Landbauforschung – Journal of Sustainable and Organic Agriculture, Vol. 72 No. 1 (2023). S. 1–14, | DOI: 10.5073/LBF.2023.01.04 | Saltzmann et al.

(c) The author(s) 2023 This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/deed.en).

Submitted/accepted for publication: 25 August 2023/28 November 2023

Summary

Plant pests, diseases and weeds threaten agricultural crops and require control methods. However, the largely used pesticides are associated with undesirable effects on environment and health. To reduce pesticide use, Integrated Pest Management (IPM) offers a comprehensive toolbox. The two selected IPM strategies (1) wide crop rotation and (2) cultivation of pathogen resistant cultivars were analysed economically based on two different field trials. Crop rotation (long-term field trial at Dahnsdorf, Brandenburg, Germany, with a six-unit crop rotation) and pesticide reduction by 25% and 50% resulted in no decline in gross margins and thus profitability in silo maize, wheat (E- and A-quality), barley and rye. However, a 25% and 50% reduction in pesticides led to a decline in gross margins by -6.3% (-331 € ha^-1) and -8.3% (-437 € ha^-1) in potatoes. The use of pathogen resistant wheat cultivars and IPM based fungicide application (tested at five field sites across Germany) resulted in reduced fungicide applications and higher gross margins compared to the “non-IPM” strategy by about +45 to 70 € ha^-1. Based on these findings, we conclude that preventive IPM strategies have a good potential to reduce pesticide use and are also economically viable for farmers.

Keywords

economic viability, potential of pesticide reduction, field trials, crop rotation, cultivar resistance, plant pests, diseases and weeds

Introduction

Plant pests, diseases and weeds threaten agricultural crops and can cause substantial economic losses (Savary et al., 2019). Plant protection therefore remains an important part of crop management. The application of pesticides has been the major measure in crop protection since many years. Pesticides are, however, associated with undesirable effects on the environment, health, and the sustained efficacy of their use (Pimentel & Burgess, 2014; Barzman et al., 2015; Tang et al., 2021). Moreover, policy aims for reducing pesticide use and risks have been formulated at EU (Green Deal and Farm-to-Fork-Strategy; European Commission, 2020) and national level, and reduction programs are introduced.

With our study, we aim to evaluate the economic viability at field level of specific preventive IPM strategies in arable crops considering their pesticide reduction potential. As exemplary case studies for IPM strategies, we selected the (1) diversity of crop rotation and the (2) use of pathogen resistant cultivars in winter wheat.

Crop rotation (1) affects spatial and temporal diversification of crops over time (Castellazzi et al., 2008) and is a cornerstone to minimize pest and weed pressure. Crop rotation is the most effective agronomic alternative to chemical pesticides (Barzman et al., 2015). In arable crop rotations, the alternation of winter and spring-summer crops and of cereals and foliar crops is known to break the life cycle of weeds but also pests. Concerning insect pests, this strategy is especially successful against specialized insects with limited mobility (Bazok et al., 2021; Vasileiadis et al., 2011). Diverse crop rotations are reported to be associated with yield increase, economic benefits for farmers and reduced production risks (Shah et al., 2021; Jalli et al., 2021; Gaudin et al., 2015).

Pathogen resistant wheat cultivars (2) are an important tool in IPM to prevent pest infestation and are considered as a cost-effective and environmentally friendly approach to control fungal diseases (Klocke et al., 2022). Still, 88% of the world's wheat production is based on wheat cultivars susceptible to (various) diseases (Carmona et al., 2020). On the other hand, Lüttringhaus et al. (2021) reported on the profitability and sustainability of resistance breeding due to a reduction of fungicide costs.

We based our economic analysis of crop rotation and the use of pathogen resistant cultivars in winter wheat on field experiments. With our economic analysis, we intend to answer the following research questions:

(1) What are the benefits and costs of reducing pesticide use in a wide six-unit crop rotation?

(2) What are costs and benefits of implementing pathogen resistant cultivars and situation specific pesticide treatments for farmers?

(3) What are the constraints to improve pesticide reduction opportunities?

Material and methods

In this paper we consider two case studies to estimate the potential of pesticide reduction for IPM concerning their effect on profitability. Research question 1 and 2 refer to one study each, the “wide crop rotation study” and the “pathogen resistant cultivar study”. For the analysis on constraints of IPM, mainly literature was considered. The statistical analysis was carried out using SAS.

Case study “wide crop rotation”

The economic reduction potential of pesticides in a wide crop rotation was determined by evaluating a long-term field trial. The trial was conducted from 2004 to 2016 at the Dahnsdorf experimental fields of the Julius Kühn Institute in Brandenburg, Northern Germany.

Description of the field trial and pesticide strategies

The trial included a wide six-unit crop rotation of: intercrop (1) silo maize – (2) A-quality wheat – (3) winter barley – intercrop (4) potatoes – (5) Elite-E-wheat – (6) winter rye. The A-quality wheat class stands for the "quality wheat" in German classification. It is mainly used as a blending wheat to complement other wheat varieties. Elite-E-wheat represents the highest quality. However, it is rather unsuitable for baking and is used in small quantities. Both, the A- and E-quality wheats stand for high protein cultivars with 13% raw protein content for A-wheat and 14% for E-wheat (Stary, 2023 and Deter, 2019). As a rule, plowing was carried out in all years and crops. In some years, plowing was not required in the two wheat crops due to the position in the crop rotation, which was expected not to have any volunteer grain after silo maize or potatoes. As described in more detail in Schwarz et al. (2018) and Saltzmann & Kehlenbeck (2018) the plant protection strategies in the field trial differed as follows:

• Situation-related dosage (sit.; 100%-pesticides): Good professional practice taking into account the principles of IPM, application of control thresholds, situation-adapted selection and dosage of pesticides.

• 75% of situation-related dosage (75%-pesticides): Reduction of the treatment frequency index (TFI, as described by Klocke et al., 2023, this issue) by 25% compared to sit. for all pesticides.

• 50% of situation-related dosage (50%-pesticides): Reduction of the TFI by 50% compared to sit. for all pesticides.

Weather and site conditions of the field trial location can be found in Klocke et al. (2023) in this issue.

Data and assumptions

For the economic evaluation, a period of two six-unit crop rotations over 12 years (2004–2015) was analysed. Field data on costs and revenues was supplemented by secondary German data sources (see Table 1). An overview on the used revenue and cost components as well as further assumptions relevant for calculations are shown in Table 1.

Calculation method

Using cost-performance accounting methods as a standardized calculation method in agricultural economics, the annual gross margins for each crop and each pesticide strategy were determined. The gross margins calculated here only include those cost and benefit components that differ between crops and pesticide strategies and thus have an impact on the result. Soil management was considered identical for all crops and strategies and was therefore not taken into account. Gross margins are defined as a result of revenues minus direct costs (Schroers et al., 2010; Table 2). For the gross margin calculations, the direct costs, labour and machinery costs caused by sowing, fertilizing, pesticide application and harvesting as well as the interest for the committed capital were deducted from the revenues. Average gross margins per crop were calculated for the entire trial period (2004–2015) and for each (6-year) rotation individually.

Statistics

The effects of the different strategies on grain yield and gross margins were analysed using linear mixed models (Moll & Piepho, 2001) with the MIXED procedure of SAS^® version 9.4. Grain yield and gross margins were the dependent variables, while years and blocks were treated as random effects. Blocks were nested with years for grain yield. In addition, the interactions between year and strategy were analysed. The analysis of the gross margins was not performed on block level and based on one single value per year and crop. Least squares (LS) means were estimated for the dependent variables by using the LS means option and a 0.05 probability level. These squares were then compared for differences in the different strategies with the simulate adjustment test. The rotations were compared using a t-test.

Case study on consequent IPM with “pathogen resistant cultivars”

The economic analysis of this case study was based on field trial data (Klocke et al., 2022), supplemented by secondary German statistical data.

Field trials

Field experiments were conducted over three years (2016–2018) at five field sites in Germany (Dahnsdorf, Söllingen, Bingen, Thyrow and Groß Lüsewitz) with different pedo-climatic properties and are described precisely by Klocke et al. (2022). Soil conditions at the five sites are characterized by sandy silt (Dahnsdorf), loamy (Söllingen), sandy loam (Bingen), sandy to loamy sand (Thyrow) and sandy loam (Groß Lüsewitz). Mean annual precipitation reaches about 565 mm in Dahnsdorf, 600 mm in Söllingen, 490 mm in Bingen, 510 mm in Thyrow and 690 mm in Groß Lüsewitz.

Plant disease control and IPM strategies

The field trials compared the three different fungicide strategies “untreated control”, “situation-related” and “practice-related” for eight different cultivars each (Klocke et al., 2022).

