Wide variations in use

Some farmers have a low input of pesticides and maintain good yields, while others use high inputs without achieving greater yields. Research by Geert de Snoo, Frank de Jong and Rob van der Poll at the University of Leiden in the Netherlands has assessed the extent of variation on this 'usage spectrum'. 

A survey of pesticide use in the Netherlands to discover farming practice covered 3,200 farmers, growing 46 of the most important crops(1). The information covered details such as the type of pesticide used, dose, time and method of application. In measuring the impact on the environment, the study used a 'yardstick' developed by the Centre of Agriculture and Environment(2). Based on the fate and toxicity of the pesticide involved, the yardstick takes into account: droplet drift of the formula­tion and its toxicity for aquatic organisms; toxicity for soil organisms; and  the risk for ground water, based on the European drinking water standard.

Overall use and environmental impact  

The highest level of pesticides use per hectare is in the cultivation of mushrooms, roses, chrysanthemums, lilies and hyacinths, and the potential environmental impact is especially high in crops like lilies, and wood and hedge plants. Taking into account the cultivated area of each crop, the total use of pesticides by weight is highest in potatoes (ware potatoes, seed potatoes and starch potatoes), with about 42% of all pesticide use by weight. Other important crops are silage maize and apples. The study showed that potatoes are responsible for about 51% of the total calculated environmental impact of pesticides in the Netherlands, followed by silage maize and apples (each about 7%), and lilies, winter wheat, and tulips (each about 4%). In most cases the environmental impact is caused by contamination of surface water, due to the use of insecticides and (in potatoes) fungicides.

Variation in farmer practice  
The results show a very large variation in pesticide use (kg/ha) between farmers cultivating the same crop. In figure 1 the variation in winter wheat and tulips is given. A comparable large variation is seen when the potential environmental impact of each farmer is considered (see Figure 1), although farmers with a high pesticide use in kg/ha do not necessarily have the biggest impact on the environment, due to different pesticides involved, application methods and other factors.
    With these data, it was possible estimate the relative compliance of farmers to environmental standards. For the different crops cultivated outdoors, the number of pesticide applications exceeding a standard, varies between 50-90%. For each crop, the calculated average of all applications always exceeded the standards: for aquatic organisms about 20-700 times (depending on crop type), for soil organisms about 1.7-150 times and for ground water about 1.5 to 35 times.

Causes of variation
To investigate why there is such variation, and understand more about farmer's perception of prevention measures, a case study was carried out in the north-east of the Netherlands(3). In January 1997, 49 farmers were interviewed on the main factors which influence their choice of pesticides. The results show that at present, environ­mental aspects are hardly taken into account by the farmer when choosing a pestici­de. The motivation seems to be mostly influenced by the sup­pliers. Therefore it seems worthwhile to investi­gate the role suppliers play in stimulating a more environ­mentally friendly agricultu­re. An interesting question is, on what basis are the recommendations of pesticide suppliers given. Are environmental aspects taken into account and if so, in what way?

Prevention strategies
The use of pesticides is still a problem in the Netherlands, especially in relation to the contamination of the surface water. However, there are large differences between individual farmers, a fact that gives opportunities for prevention. Two of these opportunities were explored. First is the benefit of drift reduction to surface water, for example by the creation of buffer zones and/or technical measures. Decreasing pesticide drift to surface water by 95% would reduce the total environmental impact of pesticides in the Netherlands by about 87%.
    Secondly, if 5% of the most polluting farms reduced their environmental impact score to the average, taking all crops together, this would lead to a 22% decrease in the total pesticide problem in the Netherlands. Large differences between crops exist.
    Although the results show that the pesticides in the Netherlands form a serious environmental problem, they also show some effective opportunities for solving the problem. 
    One possibility is to give an environmental certificate to farms with low environmental impact. In this way retailers and other customers in the agro-production chain can steer agriculture in a more sustainable direction.

1. Gewasbescherming in de land-en tuinbouw, 1995. Chemische, mechanische en biologische bestrijding. Centraal Bureau voor de Statistiek, Voorburg, 1997.
2. Milieumeetlat 1996, werkboek, milieumeetlat voor bestrijdingsmiddelen. Centrum voor Landbouw en Milieu, Utrecht (CLM), 1996. The yardstick compared predicted environmental con­centration (calculated with fate models) with the toxicity L(E)C50 or NOEC. If the predicted concentration is equal to the (European) maximum concentration, the result is 100 'points'. Drift percentages were based on figures of Board for the Authorization of Pesticides of 1997. Aerial spraying on potato crops was estimated by literature research. The use of fumigants was not taken into account.
3. Snoo, G.R. de , F.M.W. de Jong, R.J. van der Poll, S.E. Janzen, L.J. van der Veen & M.P. Schuemie, Variation of pesticide use among farmers in Drenthe: A starting point for environmental protection, Med. Fac. Landbouww. Univ, Gent 62/2a: 199-212, 1997.

Geert de Snoo, Frank de Jong and Rob van der Poll work for the Centre of Environmental Science, Leiden University, P.O. Box 9518, 2300 RA Leiden, The Netherlands Snoo@Rulcml.Leidenuniv.nl

[This article first appeared in Pesticides News No. 39, March 1998, page 5]