbicide trade names, common names, and families ................ 38















Turf Herbicide Families and Their Characteristics'

L. B. McCarty and D. L. Colvin2


INTRODUCTION


Knowing as much as possible about a pesticide
being used is essential for obtaining maximum benefit
at the lowest cost and least amount of hazard to the
applicator and/or the environment. Many publications
list herbicides and their specific uses and rates. The
objective of this publication is to provide indepth
information on herbicide chemistry, mode of action,
and fate in the environment. This publication
discusses the major turf herbicides, their chemical
family, the characteristics of each, and the safety
precautions for use. Additional herbicides, not all of
which are currently labelled for use in turf, are
included only as a reference.

HERBICIDE PROPERTIES

Subsequent discussions in the text stress the
importance of understanding the physical and
chemical properties of herbicides. The properties of
specific herbicides influence how they react in plants,
soils and the environment.

Water solubility

Water solubility is defined as the maximum
concentration of a chemical that will dissolve in pure
water at a specific temperature and pH (e.g., how
easily it dissolves in water), and is expressed as a
percent, ppm or g/100 ml. The following offers
conversion tips for determining concentration in
terms of ppm.


Solids


1 kilogram (kg) = 1 million milligrams (mg),
therefore; 1 mg/kg = 1 ppm

Liquids

1 liter (L) of water weighs 1 kg, therefore;
1 mg/L = 1 ppm and 1 ug/L = 1 part per billion,
1% solution = 1 g/100 ml = 10,000 part per
million, and
1 teaspoon per 1000 gallons of water
approximates 1 ppm

Ionic (charged) herbicides generally are more
water soluble and less volatile than nonionic
(neutrally charged) herbicides. The following, Table
1, provides relative solubility rankings depending on
actual water solubilities of a compound.

Table 1. Solubility rankings based on water solubilities of a
compound
Relative Solubility Water Solubility (ppm)
Very Soluble 1,000 to 10,000
Moderately Soluble 100 to 1,000
Low Solubility 10 to 100
Very Low Solubility 1 to 10
Extremely Low Solubility 0.1 to 1


1. This document is Bulletin 280, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida.
Publication date: August 1993.
2. L. B. McCarty, associate professor, Department of Environmental Horticulture; D. L. Colvin, associate professor, Department of Agronomy.
Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville FL 32611.






Turf Herbicide Families and Their Characteristics

As illustrated above, relative solubility
corresponds to actual water solubility values.
Therefore, if a herbicide is very soluble in water, it
dissolves readily but can easily move with rainwater as
runoff. It can also be carried through soil water
movement and become a potential groundwater
contaminant. If a herbicide has extremely low
solubility it tends to stick to soil, reducing possible
adverse non-target effects.

Soil Adsorption

The ability of a compound to bind to soil particles
is called soil adsorption. Most soil particles such as
clay and organic matter are negatively charged and
tend to repel negative and attract positive charges-
much like a magnet. Sands are often neutral in their
charges, therefore, they do not attract or repel
charged compounds.

Anionic Herbicides

Anionic, or negatively charged herbicides, show
low adsorption to negatively charged soil particles
such as organic matter and clay and generally leach
readily out of the soil. For example, 2,4-D in the
anionic form, is actually repelled by clays and organic
matter.

Cationic Herbicides

Cationic, or positively charged herbicides, are
generally tightly adsorbed to negatively charged clay
soils but less so in organic soils. For example,
paraquat and diquat are positively charged and are
adsorbed irreversibly by negatively charged expanding
type clays.

Nonionic

Nonionic, or neutrally charged herbicides, adsorb
primarily through weak physical bonds to soil
particles. The degree of adsorption is generally
related to water solubility. The nonionic type
herbicides are the largest category of herbicides.

Vapor pressure

Vapor pressure (or volatility) is the measure of
the intramolecular bonding forces of a compound and
is usually expressed as mm Hg (mercury) at 250 C,
Table 2. Compounds possessing weak intramolecular
forces readily volatilize and can easily change from a
solid or liquid form to a gaseous form at room


Page 2


temperature. Volatility is highly dependent on
temperature, moisture, soil texture, and the properties
of a specific herbicide, and is extremely important in
determining how a particular herbicide can be used.
For example, compounds with high volatility such as
trifluralin must be applied to the soil and
incorporated by watering-in to prevent loss through
volatilization to the air.

Table 2. Vapor pressure as a degree of volatility
Vapor Pressure Volatility
10-1 to 104 mm Hg, 25 C volatile (high)
10-4 to 10.6 mm Hg, 25 C intermediate (medium)
>10-6 mm Hg, 25 C nonvolatile (low)


Persistence


Persistence is a measure of how long a compound
remains in the soil and can be identified in two ways,
longevity and half-life. Longevity refers to the
amount of time a particular pesticide remains
phytotoxic to a sensitive species and is described in
terms of "carry over," or residual effects. Half-life is
a more absolute measure of persistence and is the
time it takes for half of the applied pesticide to
degrade. For example, if a herbicides's half-life is 30
days, half of the chemical will be left after 30 days,
one-quarter after 60 days, one-eighth after 90 days
and so on.

Toxicity

Toxicity is the inherent capacity of a substance to
cause injury or death. A commonly used measure of
toxicity is LD50. LD50 is the dose required to kill 50
percent of a population of test animals and is usually
expressed in the weight of the chemical per unit of
animal body weight (mg/kg or ppm). A chemical with
a small LD50 (e.g., 5 mg/kg) is extremely toxic while
a chemical with a larger LD50 (e.g., 1000 to 5000
mg/kg) is not as toxic (Table 3). LC50 is the
concentration that will kill 50 percent of the test
animals and is usually expressed in parts per million
(ppm). Terms expressing intake by animal or human
tissue are acute oral, acute dermal and chronic
toxicity. Acute oral refers to a single dose taken by
mouth while acute dermal refers to a single dose
applied directly to the skin. Chronic toxicity occurs
over a long period of time, either continuously or
intermittently and is used to describe ongoing






Turf Herbicide Families and Their Characteristics


Table 3. Toxicity rating scale of pesticides

Signal Word
Required on Oral LDso Dermal LDso
Category Pesticide Label (mg/kg or ppm) (mg/kg or ppm) Probable Oral Lethal Dose

I. Very highly toxic Danger-Poison < 51 201 a few drops to 1 teaspoon
(skull and
crossbones)
II. Highly toxic Warning 51 to 500 201 to 2,000 > 1 teaspoon to 1 ounce
III. Moderately toxic Caution 501 to 5,000 2,001 to 20,000 > 1 ounce to 1 pint
IV. Low toxicity Caution > 5,000 > 20,000 1 pint to 1 quart or more


exposures and the effects that develop
exposure time.


after a long


HERBICIDES AND HERBICIDE FAMILIES


Herbicides can be classified
characteristics including chemical
translocation method, mode of action,
symptomology and herbicide use.


by several
structure,
persistence,
No one


classification system fits all criteria. The following
text lists herbicides by their family chemistry and
covers only turf or closely related uses. Table 29, in
the Appendix, is a quick reference guide for herbicide
family, common names, and major herbicide trade
names. The Appendix also provides a cross reference
for trade names, common names, and herbicide
families (Table 30).


ACETANILIDES


Important Members (Table 4)


Uses


The acetanilides are used extensively on a wide
variety of crops for selective preemergence control of
grass and certain broadleaf weeds. In addition,
alachlor and metolachlor provide a degree of
preemergence control of yellow nutsedge.
Metolachlor is used in St. Augustinegrass and
bermudagrass sod production for preemergence grass
(particularly sprangletop) and nutsedge control.


Behavior in Plants


Absorption


The major point of uptake is by emerging shoots
of germinating grasses and secondarily by roots.

Translocation

Acetanilides are translocated upward in the xylem.
Higher concentrations occur in the vegetative rather
than in the reproductive parts.


Table 4. Important members of the acetanilide family

Water Solubility Vapor Pressure
Common Name(s) Trade Name(s) Manufacturer (ppm) (mm HG @ 20-35" C)

Alachlor Lasso Monsanto 242 2.2 x 10'5
Metolachlor Pennant Ciba-Geigy 530 1.3 x 10-5
The Acetanilides are also grouped with the Amide (or Substituted Amide) herbicide families.


Page 3






Turf Herbicide Families and Their Characteristics


Selectivity


Persistence


The acetanilides are generally active on monocots
or grassy species. Many broadleaf species are tolerant
of these herbicides because of limited uptake of the
chemical during germination. In addition, tolerant
species can internally metabolize these compounds
into non-toxic ones.

Mechanism of Action

These herbicides normally kill or affect
susceptible weeds before their emergence but do not
inhibit seed germination. They are general growth
inhibitors, especially of root elongation. Specifically,
the acetanilides interfere with protein and chlorophyll
synthesis. Cellular membrane disruption may also be
a mode of action.

Degradation

As a class, these herbicides are short-lived (< 10
days) within plants and are metabolized by hydrolysis
and disconjugation.

Behavior in Soils

Adsorption

Due to relatively moderate water solubility and
weak binding forces involved in the adsorption
process, acetanilides are adsorbed to some extent by
organic matter but not strongly. Acetanilide activity
is not strongly diminished with increasing rates of soil
organic matter making them useful in muck soils.

Leaching

These compounds exhibit low leaching potential
when associated with clay or muck soils. When
organic matter content approaches 2.0 percent, no
significant leaching would be expected, even under
heavy rainfall conditions. Leaching potential is
greater if soils are coarse and the ground water is
near the surface. Little lateral movement occurs.


All the acetanilides are moderate in persistence.
Longevity can be prolonged with excessive rates.
Acetanilides are readily metabolized by soil
microorganisms. Thus, environmental variables which
encourage microbial activity will reduce soil
persistence of this group. For example, as
temperature increases, microbial degradation
increases. Alachlor persists for 6 to 10 weeks but may
vary depending on soil type and climatic condition.
Metolachlor has a half-life of 15 to 25 days in
southern soil. Photodecomposition also plays a role
in the loss of these herbicides from soils. Soil
incorporation prevents significant losses of these
herbicides due to reduced photodecomposition.

Distinguishing characteristics

Moderate water solubility and leaching;
Moderate soil persistence
Nonionic compounds
Controls grasses and certain broadleaf species
and nutsedges
Apoplastic (xylem) movement in plants
Absorbed primarily by emerging shoot in
target plants
Inhibition of protein synthesis is a suspected
mode of action.
Corrosive to steel and black iron.

Toxicological Properties


Acute Oral toxicity
Alachlor
Metolachlor


LDsomg/kf g
930
2780


To avoid application exposure, applicants should
wear goggles or a face-shield when handling.
Contaminated clothing should be removed and
washed. Keep the chemicals out of bodies of water to
avoid contamination of groundwater.


Page 4






Turf Herbicide Families and Their Characteristics


AMIDES (ACETAMIDES)


Important Members (Table 5)


Table 5. Important members of the amides (acetamides) family
Water Solubility Vapor Pressure
Common Name Trade Name(s) Manufacturer (ppm) (mm HG @ 25-35 C)
Diphenamid Enide Nor-AM 260 nonvolatile
Isoxaben Gallery DowElanco 0.1 3.9 x 10-7
Napropamide Devrinol ICI/Zeneca 73 4 x 10-6
Pronamide Kerb Rohm and Haas 15 8.5 x 10-5
Isoxaben often is also classified as a dinitroaniline.


Uses


Translocation


Most amides are used as preemergence annual
grass and small-seeded broadleaf weed control.
Diphenamid is used in a wide range of vegetable
crops, napropamide in tree fruit, vegetables,
ornamentals and tobacco while pronamide is used in
lettuce, christmas trees, ornamentals and turf.
Pronamide also is used for postemergence annual
bluegrass and ryegrass control in turf. Isoxaben
provides primarily preemergence broadleaf weed
control. Soil incorporation by mechanical means or
irrigation will improve weed control performance of
these herbicides.

Behavior in Plants

Absorption

All amides are absorbed primarily by roots or
emerging shoots and as a class are more effective on
annual grass weeds. Specifically,

* Diphenamid is root absorbed and has a low level
of foliar absorption.
* Napropamide is rapidly absorbed by roots with
little, if any, foliar absorption.
* Pronamide is absorbed primarily by roots plus
minor foliar absorption. Soil incorporation
following application by irrigation improves root
uptake.
* Isoxaben is absorbed by roots with little foliar
absorption.


* Diphenamid and Napropamide are translocated
upward in plants via the xylem.
" Pronamide is readily translocated upward
primarily in the xylem, but may exhibit some
phloem mobility. However, pronamide
translocation from leaves is not significant.
* Isoxaben is translocated to stems and leaves
primarily in the xylem, and little movement occurs
when applied to emerged leaves.

Selectivity

As listed earlier, these materials are used
primarily as preemergence annual grass control in a
variety of crops. Isoxaben is an exception in that its
activity is greatest for annual broadleaf weed control.


Mechanism (Mode) of Action


No consistent action patterns
established for this group of herbicides.


have been


* Diphenamid's mode of action is undetermined.
Seeds germinate but seedlings do not emerge. It
causes severe inhibition of root development in
many species, particularly grass weeds.
* Napropamide inhibits root growth and
development, presumably a mitotic poison, but
the exact mechanism of action is unknown; may
inhibit RNA and protein synthesis.


Page 5






Turf Herbicide Families and Their Characteristics

* Pronamide acts as a mitotic poison, interferes
with mitosis and cell division, inhibits root and
shoot development. Protein, DNA and RNA
levels are markedly changed in treated grasses.
* Isoxaben's mode of action is similar to
napropamide and pronamide.

Degradation

Through the processes of hydrolysis,
dehydroxylation, dealkylation, and deamination, these
herbicides are metabolized into various acetic acids
and water soluble metabolites, and alterations in the
aliphatic side chains may occur.

Behavior in Soils

Adsorption

* Diphenamid and napropamide are absorbed by
soil organic matter but have good activity in sandy
and medium textured soils.
* Pronamide is absorbed by soil colloids and is
more active in high organic matter-containing
soils such as peats or mucks.
* Isoxaben is strongly adsorbed by soil organic
fractions and clay minerals due to its low water
solubility and high potential for hydrogen
bonding.

