1. Intro to Chemical Weed Control
Plant Science 280
Mr. Gomes

2. Herbicides
Defined as “a chemical substance or cultured organism used to kill or suppress the growth of plants.”
Designed to disrupt the physiology of plants over a long enough period of time to kill them or severely reduce their growth
Most people lump everything into a broader term of “Pesticide”
Herbicide is one of several sub-categories

3. Herbicides
Herbicides are by far the broadest category within the pesticide umbrella
Differ from other pesticides because their sphere of influence extends beyond the ability to kill plants
Change the chemical environment of plants
More easily manipulated than the climatic, edaphic, or biotic environment

4. Herbicide Control Herbicides can help;
Reduce or eliminate labor and machine requirements
Modify crop production techniques
When used appropriately, are production tools that increase farm efficiency
Reduce horsepower

5. Herbicide cont.
Ultimately, understanding nature, properties, effects, and uses is essential in modern weed control
Herbicides are not exclusive to weed management, but dominate the developed world
Can’t be ignored, whether liked or deplored
Ignoring their impact can lead to an inability to solve weed problems
Delays in developing better weed management systems

6. History of Chemical Weed Control
Agriculture is usually broken into three Era’s
The Blood, Sweat, and Tears Era
The Mechanical Era
The Chemical Era

8. Blood, Sweat, and Tears
Dominates virtually all of the existence of mans use of agriculture post hunter gatherer
Famine and Fatigue were common
Inadequate food supplies were frequent
Most people were farmers, and most farms were small
Still see this today in parts of the world
In 2010, 13% of the worlds 7 billion people were classified as “hungry” (1 in 7)
Those that are, generally live on the equivalent of 2 US $’s a day

9. The Mechanical Era Began with the invention of labor-saving machines
Is generally thought to have began around the late 18th century
Eli Whitney in 1793
Cyrus McCormick reaper in 1834
Moldboard plow in 1837
In farmers supported 5 non
supported 6
supported 10
supported 40
Today 1 supports roughly 100 IS, and several non

11. The Chemical Era Consensus is of 1930 rapid development
Began when N fertilizer became readily available
Production of newly available Hybrid Corn
First experiments began in 1913 with Henry A Wallace who founded Hi-Bred Corn Company in 1926
1945 Pesticides revolution begins

12. History
First synthetic organic chemical used for selective weed control in cereals???
2-(1-methylpropyl)-4,6-dinitrophenol (dinoseb) introduced to France in 1932
Historians of weed science note 1941 as the year 2,4- dichlorophenoxy acetic acid is first synthesized
Noted to have selective control of some broadleaved weeds and grasses in large seeded crops like beans

13. History Cont.
Originally designed with the intent of being a plant growth regulator
Later noted that the molecules had physiological activity on;
Cell elongation
Morphogenesis
Root development
Fruit development
University of Chicago Botany department concluded that it’s use as an herbicide was more logical and effective
First patent for 2,4-D happens in 1945

14. When the time is right…
This all coincided with a multitude of factors allowing for the herbicide revolution to blossom
It came at a time when genetic improvements and hybridization was taking off
The country was ready to improve, coming off the hardest economical time of American history
Farmers welcomed new technology to improve weed control
Profitability was minimal, they needed to be more efficient
Philosophically, farmers were willing to accept that part of their task was to control nature

15. But when did it really begin???
In 1000 BC Greek poet Homer discussed the use of sulfur in pest control
Theophrastus in 300 BC, use of olive oil to kill unwanted trees
Romans used salt to kill crops when they sacked Carthage in 146 BC
1763 nicotine was used for aphid control
1803 copper sulfate was used as a foliar for disease
1855 sulfuric acid was used for selective weed control in wheat and onions

16. Fun Facts
In 1933, corn sold for 10 cents/bushel and less than 1% of Iowa was planted with hybrid corn
By 1943, 99.5% of Iowa was hybrid corn
Yields went from 24.1 bu/ac to 31 bu/ac
By 1981 it was 109, and 173 by 1973
Less than 1% of the population farms
Number of family farms has decreased, while acres /farm has increased
90% of farms in the US are family owned
3% are corporate, but capture 28% of total sales
3.6% of US farms capture 56% of all Ag Sales

17. Advantages of Herbicides
Energy Use
Herbicide use accounts for only 3% of energy in ag production. Ag uses 18% of all energy used in the entire US Food System. Petroleum based
Time/Profit
Increased yield by better weed management and earlier planting. Availability
Estimates show net losses of over $21 Billion, and an increase of 220 million acres on the top 40 crops
Labor Requirement
Statistics show an $8/acre herbicide app can replace 55 hours or labor ($41/acre)
Organic veg labor can cost over $1,000/ac
But, progress has a price. Creative destruction
Tillage
Cultivation can injure crop roots and foliage
Soil erosion (1 billion tons in 1997) and soil structure benefits

18. Disadvantages Cost Mammalian Toxicity Environmental Persistence
Weed Resistance
Monoculture
Other

19. Disadvantages Cont. Cost Mammalian Toxicity
New chemistries are much more expensive as older chemistries leave the market
Research and developmental costs eliminate some crops
Equipment for use
Societal cost?
Use around animals an people as we experience more urban sprawl
DDT
Residue???
Pesticide poisoning???

20. Environmental Persistence
Disadvantages Cont.
Environmental Persistence
Weed Resistance
Half life
Longevity in the soil
Effects on plant rotation and plant back
Drift and inappropriate applications
Increasing concern from weed scientists, manufacturers, and growers
Changes in chemistry to adjust, legislation
GNO is not the answer long term necessarily

21. Disadvantages Cont. Monoculture Other
US Ag is characterized by monoculture
Loss of diversity can be challenging
Sustainability
Is much more conducive to selective herbicides
Idea of eliminating all life but crops
Disposal
Invitation to more invasive species that could be far more harmful1