Intro to Chemical Weed Control Plant Science 280 Mr. Gomes

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

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

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

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 in 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

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

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

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 1830 4 farmers supported 5 non 1910 1 supported 6 1930 1 supported 10 1965 1 supported 40 Today 1 supports roughly 100 IS, and several non

The Chemical Era Consensus is of 1930 repaid 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

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

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

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

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

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

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

Disadvantages Cost Mammalian Toxicity Environmental Persistence Weed Resistance Monoculture Other

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???

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

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