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Awash with weeds

Weeds in vleis are difficult to manage and if left unchecked can result in 100 per cent losses (Jim Ellis-Jones, Silsoe Research Institute)
Weeds in vleis are difficult to manage and if left unchecked can result in 100 per cent losses
Jim Ellis-Jones, Silsoe Research Institute

Farming on Zimbabwe's environmentally-sensitive vleis (wetlands) may be a contentious issue, but with their moist soils that allow two or even three crops each year, the attractions of cultivating these areas are plain to see. However the potential of the soils is rarely reached as rice and maize intercrops are plagued by perennial weeds. Hand-hoeing makes little impact and until now, research into alternatives has been lacking due to legislation that attempts to conserve the vleis by restricting their use.

The most troublesome weeds are sedges (Cyperus Spp), for example C. esculentus and C. rotundes, but perennial grasses such as the Panicum species are also difficult to control and farmers are often forced to abandon the vleis. Waterlogging, especially of maize, is another major problem. But if the waterlogging can be overcome, says Arnold Mashingaidze from the Crop Science Department of the University of Zimbabwe, the crops are stronger and more able to suppress the weeds.

Technologies on trial

The University of Zimbabwe is one of three research organisations* involved in a collaborative project, which is working with farmers to determine the best approach for combating both the waterlogging and the weeds. With suggestions from the farmers, trials on farmers' fields have included testing drainage furrows and ridges or beds in order to tackle the water problem, as well as nine weeding treatments, including combining hand hoeing with the mechanical process involved in making the ridges or beds, use of herbicides, and increasing plant population to suppress the weeds.

Farmers discussing the merits of maize and rice intercrops (Jim Ellis-Jones, Silsoe Research Institute)
Farmers discussing the merits of maize and rice intercrops
Jim Ellis-Jones, Silsoe Research Institute

The trials were carried out over two seasons on maize, rice and maize-rice intercrops across four areas, including smallscale commercial farms, and resettlement and communal areas. High returns to labour were experienced in both years using herbicide. However, when labour is readily available, traditional farmer practices were considered more productive. With the beds/ridges approach, the maize was planted in water-free soil at the highest point of the bed or ridge, while the rice was planted in the furrows where the water collects. Beds and ridges were the best technologies in terms of crop vigour for both the maize and rice, reported Mr Mashingaidze. This was better than planting on the flat, which is the normal farmer practice and it was also considered better than drainage furrows. And the yields and mid-season assessments proved the point. Yield increases of up to 30 to 40 per cent were achieved for rice when planted at a higher density than usual. This was considered a particularly successful technique, as it did not require use of herbicides. Herbicides are a new technology for the vlei farmers, the main problem being affordability.

In the future, declining labour availability, aggravated by HIV/AIDS, is set to further stimulate demand for herbicides. Coupled with increasing local costs of imported commodities due to the deteriorating economic conditions in Zimbabwe, there is a real challenge to provide herbicides and technologies that are not only effective in beating weeds, but are within the financial reach and labour constraints of the average farmer. Making this possible would also have the environmental benefits sought by policymakers, by avoiding abandonment of infested land and preventing over-use of the vleis at the expense of future generations.

*The University of Zimbabwe, the Natural Resources Institute, and Silsoe Research Institute (both in the UK). Funded by the UK's Department for International Development (DFID) Crop Protection Programme.

Date published: January 2004


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