Exploring Herbicides Used
to Control Invasive Weeds
Herbicide History
Chemical Weed Control
Chemical weed control
• Advanced human ability to manipulate
environment to our advantage
Herbicide development
• Stimulus:
 realized chemical environment of plant easier to
manipulate than climatic, edaphic, or biotic
environments in which they grow
Herbicide Development
Herbicides used to:
• Reduce or eliminate labor and machine
requirement for ag production
• Modify existing crop production techniques
• Improve farm efficiency
• Reduce horse power and other energy
inputs
 Capacity to do work
 Obviously remembering herbicides are derived
from petroleum
Chemical Control History
Three ages of agriculture
• Blood, sweat, tears period
 Fatigue, famine
• Mechanical age
 1701 Jethro Tull; seed drill; horse hoe
 1791 Eli Whitney; cotton gin
 1834 Cyrus McCormick; Obed Hussey; reaper
 1837 John Deere; steel plow
• Chemical age
Chemical Control History
1200 BC armies salt & ash fields
1000 BC Homer wrote about sulfur &
pest control
470 BC Democritus, clear forests
w/hemlock juice in which lupine flowers
soaked
400 BC Theophrastus, trees killed by
pouring oil over their roots
Chemical Control History
146 BC Romans sack Carthage & salt
crop fields
1st Century BC Cato, amurca (watery
residue after oil drained from olives)
for weed control
1594 salt used for selective & nonselective weed control
1676 soot used for moss control
1785 soap boiler’s ashes for weed
control
Chemical Control History
70 AD, 1759 ferrous sulfate known to
be phytotoxic
1804, 1821 copper sulfate shown to be
phytotoxic
1896 copper sulfate used to selectively
control mustards in cereals
1854 salt (NaCl) first recommended in
Germany
Chemical Control History
1855 sulfuric acid used in Germany in
cereals & onions
1865 Bordeaux mixture France in grapes
for downy mildew; blackens yellow
charlock
1902 sodium arsenite used by Army
Corps Engineers for water hyacinth, LA
Chemical Control History
1906 carbon bisulfide soil fumigant for
thistle and bindweed
1914 petroleum oils used
1923 sodium chlorate first used France
for bindweed
1930 sulfuric acid used in England
1932 introduction of first organic
chemical weed control; DNOC
Chemical Control History
1940 ammonium sulfamate for brush
control
1941 Porkony synthesizes 2,4-D
1942 2,4-D growth regulator, not yet
reported herbicidal
1944 2,4-D herbicidal properties
recognized
1945 MCPA first tested as herbicide
Chemical Control History
 1946 first reported use 2,4-D for dandelion
control in turf
 1951 monuron effective grass control
 1958 atrazine & paraquat introduced
 1960 trifluralin available
 1960s pyridines introduced
 1971 glyphosate introduced
 Late 70s sulfonylureas introduced
 1980s imidazolinones introduced
 2003 pyrimidines introduced
Chemical Control Advantages
Economic
• Primarily due to decreased farm labor
Apply in crop rows where cultivation
impossible
• Also decrease tillage and subsequent injury
Preemergence treatments early season
weed control
Chemical Control Advantages
Decrease tillage soil destructive
effects
• Alterations to soil structure
Better perennial weed control
• Poorly control by hand labor
Decrease fertilizer, harvest, seed
conditioning costs
Chemical Control Disadvantages
Cost
• Although least expensive portion of weed
management
Toxicity
Environmental contamination
Restrict crop rotation
Non-target plant hazard
Weed shifts
Chemical Control Disadvantages
 Encourages monocultures
 Soil erosion – bare ground treatments
 Over dependence
• Tendency to make up for other poor mgmt
practices
 Application expertise & precision needed
 Pest resistance
 Inconsistent environmental interactions
 Waste disposal