Imagine you are a farmer and are told you are using more pesticide than necessary to control a pest. Would this advice be enough to change your approach? Maybe not. But what if an adviser could show you, clearly and scientifically, exactly what dose needs to be applied to achieve an acceptable level of control while saving you money on your pesticide bill?
It was to solve this kind of problem that advisers in Denmark turned to logarithmic spraying, a technique used to test various pesticides, most commonly herbicides, which is also proving very useful as a demonstration tool.
Logarithmic spraying is the focus of the latest leaflet in the Training in Integrated Pest Management series and presents the technique behind logarithmic spraying alongside examples of how to use it in a training situation. Information on how to use logarithmic sprayers to identify the dose necessary to control a given pest is also provided.
Using logarithmic spraying to visualise pesticide efficiency , written by Rolf Thostrup Poulsen and Jens Erik Jensen of the Danish Agricultural Advisory Service (DAAS), begins by explaining the background to logarithmic spraying. Essentially it is a simple technique that uses a small container containing a dose of pesticide equivalent to the maximum dose required in the experiment or demonstration which is continuously diluted with water from a large container which is under pressure (see Figure 1).
Assuming that the liquids in the small container are mixed well and that the hoses connecting the small container to the nozzles have the same length, it is simple to show that the logarithmic sprayer will provide an exponentially decreasing dose of pesticide (the leaflet explains how to perform the calculations).
The leaflet explains that it may be possible to modify an already available experimental sprayer to perform a demonstration or more advanced systems can be purchased. Either way it recommends that an untreated plot be left next to a treated one in the experimental field to ensure maximum visibility of the effect of the treatment.
In the photograph on the right you can see a Danish experiment concerning the control of Rough Meadow-grass (Poa trivialis ) in winter wheat. In this demonstration the weed was sown into the plots to create an even population of Rough meadow-grass and the pesticide Monitor (active ingredient (a.i.) sulfosulforon) was used. In this experiment the initial dose of Monitor was 50g a.i./ha and the final dose at the end of the plot 5g a.i./ha.
The leaflet suggests asking farmers to identify the location in the plot where they think satisfactory control of the weed has been obtained. It is then possible to calculate the dose at this distance, and use this to initiate discussions between complete control of a weed and economically optimal control. In many cases, say the authors, it may not be necessary to apply the label dose of a product to obtain satisfactory control.
Finally the leaflet explains how to calculate what dose is necessary to achieve satisfactory control. This involves visual inspection of the plots and can be done, for example, by assessing the relative biomass of the weed in the plot at various distances to provide a dose-response curve (more details on this and an example of a Danish trial can be found in the leaflet).
This is the fourth leaflet in the Training in Integrated Pest Management series. Download the others below:
Cover | Title | Download pdf |
Number One: Using Experience Groups |
Training in Integrated Pest Management Number One [pdf - 53686 kB]
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Number Two: Participatory IPM Training |
Training in Integrated Pest Management Number Two [pdf - 16514 kB]
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Number Three: Advanced Participatory IPM Training |
Training in Integrated Pest Management Number Three [pdf - 59856 kB]
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