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Effects of reduced pesticide use on flora and fauna in agricultural fields

7 General discussion

(Petersen, B.S., Jensen, A.-M.M., Navntoft, S. & Esbjerg, P.)

7.1 Wild flora

The aim of the botanical investigations was to analyse whether the reductions in dosages of herbicides and insecticides caused changes in performance and diversity at the primary production level, not to evaluate the activity and efficiency of the herbicides.

Weed density expressed as total number of plants per m², and as number of plants per species per m², was highly dosage dependent. The total weed density was significantly higher at quarter and half dosage than at normal dosage, whereas no statistically significant difference was found between quarter and half dosage. No between years differences in the effect of dosage were found, so no traceable accumulation in weed density could be detected at reduced dosages over the three years. Both target weed species and non-target species (weak competitors) increased in density at reduced dosages. The total weed density is a measure of the potential non-crop plant food supply for herbivores, and increased weed densities may thus improve living conditions for these.

The relation between total weed density and weed diversity is obvious; the weed diversity (species richness) increases with an increase in total weed density, as was also found in this study. In addition, it was found that weed species richness expressed as number of species per plot was negatively correlated with dosage, especially in spring barley fields. This was, e.g., reflected in the fact that several non-target weed species occurring at low frequencies in the experimental fields were found more often at quarter dosage than at normal dosage. This increased richness was found though the species pool in the arable fields has diminished strongly during the last decades (e.g. Jensen & Kjellsson 1995). The potential herbivore non-crop food supply thus became not only more abundant, but also more diverse as the pesticide dosages were reduced. This effect was most pronounced at quarter dosage.

The numbers of flowering species and plants were recorded, and only at quarter dosage a significant increase in the number of flowering species was observed. The future weed population is directly related to the success of the flowering plants, and they provide nectar and pollen for pollinating insects.

In the analyses of the composition of the seed rain, only 2/3 of the species observed in the vegetation were found as seeds. This infers, methodological difficulties excepted, that many species do not reproduce by seeds, either because they reproduce vegetatively or because they never reach reproductive age. Furthermore, the diversity in the soil seed bank (which is composed of seed rain from many years) is higher than in the seed rain from any single year.

The conclusion of the seed rain study is not straightforward, and possible consequences of dosage-dependent changes in weed seed production for seed-eating birds must also be related to the waste of grain in the fields, considering that the grain biomass is tenfold the weed seed biomass. When available, grains may be preferred to weed seeds by several bird species (e.g. Berthelsen et al. 1997).

7.2 Arthropods

The general trend was that arthropod biomass (mg dry weight/unit area) was increased at reduced pesticide dosages. There was a noticeable difference between the three crops. In barley, a significant difference of the estimated dry weight between dosages was revealed, with estimates at quarter dosages being significantly higher than at half and normal dosages. In wheat and beets there were no significant differences, but there was a clear tendency towards more arthropod biomass at reduced dosages. Possible reasons for the pronounced effects found in barley compared to wheat could be that the pesticide applications in this crop were more efficient because of the more open structure, allowing the pesticides to penetrate deeper into the canopy. Weeds may also affect the microclimate relatively more in barley than in wheat because of the more open canopy structure in barley, benefiting arthropods at the higher weed density found at quarter dosage. Furthermore, the early insecticide spraying in barley may have affected more arthropod species at critical stages. The insecticide application history of barley and wheat are quite similar. When the insecticide applications in barley and beets are compared, obviously barley was sprayed more intensively than beets and often with more broad-ranged products, probably resulting in more devastating effects. Furthermore, weed hoeing in beets was consistently conducted at half and quarter dosage, whereas hoeing in normal dosage plots was only carried out at Gjorslev and Oremandsgaard. Generally it may be assumed that soil-tilling has a negative impact on arthropods (Holm et al. unpubl.), probably counteracting the effect of reduced dosages, since weed hoeing mostly was conducted in plots treated with reduced pesticide dosages.

