In its quest toward reducing environmental risks associated with pesticide use by 25% by 2020, Germany has developed a new assessment tool, the “necessary minimum”. The concept, which defines a level of pesticide use above which further use would be unnecessary, is not as simple or simplistic as it seems.
At the policy seminar Sustainable use of pesticides and Integrated Pest Management in East-Central Europe and the Baltics held in Poland in September 2011, this communications and evaluation tool was questioned by some delegates. Bernd Hommel and Bernd Freier from the Julius Kühn-Institut provided a thorough explanation of it.
To start with, a few definitions are in order.
First, there is Germany’s own definition of Integrated Pest Management (IPM) (Plant Protection Act, 2012): “IPM is a combination of measures - with priority consideration of biological and biotechnical measures, resistant cultivars, cropping and cultural control measures - where the use of chemical plant protection products is restricted to the necessary minimum. ”
Then, there is the definition of the necessary minimum itself ( 2008 National Action Plan): “The necessary minimum can be described as pesticide use intensity where optimum efficacy is combined with the minimum quantity necessary. It depends on application parameters (pesticide selected, dosage, time, application equipment available), local conditions and using alternatively reliable non-chemical measures .”
In practice, “pesticide use intensity” is described by the Treatment Index (TI): “The TI is used as indicator of the intensity of plant protection product use. It considers dose reduction in proportion to the authorised one and partial field application of each plant protection product. For example: authorised dose in entire field: TI = 1.0, half dose in entire field: TI = 0.5, half dose in half field: TI = 0.25. ”
And finally, we need to look at how a certain minimum quantity is deemed necessary or unnecessary. This is an assessment made retrospectively by experts from the plant protection services in the Länder (individual States) using data from a large network of reference farms. They take into account a number of factors including profitability and the feasibility of using alternatives. Selected experts endeavour to carry out this retrospective evaluation from the point of view of the farmer only taking into account the knowledge available to farmer at the of decision-making. Later developments or efficiency of measures are not included in the evaluation procedure to identify the necessary minimum.
Behind the concept of “necessary minimum”, there is the following rationale. In a cropping region under similar conditions, TIs on a particular crop in a particular season vary between farms. Many observed farms do not exceed the necessary minimum, presumably thanks to factors such as adoption of good plant protection practices, farmer experience, extension services and appropriate decision support systems. There are also some farms characterized by higher TIs than in an “average regional farm” which are deemed as unjustified. The interesting part is to understand the factors explaining justified and non-justified TI differences. Experts and researchers analyse these differences and look for explanations that are translated into areas for improvement in terms of future training, extension, demonstration and research activities. For example, looking at data from 2007-2010 in arable farming, experts evaluated the effect of factors such as field and farm size, soil quality, previous crop, tillage, sowing date, variety resistance, and decision making aids on pesticide use intensity. One interesting aspect of this analysis is its propensity to elicit a dialogue between the experts and farmers or their advisers. Indeed, when faced with outlying data, experts get back to the source to explore causes. The necessary minimum is also used as a communication tool, for example with farmers and advisers during a winter training course or an extension field day.
At the meeting, upon presenting this original approach, there were aspects of the necessary minimum which brought challenging reactions from participants--regarding its purpose, its scope and its objectivity. It became clear that the necessary minimum, which is locally defined and shifts annually is not intended to show trends reflecting progress. Rather, it is used in annual reports to show a “corridor of TI”. Where rates of uses are above the necessary minimum is where geographical areas, crops, pests or pesticide categories require attention. Percentages of farm-crop-pesticide uses above that region- and year-specific corridor represents the “mitigation potential” and provide clues to needed advisory, training and demonstration activities in subsequent years (Fig. 1).
Another point is that reducing those uses that are above the necessary minimum, i.e., hitting on the mitigation potential, is one of the main approaches toward reaching the overall 25% risk reduction goal (Fig. 2). Targeting research and extension programmes on outlying pesticide users is doubtless a beneficial approach, but one can wonder if that means neglecting the bulk of pesticide users which happen to be at or below the minimum required. At the very least, the necessary minimum is an interesting tool for communications and identification of research, demonstration and extension priorities.
The presentation given at the policy seminar in Poland is available as a pdf here: