This website was created for Biology 361: Genetically Modified Organisms at Davidson College.by Mike Chase and Monica Siegenthaler

Herbicide Resistance
Many crops and weeds have created a tolerance to herbicides by prevention of translocation and/or absorption into the cells. Resistance selected for when a common mode of action is used repeatedly over crop seasons. Weeds that are susceptible to that herbicide will decrease in numbers from year to year, allowing other weeds that are resistance to the herbicide to establish themselves in the crop fields. If the same mode of action herbicide is used each year, then there is no disruption of the reproductive cycle of the resistant weed, resulting in a continually growing population of the resistant weed (Gunsolus, 2002).

Monsanto's "Roundup Ready" soybeans are engineered to resist the widely used herbicide Roundup. Crops survive in fields sprayed with Roundup, but weeds are killed. Photo: Courtesy of Monsanto. Permission pending from http://www.npr.org/programs/morning/features/2001/nov/biotech/011115.crops.html
 

Prevention of Weed Resistance

To prevent a weed from becoming resistant to the current herbicides used, farmers must follow three techniques:

  1. Herbicide Rotation

    The mode of action of each herbicide must be rotated to from crop season to crop season. If there are multiple applications of herbicides within a single planting season, each individual application should have a different mode of action then the previous treatment (Future Trends In Weed Managment, 2002).
  1. Crop Rotation

    Crop rotation and herbicide rotation go hand in hand. If the crops are rotated each planting season, then the corresponding herbicides will also be rotated. As long as each crop does not have the same mode of action herbicide, the rotation should eliminate the growth of a single powerful weed. The rotating crops also disrupt weed life cycles and stops any weed from becoming established in a field (Future Trends In Weed Managment, 2002).
  1. Post Emergence Practices

The cultivation or herbicidal treatments of post-emergent weeds are also possible solutions to controlling resistant weeds. The cultivation of weeds before they go to seed will greatly reduce the spreading of certain species of weeds (Future Trends In Weed Managment, 2002).
  Resistance to Glyphosate

Glyphosate (roundup) is the world’s most commonly used herbicide.  Monsanto, the biotech creator of Glyphosate, claims the use of glyphosate-resistant crops will reduce the use of normal toxic herbicides. It is argued that in the long run, other factors will play into the total chemical use in the future. Other considerations that must be accounted for included:

  1. Glyphosate resistance in weeds
  2. Presence of glyphosate-resistant volunteers (unintentionally grown plants). These plants will require the use of more chemicals to control their population.
  3. The use of glyphosate may increase insect populations and the use of insecticides and fungicides to control them.

(Connor, 2002)

 

 

 

© Copyright 2002 Department of Biology, Davidson College, Davidson, NC 28035
Send comments, questions, and suggestions to: michase@davidson.edu or mosiegenthaler@davidson.edu