The obvious question is which specific mechanism(s) caused this effect of increased arthropod dry weight at reduced dosages. Due to the complexity of this project it is not possible to answer this question precisely, since it is impossible to isolate and quantify all the specific mechanisms, and not least their interactions. It might, however, be expected to find a positive correlation between the two trophic levels, weeds and arthropods, through effects of weeds on food availability and microclimate. The combined analyses of the biomass of arthropods, estimated by suction sampling, in relation to vegetational data did, however, not reveal any explainable significant findings. This result may not be surprising, since the vast majority of the arthropods in arable land inevitably have to be generalists in order to survive the constantly changing environment. Weeds as a food resource may therefore be less important compared to the effect of weeds on the microclimate. Dominating arthropod groups, however, which may benefit from an altered microclimate due to their location near the ground are not extracted in high numbers by suction. The most obvious example is the important Carabidae (ground beetles), which contribute significantly to the fauna both as food items and as predators. The lack of precise estimates of their dry weight in the suction samples may consequently affect the analyses of arthropod biomass in relation to vegetation (carabids were efficiently sampled by fenced pitfalls, see later).

The fact that no general correlation between arthropod dry weight and the weed community was revealed does not mean that no correlations between the two trophic levels were found. Significant correlations, which were not dosage related, were among others found for Symphyta (sawfly) larvae (Fig. 6.1), Lepidoptera (butterfly and moth) larvae (Fig. 6.2), Miridae (plant bug) adults (Fig. 6.3) and Curculionidae (weevil) adults (Fig. 6.4); all true herbivores and important food items. This is in line with findings of Chiverton & Sotherton (1991), who found that headland that was not sprayed with herbicides supported significantly higher densities of non-target arthropods, especially some species that are important in the diet of insect-eating game-bird chicks.

The estimated total carabid dry weight in wheat differed significantly between quarter and normal dosages. This effect could only be revealed by use of fenced pitfalls, because suction sampling is an insufficient method for sampling carabids. For the dominating family Carabidae, weed cover may be an explanatory factor of the significant dosage effect found in wheat. In the field the canopy often protects the epigaeic carabids by inhibiting the routes of exposure of pesticides (Gyldenkærne et al. 2000). Nocturnal species may also be protected from direct exposure within the refuges at the time of insecticide application, resulting in lower mortality. Furthermore, the relatively large size of carabids also reduces their susceptibility to insecticides. Overall weed cover, rather than a lethal effect of insecticides, may play a key role in the differences found between dosages. The most abundant species of Pterostichus, of which the population was significantly higher in quarter dosage, are nocturnal and desiccation may be a problem. Therefore they probably prefer the dense plant cover found in quarter dosage whereas the most abundant Bembidion species, which occurred at significantly higher density at normal dosage, are known to prefer open soils and thus a less dense plant cover as found at full dosage. Generally, when evaluating population results, competition should be considered in line with other factors, which of course complicates the analyses. In this example Bembidion is part of the diet of Pterostichus, a fact that may also enhance the populations of Bembidion at lower densities of Pterostichus.

Insecticides may be of greater importance than the herbicides/weed community for the significant dosage differences of arthropod dry weight that were revealed by suction sampling. The significant covariate treatment intensity index of insecticides in the dry weight analyses from barley and wheat, compared with the lack of correlation between arthropod dry weight and weeds, leads to the conclusion that insecticides have the biggest overall impact on the amount of available estimated arthropod food. This was supported by the fact that it actually was possible to reveal a significant difference between dosages for arthropod biomass in beets, but only on data comprising the 14-day period after insecticide application. One of the problems with isolating a pure insecticide effect is that some herbicides may act as insecticides (Candolfi et al. 1999) and that various insecticides used affect arthropods differently. The widely used aphid specific Pirimicarb does not harm most predators directly whereas Dimethoate and pyrethoids (e.g. "Karate") have broad ranged effects. The impact of lethal effects of herbicides can be considered minor, because the predominant herbivores and many predatory insect groups are little active in the field early in the season when herbicide application occurs. It is therefore most likely that the direct lethal effects on arthropods are effects of insecticide applications.

Non-parametric tests revealed that numbers of the most common arthropod groups generally increased under a reduced pesticide regime, except for the non-carnivore taxa in wheat. Overall there was a clear effect of quarter dosage, whereas there was no general effect of half dosage. The dominating pest problem of Danish farmland crops is Aphididae (aphids), and most insecticide applications are directed entirely against these pests. Generally in this experiment, a dosage effect on aphids was found in all three crops, with higher populations at reduced dosages. The aphicide Pirimor (Pirimicarb), which is considered less harmful to most arthropod predators, proved more effective than pyrethoids and Dimethoate. Furthermore, in the cereals quarter dosage seemed to be at the borderline of the required minimum. It is apparent that a major part of the most affected arthropod carnivores in all three crops are aphid specific, often at their juvenile stages. It is possible that the effect was due to prey removal, rather than being a direct lethal effect on the predators. On the other hand, aphid-specific carnivores are among the most exposed to insecticide applications due to their location high in the canopy, which may lead to increased lethal effects.

