The search for more environmentally friendly pest control solutions is particularly urgent in the vegetable sector, where the combination of Europe’s new pesticide regime and the relatively small returns for the pesticide industry have placed the emphasis firmly on alternatives.
Fortunately for vegetable producers, and indeed consumers, interesting alternatives do exist and are the subject of research right across the continent and further afield, as outlined in two recent reports from ENDURE’s field vegetable case study team.
The reports, Deliverable DR1.20 Field vegetables: Guidelines for (i) soil steaming, solarisation and biofumigation as alternatives to soil chemical disinfectants, (ii) landscape management to improve conservative biological control in field vegetables cropping systems and Deliverable DR1.21 Field vegetable case study: Report on gaps of knowledge on methods to control soil-borne diseases through soil biofumigation and/or soil steaming and insects through landscape management and suggestions to fill these gaps , can be downloaded below, and provide readers with an update on some of the research being conducted by ENDURE partners.
In this report:
Soil steaming: Research in Italy
Soil steaming: Research in Denmark
Biofumigation: Research around Europe
Biofumigation: Beyond brassicas
Biofumigation: Breeding a possibility?
Controlling insects: Landscape and field margin management
Spain: Successful conservation biological control
Netherlands: Functional agro-biodiversity
France: Landscape and chemical ecology
Conclusions on insect control
Identifying knowledge gaps
Download the reports
For further information
Key challenges for research
DR1.20 identifies the most urgent problems in the vegetable sector which, through a combination of the new regulations and the phasing out of methyl bromide, an effective but ozone-destroying soil fumigant, are soil-borne pests, diseases and weeds, alongside insect pests. The latter are a concern as insecticides with neurotoxic effects may no longer be available to growers.
The report examines alternatives such as soil steaming and biofumigation and, for the control of insects, methods relying on biological control and/or chemical ecology on scales ranging from field margins to landscape management.
Of these alternatives, soil steaming has been used for over a century to control soil-borne pests, diseases and weeds, but recent advances have overcome some of the drawbacks of the method. Soil steaming is as simple as it sounds: steam is passed through soil, heating it and killing, for example, weed seeds and fungal diseases. Unfortunately, until recent advances were made, it was both time-consuming and costly, using significant amounts of fossil fuel.
The report contains details of research being conducted by scientists from ENDURE partner Scuola Superiore di Studi Universitari e di Perfezionamento Sant'Anna (SSSUP) in Pisa, alongside colleagues from the University of Pisa and agricultural machinery manufacturer Celli .
They are combining soil steaming with the addition of activating compounds such as potassium hydroxide (caustic potash) or calcium oxide (quicklime) in what they have registered as the Bioflash® system. These compounds react with steam to allow higher temperatures to be reached over a longer period of time and can also directly control parasites and germinating weed seeds. The Italian team is combining this with the introduction of new machinery which should help drive down costs and improve efficiency.
The report also includes research from one of ENDURE’s Danish partners, Aarhus University, which is conducting research into band steaming (treating only the area where crops will be sown). Researchers at Aarhus are examining whether reduced temperatures can be used for effective control (thus reducing time and fuel costs) and whether the addition of biological substrates, including biocontrol agents, and organic substrates such as pea meal can stimulate the re-colonisation of steamed soil, in particular whether beneficial organisms can do so more quickly than those with pathogenic or antagonistic features.
The ENDURE report believes this is a priority area for more research. “Biological activation after soil steaming must be an objective for research as this offers the opportunity for re-colonisation of the disinfected soil with useful microorganisms like biocontrol agents for example,” says the field vegetable case study team.
Biofumigation is another interesting technique, typically employing plants from the brassica family which are grown in the field, crushed and the residues incorporated into the soil. These plants produce methyl isothiocyanate (methyl ITC), a broad-spectrum biocide that acts against nematodes, fungi, insects and weeds.
The various mechanisms by which biofumigation works are somewhat complex and the report includes details of research conducted by three ENDURE partners to explore further the potential the technique can offer vegetable growers.
INRA, the French National Institute for Agricultural Research, for example, has been examining the possibilities of using biofumigation for controlling root diseases in carrots at its Le Rheu base in Brittany. This has included laboratory testing of various brassica species for their ability to inhibit the growth of Pythium violae , the main cause of cavity spot, followed by field tests growing Indian mustard (Brassica juncea ) as a biofumigant between carrot crops.