Our economic assessment considered those changes in costs and benefits that were related to the implementation of the IPM measures “resistant cultivars”, “intensive pathogen moni­toring” and consequent use of “disease thresholds” in comparison to not doing so. We therefore only compared the two variants “IPM”, which is represented by the “situation-related strategy” and “non-IPM”, represented by the “practice-related strategy” as described by Klocke et al. (2022; see Table 3).

The resistance classification of the eight wheat cultivars is listed in Table 4.

Calculation method

Costs, revenues and gross margins (for details see above and Table 2) were calculated for the yearly mean of four field data replicates based on standard procedures.

For the economic analysis we chose a comparison of gross margins between “IPM” and “non-IPM” and a cost-benefit-analysis for the implementation of the IPM strategies (with resistant cultivars, monitoring and fungicide application). Here, all input factors with their costs were considered.

Economic benefits in a cost-benefit comparison are in general considered as exceeding of the revenues compared to the costs. Other benefits such as environmental aspects were not taken into account.

Assumptions for costs and revenues

Calculations of variable costs for input factors were based on individual treatments and measures according to the field trials. Variable costs comprise sowing, plant protection measures, fertilization, tillage, and harvesting. They were calculated separately, based on site-specific data in the field trials of the investigated strategies in 2016, 2017 and 2018 at the five locations. Sowing costs were calculated based on the site-specific seed rates (kernels per m²) which differed between the five locations. The seed costs per variety were derived from price lists of trade companies (Beiselen GmbH, 2023; Saa­ten-Union GmbH, 2023) and the labour and machine costs for sowing based on KTBL (2016–2018). One working hour was assumed with costs of 17.50 € (KTBL, 2016–2018).

Plant protection measures included herbicide, insecticide, fungicide and growth regulator applications. Costs were calculated based on the site-specific application rates and pesticide product costs were derived from AGRAVIS (2004–2018). For the estimation of pesticide application costs, average labour costs to conduct sprayings were calculated as mean of field sizes ranging from 1 to 20 hectares and farm-field distances from 1 to 30 kilometres and with a diesel price of 0.70 € l^-1 (KTBL, 2016–2018; see Table 5).

Costs of fertilization were calculated based on the site-specific fertilizer rates (kg ha^-1), the fertilizer costs from price lists of trade companies (BayWa AG München, 2023) and the labour and machine costs for fertilizer application according to KTBL (2016–2018). Tillage costs were calculated according to KTBL (2016–2018) based on the site-specific tillage and machinery. Harvesting costs were considered according to KTBL (2016–2018).

Monitoring costs for assessing disease infestation

The costs of assessing disease infestation vary depending on the size of the field, the distance between the field and the farm and the number of rides per growing season. On average, monitoring costs were considered with 3.56 € ha^-1 per trip to the field. The number of trips for monitoring disease infestation ranged from 3 to 5 and the monitoring costs per year from 11 to 26 € ha^-1, depending on the year, the site and the cultivar. Klocke et al. (2022) have described monitoring results and disease infestation comprehensively.

Results

We first present the results of the economic assessment of the case study on pesticide reduction in a wide crop rotation and describe secondly the case study on costs and benefits of the use of pathogen resistant cultivars with an IPM based and situation-related crop protection considering disease thresholds per cultivar.

Reduction potential for pesticides and economic viability of a wide six-unit crop rotation

The economic evaluation of the six-unit crop rotation at the Dahnsdorf experimental field site has shown a clear potential for pesticide reduction in certain crops without economic losses. The average annual gross margins for each of the six crops were calculated and are presented in Table 6.

In addition, the differences in the average gross margins of the reduction strategies (75%, 50%) and the situation-related crop protection strategy are shown (Fig. 1). These results indicate a potential for a reduction of pesticide use from an economic perspective in most crops.

Fig. 1. Differences in average gross margins (2004-2015) of the pesticide reduction strategies (75 %, 50 %) and the situation-related pesticide strategy (sit.) per crop in € ha^-1 of the field trial in Dahnsdorf.

