Methods to Reduce the Use of Pesticides in Greenhouse Crops (Ornamentals and Vegetables)
SummaryThis report describes methods to reduce the use of pesticides in greenhouse crops (ornamentals and vegetables). Furthermore, the report reviews existing knowledge of the extent to which the surrounding environment is exposed to pesticides used in Danish greenhouses. The report was prepared for the Kirsten Jensen Committee, and will be used in their assessment of the consequences for the Danish horticultural industry of introducing additional restrictions on the use of pesticides in plant production. The use of pesticides in greenhouse crops To obtain a clearer picture of pesticide use in the production of potted plants and vegetables in greenhouses, growers were interviewed in the spring of 2001. The growers surveyed were selected on the basis of the crop they produced. The aim of the project was to estimate total pesticide use in five large potted plant crops: miniature roses, Kalanchoë, Hedera, Chrysanthemum and Poinsettia, representing some 30% of the total number of potted plants produced in Denmark, and four greenhouse vegetable crops: tomato, cucumber, lettuce and mushrooms. Interviews with growers were performed in collaboration with advisors from the Danish extension service. Planned interviews with miniature-rose growers did not take place, as the growers concerned were not interested in participating in the project. Growers who participated in the interviews did not use several of the pesticides sold in the period 1998-2000. It can therefore be assumed that growers who did not participate in the investigation used them. However, the growers interviewed used certain pesticides that were no longer available on the market, but that could still legally be used from stock. The use of growth regulators was very high, but with considerable variation from crop to crop. An attempt was made to estimate the total use of pesticides in the species investigated. However, the limited data made it impossible to draw general conclusions, and could therefore only be used to describe pesticide use by individual growers during the period investigated. Table 1 shows estimated pesticide use in Danish greenhouses for the period 1996-99. Table 1. There is considerable use of pesticides in many greenhouse production facilities. When evaluating pesticide effects on the outside environment, greenhouse crops are considered less complicated than field-grown crops. However, there have been cases of environmental pollution from greenhouses. It is mainly insecticides that cause environmental problems, especially pollution of brooks and streams. Pollution of the environment (watercourses, soil, ground water, etc.) has been observed as a result of: a) condensation droplets that contain pesticides running to drains via gutters; b) overflow of water-recycling tanks; or c) leaching of pesticide residues through cracks in the floors. On Funen, there has been a 40% reduction in the number of affected watercourses over the past 5-10 years. The local authorities believe that this reduction was mainly achieved through greenhouse inspection and supplying growers with information. It is assumed that it is fairly easy to construct facilities that do not leach pesticide via the above-mentioned routes, but there seems to be a need for inspection or approval of greenhouse facilities. If pesticides are not leached from greenhouses via gutters, cracks in the floor, etc., environmental pollution will probably be rare. Handling relatively large quantities of pesticides will, however, always pose a risk of spills and pollution via sewers. Environmental effects of alternative methods All alternative methods described in this report can reduce pesticide use, and therefore potentially reduce the risk of environmental pollution and improve workplace safety. Alternative methods to prevent or control insect pests All methods that prevent the attack and spread of insect pests can reduce pesticide use and increase the chances of effective and stable biological pest control. Some of the methods mentioned in the report could be used by growers immediately. Other methods are more specific, and require time and investment to implement. In greenhouse vegetable crops such as cucumber and tomato, there is no requirement for plants to be totally insect-free, as is the case for ornamentals. For most insect pests, minor attack can be tolerated, and this is why biological pest control is used with such great success in tomato and cucumber crops. If pesticides are used at all in these crops, they are only used when necessary to reestablish biological pest control or to disinfect the greenhouse after the crop. Biological pest control is used to a much lesser extent in ornamental crops. The greatest potential to increase biological pest control is therefore in ornamentals. In principle, all insect pests can be controlled biologically in the plant species grown as ornamental crops in Denmark. However, there are several factors that may complicate the use of biological insect pest control in ornamentals. Development and implementation of static or dynamic decision support systems under Danish conditions will improve the possibilities of using alternative methods of pest control. Insect pest control with gasses like N2 and CO2 is an interesting method, especially for "cleaning" plants of all insects before they are exported to countries with requirements for zero-tolerance of any insects. The method needs further development before it can be used efficiently without the risk of damage to plants. Alternative methods to prevent or control disease The biological effect of host plant resistance to pathogens varies from 100% in fully resistant cultivars to 0% in fully susceptible cultivars. The costs of developing and implementing screening methods for pathogen resistance and of maintaining isolate collections may exceed the costs of using pesticides. Since new cultivars of greenhouse crop species are continuously introduced, there is also a continuous need for screening disease-resistant plants. Several scientific studies with microbiological control of root and leaf pathogens have shown promising results. However, evidence is needed to show that this method is also effective under greenhouse conditions. More large-scale investigations in commercial greenhouse crops are needed, and methods should be tested in combination with other alternative methods of controlling disease. Table 20 in the report gives an overview of various strategies. Alternative, non-chemical methods for the growth regulation of ornamentals The greatest proportion of pesticides used in greenhouses is for the chemical growth regulation of ornamentals. Despite this, there has previously only been limited interest in studying alternative, non-chemical methods of growth regulation, and this area of research has only been included in very few research programmes. However, there are research results indicating the potential of alternative methods to significantly reduce chemical growth regulation, or in some species even to replace it. More research on developing alternative methods of growth regulation is needed. Only a few methods are so well developed that growers can use them on a larger scale. Besides the need for more research on developing alternative methods, there is also a need for consultancy support to growers on how to implement the methods in their production systems. Table 21 in the report shows an overview of various alternative methods of growth regulation. Alternative methods to reduce the use of other pesticides (for disinfection and for improving keeping quality) Disinfection is not subject to the Danish pesticide legislation, and there are therefore no restrictions on the use of chemicals for disinfecting greenhouses. The amount of chemicals used for disinfection purposes is not known. Flowering potted plants are often exported to other countries. To meet the keeping-quality requirements of marketing organisations and consumers, some plant species are treated with STS (silver thiosulphate). This is currently the only chemical permitted for use in ornamentals to improve the post-production stress tolerance of the flowers. Recently, a new chemical to improve post-production tolerance (1-MCP) was introduced. 1-MCP is used with great success in the USA in cut-flower production, but it has not yet been approved for use in Denmark. Reduced water and nutrient (especially P and N) availability has shown promising potential as an alternative method to improve keeping quality. Table 22 in the report shows an overview of alternative strategies. Incorporation of alternative methods into various environmental control systems All strategies mentioned in the report can be incorporated directly into environmental control systems such as MPS and EMAS. An increasing number of growers participate in such systems. In the MPS system, for example, growers achieve credits especially by reducing their use of pesticides, but also by saving energy and using less fertiliser. |
