Weed succession

Unsuccessful in controlling emergent aquatic weeds successful in eliminating filamentous algae and most submerged species... 

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). 

Extensive use of two more recendy developed classes of herbicides will further dramatically reduce the amount of appHed to control weeds. The sulfonylurea herbicides are extremely active compounds first discovered in the mid-1970s at DuPont they have been discussed extensively (78). Sulfonjiurea herbicides have experienced a rapid and widespread success since thek commercial introduction in 1982 with chlorsulfuron (Table 5). The sulfonylureas are appHed at rates of 2—75 g/ha. The chemistry of the sulfonylurea molecule permits the synthesis of a very large number of useful analogues, consequentiy many new herbicides are anticipated for crop production. As of this writing (1996), over 350 patents have been issued to about 27 agricultural companies covering tens of millions of stmctures known or expected to be herbicidaHy active. 

There is a further complication in shallow lakes containing macrophytes (aquatic flowering plants, pteridophytes, and macroalgae). These take up and accumulate nutrients from the water and from the aquatic soil in which they are rooted (sediment). Although these plants are sometimes classed as nuisance weeds, they nevertheless act as an important alternative sink for nutrients which are denied to the plankton. In recent times, a key role of macrophytes in the successful and sustained management of water quality has been identified and explained. ... 

The recommended field application rates for terrestrial weed control usually range between 0.28 and 1.12 kg paraquat cation/ha (0.25 and 1.0 pounds/acre), between 0.56 and 2.24 kg paraquat dichloride/ha (0.5 and 2.0 pounds/acre) — both applied as an aerosol — and between 0.1 and 2.0 mg/L for aquatic weed control, although sensitive aquatic plants may be affected between 0.019 and 0.372 mg/L (Ross etal. 1979 Summers 1980 Bauer 1983 Dial and Bauer 1984). Paraquat is frequently used in combination with other herbicides (Fletcher 1974 Summers 1980). Water solutions of the dichloride salt, which usually contain 240 g/L, have been successfully mixed with 2,4-D, substituted ureas, dalapon, amitrol, and various triazines (Anonymous 1963, 1974). 

Soil-applied pesticides have been successfully used to control soilbome diseases, weeds, and nematodes in most vegetable and fruit crops over the past decades. Toxicity of these materials to animals and humans and their environmental and economic costs (Pimentel et al. 1992 Ruzo 2006) raised serious environmental and human safety concerns, leading to the phase-out of the most effective and largely used chemical, the methyl bromide (Luken and Grof 2006), and the increasing restrictions on the applications of available pesticides (Perkins and Patterson 1997). The limited availability of chemicals resulted in an increased emphasis on... 

Crop rotation is a system where different plants are grown in a defined sequence. The well-designed crop rotation is the basis of the success in organic farming. Continuous monoculture is unacceptable due to the increased pressure of weeds and pathogens and difficulties with maintaining soil fertility. Diversity of crops in... 

Dicamba (3,6-dichloro-2-methoxybenzoic acid) is primarily used as a postemergence broadleaf herbicide, which interferes with normal plant auxin function, subsequently causing uncontrolled growth and the inhibition of the phototropic and geotropic function. Cumulative response results in plant death. The success of auxinic analogues such as Dicamba and 2,4-dichloropheno-xyacetic acid in weed control has led to widespread manufacturing and use. Estimated U.S. production for Dicamba was 5 million kg in 1990 [391]. 

In this way, Crosby demonstrates that environments and societies create one another, or more abstractly, they are mutually produced. The success of grasses depends on the success of the human settlement efforts that surround them, and vice versa. While these introduced Old World grasses benefited from European behaviors (grazing, and so forth), so too, settlers catered to the needs of the grasses, by planting and weeding, and animal grazing as they went. 

In this sense, weeds are desirable and inevitable plants that colonize barren areas allowing for later overgrowth and succession. The appearance of patches... 

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