7.3 Birds

With the field-nesting Skylark as an obvious exception, the common farmland bird species breed in natural and semi-natural vegetation outside the agricultural fields. The vast majority of these species, however, in some period(s) of the year make use of the resources available inside the fields. In general, the number of birds visiting the fields has been found to increase during the breeding season (early May to early August), especially in July. This increase is far more pronounced in beets than in cereals and accompanies the increase in structural diversity of the crop vegetation. A parallel rise in the total abundance (dry weight) of arthropods inside the fields has been found, especially in beets. It can be presumed that the birds exploit this food resource, so that there is a causal relationship between the increase in arthropod abundance in the fields and the number of birds visiting the fields. This relationship may be enhanced by the fact that the amount of arthropods available in the surrounding hedgerows probably decreases from early July onwards (Nielsen & Sell 1986).

In the Skylark, the changing use of the different crops during the breeding season is probably mainly due to changes in the value of each crop as a nesting habitat, although the strongly increasing amount of arthropods in beet fields from mid-June onwards may be part of the explanation for the increasing use of this crop. Food accessibility is just as important as food abundance, and as a crop grows tall and dense it becomes less suited to the Skylarks' feeding behaviour. Odderskær et al. (1997b) found that Skylarks preferred tramlines and unsown patches to the interior of the fields, even if the latter held higher densities of food items. Jenny (1990a) states that when ground coverage exceeds 50%, the Skylarks' use of a crop for foraging is severely impeded, and he concludes that food accessibility (rather than food abundance) is a limiting factor. Viewed in this light, it is not surprising that our analyses did not reveal any significant relationship between Skylark abundance and arthropod biomass as measured by the suction sampler. Odderskær et al. (1997a) were also unable to relate Skylark nestling survival to food abundance (measured by D-vac sampling) in their regression analyses.

Within certain limits, the presence of weeds inside a field improves breeding conditions for Skylarks (Schläpfer 1988). This may explain the positive effect of weed species richness on Skylark densities in barley fields (Fig. 6.1). It may be surprising that weed diversity, rather than weed density, is the factor of significance in the present analysis. However, the two weed variables are mutually correlated (r = 0.57), and it may to some extent be accidental which of them turns out as the best predictor in an analysis of covariance (actually, the effect of Weeddens is almost significant (p = 0.051)). In wheat fields, no effect of weed diversity or weed density is seen - and no effect was to be expected, because the crop alone gives a ground coverage above the 35-60% regarded as optimal (Toepfer & Stubbe 2001). A positive effect might be expected in beets, where ground coverage is even lower than in barley. Green (1980) found that Skylark densities in beet fields in April and May were positively correlated with weed seedling density. Later in the season the pattern may well be distorted by the hoeing which (at least in theory) may cause severe disturbance of nesting attempts in a ground-nesting species like Skylark. Generally, however, the effect of mechanical weed control on birds of arable fields is not well known and should be a subject of future research.

Whitethroats chiefly search their food in the hedgerows, especially in the hedge-bottom, but locally and on occasion a major part of their foraging takes place in agricultural crops (Cracknell 1986, Nielsen & Sell 1986) - probably as a response to a flourishing of suitable prey items. In the present study, a positive effect of total arthropod dry weight on Whitethroat densities has been found in all three crops, although the effect is not significant in barley (which is used the least). The effect is strongest in beets (Fig. 6.4 A-B); beet fields are mainly used from July onwards.

Whitethroats are the most specialised insectivores among the bird species analysed, so it makes good sense that it is in this species a clear relationship between arthropod and bird abundance is revealed. In the analyses of covariance, total arthropod dry weight proved a better predictor of Whitehroat densities than dry weight of "preferred birds' food items", possibly because the latter group was selected mainly with Skylarks in mind (cf. chapter 3). Important Whitethroat prey items are larval and adult Lepidoptera (esp. Geometridae and Noctuidae), spiders, Hymenoptera (esp. Tenthredinidae larvae), Hemiptera (Aphidoidea, Psylloidea, Cicadellidae) and Coleoptera (esp. Curculionidae and Chrysomelidae) (Cramp & Simmons 1977-94, Nielsen & Sell 1986, Christensen et al. 1996). In beet fields, Elateridae and larval Silphidae may also be of importance (P. Odderskær pers. comm.).

