Application of Herbicides

Today s herbicides can be applied in a variety of different ways to the crop. They can be applied as single component products or as combination products, using the different properties and weed spectrum of the components of the mixtures. 

Pre-emergence herbicides are applied pre-weed emergence and this will usually mean pre-crop emergence as well. Such compounds are taken up underground by the roots or hypocotyls of the weed. It is important for such compounds to possess some water solubility, in order that they become available to the germinating weed, but not so much that they are leached away from the weed germination zone. They must also be relatively persistent in the soil so that weeds that germinate over a period of time are all controlled. 

Pre-plant incorporated herbicides are applied before the crop is sown and are incorporated into the soil. Hence, they are also applied before weeds emerge. The reason for incorporation is usually because the herbicides are volatile and would be lost if they were not incorporated, or light unstable and they would be degraded if they remained on the soil surface. Volatility is a useful characteristic as it allows the redistribution of the compound throughout the soil following incorporation. 

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For many years, the primary means of hydrilla control has been the application of herbicides to affected waterbodies. Various... 

From January 1962 to April 1970, a program of aerial application of herbicides was conducted in Southeast Asia by the United States Air Force (USAF). At the conclusion of this program, considerable amounts of herbicide were left unused. 

Young, A. L., C. E. Thalken and W. E. Ward, 1975. "Studies of the Ecological Impact of Repetitive Aerial Applications of Herbicides on the Ecosystem of Test Area C-52A, Eglln,... 

Figure 4.6 Granular application of herbicides was quickly adopted by farmers who were already familiar with granular fertilizer applicators in the Com Belt. (Courtesy of Dr. Ellery Knake, Professor Emeritus, University of Illinois.)...

Midcontinent Herbicide Project. During 1989, a reconnaissance study of 147 streams in 10 midwestem states was conducted to determine the geographic and seasonal distribution of herbicides and their degradation products. Sites were selected to ensure geographic distribution and regional-scale interpretation of the data (Figure 30.4). The streams were sampled before application of herbicides, during the first major runoff period after application of herbicides,... 

Malac, B. F. 1961. Early indications of growth responses following foliar applications of herbicides. South. Weed Conf., Proc. 14 222-227. 

The environmental implication of the results with atrazine is that application of herbicides, which are widely used in corn agriculture, can lead to mutagenic plant metabolites in crops. More generally, this result suggested that, like mammalian metabolism of promutagens,... 

Improved crop varieties and protection methods have demanded the application of many herbicides and fungicides to attain increased crop yields, decreased food costs, and enhanced appearance of food. Without proper controls, however, the residues of some pesticides on foods can create potential health risks. Proper application of herbicides and fungicides (as discussed previously) has not only lead to increased crop yield but also has reduced the hazards of persistent pesticides, such as organochlorine insecticides. However, further studies are needed to arrive at meaningful conclusions before establishing a safety in toto to biological systems and the environment. 

The widespread application of herbicides in agriculture has resulted in many polluted surface waters. As a result, numerous pesticides/herbicides have been treated in bench-scale laboratory studies with 03/UV/H202 processes during the last 10 years (see Table 10). Among them, many studies focused on the treatment of atrazine and other. v-triazine herbicides (simazine, prop-azine, etc.). Atrazine is a priority pollutant that similar to other individual pesticides has a very low maximum contaminant level (MCL) (0.1 pg L 1 for the European Environmental Commission according to Directive 80/778/ EEC). In some countries atrazine cannot be used but it is still found in many surface waters. In France, for example, atrazine was banned on September 28, 2001. From applied technologies, only carbon adsorption [180] and possibly advanced oxidations can be recommended to remove some of these... 

Another major application of herbicide resistance is its utility as a selectable marker. Like antibiotic resistance in bacterial transformation, herbicide resistance should prove extremely useful for selecting transformants that are insect resistant, disease resistant, or engineered for other non-selectable traits. Many of these herbicide resistant markers have already been integrated into plant cloning vectors (32.43). 

Figure 6.5 Using a backpack sprayer for spot applications of herbicides (courtesy of University of Wisconsin-Extension). 