Economic effects of the pesticide reduction strategies

The average gross margins in the situation-related pesticide application strategy (sit.) over both rotations (2004–2015) are 1,134 € ha^-1 in silo maize, 796 € ha^-1 in winter wheat (A-quality), 578 € ha^-1 in barley, 5,281 € ha^-1 in potatoes, 638 € ha^-1 in the second winter wheat (E-quality) within the crop rotation and 533 € ha^-1 in winter rye (Table 6). Compared to the situation-related scenario, no major economic losses occurred in silo maize and grain for the pesticide reduction scenarios (75% and 50%; Fig. 1). In these crops, the 75% reduction scenario was even slightly advantageous compared to the situation-related pesticide treatment. In detail, the average gross margins of silo maize was +59 € ha^-1 (+5.2%), A-wheat +21 € ha^-1 (+2.1%), barley +4 € ha^-1 (+0.6%), E-wheat +22 € ha^-1 (+3.5%) and rye + 15€ ha^-1 (+2.7%) compared to the situation-related pesticide treatment without pesticide reduction. The 50%-strategy achieved almost the same gross margins as the situation-related pesticide treatment (silo maize: +25 € ha^-1 (+2.2%), A-wheat: -12 € ha^-1 (-1.5%), barley: +20 € ha^-1 (+3.4%), E-wheat: +0 € ha^-1 (0.0%), rye: -4 € ha^-1 (-0.7%)) with barley showing even a better result in the 50%-strategy than in the 75% or situation-related strategy. Results are different for potatoes with clear economic disadvantages for the pesticide reduction scenarios. A pesticide reduction in potatoes by 25% led to a -331 € ha^-1 (-6.3%) lower gross margin while a pesticide reduction by 50% caused a gross margin loss of -437 € ha^-1 (-8.3%).

A statistical evaluation of the gross margins and yields for the three crop protection strategies is shown in Table 7. With regard to the gross margins, there is only a significant difference for potatoes between the situation-related plant protection treatment and the 50% reduction. In all other crops, even a 50% reduction in pesticide application did not lead to any significant economic disadvantages. The contribution margins were also evaluated for each rotation separately, but did not show any significant results.

There were more differences at yield level. A 25% reduction in pesticide use compared to a situation-related pesticide application only had significant effects on potato yields. A reduction from 75% to 50% resulted in significant yield differences in winter wheat (both A- and E-quality). A pesticide reduction of 50% compared to situation-related pesticide application led to significant yield differences in winter wheat (A-quality), potatoes, winter barley, winter wheat (E-quality) and winter rye. With the exception of potatoes, the yield effects of the pesticide reduction in these crops were offset by lower pesticide costs and changes in input and producer prices. In potatoes, pesticide savings or price effects could not compensate for yield losses due to the pesticide reduction by 50%, resulting in significantly lower gross margins.

Effect over time – comparing rotation 1 and rotation 2

A closer look at the single rotations shows that rotation 1 has a slightly lower profitability in most crops than rotation 2, with two exceptions: rye was more profitable in rotation 1 (2004–2009) in the situation-related strategy and silo maize was more profitable in rotation 2 (2010–2015) in the 75%-strategy (Table 6).

However, when comparing rotation 1 with rotation 2 the positive trend can be seen in the gross margins only. Considering yields, it is the opposite. Except for silo maize, average yields in the second rotation were lower than in the first rotation in all crops and strategies (sit./75%/50%). For silo maize, average yields in the second rotation were slightly higher than in the first rotation. One reason for the favorable performance of silo maize could be the frequent spring drought at the Dahnsdorf site. In rotation 1, the year 2006 was a very dry year, while in rotation 2 the years 2011, 2012 and 2015 had dry early summers. Silo maize was less affected by spring drought due to its late emergence. In 2013, A- and E-wheat, as well as winter rye, were affected by hail, shortly before harvest.

However, a statistically significant difference between the yields in rotation 1 and 2 could be found in barley (in all strategies), in rye (in sit. and 50%), in A-wheat (in sit. and 75%) and in potatoes (in 75%; Table 8). The lower yields are not reflected in lower gross margins, as these were compensated for by higher producer prices or input changes.

Overall, concerning gross margin calculation, it is remarkable that the effect of the pesticide reduction strategies on profitability is quite small, and does not weigh heavily, except for potatoes.

Consequent IPM with pathogen resistant winter wheat cultivars

The average gross margins for the two strategies “IPM” with resistant cultivars, infestation monitoring and situation-related fungicide application and “non-IPM” practice-related fungicide application are summarized for the five different field sites in Fig. 2. For all five sites, gross margins of the “IPM” strategy exceed those of the “non-IPM” strategy. The differences in the gross margin amounts between the field site locations result from their different yield potential due to different pedo-climatic conditions. Thyrow shows the worst prerequisite for growing winter wheat resulting in negative gross margins. The outcome of the “IPM” strategy, however, is less negative.

