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9. Environmental and health assessment of alternative or new methods of weed control and control of pests

9.1 Introduction

In the following, an assessment is made of the environmental and health consequences of non-chemical methods of preventing and controlling pests in agriculture. The assessment is based on the work of the Sub-committee on Agriculture. It is followed by a discussion of:

	possible improvements at sites for washing and filling sprayers
	the interaction between pesticides and the production of toxins
	mineralisation in the soil with increased soil treatment in connection with no use of pesticides
	changes in energy consumption and emission of greenhouse gases in connection with no use of pesticides
	new pesticides.

9.2 Weed control

To achieve adequate control of weeds in the event of a total or partial phase-out of pesticides, it would be necessary to combine prevention and control through cultural practices and non-chemical, alternative methods. That means that the crop rotation would have to be adjusted towards less winter cereal, leading to a more diversified crop rotation and greater biodiversity than in a crop rotation including monoculture of cereals. In addition, the autumn sowing would have to be done later and it might be necessary to sow some crops with a wider row spacing to enable mechanical weeding. If the mechanical weeding were very effective, the amount of weeds would not differ much from the amount in fields treated with pesticides, so there would be no environmental benefit for the wild flora. In crops such as rape, mechanical methods are already competitive, compared with chemical methods. Mechanical weed control has a considerable negative impact on the soil’s mesofauna and macrofauna, particularly springtails and earthworms, and harrowing can damage the crop. On the other hand, increased mechanical control of weeds in farming would be generally environmentally beneficial because it does not involve any risk of pollution of groundwater or of spreading of pesticides to adjacent areas. Placing fertiliser at the individual plant is deemed to be another good way of improving the crop’s ability to compete with weeds. All else being equal, this could reduce fertiliser consumption and thus reduce the loss to the surroundings.

According to Action Plan II, "Organic Farming in Development", it is possible to keep the soil covered with vegetation all year round (Danish Directorate for Development 1999). In organic farming, extensive use is already made of undersown and second crops. Consideration could also be given to the use of "undersown crops" in the form of low-growing herbaceous plants, such as white clover, but other plant species could also be grown. Leguminous plants are an obvious choice with respect to nitrogen fixation, but species that are good "catch crops" could also be used and would be advantageous with respect to holding on to the nitrogen until the crop can absorb most of the amount available. In addition, undersown crops would give more varied cover, thereby promoting part of the fauna – particularly earthworms and surface predators. Lastly, a cover of undersown crop would reduce the weed’s possibility of germinating both in the crop and after harvesting.

On the health side, the main change in connection with the prevention of weed problems and the use of mechanical control methods instead of pesticides would be reduced exposure of agricultural workers and less pesticide residue in the crops. Potential problems with physical loading in connection with increased mechanical or manual weed control are discussed in section 6.1.

9.3 Prevention and control of diseases

In a scenario without pesticides it would be important to use crop species with good resistance to diseases in order to reduce the loss from infection by leaf diseases. The biggest losses from diseases occur in potatoes, wheat and winter barley. There are at present no varieties with sufficient resistance to all leaf diseases in these crops.

There is a big potential for improving the resistance of the varieties both by traditional breeding and by genetic modification, but it is difficult to breed, at one and the same time, resistance to leaf diseases and seed-borne diseases, better weed competition, stem strength, winter resistance, a high yield and high quality.

The environmental benefit of developing and using resistant varieties is the obviously reduced consumption of pesticides, with consequently reduced risk of pollution of the groundwater and the surroundings. The health benefit would be less exposure of farm workers and less pesticide residue in crops.

In Denmark today, 85-90 % of all cereal seed is dressed today, as is a large proportion of other crops in Denmark. It is believed that generally omitting such treatment would lead to a rapid spread of many of the seed-borne diseases that cause heavy losses.

It would be possible to reduce the consumption of pesticides by continuing to dress the first generations of cereal and then assessing the need to dress the subsequent seed batches. However, this practice would first have to be more thoroughly analysed and tested. An assessment of the need for dressing would require fast and reliable methods of analysis, separation of seed batches and presumably rejection of substantial quantities of grain for multiplication. In beets, too, there could be considerably losses owing to uncertain establishment if dressing products were prohibited. In this case, however, the losses would be due to a combination of both diseases and pests. Today, research is in progress on several alternative methods of combating seed-borne diseases, including use of resistant varieties, use of biological products and technical methods involving the use of hot water/air or brushes. None of these methods is yet ready for use and a great deal of research and development remains to be done.