In the small seed-eaters, the ancovas revealed a highly significant, negative correlation between weed densities and bird numbers. There are no obvious reasons for this and, as discussed in section 6.2.2, the correlation may well be accidental. This conclusion is supported by the fact that, unlike in the other species, the analyses of morning and afternoon counts of seed-eaters resulted in different models with respect to the covariates. Also, analyses of (more or less homogeneous) species groups may be subject to greater variation and more difficult to interpret than analyses of single species.

Nevertheless, the labelling of a highly significant correlation as "accidental" is of course debatable. Invariably, it calls for caution with respect to the interpretation of the relationships found for Skylark and Whitethroat, although those models, at least on the face of it, seem more credible.

Comparison of the models with and without covariates reveals that the covariates mainly explains density differences between years (Whitethroat) and farms (Skylark), but only to a minor degree differences between dosages. That is, in all three species (groups) analysed, there are significant (or almost significant) between-dosages differences in bird densities during the breeding season which cannot be explained by the measured variation in arthropod abundance, weed density or weed diversity. These dosage effects do not vary significantly between crops, nor do they vary between years, and the few cases of an apparent farm dependence may be explained by the lack of full comparability of plots (cf. section 4.4).

The largest differences between dosages are found in Whitethroats and the second largest in small seed-eaters, whereas the differences in Skylark densities are less pronounced (section 4.4.1). As might be expected, a 75% reduction of the dosages of herbicides and insecticides results in a greater increase in bird densities than a 50% reduction, but the latter has significant effects on all three species (groups) as well. A tentative conclusion could be that at least half of the effect achieved by a 75% reduction of the herbicide and insecticide input may also be achieved by reducing the dosages to 50%.

The differences in bird density largely result from a redistribution of birds at the local scale; the population effects (if any) are unknown. Odderskær et al. (1997a), studying Skylarks in barley fields, did not find any differences in territory density between pesticide sprayed and unsprayed fields. However, the number of successful breeding attempts was higher in unsprayed fields (especially in late season), perhaps because a more abundant and diverse food supply allowed the birds to stay in a better body condition. Based on estimated breeding success and survival rates, Wilson et al. (1997) concluded that two or three nesting attempts per season are necessary for a Skylark population to be self-sustaining and that suitable conditions for this rarely exist in conventional cereal fields. By attracting higher numbers of birds and providing them with a richer food resource (as indicated in the present study), areas with reduced pesticide use may help increasing breeding success, and hence population size.

It must be assumed that the differences in bird occurrence between dosage plots found in the breeding season have been caused by the experimental differences in pesticide treatments. It is unlikely that the products used have appreciable direct effects on birds. Thus, the pesticides must affect the birds chiefly through indirect means, i.e. through a deterioration of habitat structure or food supply. Insecticides reduce the amount of arthropod food items directly, whereas herbicides affect vegetation structure directly and food abundance indirectly by reducing the amount of suitable host plants (e.g. Campbell et al. 1997). Nonetheless, in the analyses the differences in bird occurrence are only to a minor degree explained by differences in arthropod abundance and weed density/diversity. This does not mean that the positive effects of reduced pesticide use are not mediated through improved supplies of arthropod food items or a more suitable (weed) vegetation structure. Rather, it probably means that the variables used as predictors in the analyses have been too crude to include sufficiently detailed information about the resources available within a plot. Birds are often opportunistic in their choice of food items and feeding sites, and direct modelling of bird density as a function of resource availability may just be possible on a (spatially or temporally) fairly small scale.

After the breeding season, many farmland bird species gradually switch to a vegetable diet (mainly seeds) as the availability of arthropods declines. On the autumn counts, no effects of pesticide dosage on the distribution of birds on the fields were found. Also, bird densities could not be related to the amount of seeds available on the ground surface. Arthropod abundance was not measured. In the botanical as well as in the ornithological investigations, the variation between farms and fields was large, and this may, in combination with the incomplete, unbalanced design (cf. section 4.2.2), be one reason for the lack of significant results. Another reason, however, may be that food on stubble fields in early autumn is superabundant, so that other factors, e.g. the risk of predation, are the major distributing factors. In winter, when resources are sparse and the demand for energy-rich food is high, differences in seed densities may be of greater importance. Robinson & Sutherland (1999) and Wakeham-Dawson & Aebischer (1998) found that densities of Skylarks and Yellowhammers on stubble fields in winter were positively correlated with seed density. However, Donald et al. (2001) were unable to detect any correlation between soil surface seed density and Skylark occurrence in November-March.

