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Principles of Weed Management Introduction

The correct definition of a ‘weed’ is a very subjective, but in simple terms it can be described as an undesirable plant species in that particular habitat. Weeds are considered undesirable as they have the potential to reproduce rapidly and if left unmanaged can have a significant effect on the economics of the crop production. Any plant by definition can be classed as a weed. Even crop species themselves are occasionally weeds, as they can occur in the subsequent crop, often referred to as ‘volunteers’ and require some method of control.

Generally weeds are very successful species at colonising land, as they are very competitive, aggressive and have the ability to adapt to varying environmental conditions due to complex survival mechanisms.

One of the major disadvantages of weed species within an arable cropping system includes their ability to compete with the crop for water, mineral nutrients, space and light, which in turn will have a major impact in the final yield of that particular crop. Their presence within the crop affects the crop environment and disease pressure.

If left until harvest weed species can hinder the combine harvesting of the crop, by either causing the crop to lodge pre-harvest or by physically blocking the mechanics of the combine slowing down the whole process and inevitably wasting valuable time and money. The weed seed can contaminate the grain sample and lead to a poor quality of crop seed, therefore also reducing the profit.

Modern agricultural systems tend to favour minimum tillage and early drilling to increase profit margins, but careful consideration must be made in situations where troublesome weeds are present. The ability to identify weed species at an early growth stage will increase the choice of control mechanisms, whether they are cultural or chemical control.

However, not all weeds are so aggressive and actually can be desirable at particular thresholds, as they provide an important source of food and shelter of animals and birds. Some species are now so rare that it may be considered desirable to encourage their survival. It is therefore important to get the correct balance of weed control within the crop by careful forward planning.