Weed control techniques

The focus of this chapter is on various nonchemical weed control techniques and the challenges involved when they are used as replacements for herbicides in com production. 

The limitation in cropping systems, lack of rotation of herbicide chemistry or mode of action, limitation in weed control techniques, reduction of dose rates, etc. are major drivers for the selection of herbicide resistances. Regular country based surveys often make clear that farmers are aware of the problems and their causes. A survey in Germany in 2004 showed that 94% of the farmers are aware that the repeated use of the same herbicide, and 89% that the reduction of dose rates, causes the development of herbicide resistance. However, 86% of the farmers are forced to reduce their costs and they do not have a lot of scope with their weed management techniques [6]. 

Intensive soil cultivation techniques and stubble burning were always common weed control techniques in agricultural areas in the past. The increasing limitation or ban of stubble burning caused increasing weed coverage, an increasing... 

Chemical weed control in the tropics is still in an experimental stage in most crops. With the exception of sugar cane, few applications have been made on a commercial scale. Even in the sugar cane, where 2,4-D is used almost universally, there is considerable variation in the techniques, the kind of 2,4-D employed, and the use of subsidiary chemicals. This is partly due to different environmental conditions in operation at various times and situations, including the types of weeds present, age of the weeds and crop, soil, and rainfall. Personal idiosyncracies are also an important factor. 

While allelopathy is not covered in this chapter, excellent weed control can be achieved at reduced herbicide rate when used in conjunction with allelopathic rice varieties. Therefore, selection of highly allelopathic crop varieties, either through traditional breeding or using genetic engineering techniques, may also provide novel and low input approaches to weed control. 

Ascard, J. 1998. Comparison of flaming and infrared radiation techniques for thermal weed control. Weed Research 38 69-76. 

Herbicides have resulted in a great improvement and diversity in weed management techniques among the various crops grown in North America. An example closely correlated with the triazine herbicides is that of row crop production in the Midwest. If we follow the trends of com and soybean production, we see how the management of weed control has evolved in response to economic, cultural, and social influences and needs. Because the State of Illinois... 

During the late 1950s and early 1960s, most soil-applied herbicides typically did not receive mechanical incorporation, and when rain was insufficient, lacked reliability in controlling weeds. The reason for the slow adoption of mechanical incorporation techniques was probably three-fold (a) banded applications were preferred from a cost standpoint (b) the advantages of soil incorporation were not universally recognized and (c) the equipment and techniques for adequate incorporation were not available. Poor soil incorporation not only resulted in poor weed control, but in some cases resulted in crop injury. Simazine, in spite of its good weed control spectrum in corn, was never widely used in the Central Plains. Its lack of acceptance was attributed to its soil residual with the potential to injure... 

Yield loss in fruit and nut crops caused by weeds that are not adequately controlled by available herbicides or weed management techniques was estimated at 450 million annually in the United States (Chandler et al., 1984). 

Farmers use cultivation and herbicides in their weed control programs because of their complementary nature in controlling weed species that are missed if exclusive reliance were to be placed on either technique alone. One way to decrease herbicide use with additional cultivation while controlling weeds in the corn row is to band the herbicide over the row of corn plants. Essentially, the herbicide controls the weeds within the row, while the weeds between the rows are effectively controlled with mechanical cultivation. 

Such techniques are generally categorized under the term forest vegetation management and involve the use of machinery, fire, and or chemicals during silvicultural practices such as site preparation, weed control for plantation establishment, pine release from overtopping brush, timber stand improvement, etc. 

There are no approved chemical methods to control weeds in organic crops. Growers have to rely primarily on preventive or physical measures to maintain weed control. These measures include rotation, timing of cultivation, undersowing and the use of mulches. Physical methods may also be used and these include hand weeding, the use of mechanical techniques such as brush hoes and thermal destruction. 

Si other control techniques in an integrated weed management system. Many... 

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