The importance of synthetic weed-killers is largely one of economics. Any other method of weed control is apt to be so expensive that the crop in question may be uneconomic to grow without herbicides. These alternative methods consist of hand-weeding, mechanical cultivation, and weed-suppressing crops.

Hand weeding is feasible only in subsistence cultivation, which is labour-intensive anyway. This high labour requirement results very largely from the need for weeding. Mechanical cultivation is much cheaper than hand labour, but it is also much less efficient than herbicides.

Some species of crop are referred to as 'cleaning crops' because they do much to suppress weeds. Potatoes are useful in the respect, and other crops, such as beans, can be useful if they are densely planted.

Herbicides are likely to remain an essential component of commercial agriculture, but we can take comfort from the fact that they are much less hazardous to people than the insecticides and fungicides.

A recent controversy has developed over the use of genetically modified crops that are immune to glyphosate. For example, glyphosate-resistant soybeans grown with this herbicide can produce a major reduction in weeds. But a crop such as canola (rapeseed) is open-pollinated and it tends to shed seed. Glyphosate-resistant canola can itself become a weed, and it can lead to various environmental and legal problems.

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