Yield weed control

Chemical, cultural, and mechanical weed control practices have been relatively successful ia reducing yield losses from weeds (448). However, herbicide-resistant weed populations, soil erosion, pesticide persistence ia the environment, and other problems associated with technologies used (ca 1993) to control weeds have raised concerns for the long-term efficacy and sustainability of herbicide-dependent crop production practices (449). These concerns, coupled with ever-increasing demands for food and fiber, contribute to the need for innovative weed management strategies (450). 

Weeds constitute one of the major problems in agriculture. They are an important constraint on yield in most crops across the world. These days, growers spend much money on weed control. About 6 million ton of herbicides was sold in the world in 2006 and herbicides are the most used pesticides they form approximately 38% of the total amount of pesticides (FAO 2006). Nowadays, an effort to tighten rules for authorization and application of pesticides, research and develop products that are target-specific, degrade quickly and do not accumulate in the food chain, exists in... 

Intercropping may facilitate weed control if intercrops are more weed competitive than sole crops or are able to suppress weed growth through allelopathy (the weed species is more susceptible to such phytotoxin than crops). If intercrops do not suppress weeds more than sole crops, they should provide yield advantages due to better utilization of resources or by converting resources than in case of sole crops (Liebman and Dyck 1993). 

Non-crop plants associated with the crop species offer possibilities for allelopathic weed control. In this study Brassica campestris (wild mustard), which is an important weed in Santa Cruz County, and broccoli, a common crop, were intercropped, The allelopathic potential of both species and the changes in this potential throughout their life cycle were demonstrated with experiments in the laboratory. Effects of different planting densities and sowing time of canpestris on the crop yield are analyzed. Preliminary steps to separate the physiologically active compound(s) are described. The possibilities for the use of Brassica campestris in agroecosystem design as a non-crop plant that promotes pest control are described. 

The remainder of this discussion examines the possibility of a direct feedback mechanism in response to light as an explanation for crop yield reduction from early weed presence. Three types of data will be examined 1) results of our research on velvetleaf interference with light in soybeans 2) a comparison of observed and estimated soybean yield reductions for weed presence versus leaf removal and 3) the poor correlation between weed control and crop yields. 

Table 11. Relationship Between Percent Weed Control and Crop Yield, North Central Region, 1983 and 1984...

Crop Yields for 90% or Better Weed Control Compared to 3 Lower Control Ranges ... 

The average obtained after dividing the yield for 90% or better weed control by the yield in the given lower weed control range. — 69 yield comparisons. 

Melander, B. and Rasmussen, G. 2001. Effects of cultural methods and physical weed control on intrarow weed numbers, manual weeding and marketable yield in direct-sown leek and bulb onion. Weed Research 41(6) 491-508. 

Rasmussen, I.A. 2004. The effect of sowing date, stale seedbed, row width and mechanical weed control on weeds and yields of organic winter wheat. Weed Research 44(1) 12-20. 

This book is about the revolutionary impact of the triazines herbicides, likely the most important class of agricultural chemicals ever developed. For five decades the triazines have provided weed control in more than 50 crops around the world and have helped farmers boost yields and produce enough food to feed a rising global population. The triazine herbicides, and especially atrazine, are the most well-researched herbicides in history, with thousands of scientific studies on their safety to humans and the environment. Data from studies on the triazines have been evaluated extensively by regulatory authorities around the globe to ensure their safe use. 

The historical record reveals that herbicides have replaced or reduced the use of hand weeding and cultivation for weed control, with an associated reduction in cost and an increase in yield. Today herbicides are used routinely on more than 90% of the area of most US crops, representing 87 million ha of cropland (Gianessi and Reigner, 2007). 

The benefits of the triazines in multiple cropping systems range from their application flexibility, effective weed control, soil residual activity, and crop selectivity to their important role in resistance management and conservation tillage. The triazines also have made a major impact on agricultural sustainability and crop yields, as evidenced by the use of atrazine, especially in com. 

Geigy started production of simazine in 1956 in Schweizerhalle, near Basel, Switzerland 2 years later, atrazine also was produced. Use of triazines for weed control to improve crop yields grew quickly, and a production facility was installed at McIntosh, Alabama in 1959. Smaller production units were operated in Mexico, Brazil, and Australia, and important development work by Geigy led to improved production processes. In 1970 a continuous process production unit was built by Geigy Agricultural Chemicals in the United States. 

This chapter describes the role played by atrazine, which became commercially available in the 1950s and was used extensively in com and for amenity (beautification) weed control. Corn area and yields have expanded significantly during the period since the introduction of this herbicide. Atrazine played a significant role in facilitating this expansion. 

The CEEPES (1993) model describes farmer weed control choices with approximately 500 herbicide and tillage options. The expert opinions of Iowa state economists and weed control specialists were used to obtain the yield and cost changes shown in Table 12.3 for the entire country. The description of the CEEPES model does not explain how replacement herbicides were chosen. However, the actual herbicides chosen are given, and they are very different from those in the Pike et al. (1994) and Danielson et al. (1993) studies. The state weed scientists in the Pike et al. (1994) and Danielson et al. (1993) studies estimated that cyanazine, dicamba, 2,4-D, and bromoxynil would replace 80% of the atrazine on com, while the CEEPES experts said that these four herbicides would only replace 36% of... 

The Ciba Crop Protection and Novartis Crop Protection studies use the AGSIM-2 model. In addition, these studies have shown that a comprehensive study should include all regions and all crops. The baseline herbicide use pattern is based on those weeds that are controlled in all areas on all crops. The Ciba Crop Protection and Novartis Crop Protection studies include cost changes on 19 other crops besides com and sorghum. In addition, yield changes on sweet com and popcorn are included because the weed control problems are similar to those in field corn. 

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