Scientific evidence for sustainable plant disease protection strategies for the main arable crops in Sweden. A systematic map protocol

The intensification of agriculture has to a large extent met the demand of feeding a growing population, but the increase in agricultural production has reached a plateau in many countries [1]. The increase in yields can partly be attributed to improved plant pest and disease management, including better understanding of the disease causing organisms and the use of a range of different control measures. Efficient and sustainable crop protection is of vast economic and ecological significance for food and feed production worldwide [2]. Future crop production faces a number of challenges, e.g. climate change, population growth and increased global trade [3, 4]. These challenges have already resulted in increased risks of establishment, spread and propagation of plant pests and pathogens [5, 6], potentially leading to unfavorable consequences for the environment and public health [7]. One of the greatest challenges is the development of resistance in pathogens towards pesticides, making the products less efficient or even inefficient. Current legislation aims to limit negative environmental impact of chemical control. As a result, several active substances in pesticides have been or will be prohibited for agricultural use, and thus development of alternative control strategies is crucial. Modern, efficient sustainable crop protection must provide the growers with tools to produce safe food of high quality and concurrently fulfill several environmental goals such as reduced climate impact, a non-toxic environment, good quality ground water and sustainable management of ecosystems [8].

Crop protection is a wide and complex topic that includes several research fields. Different interventions can be used to limit the impact of plant diseases, and crop protection measures are commonly used in all cropping systems. During the last century, research has led to significant increase in agricultural production, which to a large extent has relied on the introduction and use of agrochemicals. Until the 1940s, chemical treatments against plant diseases relied on inorganic chemical substances such as the “Bourdeaux mixture”, a mixture of copper sulfate (CuSO₄) and slaked lime (Ca(OH)₂) [9]. Between the 1940s and 1970s, a range of effective organic compounds for managing plant diseases were developed and widely used. This created an over-reliance on chemical control. However, the use of pesticides is often a temporal solution, and several pathogens (and pests and weeds) have developed resistance, limiting the efficiency of their use [10]. Strategies to combine different methods that, alone, have limited efficiency can generate valuable synergies and limit the need of chemical control.

The EU directive on sustainable use of pesticides (2009/128/EC) promotes the application of Integrated Pest Management (IPM). The integration of several management methods are gathered under the eight principles of IPM [11]. These principles emphasize the production of a healthy crop with the least possible impact on the agro-ecosystem, and encourages the use of non-chemical control measures. The directive is now being implemented in all EU member states, however in Sweden and several other countries, IPM was applied already before the EU directive came into force. The scientific evidence necessary for developing IPM recommendations are similar between countries. To achieve the long-term goal of implementation of IPM, knowledge from many disciplines has to be combined, and researchers and practitioners with different experiences and backgrounds need to be involved [12, 13].

The agricultural crop production in Sweden faces several economic and ecological challenges. To meet these challenges, the growers need sound recommendations based on scientific results. The Swedish board of agriculture is a public authority, and its regional plant protection centers are key players in Swedish plant protection. The centers act as a link between research and implementation of pest and disease management, and they provide official recommendations for plant protection measures [14]. The information provided by the centers is commonly used by advisors and growers in decisions about control of diseases in commercial crop production. The official recommendations are updated annually and are based on a mixture of scientific evidence, field trial evaluations and practical experience. Recommendations on crop protection strategies are also provided by other organizations and private companies active in Sweden. To a large extent, these organizations utilize the recommendations compiled by the plant protection centers at the Swedish board of agriculture.

Plant protection strategies can be preventive, including crop rotation and cultivar selection, or direct with the use of pesticides or removal of diseased plants when an outbreak occurs. A decision to take any plant protection measure is based both on the risk of yield loss caused by a disease, and the grower’s perception of the risk of missing a treatment, that could have been justified, against a disease. As an example, in many cases pesticide treatments are done unnecessarily, but are regarded as an insurance by the growers [19]. Scientifically based evidence in decision support for both preventive and direct plant protection measures could limit economically unjustified pesticide treatments and limit the negative impact of pesticides or other crop protection measures on the surrounding environment. Sustainable plant protection requires a joint effort among stakeholders such as advisors, growers, experts at authorities, and researchers. The development and improvement of molecular methods makes it possible to detect, identify and better understand the agents that cause plant diseases. In addition, the computer capacity to develop models for disease forecasting has significantly improved. Combined, the tools currently available should allow for improved plant disease management with less impact on the surrounding environment.