The environmental benefit from developing alternative methods, including the use of resistant varieties, increased assessment of the need and biological protection products, is reduced use of pesticides, although the pesticide consumption is very small. With seed dressing, between 10 and 50 g pesticide per hectare are often used, which is of the same order of magnitude as when spraying with mini-products and pyrethroids. Since the seed is covered with soil, very little pesticide is spread to the air and surface water. However, pesticides in seed-dressing products can leach in the soil in the same way as spray products. Seed dressing also involves a risk to birds and small mammals, which eat the seed. The plants and thus food products made from them can also contain residues of systemic seed-dressing products.

The health benefit of omitting treatment with seed-dressing products would be no exposure during production, although this is usually in the form of wet-dressing in large, closed dressing plants. Exposure also occurs during handling of the seed in connection with sowing. Lastly, some residues of the systemic pesticides (i.e. the pesticides absorbed by the plants) could be present in the crops and thus in food products.

Very little is known about the insect resistance of Danish varieties. Simple screening for receptivity to pests may reveal an unexploited potential. Only limited use is at present made of biological control of pests in fields, so such methods are not yet a realistic alternative to chemical control. It is a well-known fact that the field’s natural fauna affect the pest population, but little is known about how much these beneficial organisms affect the development of, for example, aphids.

The environmental and health benefit from developing and using insect-resistant varieties is obviously less use of insecticides with a consequent reduction in the risk of pollution of surface water, groundwater and the surroundings in general.

The health benefit would be less exposure of farm workers and less pesticide residue in crops.

Biological methods, which include both beneficial organisms and microbiological products, have a big potential against pests in greenhouse production. They are already used extensively in greenhouse vegetable production but not within greenhouse production of ornamental plants. Effective biological methods of combating diseases in greenhouses are still limited. In fields, biological methods of controlling pests are believed to have some potential within special crops, whereas, in the short term, biological methods of combating diseases are only thought to have a potential in the case of seed-borne diseases and fungi that affect germination.

Table 9.1
A number of microbiological insecticides and fungicides are at the application stage.

As in the case of disease-resistant or insect-resistant varieties, biological control would result in an obviously reduced consumption of pesticides and a consequently reduced risk of pollution of groundwater, food products and the surroundings. There would be a corresponding health benefit of less exposure of agricultural workers and less pesticide residue in crops.

However, the use of beneficial organisms and microbiological products would involve a serious risk of proliferation of foreign organisms, which could have a detrimental effect on the environment. It should be noted that the beneficial organisms currently used in greenhouses cannot survive out of doors in Denmark. Theoretically, the proliferation of indigenous species could also upset natural ecological balances. The use of microbiological products could involve a risk of harmful effects in the form of allergies and bronchial diseases. An authorisation scheme for these products is under construction and will include an assessment of possible health effects.

The crop rotation used and the crops grown are of great importance for the level of diseases, weeds and pests. Generally speaking, the level of pests can be reduced by means of a varied and diversified crop rotation, alternating between spring and winter crops, monocotyledonous and dicotyledonous crops, and annual and perennial crops. As a rule, there are fewest problems with pests in dairy farm crop rotations with a large proportion of grass compared with large areas with specialised plant production. When planning the crop rotation it is important to take account of crop-rotation diseases and ensure a sufficient number of years between such crops as potatoes, rape, sugar beets, etc. There does not seem to be any direct possibility of cultivating new, alternative crops or intercropping.

According to Action Plan II, "Organic Farming in Development", mulching could reduce evaporation from the surface of the soil, which would promote both plant growth and the soil fauna, particularly in dry summers (Directorate for Development 1999). Mulching would also promote surface predators (spiders and ground beetles), which play a role in combating pests, and would reduce the weed’s possibility of germinating. It would be possible to mulch after the cereal harvest by cutting the straw and leaving it on the field. One of the problems of mulching is whether it is possible to sow the crop directly in the mulch in such a way that it can germinate unhindered. The effects of such a procedure on diseases and pests and on crop growth should also be investigated.

