Download Herbicide Mode of Action - Montana State University

Herbicide Mode of
Action
Celestine Duncan
Weed Management Services
Mode of Action
Sequence of events from absorption into
the plant until the plant dies
Systemic herbicides – translocated from
site of entry to area in plant where they are
active
Contact herbicides - kill only the area
where they are applied.
Classification by Mode of Action
1)
2)
3)
4)
5)
6)
7)
Photosynthesis Inhibitors
Plant Growth Regulators
Amino Acid Biosysthesis Inhibitors
Growth Inhibitors
Pigment Inhibitors
Grass Specific herbicides
Membrane Disrupters
How many MOA are represented in
this list of herbicides?
•
•
•
•
•
•
•
Tordon 22K
Transline
Curtail
Banvel (Clarity)
Garlon
2,4-D
Redeem
?
Range and Pasture
Herbicide MOA
• Plant Growth Regulators
• Amino Acid Biosynthesis
Inhibitors
Plant Growth Regulators (PGR)
Tordon 22K, Transline, Curtail, Redeem, Banvel,
2,4-D
 Referred to as synthetic auxins (regulate growth in
plant tissues)
 Translocate in both xylem and phloem.
 Can act at multiple sites in a plant to disrupt
hormone balance and protein synthesis
 Abnormal growth resulting in twisting stems
 Stems swelling due to rapid cell division
Plant Growth Regulators (PGR)
Accumulation at growing points
Specific biochemical change responsible for
killing plant is not known (probably several
processes)
Grasses are not susceptible (may be due to
differences in vascular tissue structure or
differences in translocation or metabolism)
Common Leaf Symptoms from PGR
Exposure
normal
cupped and blistered from
PGR exposure
Foliar PGR Application
short internode
accumulation
In new growth
Root Absorption of
Plant Growth Regulator Herbicides
translocation to
growing point
swollen
hypocotyl
callus formation on roots
lack of root
development
Amino Acid Inhibitors
(Glyphosate, Escort, Plateau)
• Very important group of herbicides
• Roundup introduced 1971
• First sulfonylurea introduced in 1979
(Telar)
Amino Acid Inhibitors
Prevent synthesis of certain amino acids
produced by plants but not animals.
Excellent foliar and root absorption
Broad weed spectrum
Translocates to shoot and root new growth
Plants stop growing shortly after application
Plant death may be slow (10 days+)
Plateau or Escort Injury Symptoms
Stunting
Chlorosis of
youngest tissue
Glyphosate (Roundup) Drift
chlorosis
stem proliferation
shortened
internodes