Fig. 2. Average gross margins of eight winter wheat cultivars (Apertus, Attraktion, Capone, Dichter, JB Asano, Julius, Patras, Spontan) in € ha^-1 and standard error for the strategies “IPM” and “non-IPM” at the five different German field site locations Dahnsdorf, Bingen, Söllingen, Thyrow and Groß Lüsewitz from 2016 to 2018 (except Groß Lüsewitz with the years 2017 and 2018)

Average gross margins for the different winter wheat cultivars that were studied (Fig. 3) showed that the “IPM” strategy resulted in higher gross margins compared to the ”non-IPM” strategy with one exception, the highly susceptible cultivar JB Asano. The high susceptibility of the cultivar JB Asano to the diseases yellow rust and septoria leaf blotch led to early and frequent fungicide treatments in all years. Those cultivars showing a good to medium resistance, like Attraktion, Capone or Julius resulted in higher gross margins in the “IPM” strategy exceeding those of the ”non-IPM” strategy by about 45 to 70 € ha^-1.

Fig. 3. Average gross margins in € ha^-1 and standard error for the strategies “IPM” and “non-IPM” for the eight winter wheat cultivars (Apertus, Attraktion, Capone, Dichter, JB Asano, Julius, Patras, Spontan) grown at the five different German field site locations Dahnsdorf, Bingen, Söllingen, Thyrow and Groß Lüsewitz from 2016 to 2018 (except Groß Lüsewitz with the years 2017 and 2018)

Variable costs differed between the field site locations (Fig. 4). Due to the experimental design, variable costs of the different sites were only different for the fungicide strategies. The fungicide cost (including tractor rides with labour and machinery cost) for the “IPM” strategy were with about 40% to 85% on average (depending on the field site) considerably lower compared to the fungicide costs of the “non-IPM” strategy. Monitoring costs like insecticide costs were comparably low while fertilizer costs were the highest cost component.

Fig. 4. Average annual variable costs for the two strategies “IPM” and “non-IPM” at the five different field site locations (Dahnsdorf, Bingen, Söllingen, Thyrow, Groß Lüsewitz) from 2016 to 2018 (except Groß Lüsewitz with the years 2017 and 2018)

Discussion

Our study evaluated the economic viability of the preventive IPM strategies “wide crop rotation” and “pathogen-resistant cultivars and disease thresholds” with their associated pesticide reduction potential. Average gross margins per crop did not decrease for pesticide reductions of 25% and 50% and were comparable to the 100% pesticide application strategy, except in potatoes. In some crops, the reduction scenarios were even economically advantageous. Pathogen-resistant cultivars and disease threshold considerations resulted in economic benefits and higher gross margins for the “IPM” compared to the “non-IPM” strategy. We discuss our results regarding the applied methodology and our research questions.

Methodology

The methodology we applied was based on small scale field plots and an economic assessment of the field trial data. Frisvold (2019) stated limitations of such an approach and promotes the evaluation of IPM and its performance under actual farming conditions. We agree and realize the obstacles connected to the upscaling of field plot experiments to farm level conditions. Yields and probably also pesticide reductions are mostly higher under experimental conditions and may not be transferred directly to farming conditions. However, since we compared strategies to each other thus looking at relative changes by implementing a strategy, the absolute values that may differ from practice, have not been in the main focus. We therefore assume that our results are relevant for IPM implementation under farming conditions. Nevertheless, this should be proved by further on-farm research.

Research questions

(1) What are the benefits and costs of reducing pesticide use in a wide six-crop rotation?

