GMO COMPASS - Information on genetically modified organisms
  Feb 10, 2012 | 3:15 am
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 Breeding Aims

Herbicide resistant crops

Excessive weed growth forces crops to compete for sunlight and nutrients, often leading to significant losses. Because herbicides cannot differentiate between plants that are crops and plants that are weeds, conventional agricultural systems can only use 'selective' herbicides. Such herbicides do not harm the crop, but are not effective at removing all types of weeds. If farmers use herbicide resistant crops, 'non-selective' herbicides can be used to remove all weeds in a single, quick application. This means less spraying, less traffic on the field, and lower operating costs.

Bild vergrößern

Herbicides for controlling weeds in sugar beet fields (left: field treated with herbicides; right: without herbicides)

'Non-selective' herbicides: Not always useful

'Broad-spectrum', or non-selective herbicides are effective at killing a wide range of weeds. The problem is, they can also kill valuable crops. Therefore, broad-spectrum herbicides are only useful before seedlings emerge or in special cases like fruit orchards, vineyards, and tree nurseries.

Herbicide resistant crops are changing weed managment

Several crops have been genetically modified to be resistant to non-selective herbicides. These transgenic crops contain genes that enable them to degrade the active ingredient in an herbicide, rendering it harmless. Farmers can thereby easily control weeds during the entire growing season and have more flexibility in choosing times for spraying.

Herbicide resistant crops also facilitate low or no tillage cultural practices, which many consider to be more sustainable. Another advantage is that farmers can manage weeds without turning to some of the more environmentally suspect types of herbicides.

Critics claim that in some cases, the use of herbicide resistant crops can lead to an increase in herbicide use, promote the development of herbicide resistant weeds, and damage biodiversity on the farm. Extensive ecological impact assessments have been addressing these issues.

Among the field trials conducted on herbicide resistant crops, studies in the United Kingdom have shown that different herbicides and different herbicide application practices can affect the amount of wild plants on the farm. In comparison with conventional cropping systems, weed and animal populations were negatively affected by herbicide tolerant sugar beet and rapeseed, but biodiversity was increased with the use of herbicide tolerant maize.

Currently, two herbicide resistant cropping systems are common for soybean, maize, rapeseed, and cotton: RoundupReady (active agent: glyphosate) and Liberty Link (active agent: glufosinate).

See also on GMO-Compass:

 
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