Leaching

a Diphenamid leaches readily in sandy soils and
slowly in clay and loam soils.
a Napropamide does not leach in most soils
probably because of its adsorption to organic
matter and colloidal material and its low water
solubility. Napropamide must be incorporated in
soil by mechanical means or irrigation to reach
weed seed zone for consistent results.
* Pronamide is the same as napropamide but may
not need to be incorporated because of its use
which is recommended only during the cool
seasons of the year.
* Isoxaben is relatively immobile in soils and does
not readily leach.


Page 6


Persistence

* Diphenamid is intermediate in persistence which
ranges from 3 to 6 months depending upon
moisture, temperature, and soil type and may
persist in soils longer if rainfall is absent. Soil
microorganisms appear to degrade the material.
It is nonvolatile and non-photodecomposed.
* Napropamide is generally persistent in soils, with
an average half-life of 8 to 12 weeks, but can
persist up to 9 months. Soil microorganisms
slowly break this material down. It is nonvolatile
but somewhat susceptible to photodecomposition.
* Pronamide has medium persistence, ranging from
3 to 8 months depending upon soil type and
climatic conditions, particularly temperature.
Herbicidal activity is lost due to volatility,
photodecomposition and microbial action.
a Isoxaben has a half-life of 5 to 6 months. Soil
microorganisms degrade this material.

Distinguishing characteristics

" Nonionic class of herbicides
* Moderate to low water solubility
" Apoplastic (xylem) movement in plants with
possible exception of pronamide
" Interact with soil colloids, particularly organic
matter
" Preemergence herbicide activity
" Mode of action is mitotic poison, however, many
effects have been identified but no consistent
patterns are known
a Short to long soil persistence

Toxicological Properties


Acute oral toxicity
Diphenamid
Napropamide
Pronamide
Isoxaben


Rats LDso (mg/kg)
1717
>5000
8350
10,000






Turf Herbicide Families and Their Characteristics


ARYL-OXY PHENOXY


Important Members (Table 6)


Table 6. Important members of the aryl-oxy phenoxy family*
Water Solubility Vapor Pressure
Common Name Trade Name(s) Manufacturer (ppm) (mm Hg @ 20-30" C)
Diclofop Hoelon Hoechst-Roussel 3000 3 x 107
Illoxan
Fenoxaprop Whip Hoechst-Roussel 1 0.19 x 107
Acclaim
Horizon
Fluazifop Fusilade ICI/Zeneca 2 5.5 x 10-5
Haloxyfop Verdict DowElanco 9 6.5 x 10-7
Quizalofop Assure DuPont 1 3 x 10-7
Due to its similar post-grass activity, sethoxydim is often classified as an aryl-oxy phenoxy.


Uses


Mechanism of Action


All are used primarily for postemergence grass
weed control. Diclofop is used specifically for
goosegrass control in bermudagrass. Fenoxaprop
provides annual grass control in selective cool-season
and warm-season turfgrasses.

Behavior in Plants

Absorption and translocation

Aryl-oxy phenoxy herbicides are applied primarily
postemergence and rapidly absorbed by plant foliage.
Varying degrees of translocation occur in the symplast
and these herbicides accumulate in meristematic
regions. Diclofop is rapidly absorbed by plant foliage
but has limited translocation. This may be the reason
it is ineffective for perennial grass control compared
to the other members listed.

Selectivity

Selectivity in tolerant species is believed to be due
to the alteration of the acid form. Hydroxylation of
one of its rings and subsequently conjugation appear
to be involved in detoxification. Virtually all
broadleaf plants and sedges are tolerant to these
herbicides. Control is greatest at its two to five leaf
stage. Treated grass nodes react by blackening of
grass weeds and dying. Their leaves are then easily
pulled from the nodal region.


These herbicides accumulate in meristematic
tissue where they are primarily active. The mode of
action is believed to be interference with lipid
metabolism (specifically 'acyl' lipids), possibly fatty
acid and/or phospholipid synthesis. More specifically,
as a class, these may inhibit acetyl-coA carboxylase,
which acts as a catalyst in the steps in fatty acid
biosynthesis. This leads to cell membrane
dysfunction, leakage of amino acids, and eventual cell
and plant death.

Degradation

All are formulated as esters and must be
hydrolyzed by plant esterases to become activated.
The resultant acid is the mobile form, and presumably
the toxic form, in the plant.

Behavior in soils

Adsorption

The esters of the herbicides are rapidly
hydrolyzed in soils, releasing the acid.

Leaching

The ester forms of these herbicides would leach
slowly, whereas the hydrolyzed forms would leach
more readily. Diclofop and fenoxaprop do not leach
downward nor move laterally.


Page 7






Turf Herbicide Families and Their Characteristics

Persistence

Herbicides in this class are degraded very rapidly
into acid form by soil microbes, which persists 1 to 4
weeks. Diclofop has a half-life of 10 days in sandy
soils and about 30 days in clay soils. Fenoxaprop has
a half-life of 5 to 14 days. Negligible losses occur
from photodegradation or volatilization. Fluazifop's
half-life is between 1 and 3 weeks.

Distinguishing characteristics

* All are weak acids and are formulated as esters.
a All are specific for postemergence grass control.
a Diclofop has some preemergence activity but is
more effective postemergence.
a Most broadleaf crops and sedges are tolerant to
these herbicides.
* Control is slow to occur, requiring 2 to 3 weeks
for maximum results.
* Control is greatest at the two to five leaf stage.


Page 8


* Antagonistic effects result when tank-mixed with
postemergence broadleaf herbicides such as 2,4-
D.
" Most members require a surfactant for optimum
postemergence activity.
* Should not be stored below 200 F.
* Not known to be corrosive.

Toxicological Properties

Diclofop is toxic to fish and should not be used
adjacent (within 100 ft) to bodies of water (lakes,
streams, ponds, drainage basins, tidal marshes,
estuaries, etc.).

Acute Oral Toxicity
Herbicide LDo (mgkg)
diclofop 580
fluazifop 3328
haloxyfop 2397
quizalofop 5700
fenoxaprop 3310


BENZOIC ACIDS


Important Members (Table 7)


Table 7. Important Members of the Benzoic Acid family
Water Solubility Vapor Pressure
Common Name Trade Names(s) Manufacturer (ppm) (mm Hg @ 25-30 C)
Dicamba Banvel and Sandoz and 4500 3.75 x 10-3 @ 100 C
others others


Available formulations (dicamba)

Spray applications
1. 4 lb/gal (dimethyl amino salt) no additional
surfactant is needed water soluble liquid.
This formulation is compatible with most
organic pesticides and nitrogen fertilizers.
2. 2 lb/gal (sodium salt) water soluble liquid.
3. 1 lb/gal water soluble liquid for cut surface
treatment of woody species.
Dry application
1. 5% and 10% granule

Uses

Benzoic acids provide broadleaf dicott) weed
control with less activity on grass monocott) weeds.
Dicamba is used for postemergence broadleaf weed
control in corn, small grains, turf, and noncropland.


Dicamba provides control of many phenoxy tolerant
broadleaf weeds and is often mixed with 2,4-D,
MCPP, MCPA or 2,4-DP to provide a broader range
of weed control.

Behavior in Plants.

Absorption

Benzoic acids are rapidly absorbed in both shoots
and roots.

Translocation

Dicamba is translocated via symplast and apoplast
and tends to accumulate in regions of high metabolic
activity such as meristems. From root uptake,
dicamba follows the transpiration (xylem) stream.






Turf Herbicide Families and Their Characteristics


Selectivity


Leaching


The benzoic acids are specific for dicots with less
activity on monocots or grassy weeds. Dicamba
sensitive species generally retain the parent
compound longer than the others and are thus killed
while tolerant plants rapidly degrade dicamba
metabolically.


Mechanism of Action


The benzoic acids are considered growth regulator
or hormone disrupting herbicides. Morphogenetic
growth effects such as epinasty and other auxin-like
growth regulator responses follow application. The
specific mode of action is unknown but are believed
to interfere with nucleic acid (DNA and RNA)
metabolism and protein synthesis. Disruption of the
transport system in plants due to massive cellular
proliferation is the final cause of plant death.

Degradation

Varies as a group but these are generally
persistent in plants.

Behavior in Soils

Adsorption

Dicamba has little or no adsorption in most soils.


Dicamba leaches in sandy soils, especially during
heavy rains. Application around sensitive
ornamentals and tree roots should be limited as
leaching of the material may cause injury. Dicamba
also "leaks" from the roots of treated plants into the
soil.


Persistence and degradation


Under favorable warm-moist environmental
conditions, dicamba has a half-life of less than 14 days
but longevity can occur from 2 to 6 months. Most
benzoic acid herbicides are slowly degraded by soil
microorganisms but are not persistent in soils.

Distinguishing characteristics

* Benzoics are ionic herbicides and weak acids that
form an anion upon dissociation.
* Selective for broadleaf weeds
* Symplastic and apoplastic movement within
susceptible plants
* Act as growth regulators or hormones producing
epinasty effects
* Not bound tightly in soils and, for the most part,
leach readily
* Dicamba is formulated as a liquid in the
dimethylamine salt form, and in granular form as
the acid or amino salt.


Toxicological Properties

Acute Oral Toxicity LD50 (mg/kg) 2900


BIPYRIDYLLUMS


Important Members (Table 8)


Table 8. Important members of the bipyridyllum family
Water Solubility Vapor Pressure
Common Name Trade Name(s) Manufacturer (ppm) (mm Hg @ 25-35 C)
Diquat Diquat Herbicide Ortho/Valent completely soluble nonvolatile salts
in water (<10-5 mbar)
Paraquat Gramoxone Extra ICI/Zeneca completely soluble nonvolatile salts
in water


Page 9






Turf Herbicide Families and Their Characteristics


Uses


Degradation


Bipyridyllums herbicides are nonselective,
postemergence herbicides used to control unwanted
vegetation. Diquat, in an aqueous salt solution, is
used in aquatic situations while paraquat is used in
no-till programs, vine desiccation, direct sprays, and
for pre-plant vegetation control.

Behavior in Plants

Absorption and translocation

These herbicides are absorbed very rapidly by
foliage. Neither are translocated to any great extent
in plants due to damage in membrane integrity,
therefore, thorough coverage is essential for greatest
activity. Root uptake is minor because these
herbicides are tightly bound to soil colloids and
organic matter.

Selectivity

The bipyridyllums are non-selective, injuring all
green foliage they contact. Plant selectivity is
achieved by applying the herbicides in a manner to
avoid contact with desired plants (shields, row-middle
treatments, etc.). Diquat is used for aquatic weed
control in ponds while paraquat is used as a
nonselective spot treatment much the same way as
glyphosate. The main advantage is its quick response,
killing weeds within hours of treatment. Symptoms
include rapid plant wilting and desiccation, followed
by necrosis. It is possible to have one-half of a leaf
desiccated while the other half may still be green
since little translocation of the chemical occurs within
the plant. These herbicides provide top-kill of
perennials but do not affect their underground
structure and regrowth soon follows.


Mechanism of action


Limited research indicates that bipyridyllums are
not degraded by higher plants. Bipyridyllums undergo
photodecomposition when exposed to light such as
would be the case where they may be on leaf surfaces.
Paraquat loss from UV radiation can be up to 50
percent in 24 hrs and 75 percent in 96 hrs. However,
once absorbed by the leaf tissue these herbicides are
protected from photodecomposition.

Behavior in soils

Adsorption and leaching

Paraquat and diquat are tightly adsorbed by ionic
bonding to most soils and on the inner and outer
surfaces of nonexpanding clays such as kaolinite
(outer surfaces) and expanding clays such as
montmorillonite (inner and outer surfaces). These
herbicides carry positive charges cationicc) while clay
minerals and certain fractions of soil organic matter
are negatively charged (anionic). These herbicides
have no preemergence activity in normal agricultural
soils and there is no leaching because of the tight soil
adsorption.

Persistence

Bipyridyllum persistence is based on its biological
availability in soils and is nonexistent due to its
adsorption. However, persistence of the intact form
(but unavailable) bound to clays may be quite
extended (for example, paraquat can persist for up to
13 years.). Microbial, chemical, and photo-
decomposition is minor due to the tightly bound
paraquat which is unavailable for exposure to these
processes. In contrast, diquat's half-life in water is
less than 48 hours.


Distinguishing characteristics


Bipyridyllum herbicides disrupt plant membranes.
They intercept electrons from photosynthesis and
transfer the energy to form various free radicals that
damage cell membranes and permit the cell contents
to leak into the intercellular spaces. Sunlight is
needed for its activity and plants treated on cloudy
days or in the dark will not show symptoms until they
are placed in the light.


* Cationic, high water solubility, and is nonvolatile
* Contact, rapid acting herbicide family with little
or no mobility in plants;
a Not degraded in plants, but is slowly degraded in
soils;
* Adsorbed by clay minerals in soils;
* Used as nonselective herbicides in directed sprays,
aquatics, desiccation, etc;
* Corrosive to aluminum and should be flushed
immediately after use;
* Nonionic surfactant is needed to enhance
paraquat's herbicidal effectiveness.


Page 10






Turf Herbicide Families and Their Characteristics


Toxicological Properties


Acute Oral Toxicity
diquat
paraquat


LDso (mg/kg)
230
138


Paraquat is highly toxic to mammals and this
accounts for its restricted use status. It is extremely


toxic to mammalian lungs, where it can cause sores
and bleeding. Always wear approved safety
equipment when handling these materials. Cows are
particularly sensitive to diquat with an oral LD50 of
30 mg/kg.

ALWAYS WEAR PROTECTIVE CLOTHING AND
OBSERVE ALL PRECAUTIONS WHEN
HANDLING DIQUAT OR PARAQUAT.


CARBAMATES


Important Members (Table 9)


Table 9. Important members of the carbamate family

Vapor Pressure
Common Name Trade Name(s) Manufacturer Water Solubility (mm Hg @ 25-35" C)
Asulam Asulox Rhone-Poulenc 5,000 1 x 108


Uses


Degradation


Asulam provides postemergence annual and
perennial grass and broadleaf weed control in
sugarcane, orchards, St. Augustinegrass and Tifway
(419) bermudagrass turf.

Behavior in Plants

Absorption and Translocation

Asulam is readily adsorbed by shoots, with minor
root adsorption. It is primarily translocated
apoplastically but also has some symplastic movement.
Translocation to underground structures makes
asulam effective for controlling established perennial
weeds.