Diverse crop rotations offer several benefits, including improved soil health, increased yields, reduced pest and disease pressure, and enhanced profitability for farmers with the authors noting a need for research on economic impacts of long crop rotations (Beillouin et al., 2021). Sánchez et al. (2022) conducted a global meta-analysis and showed that on average diverse cropping systems lead to higher profits than homogeneous cultivation structures especially in developing countries. Rosa-Schleich et al. (2019) point out the economic long-term benefits for farmers of diversifying crop rotations, as well as input and risk reductions. However, no economic evaluations on the potential of crop rotations to reduce pesticides were found for Germany. The potential of diverse crop rotations to reduce pesticides has been described, e.g., by Andert et al. (2016) and showed a decrease in fungicide and herbicide use with an increase in crop diversity by analyzing data over 10 years in Northern Germany. Despite the advantages diverse cropping patterns offer, they receive little attention in agricultural practice. Steinmann & Dobers (2013) analyzed crop sequence patterns over six years on an area representing 645,870 ha arable land in Northern Germany. They showed an opposite trend towards less crop diversity, especially due to the expansion of corn cultivation. Stein & Steinmann (2018) analyzed with a time series approach on administrative data for Lower Saxony (Northern Germany) cropping patterns over seven years. Over 60% of the area investigated was cropped with the ten largest crop sequence types during the years 2005–2011, with maize as a driver for simplified cropping patterns. 34.1% of the arable land was cultivated with a sequence of only one or two crops. 24% were cropped with three crops. 39.3% were cropped without any leaf crop.

Economic studies on the reduction potential for pesticides of long crop rotations are scarce. Saltzmann & Kehlenbeck (2018) showed for winter wheat of different quality levels that pesticides could be reduced by 50% compared to a situation-related application without leading to significant economic disadvantages. The results were based on an isolated evaluation of wheat from the complete crop rotation evaluated in this paper. Karpinski et al. (2020) carried out an overall consideration of a six-year crop rotation. They showed the positive economic and stabilizing effects in the long-term over a period of 18 years, which is in line with the results here. In a wide six-unit crop-rotation under field test conditions a reduction potential for pesticide use without economic losses could be shown for all crops, except for potatoes. Even though slightly lower yields were achieved in the second rotation, these were compensated for by higher producer prices or input changes. It must be mentioned, that the choice of crops in the crop rotation is intended to achieve a compromise between site-adapted crops and economic viability. Due to frequent early summer droughts at the trial site, summer crops are exposed to a particular risk. Therefore only two of the six crops are summer crops. There is further potential for improvement and the results should be verified by further investigations under practical conditions.

(2) What are costs and benefits of implementing pathogen resistant cultivars and situation specific pesticide treatments for farmers?

Results on the IPM strategy show, that this strategy was overall of economic advantage and resulted in higher gross margins compared to the “non-IPM” strategy. The results are in line with Klocke et al. (2022) who calculated net returns but no gross margins. They also demonstrated that the intensity of fungicide use in terms of the TFI of the resistant cultivars were significantly reduced within the “IPM” strategy for all cultivars except the highly susceptible cultivar JB Asano. The cultivars Capone and Dichter showed the lowest TFI across all years and locations, which could reduce the use of fungicides by more than 80% compared to the “non-IPM” strategy. Klocke et al. (2022) reported that this reduction was still 59% on average across all cultivars using the IPM strategy. In the susceptible cultivar JB Asano only a reduction of 7% was possible. Pathogen resistant cultivars also provide pesticide use reduction potential in permanent crops, as reported, e.g. by Kaczmarek et al. (2023).

The decrease in fungicide intensity leads to lower fungicide costs, which also resulted from our study. Other studies on disease resistant cultivars reported similar results (Wegulo et al., 2011; Loyce et al., 2012; Beest et al., 2013). Gross margins were strongly affected by the decrease in fungicide costs. Combined with the not-occurrence of yield losses, the lower fungicide costs lead to the positive outcome of the gross margins. Costs of implementing IPM (seed costs of the resistant cultivars and monitoring costs) on the other hand did not compromise gross margins. The results thus clearly show the economic excellence of this IPM strategy.

Although farmers select cereal cultivars also with respect to their resistance traits (Thiel et al., 2021), they often treat different cultivars with fungicides at the same time, regardless of their resistance level and disease thresholds (Klocke & Dachbrodt-Saaydeh, 2018). In addition, control thresholds are not sufficiently used in practice and farmers perceive especially the additional time needed for monitoring as an obstacle for implementing IPM (Thiel et al., 2021). For oilseed rape, Thiel et al. (2023) concluded, that costs of monitoring are relevant and can only be recovered when labour costs are low and insecticide costs are high. In our study, monitoring costs were comparably low, although the time needed for monitoring in winter wheat taken as a basis was in line with Thiel et al., (2023). Here, probably more research work is still needed.

(3) What are the constraints to improving pesticide reduction opportunities?

