Weed control objectives

For farmers, controlling weeds in crops is absolutely essential. Lacy (1985) summarized weed control objectives as reducing the competitive ability of an existing population of weeds in a crop establishing a barrier to the development of further significant weeds within that crop and preventing weed problems in future crops either from an existing weed reservoir or from additions to the weed flora. 

In essence, the overall objective of chemical regulation is to minimise the aggregate cost of (1) agricultural losses due to weeds and weed control,... 

The primary breeding objectives for winter HEAR cnltivars are to increase seed yield, increase oil production, improve meal qnaUty, increase erucic add concentration, improve disease resistance and, for the winter habit types, improve winter hardiness and frost tolerance (Downey and Rdbbelen, 1989). The objectives for breeding spring HEAR cultivars are similar. Improved weed control via development of herbicide-tolerant HEAR cnltivars is also a major breeding... 

As new herbicides were introduced over the years, weed scientists and farmers looked for the best mixtures, rates, and ratios to determine where the new ones would fit. The objective was always to provide the grower with the most dependable and efficacious control of major weeds, with the least amount of herbicides and cost, and with little or no risk to the applicator, consumers, and environment. With corn, sorghum, sugarcane, and certain other crops, such mixtures most often included atrazine or other triazine herbicides. Many times as weed scientists or farmers would discuss the virtues and performance of new herbicides, they would state The new products performed well, but it sure helped to add a little atrazine. ... 

This approach should be used to enhance herbicide selectivity in crop varieties, to avoid carry-over injury, for specific and limited special problems, and for minor acreage and high value crops. A major objective of developing herbicide resistant crops should be to provide more flexibility in control of resistant weeds. 

Class C turf is mowed two to three times per year, usually never fertilized but control of certain broadleaf weeds may occasionally occur when infestations become severe. The key objective with this mowing frequency is to cut down seedheads (which result in brown color) and excessive vegetation which may harbor unwanted animals. An example of this type of turf area would be highway roadsides and remote industrial sites. Type I, herbicide Type I and Type II PGRs can be used effectively all be used effectively. One pass of the spray boom along each side of the highway provides sufficient vegetation control without the possibility of overlap injury. 

Usually the first phase is the functional phase the object must satisfy some functional requirement, for example, the mulch film must control growth of weeds. If degradation happens during this phase, it will be considered a negative factor. The second phase corresponds to the disposal phase, when the item must disappear and be recycled through natural processes. In this phase, fast and complete degradation is a positive factor. 

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