Selectivity

Asulam is selective for a number of perennial
grasses (i.e. johnsongrass), annual grasses (crabgrass)
and perennial broadleaf weeds (Rumex sp.).

Mechanism of action

Asulam interferes with meristem growth by
inhibiting cell division. It is considered a mitotic
poison by arresting metaphase and altering cell
expansion. Carbamates also may be involved in the
inhibition of RNA and protein synthesis by inhibiting
folic acid biosynthesis.


Asulam rapidly degrades in tolerant plants and
may also have less translocation of the compound
when compared to susceptible plants.

Behavior in Soils

Adsorption and leaching

Asulam is readily leached because of its high
water solubility and low level of adsorption.

Persistence

Asulam has a low order of persistence in soils
with a longevity of 1 to 2 months, or a half-life of 6 to
14 days. Losses can be due to volatilization
(especially from the surfaces of moist soils) and/or
microbial degradation in other instances.

Distinguishing Characteristics

* Nonionic
a Some volatility can occur
* Highly water soluble and readily leached
a Absorption is increased with the addition of a
wetting agent or adjuvant.


Page 11






Turf Herbicide Families and Their Characteristics


Toxicological Properties

Acute Oral Toxicity
LD50 >5000 mg/kg


CYCLOHEXENDIONES


Important Members (Table 10)


Table 10. Important members of the cyclohexendione family

Water Solubility Vapor Pressure
Common Name Trade Name(s) Manufacturer (ppm) (mm Hg @ 25-35" C)

Sethoxydim* Vantage BASF 48 1 x 10"7
Poast
Sethoxydim is sometimes classified in the Aryl-oxy Phenoxy herbicide family due to similar weed activity.


Uses

Sethoxydim provides selective postemergence
annual and perennial grass control in broadleaf crops,
rice, and centipedegrass turf. Broadleaf weeds and
sedges are not controlled by sethoxydim.

Behavior in Plants

Absorption

It is rapidly foliar-absorbed. Use of an oil
concentration at 1 percent (v/v) is required for
adequate grass control.

Translocation

Translocates both acropetally and basipetally in
the symplast. Accumulates in the meristematic
regions of grasses.

Selectivity

Sethoxydim controls annual grasses; plants in the
seedling and early tillering stages are most
susceptible.

Mechanism of action

The mechanism of action is not fully known but
it is believed to be similar to the aryl-oxy-phenoxies,
interfering with lipid metabolism. More specifically,
sethoxydim may inhibit acetyl-coA carboxylase, which
catalyzes an early step in fatty acid biosynthesis. This


inhibition leads to cell-membrane dysfunction and
eventual cell and plant death. Treated foliage will
redden, become chlorotic, and die in an inward
direction from the leaf tip. Nodes blacken and die
and leaves will easily break or pull from the nodal
region. Sethoxydim is relatively slow acting and
symptoms occur over a 3 week period.

Degradation

Sethoxydim is rapidly transformed into many
metabolites in soils and plants through oxidation,
structural rearrangement, hydroxylation, and
conjugation.

Behavior in Soils

Adsorption and leaching

Adsorption is dependent on the soil organic matter
content.

Persistence

Soil microbes break down sethoxydim. Soil
persistence is short with a half-life of the parent
compound being 4 to 5 days in loamy sand and 11
days in a loam media. Little preemergence activity
can be expected.


Page 12






Turf Herbicide Families and Their Characteristics

Distinguishing Characteristics

* Rapid uptake and translocation from foliar
applications
* Controls many annual and perennial grasses
except centipedegrass
* Its absorption is increased with the addition of a
surfactant, wetting agent or adjuvant.


Page 13


* Most broadleaf plants and sedges are tolerant.

Toxicological Properties

Acute Oral Toxicity
LDs0 (mg/kg) 2767-3124


DINITROANILINE (DNA'S)


Important Members (Table 11)


Table 11. Important members of the Dinitroaniline family
Water Solubility Vapor Pressure
Common Name Trade Name(s) Manufacturer (ppm) (mm Hg @ 25-30 C)
Trifluralin Treflan DowElanco 0.2-0.3 ppm 2.2 x 10-7
Benefin Balan DowElanco 0.1-0.3 ppm 6-9 x 10-5
Ethalfluralin Sonalan DowElanco 0.2-0.3 ppm 6-9 x 10-5
Pendimethalin Prowl American Cyanamid 0.2-0.5 ppm 1-3 x 10-5
Pre-M
Oryzalin Surflan DowElanco 2.5 ppm 1-2.5 x 107
Prodiamine Barricade Sandoz 0.1 ppm 1-2 x 107
Various combina- XL, Team, Snapshot,
tions are available etc.
*lsoxaben is also often listed as a dinitroaniline.


Uses


Behavior in Plants


Dinitroanilines are the backbone of preemergence
herbicides currently used in turf. They have no foliar
activity, applications must be made prior to weed
germination. They provide excellent annual grass
weed control. Sequential applications are needed
approximately 90 days after initial treatment for
season-long control in Florida. Application timings
for control of summer annual grass weed range from
February 1 in south Florida, February 15 in central
Florida and March 1 in north Florida. To control
winter annual weeds, application timings are October
1 to 15 for north Florida, October 15 to November 1
for central Florida and October 15 to November 15
for south Florida.


Absorption

Dinitroanilines (DNA's) are absorbed by plant
shoots and roots. The major site of uptake for
monocot (grasses) is the emerging shoot while in
dicots (broadleaves),!root uptake may predominate.

Translocation

Translocation of DNA's from absorption sites is
poor to nonexistent.

Selectivity

The dinitroanilines are very specific in their
control of many annual grasses. Dinitroanilines
appear to be absorbed primarily by emerging grass
shoots as they pass (germinate) through the treated
soil. Therefore, the primary mechanism of weed
selectivity is based on spatial herbicide placement in






Turf Herbicide Families and Their Characteristics

the soil in relationship to the germinating crop or
weed seed.

Mechanism of action

DNA's prevent nucleic acid metabolism and thus
prevent cell division. They strongly inhibit root
growth especially lateral or secondary root
development. As roots develop, they are somewhat
thickened, stubby and have few secondary roots. They
are also called mitotic inhibitors. Specifically, they
prevent tubulin from polymerizing into microtubules.
Microtubules, in association with other proteins, form
spindle fibers, determine the plane of cell division,
and orient microfibril deposition in the walls of
growing cells. The lack of spindle fibers due to a
treatment of DNA does not allow the normal
separation of chromosomes, and chromosomes are
then found scattered throughout the cytoplasm.

Degradation

Dinitroanilines are poorly absorbed in tolerant
plants. Little reaches the internal portions of plants.
It is believed they are either slowly degraded or not
degraded by higher plants.

Behavior in Soils

Adsorption

Low water solubility and high potential for
hydrogen bonding cause DNA's to be strongly
adsorbed by the soil organic fraction and clay
minerals. Dinitroanilines bound by the organic
fractions of soils are unavailable, thus diminishing
their capability for weed control. Because of this,
soils high in organic matter require higher rates to
overcome adsorption affinity. DNAs are not
recommended for use on peat or muck soils that have
more than 10 percent organic matter due to their
unavailability.

Leaching

Dinitroanilines are relatively immobile in soils and
do not readily leach.

Persistence and Degradation

Over time, dinitroaniline herbicides can be lost
from soils through volatility, photodecomposition, and
microbial degradation, Table 12. Wet soil surfaces,
high soil temperatures and sunlight increase the loss


Page 14


rate of DNA's due to increased volatilization,
microbial degradation and photodecomposition.
Benefin and trifluralin have the highest volatility of
the DNA's and require incorporation through
irrigation. Pendimethalin is less volatile and should
receive irrigation within seven days of application.
Oryzalin is the least volatile of the DNA's and should
be irrigated within three weeks of application. Half
life values range from 7 to 27 days under anaerobic
conditions and from 19 to 132 days under aerobic
conditions.

Table 12. Longevity of various dinitroanilines in soils
Herbicide Months
trifluralin 6- 12
benefin 4 8
oryzalin 4 12
profluralin 6 12
pendimethalin 3 6
prodiamine (half life) 4


Distinguishable Characteristics

* Posesses a yellow color because of their
chromorphic nitro groups
a Posesses a characteristic odor due to high to
moderate vapor pressures
* Subject to varying degrees of photodecomposition
* Readily absorbed by roots and emerging shoots
a Low water solubility
a Selective for grasses and certain broadleaves
* Not readily translocated or degraded in plants
" Suspected mechanism of action is nucleic acid
metabolism interference which inhibits cell
division
a Little, if any, postemergence activity
a Persistent in soils, generally 6 months or less
a Rainfall, irrigation, or soil incorporation are
needed to activate the DNA's and minimize losses
from volatilization or photodecomposition
a Most pesticide tank mixes are compatible with the
DNA's if proper agitation is used in the spray
tank. They also are compatible with ammonium
nitrate solutions
B Often impregnated on granular fertilizer
a Non-corrosive






Turf Herbicide Families and Their Characteristics

Toxicological Properties

These properties list like toxicological properties
for the Aryl-oxy Phenoxy family.

Dinitroanilines are toxic to fish when added
directly to bodies of water. Therefore, runoff directly
into ponds should be avoided.


Acute Oral Toxicity
Herbicide
trifluralin
benefin
oryzalin
pendimethalin
prodiamine


LD2(mg/kg
10,000
10,000
10,000
1,250
15,380


DIPHENYL-ETHERS


Important Members


Table 13. Important members of the diphenyl-ether family

Water Solubility Vapor Pressure
Common Name Trade Name(s) Manufacturer (ppm) (mm Hg)

Acifluorfen Blazer BASF infinitely 24
Bifenox Modown Rhone-Poulenc insoluble (0.35) 2.4 x 10-6
Lactofen Cobra Valent 0.1 4 x 109
Oxyfluorfen* Goal Rohm and Haas 0.1 2 x 106
Oxyfluorfen is also sold in combination with pendimethalin as OH-2 and in combination with oryzalin as ROUT.


Uses


Translocation


Diphenyl-ethers control many annual weeds in
several crops with preemergence or early
postemergence applications. In general, these
herbicides are more effective for the control of
broadleaf seedlings. However, they do effectively
control species of certain grass weeds. Oxyfluorfen is
used in tree fruit crops and ornamentals where it has
more activity on broadleaf weeds, especially when
applied during early postemergence versus
preemergence. Acifluorfen is used primarily for
selective broadleaf weed control in soybeans. Bifenox
is used pre- and postemergence in corn, rice, small
grains, soybeans, and sorghum. Lactofen controls
broadleaf weeds in soybeans and conifer nurseries.

Behavior in Plants

Absorption

Shoot uptake, which is rapid, is the primarily site of
absorption. Injury to crops can occur when excessive
moisture is present at the time of emergence due to
increased absorption.


All have very limited, if any, movement from
either root or foliar applications.

Selectivity

Generally more active on broadleaf weeds than on
grasses. Crop tolerance to diphenyl-ethers is due to
rapid metabolism as compared to susceptible plant
species. Susceptibility among cabbage cultivars is
determined by the amount of leaf-surface wax.

Mechanism of Action

Contact mode of action occurs when applied
postemergence because of limited mobility and rapid
activity. Due to this contact action, diphenyl-ethers
are not readily metabolized in plants. They disrupt
cell permeability and cause watersoaking, wilting, and
foliage burn within 24 hours after postemergence
treatment. Diphenyl-ethers interfere with ATP
production in oxidative and photophosphorylation.
These compounds may generate a toxic intermediate
which form single oxygen radicals in the light, causing
membrane disruption and leakage of cell contents.
I


Page 15






Turf Herbicide Families and Their Characteristics

Therefore, when applied as soil treatments, seedlings
must emerge before herbicide symptoms develop.

Degradation

Cleavage of the ether linkage is the primary means of
degradation. Most are, however, subject to
photodecomposition.

Behavior in Soils

Adsorption

They are strongly adsorbed by soil colloids and
organic matter.

Leaching

Diphenyl-ethers do not readily leach because of
low water solubilities and adsorption to soil organic
matter and colloids.

Persistence

Relatively short in soils.
* Oxyfluorfen Half-life of 30 to 40 days.
* Acifluorfen Estimated half-life between 14 to 60
days.
m Bifenox Average half-life is between 7 to 14
days.


Page 16


Distinguishing Characteristics

* Nonionic and have low water solubilities;
* Absorbed by plants but not translocated
extensively;
* Light required for activity of ortho substituted
diphenyl-ethers;
* More active on annual broadleaf weeds than
annual grasses;
* For non-light requiring dipheny-ethers,
mechanism of action is tied into energy relations
in plants, possibly ATP production or electron
transport;
* Pre and postemergence herbicides; Primarily
contact in nature;
* Symptoms are generally expressed on the foliage
as a contact burn resulting in leaf crinkling and
cupping, interveinal chlorosis and necrosis;
* Surfactant (crop oil) is needed for postemergence
activity.


Toxicological Properties

Acute Oral Toxicity (mg/kg)
Oxyfluorfen
Bifenox
Acifluorfen
Lactofen


Oral LD50
>5,000
>5,000
1,300
2,533


IMIDAZOLINONES


Important Members (Table 14)


Table 14. Important members of the imidazolinone family

Water Solubility Vapor Pressure
Common Name Trade Names(s) Manufacturer (ppm) (mm Hg)

Imazaquin Image, Scepter American Cyanamid 60-120 < 2 x 108 at 450 C
Imazapyr Arsenal American Cyanamid 10,000 15,000 < 2 x 20-7 at 600 C
Chopper (isopropylamine salt)
Imazethapyr Pursuit American Cyanamid 140 < 1 x 10-7 at 600 C
Imazamethabenz Assert American Cyanamid 857 1,370 < 2 x 107


Uses

Imazaquin provides selective purple nutsedge
control in warm-season turfgrasses. Other sedges,
broadleaf and several grass weeds have varying
degrees of susceptibility. Imazethapyr provides


selective broadleaf weed control in soybeans and
peanuts. Imazapyr is used for deciduous tree, vine
and bramble control in noncropland situations and for
pine tree release. Imazamethabenz is used in small
grain production.