British studies have demonstrated that many bird species, especially seed-eaters, strongly prefer stubble fields to other field types during the winter, probably due to the rich supplies of weed seeds and spilt grain (e.g.Wilson et al. 1996, Robinson & Sutherland 1999, Donald et al. 2001). The value of these fields increases with increasing weed cover (Wilson et al. 1995 cited in Campbell et al. 1997) whereas undersown fields are less used by birds (Robinson & Sutherland 1999). The importance of stubble fields as foraging sites is so high that the loss of winter stubbles, caused by the switch from spring to autumn sown crops, may be one of the major reasons for the widespread population declines in many farmland birds (e.g. Baillie et al. 1997, Evans 1998).

7.4 Yield and economy

It has to be noticed that while investigations of plants, insects and birds were high priorities the effects of reduced yields of dosages only had to be considered as a fair background for possible compensations to landowners. Therefore of course also aspects of economy were treated in another way than if it was an area of high priority.

This being said, the picture was, however, rather uniform. Thus losses in cereals never reached any serious level. Only in 3 of 58 cases yields were significantly below the corresponding normal dosages (Appendix E.2). All the three cases were at quarter dosage. Similarly in sugar beets only in 5 of 32 cases yields were significantly decreased (Table 5.3). The proportionally higher occurrence of decreased yields in sugar beets corresponds very well with both the much more crucial weed situation in the less competitive sugar beets and the difficulties with the very precise field operations (band spraying and mechanical hoeing).

The follow-up on the above results with economic scenarios (Tables 5.4.1 and 5.4.2) shows that to some degree the few cases of yield losses in winter wheat are counterbalanced by cost savings on herbicides and insecticides when applied at reduced dosage levels. The overall picture very clearly is that on the short term the pesticide reduction is rather unproblematic, at least in cereals. However, the costs of cleaning up particular weed patches after the projects points at a problem-area not fully incorporated in the present project but at the same time a problem which may easily be avoided in practice. The clue of course will be not to continuously reduce the dosages of all herbicides on the same piece of land but rather record problem patches and treat these accordingly at some intervals. Such a strategy will also counterbalance the slight decrease in production stability which might be a side effect of a more widespread use of reduced dosages. In this connection also the possibly increased cost of management is a factor which might also deserve some attention.

7.5 Biodiversity vs. economy: getting the balance right

The botanical, entomological and ornithological studies clearly indicate that a reduction of the pesticide dosages leads to increased biodiversity in the fields (see section 1.2.1 for a definition of "biodiversity" as used here). At the primary production level, a general increase in weed density and weed species richness at reduced dosages was found, and a greater proportion of species reached the flowering stage. The most prominent density responses occurred in target weed species, but effects on non-target weed species (weak competitors), including some scarce species, were also found. Arthropod amounts tended to increase at reduced dosages, with respect to total biomass as well as to numbers of individuals of a broad range of taxonomic groups. The clearest differences were found in barley fields. Both herbivores and carnivores showed a response, but the experimental design did not allow a separation of direct and indirect pesticide effects. Finally, all three bird species studied developed a preference for areas treated with reduced dosages as the summer progressed. The largest differences (100% increase) occurred in the purely insectivorous Whitethroat, whereas the weakest response (20-25% increase) was found in the more omnivorous Skylark.

Comparable responses to the dosage reductions were recorded at all trophic levels, strongly suggesting the existence of causal relationships. However, directly relating population densities at one trophic level to densities at another level in the statistical analyses proved not straightforward, partly because of temporal or spatial scale problems, partly because the measurements were not targeted towards analyses of energy flow.