In recent years, damage thresholds and decision-support systems have been developed for many of the main agricultural crops as support for the farmer in judging the need for prevention and control and the choice of pesticides. Although the systems are now relatively widely used, not all farmers have been reached. Damage threshold systems still have to be developed for a large number of crops and several of the existing systems need improving. It is considered possible to achieve a 20-50% reduction in the use of pesticides in a number of crops by combining decision-support systems with chemical and non-chemical methods. Research has shown that targeted use of fertiliser, pesticides and other factors related to the phase-out can contribute to satisfying environmental requirements and simultaneously optimise production economically. The use of decision-support systems offers an obvious possibility of reducing the exposure of both the environment and people.

The environmental and health benefit from the use of preventive cultivation methods would be an obviously reduced consumption of pesticides and a consequently reduced risk of pollution of groundwater and the surroundings. An added health benefit would be less exposure of agricultural workers and less pesticide residue in crops.

9.5 Use of genetically modified crops in agriculture

In Denmark, researchers are working on the development of genetically modified plants. Most progress has been made on herbicide-tolerant plants, which should be ready for marketing in a few years’ time. The introduction of genetically modified, herbicide-tolerant varieties of beet is expected to result in a significant reduction in herbicide usage - about 1 kg active ingredient per ha. In the case of herbicide-tolerant rape and maize, there does not seem to be any significant reduction in herbicide consumption. Intensive research is going on all over the world in the field of molecular biology. In time, that will undoubtedly lead to significant changes in our cultivated plants. Of particular interest is the development of genetically modified disease-resistant plants, which must be presumed to create a means of reducing losses from diseases without the use of pesticides. The use of genetically modified plants with resistance to pests in maize and other crops is spreading globally. However, crops with resistance to pests are unlikely to gain a footing in Denmark for some years (around 10).

Genetically modified plants provide the possibility of reducing the use of pesticides and thus exposure of both the environment and people. However, there could be a risk of some of these crops proliferating and subsequently harming the environment. That applies particularly to plants whose ability to establish in competition with the natural flora is improved. In addition, plants that are resistant to insects could affect other species than the pest itself. This applies particularly to predatory insects and birds that eat herbivores living in the genetically modified crop. Such insects and birds could either be affected directly because the prey eaten is poisonous to them or indirectly through changed food resources. Such effects also occur with the use of spray products. However, possible effects of insect-resistant plants differ from those of spray products by being able to occur throughout the growth season. However, it is likely that some non-target organisms would be less affected by genetically modified plants than they are by conventional use of spray products. The authorisation process for genetically modified plants will include a risk assessment of both the environmental impacts and the effects on health, cf. section 7.3.

9.6 Use of spraying techniques to reduce spray drift

Efforts have been made to improve the biological effect of pesticides by using different types of nozzles, quantities of water and pressure. The aim has been to be able to use lower dosages. Compared with current spraying techniques, the use of new types of spraying equipment offers only a limited possibility of reducing the amounts of pesticide used. However, in the last few years, research has been going on within site-specific application of pesticides, which means limiting the treatment to those areas of the field where there is a need to control or regulate pests. With the present spraying practice, more than 95% of the spray product may hit the soil surface in the early growth stages of the plants.

It is believed that the development of methods that can handle such a system would help to reduce pesticide consumption considerably. There are also good possibilities of reducing the risk of spray drift by lowering the boom height and by using new nozzles that minimise the proportion of droplets with a potential for drift. Some of the new types of spraying equipment have a bigger spraying capacity than earlier sprayers, which improves the possibility of spraying quickly, while the weather is calm, e.g. in the morning hours. In fruit crops, new, shielded sprayers that collect spray residues are believed to offer a good possibility of reducing the impacts on the surrounding environment.

On the health side, a reduced need to spray would directly reduce the exposure of the sprayer operator.

9.7 Reduced pollution during cleaning and filling of spray equipment

Even small spills of concentrated spray product can greatly increase the risk of leaching, as described in section 4.6.5, on pollution from sites for filling and washing of sprayers. The risk of leaching is even greater if the spill occurs at traditional sites for filling and washing, where the surface is often covered with gravel or fine shingle, and with very thin or no topsoil or vegetation. There is also a particular risk of pollution of local water supplies or ground water when pesticides are used and tractors and spraying equipment are cleaned near wells or borings.