Turf Herbicide Families and Their Characteristics

Behavior in Plants

Absorption and translocation

Absorbed rapidly by foliage and roots.
Translocated in the xylem and phloem and
accumulates in the meristematic regions. Absorption
is more rapid when applied in an acid pH solution as
compared to neutral or higher pH solution.

Mechanism of action

These compounds inhibit the enzyme acetolactate
(acetohydroxy acid) synthase (AHAS), thereby
preventing the plant from synthesizing the essential
amino acids valine, leucine, and isoleucine. A
reduction in these amino acids eventually leads to
interrupted plant growth by disrupting protein
synthesis. Secondary effects include reduced
respiration, RNA and DNA synthesis. Plant death
occurs slowly over a period of one to several weeks.
Activity is first seen in the growing points
(meristematic tissue) of susceptible plants where
amino acid demands are greatest. Symptoms of injury
include shortened internodes and a bunching effect at
the growing points. Treated plants may remain dark
green for a few days and then show symptoms of
nutrient deficiency. They may turn red to purplish in
color as a result of a weakened root system.
Chlorosis and necrosis progresses from the growing
tip of shoots throughout the plant.

Degradation and Selectivity

Differential metabolism in plants is important in
determining species susceptibility. Tolerant species
metabolize the herbicides into non-toxic compounds.
Specifically, selectivity is based on tolerant plants
being able to quickly detoxify the herbicide, either
through destruction of the imidazolinone ring,
hydroxylation of the alkyl group, or by ester
hydrolysis. Tolerant plants metabolize the herbicide
quicker than susceptible ones.

Behavior in soils

Adsorption and leaching

These are pH dependent. There is more
absorption and less leaching in acid (low) pH levels,
while less adsorption and more leaching occurs at
neutral to basic (high) pH levels. Adsorption is also
greater in soils having pH dependent charge surfaces


Page 17


containing aluminum, iron and oxy-hydroxides like
gibbsite, hematite and kaolinite.

Persistence

Imidazolinones have less persistence in acid pH
soil and more persistent in neutral to basic pH soils
and soils having high organic matter and clay content.
Persistence in the soil may have the potential for
injuring rotational crops such as cotton, soybeans, and
tobacco, but are not a major concern in the turf
market. Imidazolinones are reduced by microbial
degradation, chemical degradation, or plant uptake.
Soil microbial breakdown is a major path of
breakdown in the soil. Imidazolinones are nonvolatile
and losses from photodecomposition are minor.

Distinguishing Characteristics

* Imidazolinones are highly mobile in plants;
* Primary mechanism of action is interference in
the biosynthesis of the amino acids valine,
leucine, and isoleucine;
* Low mammalian toxicity;
* Selectivity is primarily correlated with plant
metabolism;
* Combinations with postemergence grass
herbicides cause antagonism on grass species;
" Corrosive to mild steel, brass, copper, zinc, and
iron, but are not corrosive to stainless steel;
* Estimated shelf life of formulation in storage is 2
years;
* Can be tank mixed with the dinitroanilines
(DNA's);
* Require the use of a surfactant or crop oil for
postemergence applications.

Toxicological Properties


Acute oral toxicity
imazaquin
imazapyr
imazethapyr
imazamethabenz


LDs5(mg/kg)
>5000
>5000
>5000
>5000


m Non-toxic to fish or wildlife






Turf Herbicide Families and Their Characteristics


NITRILES (BENZONITRILES)


Important Members (Table 15)


Table 15.

Water Solubility Vapor Pressure
Common Name Trade Name(s) Manufacturer (ppm) (mm Hg @ 20-30 C)

Bromoxynil* Buctril Rhone-Poulenc 130 4.8 x 106
Brominal
Dichlobenil Casoron Uniroyal 18 25 5.5 x 10
Dyclomec PBI/Gordon
*Bromoxynil can also be considered a member of the Substituted Phenol herbicide family.


Bromoxynil is formulated as water soluble salts,
oil soluble amino salts, and esters which are
emulsifiable in water. Dichlobenil is formulated as a
wettable powder and granule. The oil soluble amino
and ester bromoxynil formulations resist removal by
rain, however, the sodium salt does not since it is
water soluble.

Uses

Dichlobenil is used as a preemergence treatment
in fruit and nut crops, woody ornamentals,
noncropland, and aquatic sites. Its activity is greatest
on annual grass and broadleaf weeds. Bromoxynil has
no soil activity and is used as a foliage-applied
herbicide in corn, small grains and turf for the control
of seedling broadleaf weeds. It is generally safer on
newly seeded or sprigged turf areas than other
broadleaf herbicides.

Behavior in Plants

Absorption and translocation

Bromoxynil Applied to foliage and is readily
absorbed. Contact herbicide with only limited
translocation, therefore, complete coverage of the
foliage is essential for good weed control. Can be
absorbed by roots but no upward movement occurs.

Dichlobenil Applied preemergence and absorbed
by emerging shoots and/or root systems. Only limited
upward movement has been reported in plants via the
transpiration stream. Little or no downward
translocation occurs.


Selectivity and Mode of action

Bromoxynil Used for selective or broadleaf
weeds especially in the seedling stage. It is
particularly effective in the control of 2,4-D or MCPA
resistant broadleaf weeds. Bromoxynil is most
effective when broadleaf weeds are in the seedling
stage, before the 3 to 4 leaf stage. Symptoms on
leaves appear as blistered or necrotic spots within 24
hours of treatment. It later causes extensive leaf
damage.

Dichlobenil Used for preemergence control of
many annual weeds and some perennials. Selectivity
is obtained by its placement, with desired species
protected at depths below the treatment zone.
Generally applied during cool periods of the year
(e.g., January through mid-February) and is
incorporated by irrigation or mechanical means.
Rapid loss is experienced during warm weather,
presumably due to volatility. Dichlobenil also is used
for aquatic weed control, particularly in submersed
rooted weeds. In general, established crop plants
tolerate dichlobenil because their roots do not come
in contact with the chemical. Sprouts of perennial
weeds are inhibited when dichlobenil is soil applied.
This barrier feature also lends its use as a broadcast
treatment under newly laid asphalt.

Mechanism of action

Bromoxynil A potent uncoupler of oxidative and
photophosphorylation. Disrupts respiration and
photosynthesis.


Page 18







Turf Herbicide Families and Their Characteristics

Dichlobenil Hydroxylated in plants into
phytotoxic hydroxy-benzonitriles that can react in a
fashion similar to bromoxynil. Dichlobenil also acts
as a mitotic poison inhibiting cell division in
meristematic regions-stopping seed germination.
Treated stems, roots and leaf petioles may swell and
collapse. Dichlobenil kills rooted aquatic weeds by
absorbing the chemical through treated hydrosol
rather than water absorption.

Degradation

Bromoxynil may be hydrolyzed to benzoic acids in
plants.

Dichlobenil is degraded or altered in plants to
toxic and nontoxic metabolites.

Behavior in Soils

Adsorption and leaching

Bromoxynil is not strongly adsorbed in soils.
Greater adsorption occurs under acidic conditions.

Dichlobenil Tightly adsorbed by soil colloids
(especially organic matter) but can move in the soil in
the vapor phase. Vapor phase is encouraged in high
temperatures, high soil moisture and low relative
humidity. Very little leaching occurs in most soil


Page 19


types, especially organic soils. Good activity in
organic soils.

Persistence

Bromoxynil. Short-lived with a longevity of 1 to
2 months.

Dichlobenil. Much more residual than bromoxynil
and can have a longevity of 2 to 12 months,
depending upon climate. Soil microorganisms are
responsible for its gradual breakdown.

Distinguishing characteristics

a Bromoxynil is a postemergence herbicide for
seedling broadleaf weeds.
a Dichlobenil is a preemergence herbicide for grass
and broadleaf weeds.
* Bromoxynil is an inhibitor of respiration and
photosynthesis through uncoupling of
phosphorylation reactions.
a Dichlobenil is a mitotic poison and its breakdown
products may be uncouplers.
* Bromoxynil exhibits rapid contact activity.

Toxicological Properties


Acute Oral toxicity
Rats LD50 (mg/kg)


bromoxvnil dichlobenil
440 3160


ORGANIC ARSENICALS


Important Members (Table 16)


Table 16. Important members of the organic arsenical family.
Water Solubility Vapor Pressure
Common Name Trade Name(s) Manufacturer (ppm) (mm Hg @ 20-30 C)
Cacodylic acid Rad-E-Cate Vineland 667,000 nonvolatile
Phytar 560
MSMA Arsenate ISK Biotech 256,000 nonvolatile
Bueno 6 etc.
Daconate 6
DSMA Crab-E-Rad Vineland 256,000 nonvolatile
DSMA Liquid ISK Biotech
MAA ------------- ------------- 256,000 nonvolatile
AMA Super Dal-E-Rad Vineland 256,000 nonvolatile
CMA Super-Crab-E- Vineland 256,000 nonvolatile
Rad-Calar






Turf Herbicide Families and Their Characteristics

Cacodylic acid is the common name for
dimethylarsonic acid. The other organic arsenicals
are salts of methylarsonic (also known as
methanearsonate) acid, varying one form or another
in respective categories:


MSMA
MAMA
CMA
DSMA
MAA
AMA


- monosodium methanearsenate
- monoammonium methanearsenate
S calcium methanearsenate
- disodium methanearsenate
S methylarsonic acid
- ammonium methanearsenate


Uses

The methanearsenates are used to selectively
remove annual grass weeds (such as crabgrass and
goosegrass,) and some broadleaf weeds and sedges,
from turf species such as bermudagrass, zoysiagrass
and tall fescue. Repeat applications will control
selective perennial weeds such as bahiagrass, thin
paspalum, or dallisgrass. Susceptible broadleaf weeds
include chickweed, woodsorrel, cocklebur, pigweed,
ragweed, and puncture-vine. Cacodylic acid is a non-
selective material used for desiccation, industrial sites,
etc.

Behavior in Plants


Absorption and translocation


The methanearsonates are absorbed by plant
foliage and show apoplastic and symplastic movement
towards the growing tips of roots, leaves, and
rhizomes. Cacodylic acid is considered to be a
general contact material and behaves as a contact
herbicide. It is applied to cuts around the base of
trees, or to foliage where only apoplastic movement
occurs. Symplastic movement is prevented by rapid
contact action, which injures the phloem and damages
membranes.

Selectivity

The methanearsonates are utilized selectively in
row crops such as cotton and turf. They are active
primarily on grassy weeds. Cacodylic acid is a non-
selective contact-type material used for desiccation,
industrial sites, ditch banks, fence rows, sidewalks, etc.
With the exception of cacodylic acid, susceptible
plants are killed slowly. Symptoms of injury are leaf
chlorosis and a cessation of growth, followed by
desiccation and eventual plant death.


Page 20


Mechanism of Action

Arsenates are absorbed and translocated much
like phosphates and can substitute for phosphates in
numerous areas of plant metabolism. For example,
organic arsenicals interfere with oxidative
phosphorylation during the production of ATP
(adenosine triphosphate), the major source of
chemical energy for metabolic processes. Arsenates
also may interfere with enzyme activity and disrupt
plant membranes.

Degradation

Methanearsenate metabolites (i.e. a MAA-sugar
complex) have been found in tolerant plants. Very
little evidence exists demonstrating the degradation of
cacodylic acid in plants.

Behavior in Soils

Adsorption and leaching

The methanearsonates and cacodylic acid almost
are completely inactivated in soils through adsorption
and ion exchange by competing with phosphorus in
the soil. MSMA, DSMA, and MAA are degraded
microbially to CO2 and arsenate and are nonvolatile.


Persistence


Phytotoxic effects of the organic arsenicals do not
persist in soils due to rapid inactivation by soil
colloids. Standard use rates contribute relatively
insignificant amounts of elemental arsenic to the soil.

Distinguishing characteristics

* Used as postemergence grass herbicides;
* No herbicidal activity in soil systems;
* Methanearsonates are translocated in a manner
similar to phosphates in susceptible grass species;
* Cacodylic acid is a contact, nontranslocated
herbicide;
* Wetting agents (surfactant) enhance the activity of
these herbicides and are either part of their
formulations or must be added to the spray
mixture;
* Centipedegrass and St. Augustinegrass are highly
susceptible to these herbicides;
* Bentgrass has intermediate tolerance, depending
on the timing of application, formulation and rate
used;






Turf Herbicide Families and Their Characteristics

* Tank mixing with foliar nitrogen or iron has
reduced turf phytotoxicity in certain cases. It is
thought that the nitrogen or iron additives
enhance chlorophyll synthesis which is interrupted
by the herbicide.


Page 21


Toxicological Properties


Acute Oral Toxicity
Cacodylic Acid
DSMA
MSMA


LDso(mZtk9)
830
1000
700


PHENOXIES

Important Members and Formulations (Table 17)


Table 17. Important members of the phenoxy family.

Water Solubility Vapor Pressure
Common Name Trade Name(s) Manufacturer (ppm) (mm Hg @ 20-30" C)

2,4-D Many Many 540-900 0.04 @ 160 C
MCPA MCPA, Weedar Several 825 200 uPA @ 21* C
Sodium, others
2,4-DB Butoxone, Rhone Poulenc insoluble
Butyrac
2,4-DP (dichlorprop) Weedone 170, Rhone Poulenc 710 ---
others
MCPP (mecoprop) Lescopex, others Lesco, others 620


Members of the phenoxy herbicide family are
distinguished from one another by the length of, and
substituents on the aliphatic chain of carbon atoms or
by the particular substituents and their location on the
ring.

Formulations:

A. Spray Applications

1. Water soluble liquids and powders
a. Amine salts These are the most
commonly available and are
nonvolatile formulations and have
high water solubility. They are also
easy to handle and have an overall
low cost. They are, however,
somewhat less effective than most
other forms of phenoxies. Amine
salts form true solutions in water, but
are the least effective of all forms of
2,4-D;
b. Salts; e.g., lithium, sodium,
potassium, and ammonium salts.
Can form insoluble precipitates
when mixed with hard water (water
high in calcium and magnesium) or


liquid fertilizer, resulting in clogged
nozzle orifices and screens;
Nonvolatile under normal field
conditions but can drift with only
slight wind movement;
A rain-free period of 4 to 6 hours is
needed for uptake and effective weed
control.

