Weed Management Tools

The Importance of Weed Management

From a human perspective weeds have been noisome or offensive plants since about 10,000 years ago when man first domesticated wild plants and heralded in crop production.

I will go root away the noisome weeds which without profit suck the soil’s fertility from wholesome flowers – William Shakespeare

It is safe to say that man will have to cope with weeds for as long as crops are cultivated under natural conditions. Like diseases and insect pests, the other two major groups of noxae or harmful organisms, weeds cause crop yield losses which generally necessitates implementation of control measures.

Weeds do harm to crops in ways distinctly different to the way pathogens and insects attack crop plants (parasitic weeds is an exception here). Weeds interfere with the growth and development of crops through two phenomena, namely: competition and allelopathy. Through competition for water, light and nutrients, weeds rob the crop of essential resources for growth. Allelopathy involves the production and release into the environment of toxic compounds that can impede and prevent normal development of other plants.

Weeds not only cause reductions in crop yield but also in the quality of such products. Moreover, weeds can physically impede the harvesting of crops, and certain weeds can act as hosts of pests and disease-causing pathogens.

Oerke et al. (1994) in a survey focussed on developed countries compared yield reductions for the world’s major crops (barley, wheat, maize, rice, cotton, soyabeans) in terms of the roles of weeds, pests and disease-causing organisms. They found that weeds, in the absence of crop protection measures in the afore-mentioned crops, caused yield reductions ranging from 21 to 36%, which on a per crop basis, nearly equalled the sum total of losses attributed to pests and diseases. This explains why the contribution of herbicides to total pesticide usage is estimated to range between 60 to 70%. Even with the application of crop protection measures, Oerke et al. (1994) reported yield losses attributable to weeds to range between 10 – 15% in the afore-mentioned crops, which is of similar magnitude to yield reductions attributed to either diseases or pests.

In sub-Saharan Africa about as many small-scale farmers attend to crops on the amount of hectares available for crop production – 170 million (Gianessi & Williams, 2011). Together, smallholder farmers contribute 70% of crop products, with the rest coming from commercial-scale enterprises. In Africa, weeds are considered the major constraint to crop production, and crop yield losses often can amount to 100% for a variety of reasons, ranging from lack of appropriate knowledge, through economics to environment. Significant untapped potential in crop production on the African continent can be unlocked simply by adopting herbicides as an integral component of best agricultural practices. Production potential on the continent can be boosted even further by the adoption of GM technology, which currently is lagging far behind the rest of the world – only three of 53 countries on the continent have thus far adopted GM crops, i.e. South Africa, Burkino Faso and Egypt.

The purpose with this website is to promote the adoption of appropriate measures for achieving effective weed control for the sake of maximising crop yield and quality. In order to achieve this goal, weed management is considered an integral part of the bigger set of crop production practices, which as a whole, constitute “Best Agricultural Practices”.



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