There are a number of simple rules and recommendations for reducing or completely avoiding pollution with pesticides during cleaning and filling of spraying equipment (Jensen et al. 1998). Filling of tanks with concentrated pesticide and washing of spraying equipment should thus be done on an area of topsoil with vegetation, which should be moved at regular intervals, or on a biobed. Filling and washing can also be done on a concrete yard with a drain to a separate tank. A grass-covered area is also suitable. Grass prevents run-off and the formation of channels in the soil. Remaining spray product should never be emptied out onto topsoil or a paved area. Remains of spray product should never be put into a liquid manure tank unless it can be done without risk in relation to later use of the liquid manure on crops.

Remaining spray product (5 - 50 l) should be diluted and sprayed onto the crop. The strongly diluted washing liquid can be emptied out on a field, over as large an area as possible. One way of doing this is to remove the bottom bung and empty the tank while driving in the field. The diluted washing liquid can also be emptied into the liquid manure tank. Washing and filling of sprayers should never be done on gravel or concreted areas from which the washing water and spills are led to seepage or to a sewer, drain or watercourse. Besides that, it must never be done near a well. The packaging and any unused pesticide residues must be disposed of through the municipal waste scheme.

International standards

As an element of the work of preventing pollution of the environment, a European standard is being prepared for field sprayers and vapour sprayers. Consideration for the environment and health and safety are key points in the standard. The work, which began six years ago, is being carried out under CEN (Comité Europien de Normalisation), in which Denmark is represented through the Danish Standardisation Council. In the introduction to the coming standard, the following main points are mentioned:

	A uniform distribution and good placing of the spray product
	Prevention of unintended spreading of pesticides to the surroundings
	Improved operation of the equipment.

To achieve these objectives, the sprayer must be equipped with a clean water tank of a specific size in relation to the size of the sprayer. The sprayer must be washed out with the water before it leaves the field. If possible, the first cleaning of the outside of the sprayer must be done with clean water in the field. In addition to the clean water tank there must be a tank with clean water for washing of hands etc. Standards will also be prepared for filling equipment and equipment for cleaning chemical packaging.

Compliance with a standard is normally voluntary, but in some countries, the standard will form the basis for authorisation of spraying equipment. In Denmark, there is already a trend towards mounting clean water tanks on sprayers on a voluntary basis. From a technical point of view, clean water tanks can be post-mounted on most sprayers without major problems.

Biobeds

An alternative to filling and cleaning the sprayer in the field is the establishment of a biobed (Helweg, Hansen 1997). A biobed is a biological filter or mini treatment plant for any pesticide that is spilled during filling or washed off during washing of the spraying equipment. The biobed material is characterised by high microbiological activity and a good sorption for the pesticides. Tests going on at the Danish Institute of Agricultural Sciences and the National Department of Plant Production have shown that biobeds have a good ability to bind and break down pesticides. The tests also show, however, that the biobed should be closed at the bottom in order to ensure against leaching through the bed. It must also be ensured that percolating water can be collected at the bottom of the bed. There are at present no real guidelines or recommendations on biobeds because they cannot be given before official authorisation of a prototype. Also lacking is official acceptance of disposal of biobed material by spreading in the field. That is not expected to be a problem. If more complicated methods of disposal were required, farmers would probably lose interest in biobeds.

Municipal environmental supervision

In 1998, DEPA directed Denmark’s local authorities to give higher priority to checking the handling of pesticides when carrying out environmental inspections at the individual farms. The main things to be checked are whether the sprayer operator holds a spraying certificate, whether washing and filling sites are properly arranged from an environmental point of view and whether the products used are properly and safely stored and disposed of.

9.8 Interaction between pesticides, including growth regulators, and production of toxins

Some of the fungi that occur in plant production can produce so-called mycotoxins, many of which are extremely toxic to humans and animals. The following survey of this area is based on a report by Elmholt (1998). Mycotoxins can be absorbed through the gastrointestinal tract, the mouth, the lungs or the skin. At least 300 different mycotoxins have been identified, but only about 20 of them are today thought to be of importance with respect to animal feed and human nutrition. Some mycotoxins, e.g. trichothecenes and ochratoxin A, are found in crops produced in the EU, while others, e.g. aflatoxin, occurs particularly in crops imported from the tropics. The occurrence of these mycotoxins is thus unrelated to changes in the use of pesticides in Denmark. It is estimated that 20% of the cereal crops used for fodder contain measurable quantities of mycotoxins (Smith et al. 1994).