2. Emulsifiable Concentrates (EC)
a. Low volatile esters;
b. High volatile esters (prohibited in
Florida);
c. Invert ester. These produce an invert
emulsion of water-in-oil when mixed
with i water. Special application
equipment is required because of
their viscous nature;
Esters form emulsions in water and
appear milky. If allowed to stand, the
oil-like droplets may separate.
Agitation is then required;
Ester formulations are usually
compatible with fluid fertilizers;
Ester formulations are quickly
absorbed by plant foliage and
relatively resistant to removal by rain;







Turf Herbicide Families and Their Characteristics


Table 18. General characteristics of different forms of 2,4-D (after Ashton and Monaco, 1991).

Appearance Precipitous
when mixed Formed in Volatilization
Form Solubility In Water Solubility in Oil with water Hard Water Potential

Acid low low milky yes low
Amine Salts
water soluble high low clear yes none
oil soluble low high milky yes none
Esters
low volatile low high milky none medium
high volatile low high milky none high
Inorganic Salts medium low clear yes none


Ester formulations should not be
used during warm temperatures
because those conditions favor
volatilization and movement of the
herbicide.

3. Acids
Due to their moderate solubility in
water and formulation expense, acid
forms are not commonly used. Acids
are generally more effective on
certain hard-to-control weeds than
amine forms.

4. Oil soluble amine salts
Oil soluble amine salts form an
emulsion in water, and like the ester
formulations, may require agitation to
maintain a suspension;
These formulations, like esters, are
quickly absorbed by plant foliage and
are relatively resistant to removal by
rain. They are nearly as effective as
low-volatile esters;
These formulations, like the water
soluble salt forms, are considered to
be nonvolatile, but spray drift could
occur with only slight wind
movement.

B. Dry Applications
Granules are for specific uses such as aquatics
and turf


Uses

The phenoxies were developed during World War
II and were first reported to control dandelions in
Kentucky bluegrass in 1944. Many formulations and
combinations of 2,4-D (Table 18) and other phenoxies
are available. Amino salts of 2,4-D are the most
commonly used form. Applications should be made
only when the weed is actively growing and not in any
reproductive (seedhead or flower formation) growth
stage. As weeds mature, repeat applications
approximately 2 weeks apart will be required for
control. For hard-to-control weeds, combinations
with dicamba, mecoprop, dichlorprop or similar
herbicide are needed. Avoid its use on juvenile
grasses. St. Augustinegrass and bentgrass may be
injured.

Behavior in Plants

Absorption and translocation

All are readily foliar absorbed. The speed and
extent of absorption depends upon their formulation.
The following shows the general relationship of
various formulations and their relative absorption
rate:

esters > ammonium and amine salts > Na and K salts

Regardless of formulations applied, the
anionic form of the molecule moves
symplastically in the plant;


Page 22






Turf Herbicide Families and Their Characteristics

Root uptake can occur but movement into
the aerial portion of the plant is limited;
"Source to Sink" type movement occurs with
the phenoxies: they move in the phloem and
tend to accumulate in regions of high
metabolic activity such as meristems. Active
movement of nutrients through plants is
required for good distribution of phenoxies in
plants. Thorough topical application of the
entire plant, especially the lower leaves, is
important, especially against perennial weed
species. 2,4-D moves with the photosynthate
sugars and the treatment of rapidly
developing leaves of perennial weeds in the
spring causes little or no translocation of 2,4-
D to the roots. Better control is obtained
when applied to more mature plants that are
sending sugars to the rhizomes or other
storage structures. Excessive rates can also
halt translocation to the roots by killing the
living phloem cells. Therefore, low rates of
chemical applications, repeatedly applied, give
better perennial weed control than a single
heavy application.

Mechanism of action

Specific mechanism of action is unknown.
Interference with nucleic acid (DNA and RNA)
metabolism and protein synthesis are possible modes
of action. Epinastic bending is a characteristic of the
phenoxies as are swollen, tumorous stems and roots
resulting in vascular tissue plugging. A slow dieback
occurs over a period of several weeks due to food and
water transport being blocked within the plant.

Selectivity and Degradation

Phenoxies are selective for broadleaf weed
species. Use depends on formulation. The salt and
long chain ester formulations are low enough in
volatility to be used near susceptible crops if spray
drift is prevented. However, high volatile ester
formulations should not be used near susceptible
plants and are illegal in the state of Florida.
Regardless of formulation, phenoxy herbicides should
not be used near susceptible plants if environmental
conditions are unfavorable, e.g. strong winds or
extremely hot temperatures. Phenoxies are degraded
in plants through hydroxylation, oxidation, hydrolysis,
and through completing with proteins and amino
acids.


Page 23


Behavior in soils

Adsorption and leaching

Depending on their formulation, phenoxies can
leach from certain soils. Amine and salt formulations
dissociate and are water soluble, leaching readily in
sandy soils. The ester formulations have low water
solubility and are resistant to leaching. Less leaching
occurs as the organic matter and clay content of the
soil increases. 2,4-D is a relatively small organic acid,
so it dissociates to form a negatively charged ion in
soil solution and is not strongly attracted by soil
colloids. It can be leached and has been used as a
preemergence treatment on muck and peat soils.
One of the first uses for 2,4-D was for early
preemergence broadleaf weed control in newly
planted corn.

Persistence

All phenoxies are degraded by soil
microorganisms and do not persist for long
periods of time in the soil (Table 19).
Minor losses occur from photodecomposition.
The half-life for 2,4-D is 10 days, 5 to 6 days
for MCPA.

Table 19. Longevity of phenoxy herbicides in soils (months).

Herbicide Months

2,4-D 1
MCPA 1 -2
2,4,5-T 1 3
2,4-DB 1
2,4-DP 1 2


Distinguishing Characteristics

Phenoxies are not readily adsorbed in soils;
Salt and amine formulations have high water
solubility, whereas ester formulations
generally have low water solubility;
Only the amine or oil soluble amine
formulations should be used during warm
temperatures; No formulation should be
used during windy conditions;
Translocated in the phloem (food channels);
Growth hormone type herbicides;






Turf Herbicide Families and Their Characteristics

Specific for broadleaf weed control in
monocot (grass) crops;
Mechanism of action appears to involve
nucleic acid metabolism;
Dry conditions slow herbicide translocation
throughout weed plants;
Combinations of 2,4-D, MCPP, and dicamba
(a benzoic acid herbicide) appear to be
synergistic. They therefore, require less of
each than if they are applied alone;
Most formulations are noncorrosive to spray
equipment although some concentrates may
be deleterious to painted surfaces. Spray
equipment should be washed thoroughly with
water and detergent solution after use. It is
recommended to have separate designated
spray equipment specifically for phenoxy
herbicides;


Page 24


Most amine formulations have no shelf life
limitations and are insensitive to light and
temperature.

Toxicological Properties


Acute toxicity
2,4-D
2,4-DB
2,4-DP
MCPA
MCPP


LD50mg/kg
375
1960
800


Some formulations of 2,4-D are relatively toxic to
fish and should not be introduced into aquatic
environments unless the label specifically indicates
they are safe.


PHTHALIC ACIDS


Important Members (Table 20)


Table 20. Important members of the phthalic acid family.

Water Solubility Vapor Pressure
Common Name Trade Name(s) Manufacturer (ppm) (mm Hg @ 25-35" C)

DCPA Dacthal ISK Biotech 0.5 < 1 x 10-2
Endothall Aquathol Elf-Atochem 100,000 nonvolatile
Hydrothol
Endothal


Uses

These are generally preemergence herbicides used
for a wide range of annual broadleaf weeds and
grasses. DCPA is used in vegetables, ornamentals and
turf. Endothall has pre and post-emergence activity
in turf, aquatics, and sugar beets. It also is used as a
nonselective material at higher rates.

Behavior in Plants

Absorption and translocation

DCPA Absorbed by emerging coleoptiles, the
roots of grass seedlings and the hypocotyls of
broadleaf weeds. It is not absorbed by the foliage and
is not translocated. Some movement is assumed in
the apoplastic system following root or shoot uptake.


Endothall Absorbed readily by .roots and
translocated to a limited extent to foliar plant parts
via the xylem (apoplast) and it is not phloem mobile.
Ammonium thiocyanate enhances its foliar activity.

Selectivity

DCPA Used as a preemergence herbicide for
annual grasses and some broadleaf weeds in a number
of floral, ornamental, vegetable and agronomic crops
as well as turf. DCPA is insoluble in water and is
formulated as a wettable powder.

Endothall Used as a pre and post-emergence
herbicide in turf and aquatics as well as a harvest aid.
Endothall also is used as a non-selective herbicide.
Several formulations are used. Different salt
formulations are considerably more water soluble
than the parent acid. The disodium salt form is used






Turf Herbicide Families and Their Characteristics

in cropland while the dipotassium salt is used for
aquatic weed control.

Mechanism of Action

DCPA Possibly involved in mitosis by inhibiting
cell division of both root and shoot tips. The exact
mode of action is unknown.

Endothall A contact herbicide, causes
desiccation and browning of plant tissue. It also
inhibits messenger RNA, and thus limits protein
synthesis. It decreases the rate of respiration and
lipid metabolism and interferes with normal cell
division. Appears to be a respiratory poison.

Degradation

DCPA Fairly stable in plants, is not considered
to be metabolized by plants.

Endothall Breaks down rapidly in water but little
is known of its metabolism in plants.

Behavior in soils

Adsorption and leaching

DCPA Not readily leached in most soils and is
adsorbed by organic matter. Activity decreases with
increasing soil organic matter. Due to its inability to
move into the soil, high rates (10 to 20 lb ai/A) are
needed for weed control. It is not affected by
photodecomposition or volatilization.


Page 25


Persistence

Endothall is relatively short-lived in soil and
water, while DCPA is moderately persistent. DCPA
has a half-life of 45 to 90 days in most soils.


Longevity DCPA
4-8 months


Endothall
< 1 month


Endothall is broken down by microbial activity
while microbes and chemical hydrolysis are the
primary factors in the breakdown of DCPA from soils.

Distinguishing characteristics

* Endothall is a weak acid and is ionic while DCPA
is an ester of an acid and is nonionic.
m Endothall is readily leached in soils while DCPA
is adsorbed and not leached.
m Endothall is primarily an aquatic herbicide while
DCPA is a preemergence row crop herbicide.
* Agitation of the wettable powder formulation of
DCPA is essential for adequate dispersal.

Toxicological Properties


Acute Oral Toxicity
DCPA
Endothall (amine salt)


LDso(mg/kg)
>3000
206


The diethylamine salt formulation of endothall is
more toxic to fish than the dipotassium salt. DCPA is
not toxic to fish or wildlife.


Endothall Readily leached in most soil types and
is not adsorbed.

PYRIDINES AND PICOLINIC ACIDS

Important Members (Table 21)


Table 21. Important members of the pyridines and picolinic acids family.

Water Solubility Vapor Pressure (mm
Common Name Trade Name(s) Manufacturer (ppm) Hg @ 25-35 C)

Triclopyr Garlon DowElanco 430 1.26 x 106
Turflon D
Dithiopyr Dimension Monsanto 1.4 4 x 10
Picloram Tordon DowElanco 430 6.2 x 107
Clopyralid Reclaim DowElanco 1000 1.3 x 10-5






Turf Herbicide Families and Their Characteristics

Several combinations of members of the pyridines
are available, e.g. tricl6pyr + 2,4-D (Crossbow,
Turflon II Amine, Turflon D); clopyralid + triclopyr
(Confront)

Uses

Triclopyr and picloram are selective herbicides for
most annual and perennial broadleaf weeds in
monocot crops. They also are used for bush control
in reforestation, rights-of-ways, and other industrial
sites. Dithiopyr is a recent proposed member of the
pyridines. It is a preemergence herbicide with control
similar to the dinitroanilines. Picloram has a
restricted product use label in the state of Florida. Its
main use is currently for the spot treatment of stumps
or suckers. Clopyralid is a recent introduction not as
persistent in soils as picloram or triclopyr and it has
a greater potential for selective use in crops. It also
controls many broadleaf and woody plants in
rangeland and mono-crop areas. Various
combinations of clopyralid with a 2,4-D, MCPA or
other herbicides are available to extend its spectrum
of control. Current uses in turf exist, but are
generally restricted to cool-season grasses.

Behavior in Plants

Absorption and translocation

Picloram, clopyralid, and triclopyr are absorbed by
roots and foliage. They translocate in phloem or
xylem and accumulate in meristematic regions.
Picloram penetrates leaves similar to phenoxys (2,4-
D) but is freely mobile, readily penetrates roots and
is highly phytotoxic. Picloram also can be exuded by
roots. A rain-free period of 4 hours is required.
Dithiopyr's behavior in plants is not entirely known.
Foliar absorption may occur with limited translocation
and effects vary with species.

Selectivity

Picloram, clopyralid, and triclopyr are used
postemergence to control most annual and perennial
broadleaf weeds. Most grasses are resistant.
Picloram, triclopyr and clopyralid are much more
active on susceptible species than 2,4-D or other
phenoxy herbicides and are more effective on certain
resprouting woody species.

Dithiopyr provides selective preemergence annual
grass and small-seeded broadleaf control with some
early postemergence activity. Dithiopyr's selectivity is


Page 26


similar to the members of the dinitroanilines, with a
wider range of broadleaf weed activity.

Mechanism and mode of action

Triclopyr and picloram both exhibit a hormonal or
growth regulatory mode of action. Picloram and
triclopyr effect nucleic acid synthesis and metabolism,
regulating protein synthesis in cells and affecting
enzymes and enzyme systems. The mechanism of
action for clopyralid is not known but appears to be
similar to that of the phenoxy herbicides. With these
herbicides, leaf shape is effected at low dosages. The
tips of new leaves may develop into narrow extensions
of the midrib. Thickening of the mesophyll and
distinct puckering of young leaves may also develop.
With increased dosage, cupping and stunting of leaves
is observed and terminal growth ceases. Tissue
proliferation along the stem may take place, first at
the stem tips, then nodes, and finally throughout the
length of the stem. Meanwhile, epinasty, bending and
splitting of the stem occurs and the roots deteriorate.
Dithiopyr disrupts spindle microtubule formation,
inhibits cell division and results in an accumulation of
mitotic cells in late pro-metaphase. Seed germination
is not inhibited but subsequent developmental
processes do not proceed normally.