To provide high quality plant protection recommendations, a systematic review is a useful tool to objectively evaluate the evidence base. Systematic reviews are well established in the field of medicine, where they are used to minimize bias and allow a consensus to be made across the evidence base [15]. These types of assessments are less common in plant disease management where only a few systematic reviews [16] and some meta-analyses have been published [16–18]. A solid evidence base is important to allow for use of the best practice and knowledge in the recommendations in order to retain the crop producers’ trust in plant protection advices. A systematic review is potentially a useful tool to underpin crop protection recommendations to growers. The evidence may lead to reduction in pesticide use that benefits the environment, increases profitability for crop producers and improves food security. A reduction in pesticide use would prolong the efficiency of different pesticides against disease causing agents that easily develop resistance against their active substances. A systematic map with a comprehensive literature overview is an important step towards more evidence based plant disease management and will help to identify subject areas suitable for systematic review or meta-analysis. The aim of these systematic maps is to perform an inventory of current knowledge and to identify future needs regarding plant disease management in the most important arable crops in Swedish agriculture. We expect to get an overview on the available scientific literature for different disease management strategies and interventions for the selected crops. The results from these systematic maps will also allow for future systematic reviews of specific topics within each of the selected crops.

The most common direct disease control measure currently available during the growing season is the use of pesticides. Many growers apply pesticide more or less routinely, which cannot always be economically justified. The reason behind this is the difficulty to handle the annual variation in net return from pesticide treatments [19], highlighting the decision making struggles that growers face. To be able to keep up with emerging new diseases and other threats to crop production, growers have to be flexible and able to adjust to future challenges and demands [20]. This underlines the need for an overview of which evidence are available to support sustainable crop production in relation to plant health. Systematic maps as well as systematic reviews, unlike traditional review articles, follow rigorous, objective and transparent processes that reduce bias in the selection of included studies and publications. The selection of literature is based on strict decision criteria regarding inclusion and appraisal, making reviews based on systematic searches transparent and readily understood. We therefore consider these systematic maps, one for each of the selected crops, to be a vital initiative to collect the scientific evidence on plant disease management, as a first step towards more evidence based advice and recommendations within disease management for agricultural practice.

The overall aim is to make systematic maps for the main arable crops in Sweden and to provide an overview of which plant disease protection measures that have a sufficient volume of scientific literature for a systematic review and to identify where knowledge is missing. The maps can also be used to enable researchers to identify areas that need further studies and to guide policy makers when allocating research resources. The literature gathered in these systematic maps can support authorities and advisory service organizations when identifying methods for crop protection measures to be included in disease management recommendations to growers.

The crop selection was based on data indicating the importance of the crop in Swedish agriculture, i.e. the area under production of the crop, the total annual harvest, the economic importance (average price during the last 5 years), and the annual use of pesticides against diseases (http://www.scb.se). Based on these criteria, the six selected crops are wheat (Triticum aestivum), barley (Hordeum vulgare), oat (Avena sativa), potato (Solanum tuberosum), sugar beet (Beta vulgaris) and oilseed rape (Brassica napus).

The systematic maps will describe the volume and main characteristics of the scientific literature (the evidence base), and identify evidence clusters and knowledge gaps in the area of plant protection for each crop separately. One searchable database per crop will provide a catalogue of evidence for researchers and stakeholders, especially authorities and advisory organizations, which could be used for future studies and as a resource base when updating plant protection recommendations.

Standardized descriptive data from all studies meeting the inclusion criteria will be stored in Excel spreadsheet, which will form the systematic maps. Data from each study will be coded as follows:

A full critical appraisal of included studies will not be carried out in these systematic maps because the breadth of the topic and the wide variety of studies included would make this complex and difficult. A basic quality assessment of the study design during data coding will be undertaken and a brief description in the form of a “free text” of the quality of the included studies can be made when considered informative.

All included studies and their meta-data will be recorded in a searchable Excel database that will be made available with the published systematic map reports, as an additional supporting file. The accompanying report will describe the review process, the amount and nature of available scientific base in text and in graphs and figures, knowledge gaps and gluts that were identified. Based on the findings, the report will also include recommendations.