IPM offers a ‘toolbox’ of complementary crop- and region-specific and sustainable crop protection solutions to address rising pressures on pesticide reduction (Birch et al., 2011). However, area-wide implementation in farming practice is still lacking. In the presented two studies of the paper, this question was not analyzed explicitly, but is discussed here based on literature. Bakker et al. (2021) identified in their research social-psychological constraints determining farmers´ intention to decrease pesticide use. So, farmers in the Netherlands are strongly influenced by how other farmers act. Furthermore, farmers perceive limited capacity and autonomy to reduce pesticide use. Motivations to reduce pesticide use were based on environmental considerations. Finally, decreasing pesticide use was considered risky. Jacquet et al. (2022) discussed behavior of farmers and their risk attitude as possible reasons for the limited adoption of IPM practices.

According to Benjamin & Wesseler (2016), the restrictions are not only at the societal level, but above all at the agronomical and economic level. Uncertainty over benefits and costs, irreversibility of effects as well as flexibility in adoption of IPM technologies are mentioned here as barriers for IPM adoption.

Early detection of pests and early reaction is one core element of applying IPM technologies in the field to effectively reduce pesticide use (Birch et al., 2011). Results in research here show that stringent monitoring of pests and optimal timing of a treatment is decisive and might lead to economically effective reductions of pesticide use in cereals and oilseed rape. However, the time factor of detecting pests and immediate reaction is not easy to implement in practice, which might be another problem for adoption of IPM practices (Helbig et al., 2021). Möhring et al. (2020) confirm these findings. Results in their study indicate that farmers often deviate from recommended timing strategies because of a lack of available information and uncertainty with respect to disease predictions. On the other hand, Mack et al. (2023) describe especially yield losses, which determine whether alternative pesticide-free cropping systems, to which IPM can also be included, are adopted or not. The widespread adoption of such sustainable systems is possible only if farmers are compensated for. Flexible policy and incentive programs are required.

Conclusions

The authors examined in this paper the economic impact and potential of pesticide reduction strategies within the concept of Integrated Pest Management (IPM) using the examples of two German case studies: “wide crop rotation” and “pathogen resistant cultivars”.

Aim of this paper was to show the economic potentials at field level of specific preventive IPM strategies in arable crops, relevant for Germany.

At least under field trial conditions, in five of the six crops in the wide crop rotation a reduction of plant protection products was possible without economic losses. The calculated gross margins indicated only little or no decline in silo maize, wheat, barley and winter rye for the pesticide reduction scenarios. A closer look at the rotations revealed no trend in profitability for the second rotation. Especially the yields of the cereals reflected the increased spring drought in the second rotation, which led to significantly lower yields in some crops. However, these were offset by changes in input volumes or price developments.

Average gross margins for the different cultivars, studied in the second case study, showed that the “IPM” strategy was economically beneficial and resulted in higher gross margins compared to the “non-IPM” strategy by about 45 to 70 € ha^-1 with one exception, the highly susceptible wheat cultivar JB Asano. Reduction in fungicide application costs were the main source for the higher gross margin. Surprisingly, monitoring costs, often named as a barrier for a successful adoption of IPM strategies in practice, were comparably low while fertilizer costs were the highest cost component.

Limitations of our research are in general, that our economic studies were based on small, controlled field trials rather than on practical “on-farm” conditions. Results from field plots certainly are not directly transferable to practice.

However, the results of this study clearly indicate positive economic results for implementing preventive IPM strategies. Based on these findings, we conclude that IPM strategies are suitable to reduce pesticides use without resulting in major farm income losses for German farms. Further research needs to investigate the reasons for the lack of successful adoption in practice in more detail and opportunities to overcome these shortcomings soon.

Acknowledgement

The research on resistant cultivars was carried out as part of the IPAS initiative of the Federal Ministry of Education and Research (BMBF). The authors thank the national funding organization BMBF for financing the project AWECOS (FKZ031A353) and the partners of the Technical University of Applied Sciences in Bingen, the Humboldt University in Berlin, the breeders company Strube Research GmbH and the Julius Kühn Institute for assistance with the field trials. We thank all the staff at the JKI's experimental field site Dahnsdorf for their support of the trials on crop rotation, the technical assistants Marion Batschon, Doreen König, Ute Müller-Ebendorf and Andreas Schober for the weekly monitoring of the trials and Christina Wagner, Andrea Albrecht and Julia Büchner for their help with data preparation.

Moreover, we would like to thank two anonymous reviewers for their very valuable comments and suggestions, which helped us to strongly improve the quality of our manuscript.

Conflicts of interest

The authors declare that they do not have any conflicts of interest.

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