Degradation

Picloram and triclopyr are stable in plants and
degraded slowly. Picloram appears to dissipate
readily in grasses but not in broadleaf plants. Due to
dithiopyr's limited translocation in plants, degradation
is not a basis of selectivity. Clopyralid remains
unchanged in plants.

Behavior in soils

Adsorption and leaching

Picloram is formulated as a potassium salt and
can dissociate forming an anion which interacts only
slightly with soil colloids. Picloram leaches readily in
coarse sandy soils containing small amounts of organic
matter. Triclopyr and clopyralid are presumed to
behave in the same fashion. Clopyralid is not strongly
absorbed. Dithiopyr has limited movement in soils.

Persistence

Picloram is persistent in soils and slowly degraded
by soil microorganisms, which is why it is a restricted
use herbicide. Picloram is not lost by volatility or






Turf Herbicide Families and Their Characteristics

photodecomposition. Longevity of picloram in soils
is 6 to 18 months. Triclopyr is not as long-lived in
soils as picloram and degrades rapidly. Triclopyr's
half life in soil averages 46 days, depending on soil
and climatic conditions. It is rapidly lost from
photodecomposition in water with a half-life of 10 hrs.
Clopyralid has an average half-life from 12 to 70 days.

Distinguishing characteristics

Triclopyr and picloram
a Weak acids which can form anions;
a Powerful growth regulators, 10 to 100 times
more effective than 2,4-D on susceptible
species;
Rapidly absorbed by foliage and roots and
translocated readily in the symplast;
Stable in plants;
Readily leached in most soils;
a Picloram is more persistent in soils than
triclopyr;


Page 27


Applied preemergence and postemergence;
Nonselective herbicides on broadleaf weeds
and crops, most grasses are resistant.

Dithiopyr
Preemergence grass and small-seeded
broadleaf weed control;
Postemergence control is weaker than
preemergence.
Not leached in most soils.

Toxicological Properties


Acute Oral Toxicity
Picloram
Clopyralid
Triclopyr
Dithiopyr


LD50(mglkg)
8200
>5000
713
>5000


SUBSTITUTED UREAS


Important Members (Table 22)


Table 22. Important members of the substituted ureas family.

Water Solubility Vapor Pressure
Common Name Trade Name(s) Manufacturer (ppm) (mm Hg @ 20-35" C)

Diuron Karmex DuPont 42 3.1 x 10-6
Diuron
Linuron Lorox DuPont 75 1.5 x 105 torr
Linuron
Monuron Telvar DuPont 230 5 x 10 -7
Flumeturon Cotoran Ciba-Geigy 90 5 x 10 7
Siduron Tupersan DuPont 18 8 x 10-4
Tebuthiuron Spike DowElanco 2300 2 x 10-6
This family is also referred to as the Phenylureas. Substituted ureas are formulated from urea, a common nitrogen
fertilizer.


Uses

The substituted ureas are widely used on a
diversity of crops and noncropland areas. As
preemergence herbicides, they control a wide range of
weed species. Monuron is a soil sterilant, while
linuron, fluometuron and diuron are used in a variety
of crops for preemergence broadleaf weed control.
Most urea herbicides are nonselective at high rates.


Siduron is used for preemergence annual grass
control in cool-season turfgrass, especially on newly
seeded turf. Bermudagrass and some bentgrass
cultivars may be injured by siduron. Preemergence
broadleaf activity is weak. Tebuthiuron is relatively
nonselective and is used in rangeland, pastures, and
noncropland for spot treatment non-selective weed
control.






Turf Herbicide Families and Their Characteristics


Behavior in Plants


Absorption and translocation

Substituted Ureas are primarily absorbed by plant
roots and move in the transpiration (apoplastic or
xylem) stream. In general, the substituted ureas are
applied preemergence, however, some such as linuron
are applied to young weeds postemergence. Some
foliar absorption of the ureas can occur and
accumulate in mature leaves.

Selectivity and Degradation

The principle mode of selectivity with the
substituted ureas is positional rather than
physiological tolerance. However, selectivity among
weed and crop species for some ureas have been
attributed to differential absorption, translocation, and
metabolism. For example, linuron is readily
translocated in susceptible plants, while tolerant
plants metabolize it into inactive products. Several
degradative reactions occur in plants leading to the
breakdown product, aniline. Demethylation is the
primary detoxification mechanism. Aniline may be
subject to oxidation in order to yield the
corresponding nitrite or to conjugation with normal
cellular constituents.

Mechanism of action

The primary site of action of the substituted ureas
is inhibition of photosynthesis. Therefore, light is
required for herbicidal activity. In addition, a
secondary phytotoxic substance is formed in the
oxygen pathway of photosynthesis. Siduron is an
exception to the class because it does not inhibit
photosynthesis. Its phytotoxic effects are on root
growth and disruption of mitosis.

Behavior in Soils

Adsorption and leaching

In general, the ureas are readily adsorbed to soil
colloids and resist leaching. The small degree of
leaching that occurs is related to water solubilities and
soil texture. Adsorption involves weak bonds and is


Table 23. Longevity of urea herbicides in soils (months).

Herbicide Months

diuron 4 12
linuron 2 4
fluometuron 4 12
monuron 4-12
siduron 4 6
tebuthiuron 12 15


lowest in sandy soils, intermediate in clay loams and
highest in organic soils with a high organic matter
content. Adsorption on organic soils can completely
negate herbicidal activity.
Persistence

The ureas, as a class, are fairly persistent (Table
23) and can lead to residual or carryover problems.
The ureas are chemically stable in soil systems and do
not undergo extensive chemical alterations. Some
ureas are subject to photodecomposition but one of
the most important degradation means is microbial
activity.

Distinguishing characteristics

Low to intermediate water solubilities;
Generally applied preemergence;
Photosynthetic inhibitors;
Absorbed primarily by root with apoplastic
movement in plants;
a Moderately persistent in soils.
Siduron is an exception to many of the
general characteristics of the group.
Most are formulated as wettable powders and
therefore, require agitation to be kept in
solution.

Toxicological Properties


Acute Oral Toxicity
Siduron
Tebuthiuron
Monuron


Rats LD50(go /kg)
>7500
644
3600


Page 28






Turf Herbicide Families and Their Characteristics


SULFONAMIDES


Important Members (Table 24)


Table 24. Important members of the sulfonamides family.

Water Solubility Vapor Pressure
Common Name Trade Name(s) Manufacturer (ppm) (mm Hg @ 25-35 C)

Bensulide* Betasan ICI/Zenaca 25 intermediate volatility
Pre-San Sierra (<133 uPa)
Bensumec PBI/Gordon +
Prefar others
+ others
*Bensulfide is also listed as an Unclassified Herbicide.


Uses

Bensulide is a preemergence herbicide used in
turf, ornamentals and vegetables, primarily for control
of annual grasses. It does not control emerged weeds.
Bensulide should not be applied to newly established
turf because root development can be inhibited for
several weeks.

Behavior in Plants

Absorption and translocation

Sulfonamides are absorbed by roots with little or no
upward movement. Bensulide is not absorbed by
foliage.

Selectivity and Degradation

Resistant plants are able to metabolize bensulide
to a complete breakdown of carbon dioxide.

Mechanism of Action

Inhibits root growth presumably by disrupting cell
enlargement or partially inhibiting cell division. The
exact mechanism of action is not known.

Behavior in Soils

Adsorption and leaching

Bensulide is adsorbed tightly by organic matter
and soils high in organic matter may inactivate the


herbicide. Leaching rarely occurs in any soil type. To
compensate for lack of movement into soil, the
herbicide is used at high rates preemergence (7 to 15
lb ai/A) and must be incorporated by irrigation. This
also places the chemical in the weed-seed germination
zone. Little volatilization loss occurs.

Persistence

Persistence is long with an average half-life
ranging from four to six months. The rate of
degradation increases with increasing soil temperature
and organic matter, but decreases with increasing pH.
Bensulide can cause carryover problems, with an 18-
month waiting period for many crops. It is degraded
slowly in soils by soil microbes, and little volatilization
occurs. A slight amount is lost due to
photodecomposition.

Distinguishing Characteristics

Nonionic
a Low water solubility
Apoplastic movement in plants
Persistent
a Must be watered into the soil after application
Corrosive to copper
a Indefinite storage life

Toxicological Properties

Acute Oral toxicity LD50 (mg/kg) 770


Page 29






Turf Herbicide Families and Their Characteristics


SULFONYLUREAS


Important Members (Table 25)


Table 25. Important members of the sulfonylureas family.
Water Solubility Vapor Pressure
Common Name Trade Name(s) Manufacturer (ppm) (mm Hg @ 20-30 C)
Sulfometuron Oust DuPont 8 (pH 5) 6.0 x 10
70 (pH 7)
Metsulfuron Ally, Escort DuPont 1100 (pH 5.4) 5.8 x 10-5
DMC Weed Control O.M. Scott 9500 (pH 6.7)
Chlorsulfuron Lesco TFC Lesco 60 (pH 5) 4.6 x 106
Glean, Telar DuPont 7000 (pH 7)
Chlorimuron Classic DuPont 11 (pH 5) 4 x 10-12
1200 (pH 7)
Bensulfuron Londax DuPont 3 (pH 5) 2.1 x 10"14
120 (pH 7)
Thiameturon Harmony DuPont 260 (pH 5) 1.3 x 10-10
2400 (pH 7)
Halosulfuron Manage Monsanto 15 (pH 5) 2.8 x 10-2


Uses


The sulfonylureas are a recently marketed family
of herbicides with many additional members currently
being evaluated. Sulfometuron is used for bahiagrass
seedhead suppression and bahiagrass and broadleaf
weed control in rough bermudagrass. Metsulfuron is
used in rough and fine turf for bahiagrass and
broadleaf weed control. Chlorsulfuron provides
broadleaf weed and tall fescue control in
bermudagrass, bahiagrass, Kentucky bluegrass, fine
fescue and bentgrass. Chlorimuron is used in
soybeans for cocklebur, morningglory, Florida
beggarweed, and sicklepod control. Bensulfuron is
used for broadleaf and sedge control in rice
production. Thiameturon is used for early
postemergence broadleaf weed control in barley and
wheat. Halosulfuron is an experimental herbicide
that shows potential for nutsedge and selective
broadleaf weed control in turf.

Behavior in Plants

Absorption

Most are rapidly absorbed by foliage and roots.


Translocation


All are mobile in plants and will move both
acropetally and basipetally via xylem and phloem.

Selectivity and Degradation

Sulfonylureas are most active on broadleaf weeds
at extremely low rates (0.25 to 1.5 oz/A). Bahiagrass
and foxtail are two grass weeds also susceptible except
for chlorsulfuron. Selectivity to the sulfonylurea
herbicides is based on each plant's metabolism to
nontoxic products. The sulfonylureas are metabolized
to nontoxic products by tolerant plant species.

Mechanism of Action

Sulfonylureas inhibit the enzyme acetolactate
(acetohydroxy acid) synthase (ALS) which is required
for the biosynthesis of the branched chain amino acids
valine, leucine, and isoleucine. This results in
inhibition of cell division in the root and shoot tips.
Growth inhibition is rapid while secondary symptoms
include enhanced anthocyanin formation, abscission,
vein discoloration, terminal bud death, chlorosis, and
necrosis. Plant death is slow, requiring one to three
weeks.


Page 30






Turf Herbicide Families and Their Characteristics

Weed Resistance

Weed resistance can develop when increasing the
number of consecutive applications on a specific site.
Resistant plants produce a form of acetolactate which
can quickly metabolize the herbicide into inactive
forms.

Behavior in Soils

Adsorption and leaching

Most sulfonylurea adsorption to clay is low, while
organic matter has some affinity. The rate of leaching
is highly dependent on soil pH, with less leaching
occurring at the acid pH levels where water solubility
is lower.

Persistence

Sulfonylureas are weak acids and stable metal
salts are formed when treated with a base alkaline
earth hydroxide or carbonate. Sulfonylurea herbicides
degrade in soils by chemical hydrolysis and microbial
mediated degradation. Persistence is drastically
affected by soil pH. Chemical hydrolysis occurs


Page 31


rapidly at acidic pH levels. Persistence is longer in
neutral to basic pH soil and some members may
persist in soil 1 to 2 years when applied to alkaline
(pH > 7.0) soils. Sulfonylureas exist primarily in the
anionic form.

Distinguishing characteristics

High level of unit activity, resulting in low use
rates;
Systemic movement in plants;
Blockage of the enzyme acetolactate synthase
is the primary site of action;
Water solubility and movement in soil is pH
dependent with less solubility and leaching at
low or acidic pH levels;
Persistence in soils is pH dependent with less
persistence at acidic pH levels.

Toxicological Properties


Acute Oral Toxicity
Metsulfuron
Sulfometuron
Chlorsulfuron
Halosulfuron


LDP5mgo( g)
>5000
>5000
5545
8865


TRIAZINES

Important Members and Formulations (Table 26)


Table 26. Important members of the triazine family.

Water Solubility Vapor Pressure
Common Name Trade Name(s) Manufacturer (ppm) (mm HG @ 20-35" C)

Symmetrical Triazines
Atrazine Aatrex Ciba-Geigy 33-70 3.0 x 107
Atrazine DowElanco
Simazine Princep Ciba-Geigy 5-85 6.1 x 109
Ametryn Evik Ciba-Geigy 185 8.4 x 10-7
Prometryn Caparol Ciba-Geigy 33-48 1.0 x 10-6
Hexazinone Velpar DuPont 33,000 2.7 x 10-7
Asymmetrical Triazines
Metribuzin Sencor Miles 1220 >1 x 10-5
Lexone DuPont






Turf Herbicide Families and Their Characteristics

Uses

Used primarily for preemergence annual
broadleaf and grass weed control in corn, sorghum,
sugarcane and rangeland. At higher rates, the
triazines are used for non-selective weed control. In
turf, the triazines are used for preemergence and
early postemergence grass, broadleaf, and sedge
control in bermudagrass, St. Augustinegrass,
centipedegrass, and zoysiagrass. Activity is greatest
for broadleaf weeds. Activity is reduced as weeds
emerge and mature. Higher rates are needed on
peat, muck and high organic clay soils. Preemergence
activity of the triazines will be reduced in these soil
conditions. Metribuzin is used alone and in
combination with the arsenical herbicides (e.g.,
MSMA, DSMA, and CMA) for postemergence
goosegrass, crabgrass and broadleaf weed control in
bermudagrass and zoysiagrass. In Florida, the
triazines (primarily atrazine) provide good to
excellent pre- and postemergence broadleaf control
and fair pre- and postemergence grass control.