Management Fields cleared of weeds by application of herbicide. No-till planting and fertilization combined in one application. Sidedressing of fertilizer applied at appropriate times. Crop harvested with self-propelled combines, which also chop it into small pieces to facilitate drying. Replanted once every 3 to 5 years. Aircraft apply insecticides and fungicides when and where needed twice annually. 

Butoxyethanol may also be directly released to surface water when excessive amounts are sprayed or drift occurs during application of herbicides that contain this compound (Dow 1993). Direct release of 2-butoxyethanol to surface water may also occur during outdoor use of consumer products that contain this chemical (e.g., liquid cleaners, varnishes, paints) however, these releases are not expected to be significant. 

Monoculture farming demanded great quantities of mineral fertilizers and wide application of herbicides, thus, the planned targets for cotton and rice were achieved through apphcation of enormous quantities of mineral fertilizers (up to 600 kg ha which is 20 times more than the norm) as well as chemicals and defoliants (15 times more than the norm). Moreover, crop rotations were not observed from year to year cotton was grown on the same lands, and the situation with rice was the same. As a result, the quality of the cotton and nutritive value of the rice were incessantly deteriorating. 

Spatially variable applications of herbicide can be made in fallow or widely spaced row-crops, such as maize or soya beans, by using spectral reflectance type detectors to determine the presence of weeds, and to actuate a spray application system directly. This approach has been developed commercially both in Australia (Felton, 1995), and in the USA, and considerable savings in herbicide use have been demonstrated - see also Chapter 3. The same approach has recently been developed in Europe for use in amenity areas, where the presence of weeds in pavements and gravel paths can be detected by systems working on spectral characteristic criteria. 

Paice, M.E.R., Miller, P.C.H. and Bodle, J.D. (1995) An experimental sprayer for the spatially selective application of herbicides. Journal of Agricultural Engineering Research, 60, 107-116. 

An important feature of using these manual sprayers is that it is possible to do selective spot treatments, for example, confining the application of herbicides to patches of weeds. Also, where there is concern about downwind spray drift, placement of the nozzle nearer to the target and using a low pressure can enable treatments closer to a sensitive area. In conjunction with an attractant such as molasses or protein hydrolysate, insecticide bait sprays have been used in discrete spots for fruitfly control. Knapsack sprayers are often used in difficult terrain where access to vehicles is difficult or impossible. However, the lack of water in some situations, and the high requirement for labour, have created a demand for alternative application systems (see below). 

Timely application of herbicide is important for attaining proper yield (Table 5.5). 

Surfactants aid in the application of herbicides to plants when they are present as wetting agents in water-based formulations and emulsions. The leaf surface is hydrophobic, and in order to ensure herbicide adhesion one has to make it hydrophilic, which is achieved by surfactant addition. The use of surfactants allows one to increase the effectiveness of fire extinguishing formulations, which is especially important in fighting peat fires, since the surface of dried peat is hydrophobic, and water does not penetrate it in the absence of a surfactant. 

It is true that to trace the movement of the herbicides studied in this work in the environment, one would need only to measure the As content of various samples. However, the results do have potential usefulness in monitoring herbicide dispersal. Quite frequently, the problem is not to establish whether or not herbicides were present but to establish who was responsible for the herbicide. Thus, drawing on this work and previous work involving multiple source tracing in fresh water (17), one should be able simply to mark a given application of herbicide wdth a... 

Presented experimental results suggest that application of herbicide-binding protein in sensor technology has a high potential. Several detection systems were tested in combination with D1 protein electrochemical (amperometry and cyclic voltammetry), optical (surface plasmon resonance and ellipsometty) and assays (ELISA and D1 protein- containing liposomes and DELFIA fluori-metric assay). The main mechanisms of D1 action are either on the ability of herbicides to replace the plastoquinone molecule in D1 protein and in this way change the electrochemical and optical... 

Drift from aerial or ground applications of herbicides... 

From applications of herbicides to control floating, submersed, and marginal aquatic vegetation... 

Table IV. Residue Dissipation in Ponded Water Following Application of Herbicides...

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