A lawn of Bermuda grass is highly desirable. But when Bermuda creeps into your flower beds, it becomes a weed. Some gardeners use herbicides to kill weeds back to the ground. An herbicide is any substance that will kill growing things. Most people associate herbicides with chemicals that kill specific weeds such as glyphosate or 2,4-D. But homemade herbicides may include vinegar or even boiling water.
The first reference to the use of an herbicide is in the Old Testament. Biblical texts refer to conquered cities being plowed with salt so that nothing would grow on their foundations. The first commercially made chemical herbicide did not appear until 1946. According to Wessels Living History Farm, farmers bought more than 631,000 pounds of 2,4-D that year. In the second year, they bought more than 5.3 million pounds of the herbicide.
Prior to the emergence of herbicides, farmers relied on cultivating to control weeds among plants. If weeds were missed or fields were not completely cultivated, the plants would steal nutrients from desirable crops. Regular use of herbicides that killed weeds also led to a dramatic increase in fruit and vegetable production. According to Wessels, one farmer tested three fields to see which practices were most effective. A field planted with corn and cultivated yielded 26.8 bushels of corn per acre. A field sprayed once with 2,4-D yielded 63.1 bushels per acre. A field sprayed three times yielded 84.5 bushels.
Gardeners can choose from two classifications of herbicides. Pre-emergent herbicides prevent seeds from germinating and growing. Post-emergent herbicides treat weeds once they have grown. Post-emergent herbicides include systemic, broad-spectrum and narrow-sprectrum herbicides such as broadleaf herbicides. Most post-emergent herbicides disrupt a plant's vascular system and slowly starve it of nutrients.
According to the Alabama Cooperative Extension Service, some people have concerns as to the long-term environmental effects of herbicides. Some of these concerns spring from the use of Agent Orange during the Vietnam War. Agent Orange is a combination of the herbicides 2,4D and 2,4,5-T, which were widely sprayed to defoliate forests and expose enemy troop movements. American troops exposed to Agent Orange reported illnesses that ranged from cancer to respiratory disease. Eventually, these diseases were linked to dioxins that were created by synthesis of 2,4,5-T. Because of this, 2,4,5-T is banned in the United States.
In recent years, some weeds have shown a developed tolerance to certain chemical herbicides. The USDA now recommends that gardeners change herbicides on a rotating schedule in order to prevent weeds from becoming resistant to specific chemicals.