Different families of fungi can form toxins under Danish conditions. The main ones are Penicillium and Fusarium (Elmholt 1998). Only a few species within the families present a real risk. The Nordic Council of Ministers (1998) carried out an analysis of the intake of mycotoxins in the Nordic countries and a risk assessment of selected fusarium toxins. There is also often some variation in the capacity to produce toxins between strains within the same species. In the case of many of the fungi that produce mycotoxins, little is known about why they produce the toxins and what triggers their formation. The main members of genera on Danish produced cereals are Pencillium verrucosum, which forms ochratoxin A and citrinin, and members of the Fusarium genera, which form zearalenon and trichothecenes.

The effects of the toxins on animals and humans are described in Smith et al. (1994). Ochratoxin A is one of the most poisonous mycotoxins in Danish produced cereals and is also found in processed products. Ochratoxin A has a toxic effect on the kidneys and is on the list of carcinogens. The Danish Veterinary and Food Administration has shown that, particularly in years with wet harvests, there is a real risk of ingesting so much ochratoxin A via cereal products that the Nordic limit value for daily intake of 5 microgrammes per kg body weight is exceeded. Citrinin and some glucopepsides also have a harmful effect on the kidneys. Trichothecenes are another of the main mycotoxins in cereals and food products containing cereals. Some trichothecenes already form while the cereal is standing in the field (Pettersson 1996). That applies, for example, to T-2 toxin and to deoxynivalenol (DON), which is found in agricultural crops all over the world, even after processing. DON (= vomitoxin) has toxic effects on the digestive system and is known to cause vomiting and reduced appetite in pigs. There are as yet no Danish rules, but, in most cases, the amount of DON normally contained in cereals lies far below the limit values used in the USA. The far more toxic, but also rarer, trichothecenes, T-2 toxin and DAS, affect the immune system and, in the worst event, can cause serious illness (ATA syndrome) in humans and animals. Trichothecenes also play a role in fungal attacks on plants. Zearalenon is also an important mycotoxin. It is formed by several different genera and is known for its oestrogenous effect, i.e. it is one of the naturally occurring hormone-like substances. Fusarin C, which can be formed by several different members of the Fusarium genera, is mutagenic and possibly carcinogenic.

The occurrence and growth of fungi increase in moist growth conditions. This is reflected by the fact that large consignments of grain are infected with, for example, Fusarium fungi after moist growth seasons. Grain harvests with a water content of more than 14-15% can cause problems with subsequent development of different types of fungi during storage of the grain. This means that unless the grain is dried immediately after harvest, a lot of toxin-producing fungi can develop. Particularly in years with long periods of unsettled weather and a lot of precipitation, it can be difficult to get the harvested grain dried. A good example of this is known from the screening for "mouldy kidneys" carried out by abattoirs. All kidneys exhibiting macroscopic lesions, which indicate that the animal suffered from "porcine nephropathy", are tested for residues of ochratoxin A. The entire carcass is rejected if a concentration of more than 25 microgrammes per kg is found in the kidneys. This threshold has been applied since 1979. The results show that "mouldy kidneys" do not occur with the same frequency every year. In many cases, they were found after pigs had been fed with grain harvested in 1978, 1983 and 1987. Closer studies of the cases in 1978 and 1983 show that they were not uniformly distributed in regions, and the occurrences could in many cases be related with the harvest conditions in the various regions of the country (Frisvad, Viuf 1986; Büchmann, Hald 1985). The Ministry of Food has shown that there is a real risk in connection with wet harvest years of so much ochratoxin A being ingested via cereal products that the Nordic limit values for daily intake are exceeded (Jørgensen et al. 1996; Danish Food Agency 1997). However, fast and effective drying of grain would in most seasons reduce the risk of toxin production during storage.

A number of members of Fusarium genera are found on malt barley (Thrane et al. 1992). It is assumed that the occurrence of Fusarium on malt barley can cause what is called gushing in the brewing industry, and a German study showed a significant relationship between the concentration of DON and gushing in beer brewed both on wheat and on barley (Niessen et al. 1993).

Today, extensive use is made of broad-spectrum fungicides in cereal crops. A number of studies indicate that different members of the Penicillium genera are not sensitive to propiconazole and other ergosterol-inhibiting fungicides, which are the predominant fungicides used today (Elmholt 1998). It should be mentioned, however, that these findings were based on fungi growing on soil. Most fungicides have only a limited effect on Fusarium, which mainly attacks grains in connection with flowering. Tebuconazole is active against several members of the Fusarium genera, and azoxystrobin is also known to affect a few of them. Generally, however, chemical control of Fusarium fungi is not recommended in Denmark because it is extremely difficult to hit the right spraying time for some effect to be achieved.

