01 August 2013

Looking ahead to reduce herbicide use

Bindweed, silky apera, wild oats ... don’t they have pretty names, those weeds that gardeners and farmers struggle so hard to control! They compete mercilessly with cultivated plants. Yield losses in a weed-infested field can be considerable, but that’s not all: a prudent grower fights weeds because he knows that allowing them to flower and fructify is only storing up trouble for coming seasons.

There’s no getting away from it – weeds must be controlled. As they rarely, if ever, have natural enemies that can be roped in to render them harmless, the answer is frequently to use herbicides to control these crop pests. When the weather conditions are favourable, tillage implements can also be used to destroy young weeds. But it would be a mistake to think only in terms of chemical or mechanical ‘weeding’. The fact is that a field’s weed population is closely linked to the cropping system, each part of which affects weed dynamics. The weed population can vary in composition and density according to crop rotation, the tillage system and intercrop management. Agricultural levers can be actuated to restrict the development of the most undesirable weeds. For example, blackgrass trials ongoing for the last four years have shown that both emergence and seed production decreased drastically if the sowing date was put back. Tillage likewise has a perceptible depressive effect on blackgrass populations. That’s useful to know for anyone dealing with heavily infested land, especially if there is a large proportion of herbicide-resistant blackgrass!

Another point is that weeds and cultivated plants compete for light. Breeding programmes for various crops are aimed at creating varieties that achieve rapid ground cover as a means of limiting weed germination.

Agricultural, chemical, mechanical and genetic means: integrated weed management is advancing along various routes.

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