Across all trophic levels, the largest gains occurred at quarter dosage. The general density of weeds was also significantly increased at half dosage and did not differ between half and quarter dosage. As for the weed species richness, however, half dosage held an intermediate position between quarter and normal dosage, with a 16% increase at half dosage (relative to normal dosage) and 28% increase at quarter dosage. The increase in the proportion of flowering species was only significant at quarter dosage. The estimated amounts of arthropods at half dosage showed no general tendency and very few significant differences between half and normal dosage were found. In many cases, the number (or biomass) of arthropods at half dosage was closer to normal than to quarter dosage. In the ornithological studies, an evaluation of the effects of half dosage is hampered by the lack of full comparability of plots. With due reservation, it may be concluded that at least half of the increase in bird numbers achieved at quarter dosage (cf. above) also occurs at half dosage. Contrary to the other studies, however, the differences in bird numbers between dosage plots result from a local redistribution of birds (reflecting feeding site preferences) rather than from differences in population sizes.

A comparison of the gains at half and quarter dosage suggests a logarithmic (rather than a linear) relationship between dosage and biodiversity. In the present study, plots without any herbicide and insecticide input only occurred in the small-scale yield experiments. It is clear from the weed counts performed there that the increase in weed density and species richness from quarter to zero dosage is at least of the same magnitude as the increase associated with a change from normal to quarter dosage (cf. Fig. 5.2). This further points towards a strongly curvilinear dose-response relationship, coinciding with dose-response curves describing the response of single species of weeds to single herbicides (e.g. Streibig 1992).

From the yield experiments and the economic calculations it can be concluded that a halving of herbicide and insecticide dosages in cereals by and large may be carried into effect without negative economic consequences. A 75% reduction may be more problematic, especially if implemented through several years, as average yield declines are larger and contribution margins may suffer. The 3-year duration of the project does not allow an evaluation of the extent to which reduced dosages lead to an accumulation of weed problems. Also Salonen (1992a) found no increase in the number of weed seeds in the soil bank after continuous application of one-third of recommended dosage over three consecutive years. The clean-up decisions, however, indicate that some problematic species, especially Elymus repens, may spread quite quickly if dosages of the appropriate herbicides are reduced. Long-term field studies of reduced herbicide use have revealed an accumulation of seeds in the topsoil (Jones et al. 1997) or a significant higher density of problem weeds as Apera spica-venti (Pallutt 1999).

In sugar beets, no differences in average yield were detected between half and quarter dosage; but in all three years, average yields were lower at reduced dosages than at normal dosage. Also, and more important, beet yields at reduced dosages were very variable - to an extent which is verging on the unacceptable in a high-value crop. Obviously, the combination of band spraying and hoeing at present does not provide the same production security as broad swath application, but reducing herbicide dosages in a broad swath is no alternative (as amply demonstrated in the pilot year).

On balance, a 50% reduction of herbicide and insecticide dosages in cereal crops results in a modest increase in biodiversity at all trophic levels without notable cultivation problems, at least in the short run. Biodiversity gains are increased, maybe following a logarithmic dose-response relationship, as pesticide dosages are reduced, but at quarter dosage the risk of significant yield losses (and hence reduced contribution margins) is no longer negligible, and a 75% reduction cannot be used indiscriminately. In sugar beet, a 50% (or even greater) reduction of pesticide amounts by band spraying may work well in combination with mechanical hoeing, but production risk is markedly increased. The dose-response relationship for the biodiversity gains seems comparable to that in cereals.

The treatment intensity indices calculated on the basis of the "normal" dosages chosen by the farm managers were in the case of herbicides within the same range as the Danish mean values for the three crops calculated on the basis of consumptions 1997-99 (Table 1.1). The "half" dosages of the project farms were well below the values stated as goal for 2002 in the Pesticide Action Plan II (spring barley 0.48 vs. 0.70, winter wheat 0.74 vs. 1.20, sugar beet 0.96 vs. 2.40). For insecticides, the picture was quite different, the "normal" dosage in spring barley being almost triple of the 1997-99 mean for Denmark, while normal in wheat was more than twice the Danish 1997-99 mean and normal in sugar beets was almost 70% higher than the Danish mean (Table 1.1). It should be noticed that all the farms hosting the project are situated on rich, heavy soils where especially aphid problems tend to be more frequent than on less rich soils. As for insecticide use in winter wheat and sugar beets, mean treatment intensity indices in Denmark were further reduced in 2000 (0.12 and 0.21, respectively (Danmarks Statistik 2001)), thus being below the goals for 2002 (Table 1.1). Apart from being possibly influenced by differences in weather, the values for 2000 may be an indication of improved use of the aphid forecastings (fewer sprayed fields) rather than of treatments with reduced dosages.

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