Although a fungicide like tebuconazole reduces the occurrence of Fusarium culmorum, it does not necessarily reduce the risk of toxins forming in the grain. A German study indicates that the opposite is the case: it showed that treatment of Fusarium culmorum with Matador (tebuconazole+triadimenol) greatly increased the content of the trichothecene NIV in relation to untreated control plots (Gareis, Ceynowa 1994). Similarly, Moss and Frank (1985) found that tridemorph stimulated production of T-2 toxin in Fusarium sporotrichoides at concentrations that inhibited the fungus’s growth. However, Swedish studies have not confirmed these trends (Pettersson 1996).

Although the fungicides used today are broad-spectrum, there are usually some fungi on which they have little or no effect (Elmholt 1998). When combating fungi in cereals, the composition of the fungal flora on the plants can change. In some cases, this means an increased proportion of the fungi that are most difficult to combat. This is particularly unfortunate if the species in question are pathogenic and/or able to form mycotoxins. Foreign studies have shown that some members of the Fusarium genera increase after fungicides are used on other fungi in cereals. Norwegian studies showed that some fungicides (including Tilt top, which contains the fungicides fenpropimorph and propiconazole) resulted in stronger attacks of Fusarium than in untreated crops. The author argues that propiconazole, in particular, perhaps makes the plants more receptive to Fusarium attack or makes them more accessible by knocking their competitors out (Elen 1997). A German study (Liggitt et al. 1997) showed, for example, that three common types of fungi on wheat inhibited the development of Fusarium culmorums. Laboratory tests showed that the fungi’s growth was affected very differently by different fungicides. In some cases (including tebucanazole), pathogenic types of Fusarium fungi were more inhibited than saprophytic types, i.e. the types that break down dead organic material, because the fungicide intensified the competitive effect. In other cases, the opposite happened, so the competition weakened. However, it should be noted that reduced growth of toxin-producing fungi can in some cases result in increased toxin production.

The Ministry of Food’s monitoring programme shows that there is a tendency towards higher occurrences of ochratoxin A in organically cultivated cereal, i.e. in cereal from areas where pesticides are not used, than in conventionally grown cereal. In a Danish study carried out by the Danish Institute of Agricultural Sciences, the fungus Penicillium verrucosum, which forms ochratoxin A, was detected in 11 of 64 localities in Denmark (Elmholt 1998). The preliminary results thus show for the first time that Penicillium verrucosum is to be found in Danish agricultural soil. They also show that the fungus seems to prefer clayey soil to sandy soil and that it apparently occurs more regularly in organically cultivated soil than in conventionally cultivated soil. One reason for that is a larger quantity of weeds in organic farming, which increases the moisture in the crop compared with conventional farming. This may have something to do with the fact that the seed used in organic farming is not dressed with fungicides. The seed lies in store for at least one year, and that may in some cases lead to an increasing population of Penicillium verrucosum and other fungi. After sowing, the population of these fungi could increase rapidly in the soil. When seed dressing is omitted, it is necessary to pay more attention to the problems of seed-borne fungi in cereals.

Lodging in cereals occurs for a number of reasons - cultivation of weak-stemmed varieties, over-fertilisation, too many plants, attack by straw-based diseases and heavy precipitation and wind. Today, farmers avoid the problem by growing mainly strong-stemmed varieties and by adjusting the plant density and the level of fertilisation. The risk of lodging is also reduced by some use of growth regulators. Greater use is made of growth regulators in rye than in wheat because the stems of rye varieties are weaker than wheat. If the use of growth regulators were to cease, an increased risk of lodged corn would be expected in certain soils and on certain farms. This would cause major problems when drying the crop for harvesting. It would also result in increased attack by soil-borne fungi, including members of the Penicillium (Hill, Lacey 1984) and Fusarium genera. The biggest problem in this connection would probably be Fusarium culmorum, which is very common in soil, and which can form a number of mycotoxins.

9.8.1 Conclusions

Mycotoxins are a general problem in both conventional and organic farming because they can develop in moist conditions. They can also proliferate if grain is dried too slowly. The sub-committee finds that mycotoxins from fungi in cereals can constitute a risk to public health and recommends strengthening of the control of the content of mycotoxins in food products.

