Weed control: the future?

Insects and fungi can have the most visually dramatic effects on crops but weeds are an ever-present challenge through their competition for water, nutrients, space and sunlight. They are also costly to control: in terms of labour, small-scale farmers spend more than 40 percent of their labour time in weeding. As countries look to increased production from the small farm sector, effective but affordable weed control is a priority.

In the past, farmers had limited options for weed control, and many still do: uproot, hoe, transplant crops from nursery beds to give them a growth advantage over weeds, or abandon weed infested land and clear fresh ground. Herbicides may appear to offer other options but, while they have been widely and successfully used on commercial farms and on estates or plantations, they have had little appeal for small-scale farmers because of their cost, and because of the challenges of accurate and timely application. When used, total or unselective herbicides tend to be favoured. Few small-scale farmers use selective weed control agents or residual soil-acting materials. Perhaps that's as well since some residual herbicides can be pollutants in run-off water and there is increasing concern over residues of certain herbicides in crops that have not been treated with the care required. (see Biological control 'silver bullet')

Then there is genetic engineering, an option that may offer windows of opportunity for commercial farmers, particularly in Australia, US, Europe, Japan and parts of Latin America. For example, US scientists at the Red River Valley Agricultural Research Center, Fargo, N. Dakota are attempting to determine those genes that control dormancy in two weeds, which are a problem in the US (Wild oat, Avena fatua and Leafy spurge, Euphorbia esula). Similarly, research at the UK's Rothamsted Research Station is striving to produce wheat with fast growing leaf canopies, which could suppress competitive weed growth. But what of many other weed species and crops? And who is going to fund such research for the tropics?

Even enthusiasts for the technology find it difficult to provide convincing examples of how gene manipulation will help the mass of farmers in Africa, Asia and Latin America. So, as land pressure limits long-term fallows, and labour shortage makes hand pulling and hoeing more problematic, what can small-scale farmers, who face the challenge of feeding themselves and their increasingly numerous urban compatriots, do in the future? One answer may be to do what they do now, but rather more effectively.

Weed early, work easy
A common sight in the tropics is farmers attempting to remove weeds that are well grown. By this stage not only have the weeds developed strong roots and stems, making it difficult to pull or to cut with a hoe, they have already compromised crop yield by their competition. It seems as though farmers cannot bring themselves to recognise that weeding needs to be done before the weeds are too obvious to ignore. If only the hoe could be applied to weeds when they are seedlings, they would be killed before they have become serious competitors, and the work would be done more quickly and with much less effort. Admittedly another flush of weed seeds will germinate and will have to be hoed in its turn but, if hoeing is done early, two quick and 'light' hoeings can take less time and energy than one delayed hoeing. Furthermore, weeds are killed long before they have a chance to set and disperse seed, reducing future weeding.

Weeding early is a strategy that should prove advantageous for another reason: hoeing at the seedling stage should suit women and even children since they could use lighter hoes to do the work. Traditional hoes are heavy, have short handles and are used with the hoer's back bent in order to apply the chopping and digging action for which they are used. But, why use a digging hoe for weeding if the work can be done with a lighter hoe, and one with a longer handle? Such a hoe can be used with the back almost straight and with far less effort. It is even more advantageous if such light hoes, if they are to be used by children, also have proportionately shorter handles.

Traditional habits are difficult to change, and often only tools of traditional design are available to farmers. But, confronted by the need to increasingly depend on women and children for this vital task, it is essential that early weeding should be encouraged and that light hoes be made available.

In February 2003 the Biennial Weed Science Society Conference for Eastern Africa, held in Malawi, concluded: "This discipline has not only the task to protect crops from losses due to weeds, but also the task to develop methods permitting reasonable engagement of available manpower resources, decrease energy input to a minimum, and secure the fertility of the soil." Agronomists may draw their own conclusions on which are the most realistic options for achieving these targets.