Applied Plant Research, part of Wageningen University in The Netherlands, has conducted a range of experiments using different plants for biofumigation against various soil-borne pests and diseases. Huub Schepers, from PPO, reports on research using 12 different crops for their effects on the nematode Pratylenchus penetrans and soil-borne pathogen Verticilium dahliae , both serious problems for potato growers. He reports that certain crops increased potato yield in the subsequent crop, even those which had no positive effect in reducing the pests under scrutiny. “Mechanisms are thus more complex than initially thought and effects on other microbial populations that might exert an indirect control of pathogens have to be looked at,” notes field vegetable case study leader Philippe Lucas.
CIRAD, the French research centre working with developing countries to tackle international agricultural and development issues, has been examining the potential of biofumigation to control bacterial wilt (Ralstonia solanacearum ), a soil-borne bacterium that causes serious damage to solanaceous crops such as tomatoes and aubergines in the French island of Martinique.
Drawing on previous research conducted in South Africa and China, the CIRAD team is screening different crops for resistance to bacterial wilt and their suitability for growing in tropical regions, not just brassicas but members of the Tagetes family such as Tagetes patula (French marigolds) and the Allium family such as Allium tuberosum (garlic chives or Chinese chives). Although these two groups of plants do not produce ITCs like the brassica family, they produce sulphurous compounds which have been shown to have similar antibiotic effects.
The ENDURE team concludes that biofumigation works through complex and different actions: during the growing phase (the equivalent of a break crop), when crushed and the residues incorporated (this is when ITCs are released and is biofumigation in the strictest sense) and during the decomposition of the residues (the green manure effect, causing changes in the soil microflora). “Looking at these different modes of action in an epidemiological perspective should help in defining criteria which make a crop a good fumigant one according to a set soil-borne pests and/or diseases,” says field vegetable case study leader Philippe Lucas. “This might even lead to plant breeding programmes for plants used specifically as biofumigant crops [in the widest sense].”
You can read more about this subject in a recently published review in Soil Biology and Biochemistry: MOTISI N., DORÉ T., LUCAS P. & MONTFORT F., 2010. Dealing with the variability in biofumigation efficacy through an epidemiological framework, Soil Biology and Biochemistry.
For the control of insect pests, the case study team has concentrated on landscape and field margin management to improve conservation biological control and/or the use of chemical ecology. The report contains details of research being conducted both in mainland Europe and in Reunion, the French island in the Indian Ocean.
Research in the latter has focused on controlling fruit flies, which can cause devastating losses in solanaceous crops, particularly field-grown tomatoes, and cucurbits, such as cucumbers, courgettes and melons. Techniques that have been applied at the field scale, incorporating field margins, include sanitation, assisted push-pull and trapping of male flies. However, concludes CIRAD’s Jean-Philippe Deguine, future fly population control will need to be implemented at the production area level “to promote a new agro-ecological balance centred on the role of functional plants, habitat management and development of natural beneficials, on a landscape scale.”
Many European consumers will have bought fresh produce grown in Spain and the report contains details of interesting research conducted by experts at the Catalonian government’s IRTA research institute in north-east Spain.
At first glance the prospects for successful biological control in the intensive production systems found in Catalonia may seem challenging: lots of small farms with a variety of species grown simultaneously all year round, overlapping fields of the same crop and greenhouses that are only partially sealed. Because many vegetables share the same pests, such as whiteflies and aphids, problems are exacerbated “as there is a continuous carry-over of pests throughout the year that is hardly interrupted, even in winter,” reported the IRTA researchers. However, the particular nature of the Catalonian vegetable growing area also gave hope to researchers as the mixed landscape could provide refuges and sources for pest-eating insects.
In the report, they give details of their research on using insectary plants (plants that attract insects) to boost natural enemies of aphids (Nasonovia ribisnigri ) and thrips (Frankliniella occidentalis ), two major pests of lettuce crops. The work consisted of three steps: determining the key natural enemies that colonise non-sprayed lettuce crops, indentifying the plants which may act as refuges for these natural enemies (providing food and/or egg-laying sites) and suggesting and evaluating the use of margin or flower strips to control aphids and thrips.
The IRTA team identified hoverflies and predatory bugs of the Orius family as the most abundant natural enemies and four plants particularly successful at attracting them: Vicia sativa (common vetch) and Lupinus hispanicus (Spanish lupin) for orius populations and Centaurea cyanus (cornflower) and Lobularia maritime (sweet alyssum or sweet Alison) for hoverflies.