9.9 Mineralisation in the soil and other environmental impacts from increased soil treatment in the event of a phase-out of pesticides

Soil treatment affects the chemical, physical and biological conditions in the soil and is therefore of great indirect significance for mineralisation, for release and leaching of nutrient salts and for persistence and leaching of pesticides. If soil treatment is increased, some of the macropores would be destroyed. As a result, pesticides may stay longer in the surface soil, where the potential for degradation is greatest, and leaching may be reduced. On the other hand, surface run-off would increase. If soil treatment were reduced or omitted, increased transport in macropores might result in increased leaching of pesticides (Fomsgaard 1998).

Mechanical control of couch grass in the autumn is believed to have an adverse side effect in the form of increased nitrogen leaching in the winter months because of increased nitrogen mineralisation, while mechanical weed control in the spring is also known to increase nitrogen metabolism, which is often seen as having a positive effect on the crops because, in the growth season, they have a good possibility of utilising the nitrogen released (Sub-committee on Agriculture 1998).

Compared with normal soil treatment, reduced treatment may cause increased evaporation of pesticides. If soil preparation were to be reduced, the content of organic material would increase in the long term. As a result, the soil has greater porosity and thus an increased potential for degradation and changed degradation kinetics for the pesticides. The effect of soil treatment on pesticide metabolism, including evaporation, is therefore important (Fomsgaard 1998).

Ploughing has a particularly large effect on root weeds but also affects annual seed weeds. In cultivation without ploughing, there is a risk of proliferation of root weeds because one loses the weakening of the vegetative propagation organs achieved by ploughing. For annual species, ordinary winter ploughing normally buries about 95% of the seed from the surface of the soil to a depth of more than 5 cm. That is deeper than most plant species are able to germinate from. In the next ploughing, many of the seeds emerge again. The plant numbers can be kept at a low level by varying the ploughing depth, ploughing very deep in years with high seed rain and then more shallowly in the following year. With this practice, most of the wild plants that germinate during ploughing come from seeds that are more than one year old, whereas, without ploughing, they come from seeds that are less than one year old. Species with low seed durability can therefore proliferate if ploughing is omitted but are less able to proliferate with ploughing. To keep the number of wild plants down, farmers grow the same type of crop for two successive years and follow that up with another type of crop. The weed seed dropped in the first crop is ploughed down before the next. Then, when the soil is ploughed again, a different type of crop is sown, in which the species in question do not have such good conditions for establishment and development (Tersbøl et al. 1998).

Soil treatment also affects the fauna. More frequent soil treatment has a harmful effect on the soil’s organisms, e.g. earthworms and springtails, and can present a risk to farmland birds nesting in the field.

9.10 Changes in energy consumption and emissions of greenhouse gases

The changes in the consumption of fossil fuel from restructuring for pesticide-free farming have been studied by Dalgaard (1998), who concludes that if livestock production is to be maintained in Denmark, then – taken overall - restructuring for pesticide-free farming would result in increased energy consumption. The increase would mainly be due to increased energy consumption for importation of feed because of the fall in yield in the 0-scenario. On the other hand, energy consumption for crop production would fall, due primarily to saved energy for production of pesticides and a falling consumption of fertiliser-nitrogen.

Table 9.2
Example of calculation of fossil fuel consumption for cultivation of winter wheat with present production (1996) and with pesticide-free production (from Dalgaard 1998).

*) incl. pre-emergence harrowing, extra ploughing of stubble etc.
**) 100% commercial fertiliser

Special factors and uncertainties

There can be a number of factors concerning production changes that are not included in the calculations, which might increase energy consumption in pesticide-free farming. For example, reduced soil treatment would not be possible in the 0-scenario, which would result in extra energy consumption for increased soil treatment. However, experience indicates that competitive second crops reduce the need for mechanical weed control in the autumn, which is relatively energy-intensive. In addition, the energy consumption for drying of crops and changes in the use of straw for energy purposes would have to be included in the energy scenarios (Nielsen 1999). Correspondingly, some items that have not been included in the analyses of the consequences of pesticide-free farming could reduce energy consumption. For example, new wells might have to be established because of pollution of the groundwater and measures might have to be taken to protect the surrounding environment.

