10/12/2015
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Angela R. Post
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PLNT 3113
Principles of Weed Science
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Acetyl-coenzyme A carboxylase (ACCase)
Rate limiting step in lipid biosynthesis
Usually sensitive in grasses, but not broadleaf
plants
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Lipid biosynthesis inhibitor herbicides
(ACCase)
Brief discussion of lipid biosynthesis
Examples of chemical structures
Characteristics
Uses
Selectivity
Mode and mechanism of action
Introduced for POST control of annual and
perennial grasses in 1975
Some selectivity between some grass
crops and weeds (wheat and wild oat –
diclofop, tralkoxydim)
Non-grass species resistant
Readily absorbed by foliage
Ambimobile (phloem and xylem)
Spray additive usually needed for
maximum activity
Wild oat control in winter wheat
Wild oat spray - diclofop
Untreated control
Fenoxaprop-ethyl 90 g ai/ha
1 to 3 leaf wild oat
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Fluazifop-butyl
Fluazifop-butyl in soybean
Soybean and oat
Diclofop-methyl
Wheat and oat
Treated
Untreated
Cotton and Sorghum halepense
CO2CH2 C CH
CH3
Cl
O
Cl
N
O CHCO2CH3
O
O C CH3
H
Cl
F
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◦ Diclofop ~2% translocation, mostly acropetal in xylem, a
little basipetal in phloem
Readily absorbed by roots and shoots (about 6090%)
Lipophilic – readily absorbed into cuticle, may be
slow to desorb into apoplast
◦ Rainfastness – depends on product
Uptake best at high humidity and warm
temperature
Spray coverage important
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Works best when applied to actively
growing, non-stressed grasses
Death is slow – week or more
◦ Root and shoot growth stops quickly
◦ Water soaked appearance at point of herbicide
contact
◦ Chlorosis in leaves within 2 to 6 days
◦ Necrosis begins at meristems and progresses
to older tissues
Variable – 2 to 50%
Accumulates in meristematic tissues including
intercalary meristems
Adjuvants sometimes can increase translocation
High RH and warmer temperature and increase
translocation
Water stress reduces translocation
Free acids translocate not the ester
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Slowly degrades in soil
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Most have little soil activity under normal
conditions
◦ Diclofop only herbicide labeled for soil application –
winter wheat (PPI, Bromus tectorum)
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Lipids are essential components of
membranes without which new membranes
are not formed
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These herbicides are active at meristematic
regions in the plant where they stop
production of cell membranes
Aryloxyphenoxypropionates (fops)
diclofop
Hoelon
Cyclohexanediones (dims)
sethoxydim
(Poast, Poast Plus, Vantage)
Chemical properties
-Are not volatile
-Will not photo-decompose
-No leaching concerns
Mode of Action – inhibit lipid production in grasses
-Lipids are used for what?
Location of activity in plant
-Site of action is the enzyme acetyl-CoA (ACCase)
Herbicidal properties
-Fairly slow acting
-Susceptible grasses will immediately stop growing
-Death of grass will occur in 5 to 10 days after treatment
-Readily translocated
-Move to meristems
Selectivity
-Broadleaves are tolerant due to lack of susceptible ACCase
enzyme
-Resistant weeds are known to exist – gene alteration
-Ryegrass, fescue
Symptoms include
“Stem Slipage in Grasses”
-Activity reduced if mixed with some herbicides
-Very sensitive to drought -- may even fail
-Most “require” a surfactant or COC
-Rainfast in 1 to 3 hours
Rotten Whorl
in Corn
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Symptoms include
“White Flash in Broadleaves”
-Clethodim / Select
-Fluazifop / Fusilade 2000
-Quizalofop / Assure II
-Diclofop / Hoelon
-Fenoxaprop / Puma
Not a major concern but common with Assure II
Labeled in Cotton, soybeans, peanuts & alfalfa
-Performs well under Oklahoma’s dry conditions
-Under very dry conditions activity declines
-Careful with tank mixes due to antagonism
Untreated
July 29
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-Has UV light protection
-Vantage - selected turf and horticulture uses
-centipedegrass and fine fescues
-Poast Plus - cotton, soybeans, strawberries, alfalfa,
sunflowers, & peanuts
Select Max
AI =
clethodim
-PRE and POST
-Does NOT control perennial grasses
-Good for ryegrass and wild oats in wheat
-Very little use in OK – Why?
-Full-season grazing restriction
-Expensive
-Very sensitive to drought
July 29
-POST grass control in rice and wheat
-Good for wild oats in wheat
-POST on cotton and soybeans
-Need an adjuvant
-Performs well in OK
Untreated
July 29
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-POST on cotton, soybeans, ornamentals
-NOT for use on peanuts or alfalfa
-Has performed very well in OK
-Affected by drought, but less so than Poast Plus
Assure II + atrazine
AI = quizalofop
July 29
LIPID BIOSYNTHESIS INHIBITORS
Fluazifop-P
LIPID BIOSYNTHESIS INHIBITORS
O
Structure:
F3C
H
O C C
O
OH
CH3
N
Method of application: Foliar.
Translocation: Phloem mobile; Symplastic
Mechanism of inhibition: Inhibition of acetyl-CoA carboxylase
(ACCase), which catalyzes the first step of fatty acid synthesis.
Plants lack lipids for new growth and repair.
Symptoms: Growth stops soon after application. Discoloration
and disintegration of meristematic tissue just above the nodes.
Leaves turn yellow and/or red and seedlings fall over at the soil
surface. Death occurs between 10 and 21 days after treatment.
Fluazifop-P
Environmental Persistence:
- Rapidly degraded in the soil, but may have some
temporary activity on germinating grasses
Special features/problems:
-Applied as the butyl ester of fluazifop; subsequent
metabolism within the plant changes it to the herbicidally
active form
LIPID BIOSYNTHESIS INHIBITORS
Others:
O
CF3
O
O
H
C
C
O
CH3
Fluazifop-P
butyl ester
CH3
N
(CH2)3
Metabolism in plants
Cyclohexanediones: (=“Dims”)
-Sethoxydim POAST
-Clethodim
SELECT
O
CF3
O
N
O
H
C
C
Aryloxyphenoxy propionates: (=“Fops”)
-Diclofop-methyl
HOELON
-Fenoxaprop-p-ethyl
SILVERADO
-Quizalofop-p-ethyl
ASSURE II
OH
Fluazifop-P
CH3
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Broadleaf plants have an
ACCase enzyme that is
relatively insensitive to
“fops” and “dims”; Some
species metabolize these
herbicides.
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