Behavior in Plants

Absorption

Triazines are primarily preemergence herbicides
that are rapidly absorbed by emerging seedling roots.
Roots are not killed directly, but the destruction of
shoot growth leads to the eventual root starvation.
Some shoot absorption can occur except for simazine
and propazine.

Translocation

Rapid translocation occurs from root absorption
and is upward in the xylem with the transpiration
stream. Triazines accumulate in the apical meristem
and leaves. Some foliage absorption occurs but is
limited in most plants. The most severe triazine
symptoms develop on lower mature leaves. On
individual leaves the symptoms appear at the leaf tips
and margins, followed by loss of chlorophyll between
the veins and death of the leaf occurs from the tip.

Selectivity and Degradation

In general, dicot (broadleaf) crops are less
tolerant than monocots (grasses). Hexazinone
tolerance, especially with woody species, is associated
with reduced uptake and translocation of the
herbicide by the tolerant plants. In general, the
triazines are degraded rapidly in resistant species


Page 32


(monocots) to hydroxytriazine and amino acid
conjugates. Susceptible species (dicots) degrade them
slowly and the unaltered triazine accumulates, causing
chlorosis and death. Resistant weed biotypes have
developed with the herbicide no longer being able to
attach and inhibit electron-transport. Certain
goosegrass biotypes have been cited as a possible
triazine-resistant turf weed.

Mechanism of action

Inhibition of photosynthesis. Interferes with
normal electron transport. Eventual membrane
destruction occurs with resulting chlorophyll loss.
Foliar chlorosis, usually interveinal, followed by
necrosis, is the usual phytotoxic symptom of the
triazines. Light is required for herbicide activity.

Behavior in Soils

Absorption and Leaching

Absorption of the triazines in soils is related to
the soil organic content, pH, and clay minerals--not to
the water solubility of the compounds. Atrazine is
more readily adsorbed on muck or clay soils.
Adsorption generally is greater under acidic
conditions, when clay minerals are present. Leaching
of the triazines is dependent on water solubility, soil
pH and texture. Metribuzin and prometon are the
most mobile of the triazine herbicides and when used
on many row crops, they are generally restricted to
soils containing at least 1.5 to 2% organic matter.
These should not be applied directly to water or
wetlands. The extent of leaching is less in soils
receiving low rainfall and in fine-textured high organic
soils as compared to coarse, low organic soils.

Persistence

As a class, the triazines are fairly persistent in
soils (Table 27).

Half-life for hexazinone ranges from 30 to
180 days
Triazine degradation in soils is generally
attributed to microbial activity.

Distinguishing Characteristics

Compatible with most other pesticides and
fertilizers
Noncorrosive under normal use conditions
Shelf life is stable over several years.






Turf Herbicide Families and Their Characteristics

Table 27. Longevity of triazine herbicides in soils (months).

Herbicide Months

atrazine 6 12
simazine 6-12

cyanazine 2 4
propazine 6 10
prometon 8 18
ametryne 2 3
prometryne 2 6
metribuzin 2 4


Agitation is necessary to keep the chemical in
suspension.
Low to intermediate water solubilities and are
essentially non-volatile.
Surfactants appear to increase the foliar
activity of these herbicides. Nitrogen solution
and other liquid fertilizers have been widely
and successfully used as carriers.


Page 33


Postemergence herbicide use of the triazines
requires the addition of oil concentrate or
surfactants adjuvantss).
Soil adsorption is greater under acidic
conditions.
All triazines are relatively persistent in soils
and can cause carry-over or residue problems,
particularly on sensitive vegetable crops.
Good activity on annual broadleaf plants with
less activity on grass and perennial
broadleaf plants.

Toxicological Properties


Acute Oral Toxicity
atrazine
simazine
ametryn
prometryn
hexazinone
metribuzin


LD5 (mg/ka)
3080
5000
1405
3750
1690
1937


UNCLASSIFIED HERBICIDES


Important Members


Table 28. Important members of the unclassified herbicide family.

Water Solubility Vapor Pressure
Common Name Trade Name(s) Manufacturer (ppm) (mm Hg @ 25-35" C)

Bentazon1 Basagran BASF 500 <1.3 x 10-7 mbar
Glyphosate2 Roundup Monsanto 12,000 1.9 x 107
Rodeo Monsanto
Ethofumesate Prograss Nor-AM 110 6.45 x 10-7
Nortron
Oxadiazon3 Ronstar Rhone-Poulenc 7 1.0 x 10-6
Quinclorac4 Drive, Facet, BASF dispersible <1 xT7
Impact
'Bentazon is also often listed in the Benzothiadiazoles herbicide family, as an Unclassified Herbicide or as an Organic
Herbicide.
2Glyphosate is also listed as a member of the Amino Acid Derivative herbicide family.
3Oxadiazon is also grouped in the Substituted Diphenyl Ether herbicide family, as an miscellaneous Organic Herbicide,
or as a Oxadiazolin.
4Quinclorac has not yet been classified in a specific herbicide family but does belong to the Quinolinecarboxylic acid
chemical family.






Turf Herbicide Families and Their Characteristics

Uses

Bentazon provides postemergence yellow
nutsedge (with repeat applications) and selective
broadleaf control. Other sedges, such as annual,
globe sedge, and kyllinga, also have varying degrees of
susceptibility. Purple nutsedge is not satisfactorily
controlled. All warm-season turfgrasses are tolerant
to bentazon.

Glyphosate is a non-selective herbicide that
provides excellent control of most annual and
perennial plants. It also is used at reduced rates to
control seedheads of low maintenance turfgrasses.

Ethofumesate is a selective preemergence
herbicide for annual broadleaf and grass weeds in
sugarbeets and overseeded dormant bermudagrass
turf. Its primary use in turf is for preemergence and
early postemergence control of annual bluegrass. If
applied to non-dormant bermudagrass, injury and
delayed "green-up" can occur.

Oxadiazon is a preemergence herbicide used for
annual grass and selective broadleaf weed control in
turf, ornamentals and rice. Irrigation is needed to
incorporate this herbicide into the soil.

Quinclorac provides early postemergence
crabgrass, torpedograss, and selective broadleaf weed
control in bermudagrass, zoysiagrass, bluegrass,
ryegrass, and tall fescue.

Behavior in Plants

Absorption

Bentazon is a contact herbicide injuring only
those parts of the plant it comes in contact with.
Very little acropetal or basipetal translocation occurs.
Good coverage is essential for control. Bentazon is
absorbed by plant foliage and initial symptoms in
weeds are a bronze cast to the leaves, followed by
necrosis. Upward movement does occur in the xylem
following root absorption, but bentazon has little
effect on germinating seeds.

Glyphosate is rapidly absorbed by foliage and
stems. Woody species may uptake glyphosate through
bark in some cases. It is absorbed rapidly due to high
water solubility, anionic nature, lack of metabolism
and slow mechanism of action. Environmental factors
that favor actively growing plants will similarly favor
glyphosate absorption and translocation. Tank


Page 34


mixtures with triazines, MSMA, phenoxy or paraquat
may reduce activity or increase the time required for
glyphosate to work. Rainfall within six hours of
treatment may reduce effectiveness. Increased
translocation to the underground storage organs of
perennial plants is achieved when treated at the later
stages of vegetative growth, near flowering.

Ethofumesate is absorbed through emerging
shoots of seedlings with relatively low root uptake.
Not readily absorbed by leaves after the plant has
generated a mature cuticle. Exposure of plants to
preemergence treatments decreases epicuticular wax
deposition on leaf surfaces, which enhances foliar
absorption of subsequently applied postemergence
herbicides.

Oxadiazon is applied preemergence and absorbed
by germinating weeds. It usually is not absorbed by
foliage. However, contact type of injury can be
observed in some plants, especially when the wettable
powder formulation is used on young seedings.

Quinclorac is absorbed by the coleoptile and
leaves as well as by roots.

Translocation

Bentazon, due to its contact mode of action, has
little acropetal or basipetal translocation.

Glyphosate moves symplastically in plants and
accumulates in metabolically active regions.
Glyphosate follows the photosynthetic pathway from
the source to the sink and can be exuded from roots
of foliar-treated plants. Cool or cloudy weather
following treatment may delay visual symptoms.

Ethofumesate is apoplastically translocated to the
foliage following uptake by roots and emerging
shoots, but is not translocated out of treated leaves.

Oxadiazon, due to its contact type of injury, does
not appear to have significant translocation in plants.

Quinclorac. Translocation studies are in progress.

Selectivity

Bentazon provides annual broadleaf control
including cocklebur, ragweed, prickly sida, wild
mustard, plus others. Yellow nutsedge also is
susceptible. Annual grasses are not affected.
Bentazon is rapidly metabolized in tolerant species,






Turf Herbicide Families and Their Characteristics

forming extractable conjugates which are then
incorporated into normal plant components.

Glyphosate has virtually no selectivity for weeds
or turf. It controls annuals, biennials, and perennials
- both herbaceous and woody species. Effective kill
of perennials is dependent upon translocation
characteristics at time of treatment. Basipetal
movement or downward flow of photosynthates
generally represents a period of greatest vulnerability
since glyphosate follows the flow of photosynthates.
This usually occurs near anthesis or flowering in most
perennials. Phytotoxicity is slow to develop requiring
one to two weeks with most perennials. Selectivity is
currently being achieved in a number of crop
situations through the use of specialized applicators.
Rope and wick applications, wipers, and shielded
equipment are used where the weed is exposed to
glyphosate and the crop is protected.

Ethofumesate is used for selective preemergence
annual broadleaf and grass weed control. It appears
to act as a growth regulator. Plant selectivity seems
to be due to rapid metabolism and reduced
translocation in tolerant plants. Differences in root
absorption are not a factor in its selectivity.

Quinclorac has visual symptoms in clover which
include twisting within 1 to 2 days following
application. In grasses, stunting, chlorosis, and
gradual reddening occur in 7 to 14 days, followed by
necrosis and death.

Mechanism of action

Bentazon appears to inhibit photosynthesis by
interfering with photosynthetic electron transport in
photosystem II.

Glyphosate prevents selected amino acid and
protein synthesis. Specifically, it inhibits
enolpyruvylshikimate-3-phosphate synthase (ESPS) in
the aromatic amino acid biosynthetic pathway in
plants (shikimic acid pathway, pathway for
phenylalanine and tryptophan production). It may
also inhibit or repress two enzymes, chlorismate
mutase or prephenate dehydratase, in this system.
Genetic engineers are working on glyphosate-resistant
plants by two methods: (1) mutation of the target site
of ESPS; or, (2) overproduction of ESPS synthase to
overcome glyphosate's phytotoxic effects.


Page 35


Ethofumesate's mechanism of action is not fully
known. It is believed to inhibit photosynthesis and
respiration.

Oxadiazon appears to affect young shoots as they
grow through the treated zone. Possible effects
include mitotic inhibition. Light is required for
herbicidal activity as oxadiazon has been reported to
effect chlorophyll biosynthesis.

Quinclorac has a plant hormone type mode of
action.

Degradation

Bentazon is rapidly metabolized in tolerant
species, forming extractable conjugates which are then
incorporated into normal plant components.

Glyphosate probably undergoes hydrolysis initially
to give the free acid form. Glyphosate can be
metabolized in plants to give CO2 and natural
products. However, plants do not metabolize
glyphosate to a significant degree and effects can
persist for long periods of time.

Ethofumesate is metabolized in tolerant plants to
a major and minor conjugated metabolite. Residue
levels generally decline during plant growth.

Oxadiazon is metabolized into non-toxic
metabolites and appears to be the major means of
degradation in resistant plant species.

Quinclorac. Metabolism studies are in progress.

Behavior in Soils

Adsorption and leaching

Bentazon is not highly adsorbed in soils, even in
organic or fine textured soils; therefore, readily
leaches but rarely reaches below 10 to 12 inches.
Non-volatile.

Glyphosate is adsorbed strongly by soil colloids
and rendered biologically unavailable. The
mechanism of adsorption has been proposed to be
similar to phosphate fixation with clay minerals.
Little leaching occurs due to this degree of
adsorption. Adsorption is a form of inactivation since
virtually no preemergence activity is observed with
soil applications. Turf usually can be planted directly
into treated areas.






Turf Herbicide Families and Their Characteristics

Ethofumesate's activity is reduced in dry soils and
soils high in organic matter such as peat or muck
soils. It does not leach in soils having an organic
matter content above 1%.

Oxadiazon is strongly adsorbed by organic matter
and soil colloids and does not leach.

Quinclorac can be adsorbed to some extent by
soil.

Persistence

Bentazon is readily metabolized by bacteria and
fungi. These metabolic residues are highly persistent,
but are not herbicidally active, and incorporated into
soil organic matter. Breakdown also occurs by
photodegradation. Bentazon's longevity in most soils
is less than one month with a half-life less than two
weeks.

Microbial degradation occurs rapidly in soils for
Glyphosate. Rapid degradation of the non-bound or
biologically available material helps prevent uptake by
plants. The average half-life is less than 60 days. The
half-life in ponds range from 12 days to 10 weeks.

Ethofumesate is rather persistent in soils; it may
last 6 months or more. However, the half-life usually
ranges from 14 or more weeks in dry, cold conditions,
to less than 5 weeks under moist, warm conditions.
A twelve-month planting restriction exists for most
crops following application. Ryegrass is an exception.
Degradation is due to the activity of microorganisms.
No loss occurs via photodecomposition and/or
volatilization.

Oxadiazon has intermediate persistence in soils
with a longevity of 4 to 6 months. Negligible loss
occurs due to volatilization.

Quinclorac appears to be degraded microbially.
Additional studies are in progress. Minimum losses
occur from volatilization.

Distinguishing Characteristics

Bentazon
a Active on selective broadleaf weeds and
sedges;
Inhibits photosynthesis;
B Contact material exhibiting very little
translocation, and requires thorough coverage


Page 36


to be effective. Visible injury usually occurs
within 48 hours.
Not corrosive
A surfactant is needed for best results.
It has a half-life in water of <24 hours due to
photodegradation.
Rain within 8 hours of application may
reduce effectiveness.