9.10.1 Conclusion

In the event of restructuring for pesticide-free farming, direct energy consumption for mechanical weed control would rise, but this would be partially balanced by saved indirect energy consumption for production of pesticides (table 9.2). The conclusion must be that total energy consumption in arable farming in Denmark would not change very much with restructuring for pesticide-free production, but that this must be seen in relation to the considerable fall in yield – about 25%. However, a real estimate of the various forms of energy consumption would require a more comprehensive analysis in line with the analyses in Dalgaard et al. (1998).

According to Dalgaard et al. (1998), the agricultural sector’s contribution to the greenhouse effect is approx. 13 Tg CO₂-equivalents. CO₂ from fossil fuel consumption accounts for around one quarter of this, and methane and nitrous oxide for the remainder. The need to import feed to compensate for the reduced yield means that energy consumption would be higher than if pesticides were used. Changes in emissions of methane and nitrous oxide have not been taken into account in the assessment of the change in the agricultural sector’s contribution to the greenhouse effect (Dalgaard 1998), nor has the extent to which a different production pattern, e.g. reduced livestock production or organic farming, would reduce energy consumption.

9.11 New pesticides

The agrochemical industry is continuously developing new pesticides. However, it is not clear how much the new pesticides will change the pattern of use, apart from the fact that there has been a trend towards substances that require smaller quantities of pesticide per hectare. For example, in the case of the products developed in the 1940s, the usage was about 1.5 kg a.i. per ha, whereas for recent products, the average is 100 grammes a.i. per ha. In addition, the cost of environmental studies accounts for a growing proportion of the total cost of developing pesticides.

Within herbicides, low-dose products, e.g. sulfunylurea products, of which only a few grammes are used per hectare, have been developed. In Denmark, efforts to synthesise herbicides from natural substances have so far produced the substance glufosinate (Basta). Attention has also focused on substances whose effect is closely linked to processes in plants in order to reduce their toxic effects on humans and animals.

Within fungicides, efforts have been made to use substances that occur naturally in bacteria and fungi. For example, the new storibilurin fungicides are based on a substance that is produced by fungi that degrade wood. Fungicides have also been developed that activate the plant’s own immune defence without having any toxic effect on the fungi. Work has also been done on a substance that is extracted from a brown alga species.

Within insecticides, products have been developed that have different action mechanisms from earlier insecticides and that can overcome resistance to previously used insecticides. The substances are effective in doses from 5 to 20 grammes per hectare. Substances that are used as pheromones for specific pests are also being developed. The pests are caught in traps treated with the pheromone and are then killed with insecticides.

There has been a move towards substances that are more specific, that originate from existing biologically active substances in the environment, and that can be used in far smaller quantities per hectare. As far as the environmental impacts of combating weeds, diseases and pests are concerned, the new pesticides are unlikely to make much difference. On the other hand, the general environmental risk will probably be reduced because of the stricter environmental requirements for the authorisation of pesticides, the smaller quantities that need to be used and the lower toxicity to non-target organisms.

9.12 Conclusions

There are a number of non-chemical and alternative methods of preventing and controlling pests in agriculture that could reduce the pesticide load on the environment and improve health and safety through omission of spraying. The methods include consistent and systematic use of damage thresholds and decision-support systems. The environmental and health advantage of non-chemical methods is the absence of pollution of surface water, groundwater and the surroundings in general. Ending the use of pesticides by using mechanical weed control, preventive production methods, development of resistant varieties, biological control of pests and the use of genetically modified plants with resistance to pests would remove the exposure of workers in farming, forestry and market gardening and would remove pesticide residues from food products produced in Denmark, although not from imported products, see section 10.4.2. The Sub-committee on Agriculture believes that it is possible to achieve a 20-50% reduction in some crops by combining decision-support systems and chemical and non-chemical methods. However, some of these methods also have various impacts on the environment and health that do not directly imply significantly improved conditions for environment and health.

It can also be concluded that there are good possibilities of reducing the load on the environment through improved spraying methods and a proper procedure for washing and filling of spraying equipment, including the arrangement of sites for filling and washing. Lastly, the sub-committee concludes that increased soil treatment in connection with a phase-out of pesticides would not result in any significant difference in the formation of fungal toxins and release of nutrients provided these factors were taken into account in cultivation practice. On the other hand, if pesticides were no longer used, energy consumption would in all probability increase.

The following specific conclusions can be drawn: