Herbicide Resistant Crops
Adequate weed control is an essential component of profitable crop production, regardless of the
farming system. Depending on the crop and weeds present, uncontrolled weeds can:
• reduce yields by 50 percent or more
• impair crop quality through reduced seed size, contamination of the harvested crop with
weed material (some of which is potentially toxic or unpalatable) or discoloration of the
harvested crop
• increase the likelihood that the crop will be attacked by insects or diseases
• increase harvest losses.
Weeds can be controlled mechanically (by cultivation or hoeing), chemically (with herbicides) or
culturally (e.g., crop rotation). Most farmers in North America rely on a combination of these
methods. In general, a combined approach including herbicides is more economical, and often
more effective, than reliance solely on mechanical and cultural control practices.
The use of herbicides to control weeds depends on the ability to kill weeds without damaging the
crop. Herbicides can be divided into two broad types:
• selective, which affect only certain species or families of weeds
• non-selective, which kill almost every type of plant they contact.
Herbicide resistant or tolerant crops are not new. Indeed, natural crop resistance or tolerance to
certain herbicides is a prerequisite for herbicide-based weed control programs. Most weed control
programs rely on selective herbicides, products that kill certain species or types of plants but do
not harm the crop or other types of weeds within the crop.
Recently, genetically enhanced crops with resistance to non-selective herbicides, such as
Roundup (which will kill virtually all plants it contacts), have been developed through genetic
engineering. Crops with resistance to a number of other herbicides, such as Liberty, are also
being developed. Previously, non-selective herbicides could be used only when a crop was not
growing in the field (e.g., before planting or after harvest), making control of some serious weeds
very difficult. Development of herbicide resistant varieties has now made it possible to use certain
non-selective herbicides in a growing crop.
Compared to the use of selective herbicides, non-selective products offer several potential
advantages:
• Application of fewer herbicides to a crop. In crops such as corn and soybeans, growers
often need to apply two or more selective herbicides to control all the weeds present
(e.g., one to control grasses and another to control broadleaf weeds. In some cases, a
non-selective herbicide is also required before the crop is planted or after it is harvested
to control other weeds). With non-selective herbicides, one product, applied at the proper
time(s), will usually control virtually all weed species.
• Ability to control weeds that previously could not be controlled in a particular crop
because of the absence of a suitably selective herbicide.
• Ability to control weeds that have become resistant to certain selective herbicides.
• Reduced cost. Roundup, for example, is less expensive than many selective herbicides,
especially if more than one is required. (For example, in one study, over half the growers
using Roundup Ready soybeans reporting saving more than $7.00 per acre.)
• Fewer applications. Often one trip over the field is sufficient, whereas 2 or 3 may have
been required in the past.
Adequate weed control is an essential component of profitable crop production, regardless of the
farming system. Depending on the crop and weeds present, uncontrolled weeds can:
• reduce yields by 50 percent or more
• impair crop quality through reduced seed size, contamination of the harvested crop with
weed material (some of which is potentially toxic or unpalatable) or discoloration of the
harvested crop
• increase the likelihood that the crop will be attacked by insects or diseases
• increase harvest losses.
Weeds can be controlled mechanically (by cultivation or hoeing), chemically (with herbicides) or
culturally (e.g., crop rotation). Most farmers in North America rely on a combination of these
methods. In general, a combined approach including herbicides is more economical, and often
more effective, than reliance solely on mechanical and cultural control practices.
The use of herbicides to control weeds depends on the ability to kill weeds without damaging the
crop. Herbicides can be divided into two broad types:
• selective, which affect only certain species or families of weeds
• non-selective, which kill almost every type of plant they contact.
Herbicide resistant or tolerant crops are not new. Indeed, natural crop resistance or tolerance to
certain herbicides is a prerequisite for herbicide-based weed control programs. Most weed control
programs rely on selective herbicides, products that kill certain species or types of plants but do
not harm the crop or other types of weeds within the crop.
Recently, genetically enhanced crops with resistance to non-selective herbicides, such as
Roundup (which will kill virtually all plants it contacts), have been developed through genetic
engineering. Crops with resistance to a number of other herbicides, such as Liberty, are also
being developed. Previously, non-selective herbicides could be used only when a crop was not
growing in the field (e.g., before planting or after harvest), making control of some serious weeds
very difficult. Development of herbicide resistant varieties has now made it possible to use certain
non-selective herbicides in a growing crop.
Compared to the use of selective herbicides, non-selective products offer several potential
advantages:
• Application of fewer herbicides to a crop. In crops such as corn and soybeans, growers
often need to apply two or more selective herbicides to control all the weeds present
(e.g., one to control grasses and another to control broadleaf weeds. In some cases, a
non-selective herbicide is also required before the crop is planted or after it is harvested
to control other weeds). With non-selective herbicides, one product, applied at the proper
time(s), will usually control virtually all weed species.
• Ability to control weeds that previously could not be controlled in a particular crop
because of the absence of a suitably selective herbicide.
• Ability to control weeds that have become resistant to certain selective herbicides.
• Reduced cost. Roundup, for example, is less expensive than many selective herbicides,
especially if more than one is required. (For example, in one study, over half the growers
using Roundup Ready soybeans reporting saving more than $7.00 per acre.)
• Fewer applications. Often one trip over the field is sufficient, whereas 2 or 3 may have
been required in the past.