Glyphosate
a Derivative of glycine or alanine
a Postemergence herbicidal activity
Essentially has no preemergence activity;
a Translocated symplastically
a Formulated as salts (glycine derivatives) or
esters (alanine derivatives);
Rodeo formulation is used for aquatic weed
control.

Ethofumesate
Mainly preemergence herbicidal activity
a Mainly absorbed through the shoots with little
translocation from treated shoots
Mechanism of action is not fully known.
Little leaching occurs, especially in soils
having more than 1 percent organic matter.
a Persistence depends on environmental
conditions which effect degradation by soil
microorganisms.


Oxadiazon
Low water solubility
Preemergence activity
a Resistant to leaching
organic matter
B Noncorrosive
B Irrigation is needed
herbicide into the soil.


and is adsorbed by


to incorporate the


Quinclorac
Pre- and early postemergence activity on
crabgrass, foxtail, signalgrass, and some
broadleaf weeds
B Appears to suppress torpedograss
a Bermudagrass, zoysiagrass, ryegrass,
bluegrass, and tall fescue are tolerant.

Toxicological Properties


Acute Oral Toxicity
Bentazon
Glyphosate
Ethofumesate


LDs((mg/kg)
1100
4320
<6400






Turf Herbicide Families and Their Characteristics


Oxadiazon
Ouinclorac


>5000
4120


REFERENCES AND ADDITIONAL READING

Anderson, W. P. 1983. Weed Science: Principles.
2nd ed. West Publishing Company. St. Paul, MN.

Anonymous. 1989. EXTOXNET. Extension
Toxicology Network. Cornell Univ. Ithaca, NY.

Ashton, F. M. and T. J. Monaco. 1991. Weed
Science Principles and Practices. John Wiley and
Sons, Inc. NY. 466pp.

Coats, G. E. 1986. Turfgrass weed control. Miss.
Agric. and Forestry Exp. Station Bull. 95.

Emmons, R. D. 1985. Turfgrass science and
management. Delmar Publishers, Inc. Albany,
NY.

Engel, R. E. and R. D. Ilnicki. 1969. Turf weeds and
their control. pp. 240-287. In A. A. Hanson and
F. V. Juska (ed.). Turfgrass Science. Am. Soc.
Agron. Madison, Wisconsin.

Goetz, A. J., G. Wehtze, R. H. Walker, and B. Hajek.
1986. Soil solution and mobility characterization
of imazaquin. Weed Sci. 34:788-793.

Herbicide Handbook. 1989. Weed Science Society of
America. 6th edition. Champaign, IL.

Hill, G. D. 1982. Impact of weed science and
agricultural chemicals on farm productivity in the
1980s. Weed Sci. 30: 426-429.

Klingman, G. C. and F. M. Ashton. 1982. Weed
Science Principles and Practices. John Wiley &
Sons, Inc. NY.

Lewis, W. M. 1985. Weeds in turf. pp. 18-34. In A.
H. Bruneau, (ed.), Turfgrass pest management
manual. NC Agric. Ext. Ser., Raleigh, NC.

Lewis, W. M. 1992. Pest control recommendations
for turfgrass managers. N. C. Agric. Ext. Ser.,
Raleigh, NC.

McCarty, L. B. 1991. Goosegrass (Eleusine indica)
control in bermudagrass (Cynodon spp.) turf with
diclofop. Weed Sci. 39:


McCarty, L. B., J. M. Higgins, L. C. Miller, and T.
Whitwell. 1986. Centipedegrass tolerance to
postemergence grass herbicides. HortSci.
21:1405-1407.

McCarty, L.B., J.M. Higgins, T. Whitwell, and L.C.
Miller. 1989. Tolerance of tall fescue to
postemergence grass herbicides. HortSci. 24:309-
311.

Moberg, W. and B. Cross. 1990. Herbicides inhibiting
branched-chain amino acid biosynthesis. Pesticide
Science. 29:241-246.

Murdoch, C. L. and R. K. Nishimoto. 1982. Diclofop
for goosegrass control in bermudagrass putting
greens. HortSci. 17:914-915.

Murphy, T. and F. D. Bullock. 1986. Know your
herbicides. Georgia Coop. Ext. Ser. Bull. 682.

Murphy, T. R., L. B. McCarty, D. L. Colvin, R.
Dickens, J. W. Everest, and D. W. Hall. 1992.
Weeds of Southern Turfgrass. Univ. of Florida.
IFAS Coop. Ext. Ser. SP-79.

National Research Council, Committee on Plant and
Animal Pests. 1968. Principles of Plant and
Animal Pest Control, Vol. 2, Weed Control.
Natl. Acad. Sci., Washington, DC.

Ross, M. A. and C. A. Lembi. 1985. Applied Weed
Science. Macmillan Publ. Comp. NY.

Shaner, D. L. 1989. Factors affecting'soil and foliar
bioavailability of the imidazolinone herbicides.
American Cyanamid Comp. Agric. Res. Div.
Princeton, N.J. pp24.

Slade, R. E., W. G. Templeman, and W. A. Sexton.
1945. Plant growth substances as selective weed
killers. Nature 155:497-498.

Turgeon, A. J. 1991. Turfgrass Management.
Reston Public. Comp., Inc. Reston, VA.

Van Ellis, M.R. and D.L. Shaner. 1988. Mechanism
of cellular absorption of imidazolinones in
soybean (Glycine max) leaf discs. Pesticide Sci.
27:25-34.


Page 37






Turf Herbicide Families and Their Characteristics


APPENDIX


Table 29. Herbicide family, common name and common trade name for turf or related pesticides
HERBICIDE FAMILY COMMON NAME TRADE NAMES
ACETANILIDES alachlor Lasso
metolachlor Pennant, Dual
AMIDES diphenamid Enide
(ACETAMIDES) isoxaben Gallery
napropamide Devrinol
pronamide Kerb
ARYL-OXY PHENOXY diclofop Hoelon, Illoxan
fenoxaprop Acclaim, Horizon, Whip
fluazifop Fusilade
haloxyfop Verdict
quizalofop Assure
BENZOIC ACIDS chloramben Amiben
dicamba Banvel + others
NITRILES bromoxynil Buctril, Brominal
(BENZONITRILES) dichlobenil Casoron, Dyclomec
BIPYRIDYLLUMS diquat Diquat Herbicide
paraquat Gramoxone Super,
Gramoxone Extra
CARBAMATES asulam Asulox
CYCLOHEXENDIONES sethoxydim Vantage, Poast
DINITROANILINES trifluralin Treflan
benefin Balan
ethalfluralin Sonalan
pendimethalin Prowl, Pre-M
oryzalin Surflan
prodiamine Barricade
DIPHENYL-ETHERS acifluorfen Blazer, Tackle
bifenox Modown
fomesafen Reflex
lactofen Cobra
oxyfluorfen Goal
IMIDAZOLINONES imazaquin Image, Scepter
imazapyr Arsenal, Chopper
imazethapyr Pursuit
ORGANIC ARSENICALS cacodylic acid Rad-E-Cate, Phytar 560
MSMA Arsenate, Bueno 6, Daconate
DSMA Crab-E-Rad, DSMA Liquid
MAA --
AMA Super Dal-E-Rad
CMA Super-Crab-E-Rad-Calar
PHENOXIES 2,4-D many available
MCPA MCPA, Weedar Sodium + others
2,4-DB Butoxone, Butyrac
2,4-DP (dichlorprop) Weedone 170 + others
MCPP (mecoprop) Lescopex + others
PHTHALIC ACIDS DCPA Dacthal
endothall Aquathol, Hydrothal, Endothal
naptalam Alanap


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Turf Herbicide Families and Their Characteristics


Table 29. Herbicide family, common name and common trade name for turf or related pesticides
HERBICIDE FAMILY COMMON NAME TRADE NAMES
PYRIDINES and dithiopyr Dimension
PICOLINIC ACIDS clopyralid Reclaim
picloram Tordon
triclopyr Garlon, Turflon, Remedy
SUBSTITUTED UREAS diuron Karmex
fluometuron Cotoran
linuron Lorox
siduron Tupersan
SULFONAMIDES bensulide Betasan, Pre-San,
Bensumec + others
SULFONYLUREAS chlorsulfuron Lesco TFC, Glean, Telar
metsulfuron Ally, Escort,
DMC Weed Control
sulfometuron Oust
halosuffuron Manage
TRIAZINES ametryn Evik
atrazine AAtrex, Atrazine + others
hexazinone Velpar
metribuzin Sencor, Lexone
prometryn Caparol
simazine Princep + others
UNCLASSIFIED HERBICIDES bentazon Basagran T\O
ethofumesate Prograss
glyphosate Roundup, Rodeo + others
oxadiazon Ronstar
quinclorac Drive, Facet, Impact


Page 39






Turf Herbicide Families and Their Characteristics


Table 30. Cross reference of herbicide trade names, common names, and chemical families.
TRADE NAMES COMMON NAMES HERBICIDE FAMILIES
AAtrex atrazine Triazines
Acclaim fenoxaprop Aryl-oxy Phenoxy
Alanap naptalam Phthalic Acids
Ally metsulfuron Sulfonylureas
Amiben chloramben Benzoic Acids
Aquathol endothall Phthalic Acids
Arsenal imazapyr Imidazolinones
Arsenate MSMA Organic Arsenicals
Assure quizalofop Aryl-oxy Phenoxy
Asulox asulam Carbamates
Atrazine atrazine Triazines
balan benefin Dinitroanilines
banvel dicamba Benzoic Acids
basagran bentazon Unclassified Herbicides
balan benefin Dinitroanilines
barricade prodiamine Dinitroanilies
bensumec bensulide Sulfonamides
betasan bensulide Sulfonamides
blazer acifluorfen Diphenyl-ethers
brominal bromoxynil Nitriles
buctril bromoxynil Nitriles
Bueno 6 MSMA Organic Arsenicals
Butoxone 2,4-DB Phenoxies
Butyrac 2,4-DB Phenoxies
Caparol prometryn Triazines
Casoron dichlobenil Nitriles
Chopper imazapyr Imidazolinones
Classic chlorimuron Sulfonylureas
Cobra lactofen Diphenyl-ethers
Cotoran fluometuron Substituted Ureas
Crab-E-Rad DSMA Organic Arsenicals
Daconate MSMA Organic Arsenicals
Dacthal DCPA Phthalic Acids
Devrinol napropamide Amides
Dimension dithiopyr Pyridines/Picolinic Acids
Diquat Herbicide diquat Bipyridyllums
DMC Weed Control metsulfuron Sulfonylureas
Drive quinclorac Unclassified Herbicides
DSMA Liquid DSMA Organic Arsenicals
Dual metolachlor Acetanilides


Page 40







Turf Herbicide Families and Their Characteristics


Table 30. Cross reference of herbicide trade names, common names, and chemical families.
TRADE NAMES COMMON NAMES HERBICIDE FAMILIES
Dyclomec dichlobenil Nitriles
Endothal endothall Phthalic Acids
Enide diphenamid Amides
Escort metsulfuron Sulfonylureas
Evik ametryn Triazines
Facet quinclorac Unclassified Herbicides
Fusilade fluazifop Aryl-oxy Phenoxy
Gallery isoxaben Amides
Garlon triclopyr Pyridines/Picolinic Acids
Glean chlorsulfuron Sulfonylureas
Goal oxyfluorfen Diphenyl-ethers
Gramoxone Extra/Super paraquat Bipyridyllums
Hoelon diclofop Aryl-oxy Phenoxy
Horizon fenoxaprop Aryl-oxy Phenoxy
Hydrothal endothall Phthalic Acids
Illoxan diclofop Aryl-oxy Phenoxy
Image imazaquin Imidazolinones
Impact quinclorac Unclassified Herbicides
Karmex diuron Substituted Ureas
Kerb pronamide Amides
Lasso alachlor Acetanilides
Lescopex MCPP (mecoprop) Phenoxies
Lesco TFC chlorsulfuron Sulfonylureas
Lexone metribuzin Triazines
Lorox linuron Substituted Ureas
Manage halosulfuron Sulfonylureas
MCPA MCPA Phenoxies
Modown bifenox Diphenyl-ethers
Oust sulfometuron Sulfonylureas
Pennant metolachlor Acetanilides
Phytar 560 cacodylic acid Organic Arsenicals
Poast sethoxydim Cyclohexendiones
Pre-M pendimethalin Dinitroanilines
Pre-San bensulide Sulfonamides
Princep simazine Triazines
Progress ethofumesate Unclassified Herbicides
Prowl pendimethalin Dinitroanilines
Pursuit imazethapyr Imidazolinones
Rad-E-Cate cacodylic acid Organic Arsenicals
Reclaim clopyralid Pyridines/Picolinic Acids
Reflex fomesafen Diphenyl-ethers


Page 41






Turf Herbicide Families and Their Characteristics


Table 30. Cross reference of herbicide trade names, common names, and chemical families.
TRADE NAMES COMMON NAMES HERBICIDEE FAMILIES
Remedy triclopyr Pyridines/Picolinic Acids
Rodeo glyphosate Unclassified Herbicides
Ronstar oxadiazon Unclassified Herbicides
Roundup glyphosate Unclassified Herbicides
Scepter imazaquin Imidazolinones
Sencor metribuzin Triazines
Sonalan ethalfluralin Dinitroanilines
Surflan oryzalin Dinitroanilines
Super Crab-E-Rad-Calar CMA Organic Arsenicals
Super Dal-E-Rad AMA Organic Arsenicals
Tackle acifluorfen Diphenyl-ethers
Telar chlorsulfuron Sulfonylureas
Tordon picloram Pyridines/Picolinic Acids
Treflan trifluralin Dinitroanilines
Tupersan siduron Substituted Ureas
Turflon triclopyr Pyridines/Picolinic Acids
Vantage sethoxydim Cyclohexendiones
Velpar hexazinone Triazines
Verdict haloxyfop Aryl-oxy Phenoxy
Weedar Sodium MCPA Phenoxies
Weedone 170 2,4-DP (dichlorprop) Phenoxies
Whip fenoxaprop Aryl-oxy Phenoxy


Page 42




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