Following trials, researchers established that combinations of plants offered no clear advantages over a single-species margin of Lobularia, so conducted trials using this species in commercials fields around Catalonia. “The results confirm that biological control shows great potential for aphid and thrips control in spring and summer lettuce…As a result of predator establishment, prey populations were reduced below the economic threshold. Moreover, no other pests were recorded from the lettuce crops as a result of adding the insectary plants,” they conclude.
In the Netherlands the Dutch farmers’ organisation (LTO), backed by the ministries of agriculture and environment and in conjunction with researchers from Wageningen, has conducted a regional scale pilot scheme focusing on landscape and functional agro-biodiversity (FAB). The FAB pilot included measures such as enhancing functional biodiversity through improving the quality and management of semi-natural vegetation and, at the field level, the farmers involved created field margin strips with perennial grasses and/or an annual flower mixture and were advised to reduce the use of insecticides, giving preference to selective insecticides that have little effect on main natural enemies.
Farmers trialled the use of trap crops, such as yellow rocket and Indian mustard to attract diamondback moth, in addition to conservation biological control through the creation of 3m-wide annual flower strips, to combat the main pests of wheat, potatoes and Brussels sprouts.
Trap cropping proved only partially successful, as Indian mustard’s life cycle appeared too short compared to that of Brussels sprouts and yellow rocket remains low during its first year, not flowering until the second year. Summarising this study, ENDURE’s field vegetable case study leader Philippe Lucas (INRA) says this indicates that not only the biological characteristics of insect behaviour need to be considered when selecting trap crops, but agronomic factors too.
There was more successful news in trap cropping for cabbage whitefly (Aleyrodes proletella ) with young kale plants in particular attracting many whiteflies. These were then treated with an experimental insecticide which killed 95% of the eggs.
The conservation biological control experiments, conducted in both experimental plots (unsprayed) and commercial fields (sprayed), yielded interesting results. Natural enemy numbers, especially hoverflies, gall midges and parasitoids (particularly important natural enemies of cabbage moths and butterflies), were much higher in experimental fields but declined rapidly by the end of August. In these experimental fields cabbage aphid (Brevicoryne brassicae ) levels remained low or at least stable through June, July and August, but increased exponentially by early September, causing economic damage to sprouts by November.
“This,” the researchers note, “suggests that natural enemies can play an important role in keeping the aphids under control during summer, although not always at a sufficiently low level.”
“When using functional agro-biodiversity as a means for pest control one can consider not only methods to augment natural enemies, but also methods to diminish pests directly,” they add . “The reduction of pest refuges that can act as sources of re-infestation is one example at the landscape scale. Trap cropping is another example at the field level.”
Neither method is problem free, they caution, as reducing pest refuges requires concerted action from growers in the region, while successful trap cropping will only be possible after the resolution of some technical issues such as the attractiveness of trap plants relative to the different development stages of the crop, the level of pest reduction that can be obtained and the type of pest management needed to prevent the secondary spread of the pest.
Finally, the ENDURE report examines work being conducted by INRA in Brittany, where flies are a major pest of cauliflower, an economically important crop for the region, and carrots. The situation is particularly pressing as the insecticides currently used to control flies may no longer be available to farmers after the end of the current year.
Flies such as Delia radicum (cabbage or cabbage root fly), Psylla rosae (carrot fly) and Brevicorne brassicae (cabbage aphid) are receiving particular attention as researchers note that current alternatives, such as protective nets, are expensive and not always effective. Furthermore, they say the number of treatments currently used is probably excessive as pest numbers can be controlled by numerous natural enemies. The challenge for the team studying landscape ecology is to demonstrate this natural regulation process and convince growers of the possibility of reducing treatments.
The team is seeking establish the relationships between landscape structure and composition and the damages caused by pest insects in Brittany’s cauliflower crops and, while the work is in its early stages, similar projects are being conducted elsewhere in western France on other vegetable crops to provide a broader view of the topic.
Another possible alternative for controlling Delia radicum comes from the field of chemical ecology, with researchers seeking to exploit infochemicals, chemical compounds which act as signalling devices in insect-insect and plant-insect interactions.
In particular, they have been seeking to capitalise on the recent identification of dimethyl disulfide (DMDS) as a compound that both attracts the main predators of cabbage fly and disrupts its egg laying. The initial study saw researchers increase DMDS levels in plots sown with broccoli and produced results that will require further investigation: DMDS produced larger numbers of the key predator Aleochara bilineata (rove beetle) and fewer cabbage fly eggs, but the damages from cabbage fly were similar in both treated and control plots.
Finally, researchers at INRA in Rennes, Brittany, point to the possibilities of bringing together plant breeding and biological control, which traditionally have been two parallel but independent pest management practices. They point to the numerous ways plants can affect not only insect pests but also the enemies of these pests. These include, for example, the fact that plants affect host/prey accessibility through morphological traits such as waxy surfaces, provide host/prey finding cues both visual and chemical, and influence host/prey suitability through devices such as toxic allelochemicals and nutritional quality.
Summing up biological control and/or chemical ecology options for insect control, the field vegetable case study says: “Behind the general concepts, they have to be adapted to local situations. For example, insectary plants must have adequate life cycles and provide shelter and resource for key natural enemies at the right periods to cover the crop length and ensure protection against the target pests. Push-pull strategies and insectarium also need local adaptation, showing the importance of local experimental stations. Landscape management is more complex to establish but is a key point to create a background reducing pest development through the enhancing of regulation mechanisms.
“The concentration of vegetable crops in specific production basins should help interactions between growers for strategies at the needed regional landscape scale. Chemical ecology should gain more interest from scientists as semiochemicals are a key component of recognition between insects and plants and insects and insects, and probably will be at the centre of new methods of biological and integrated control of insects.”
DR1.21 Field vegetable case study: Report on gaps of knowledge on methods to control soil-borne diseases through soil biofumigation and/or soil steaming and insects through landscape management and suggestions to fill these gaps brings together both DR1.20 outlined above and DR1.17 Report on protection methods available for 5 major crops chosen within participating countries (follow this link for more details).
It sets out the field vegetable situation in Europe - a great diversity of vegetables, high value crops with a strong emphasis on visual aspects and varying availability of crop protection methods - and identifies some key points. One of these, the need for harmonisation of the plant protection products available to growers within the European Union should be achieved thanks to the new EU ‘pesticides package’.
The report then identifies the need to reinforce studies on Integrated Pest Management (IPM) to enrich the IPM toolbox and design methods to build-up efficient IPM strategies adapted to local conditions. It identifies key main gaps of knowledge and offers proposals to fill these gaps.
Extending the diversity of available alternatives
Improving the efficacy of alternatives
The case study team notes that many alternatives offer partial efficacy, which leaves producers unconvinced. To break this logjam it suggests the looking for the best combinations of partial efficacy methods, including pesticides showing the best toxicity and environmental profile to provide more durable control strategies. This will involve enhancing researches in epidemiology and population dynamics, taking into account all processes responsible for pest, disease and weed dynamics at the relevant scale (time and space) and development of modelling will be essential.
Adapting alternatives to local conditions
This will be particularly important for field margins and landscape management designed to preserve pest enemy habitats or for implementing push-pull strategies. Again this will require reinforced studies on functional and landscape ecology.
Integrating alternatives for local IPM strategies
The report notes that although IPM strategies share general concepts and basic knowledge, for example system approaches, their design and validation needs to be local, to ensure both their efficacy and their acceptance by farmers. Experimentation in the growing of field vegetables will be necessary, with the creation of a European-wide IPM network, such as ENDURE, adding value to this process by making it easier to compare successes and failures. Finally, it stresses the importance of economic evaluations of proposed IPM measures, and underlines the fact that while some economic evaluations can be conducted on experimental sites, they must also be conducted on the farm, which will be the ultimate practical evaluation of their efficacy.
|Report (Deliverable)||Download (pdf)|
|DR1.20 Field vegetables: Guidelines for (i) soil steaming, solarisation and biofumigation as alternatives to soil chemical disinfectants, (ii) landscape management to improve conservative biological control in field vegetables cropping systems||
ENDURE_DR1.20 [pdf - 3.42 MB]
|DR1.21 Field vegetable case study: Report on gaps of knowledge on methods to control soil-borne diseases through soil biofumigation and/or soil steaming and insects through landscape management and suggestions to fill these gaps||
ENDURE_DR1.21 [pdf - 63.82 kB]