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Maize

Maize fact file

  • 185 million ha grown worldwide in 2013
  • 44% increase in yield since 1995
  • 5 times higher yields in most productive countries than in least
  • 2nd most widely grown GM crop
  • No-till cultivation on 25 million ha in USA

Maize, often called corn, along with wheat and rice is one of the world’s top crops. Maize provides basic staple foods for much of the world’s population. All around the world maize grain is a basic livestock feed, and the crop can be cut while still green to make silage as a winter feed. Also, increasing amounts of maize in the US are being used to make bioethanol fuel.

Maize, perhaps more than any other crop, reaches both high and low extremes of sophistication, mechanisation and technology in crop production. But, all farmers need to maximise the yield and quality of their produce, while saving the costs, time and labor needed to grow it.

Broad-spectrum herbicides, led by the introduction of paraquat in the 1960’s, have allowed the adoption and growth of soil cultivation systems which do not rely on controlling weeds by burial from ploughing. In the US Corn Belt, although some of the most highly erodable land has been taken out of production, and erosion has decreased since the ‘dust bowl’ days of the 1930s, the average annual loss of soil by erosion has been estimated to be 14 tonnes/hectare, a rate way above what can be replaced by natural processes of soil formation.

Abandoning the mouldboard plow in conservation tillage systems saves cash, time and fuel, improves soil structure, reduces erosion and provides havens for wildlife. In spring, weeds or a cover crop such as rye, wheat or oats have to be controlled by a burndown herbicide, typically either paraquat or glyphosate.

Paraquat-based burndown sprays are more reliable than glyphosate when the weather is cold and rain falls soon after application. Particularly under such challenging weather conditions, paraquat will control weeds in a few days compared to glyphosate’s 2-3 weeks. Glyphosate is a systemic herbicide and gives a thorough kill of many perennials. However, intensive use of glyphosate has resulted in changes in the spectrum of weeds towards species which are harder to control and the evolution of resistant biotypes in some species which are no longer controlled by glyphosate. This has led to the development of integrated weed management systems. 

Maize cobs formingMaize cobs forming

In the US, it is becoming accepted that over-reliance on glyphosate and the concurrent reduction in diversity, will exacerbate weed resistance problems. No more than two applications of glyphosate should be applied to any one field over two seasons. Paraquat can provide the alternative means of effective and sustainable weed control.

Maize is usually grown in a rotation with other crops, often soybeans which improve the fertility of the soil for the following maize crop, reducing the need to apply nitrogen fertilizer. In warmer climates, it is possible to grow crops of maize and soybeans in the same season. However, a fast-turn around time between crops must be achieved and conserving soil moisture is important. No-till techniques and using fast-acting paraquat for weed control can provide this, often giving as much as a 10 day lead over any glyphosate program.

In less developed farming systems, paraquat is widely used to control weeds growing between rows of the standing crop. Because it is not systemic like glyphosate, so causes only minor contact damage when sprayed carefully or using shielded sprayers, and has no activity or residual effects via the soil, it provides a fast and effective alternative to the drudgery of manual weeding.