Future challenges for agriculture involve meeting qualitative and quantitative production objectives while ensuring sustainable development. Sustainable agriculture aims to reconcile socio-economic and environmental objectives by adopting new production systems. Protecting crops from pests is a key component in crop management and needs to follow this trend. Over the last fifty years, almost generally used chemical methods have put pressure on the environment and have shown their limits with the appearance of resistance in pests, pollution and suspected detrimental effects on human health. Moreover, the Ecophyto 2018 Plan and the reviewed European Directive on plant protection products encourage farmers to restrict the use of pesticides due to their established toxicity and ecotoxicity. Integrated production involves evolution of crop protection methods and meeting societal and environmental challenges. It complies with the principles of integrated pest management (tolerance threshold concept, use of pesticides with less environmental impact), integrated protection (use of biological control methods, minimum use of pesticides). Irrespective of the system, it has become necessary to decrease pesticide use by adopting a set of alternative measures (crop rotation, no-till farming, crop diversity…) to limit the use of chemical molecules. It is therefore conducive to increased biodiversity.
It is acknowledged that outbreaks of organisms detrimental to crops are difficult to control in single-crop systems, contrary to more diversified farming systems. Through the use of plant-health products, there are direct effects on sensitive species but also indirect effects due to prey-predator relationships and to competition phenomena.
Integrated production using less inputs is likely to reduce pollution of natural environments and therefore to preserve biodiversity and improve the biological life of soils. This work method focused on indirect control measures is conducive to crop auxiliaries.
This is one of the key factors in reducing use of plant-health products.
Increasing or maintaining auxiliaries is facilitated by this production system focused on implementing elements needed to ensure their presence but also to keep them there (hedges, grassy strips, simplified cultivation techniques).
Impact on flora and fauna will be more significant if the use of inputs is reduced and if the farmer follows integrated production principles. The heterogeneous habitats created by this technique foster restored biodiversity. Plant species are those which respond quickest to changed practices. Diversification of vegetation has a direct impact on the first levels of the food chain. By choosing specific species, it is possible to attract auxiliaries. In fact, grassy strips and perennial plants serve as winter shelter and food for auxiliaries and small plain fauna. Small plots and hedges facilitate colonisation by predators and therefore increase predation on aphids, for example. Many generalist predators attack aphids, but they do not feed only on aphids and therefore need heterogeneous habitats to diversify their resources.
Through an effective strategy aimed at restricting the use of plant health products, all the components of the ecosystem benefit.
Integrated systems use less input. They therefore ensure better preservation of natural resources (fertiliser, energy, water) and are therefore less likely to pollute the environment.
Thanks to integrated systems, total nitrogen levels are more balanced, which means less loss caused by leaching. The quantities of active ingredients used and the number of treatments are reduced (30% to 50% drop in the number of spraying operations), which protects the air and water from risks of contamination by plant health products.
Implementing an integrated management strategy gives rise to plots that are generally smaller, which fragments landscapes and restores landscape biodiversity conducive to ecotourism.
- Integrated management
In the general principles of integrated management, the key techniques used are crop rotation, fertiliser management, reduced tillage, integrated management of crops to ensure protection from pests, and organisation of ecological compensation areas. With this approach, eradicating pests is sheer utopia and managing populations using appropriate farming techniques is much more constructive. Looking at the farming system as a whole, the notion of economic damage level, the preservation of natural auxiliaries, the choice of selective pesticides and monitoring of pest and auxiliary populations in the field are basic rationales for integrated production. Other direct or indirect alternative techniques which are not defined in integrated production are recommended to foster a system that preserves biodiversity.
Long and diversified rotations make it possible to limit development of diseases and adventive species. Long rotations also reduce fertilisation requirements given that different crops are capable of recycling and/or extracting nutrients present in the soil differently.
Key organisational principles for rotation:
- List the species suited to the environment.
- Include as many different families and species as possible in the rotation.
- Include at least one pulse in the rotation.
- Have at least one third straw cereals.
- At least every 3 years, include a long inter-crop product (for example, bring in a spring crop).
- Ensure that annual pulses are followed by winter crops with a high nitrogen demand, or failing that by an intermediate crop.
- Alternate high PK demand crops with crops that do not have high PK demand.
Field edges, hedges, fences and grassy strips limit the size of plots and ensure good connections conducive to the presence of auxiliaries. To calculate a good limit, estimate the maximum area that can be sown in an 8-to-10-hour working day. Depending on environments and production systems, plot area should vary from 5 to 15 hectares.
Buffer areas reduce soil erosion and leaching, prevent weed proliferation and protect biological diversity.
Simplified techniques (no-till) make it possible to increase organic matter levels and surface biological activity, reduce nitrogen leaching, slow down erosion and reduce fuel oil consumption. To succeed, the period between crops needs to be carefully managed. It is essential to have a straw chopper and spreader, as compaction and ruts should be avoided during seeding and harvesting.
Mineral fertiliser inputs should be controlled as they are a source of pollution and favour pests. Farmers should prefer use of organic fertilisers.
- Apparent nitrogen balance to establish nitrogen inputs and outputs on the different plots and adjust fertilisation accordingly.
- Transfer of nitrogen to groundwater by percolation is encouraged by bare soil in winter. Inter-crop management makes it possible to reduce these risks and is also beneficial to wild fauna.
Resistant varieties and seeding dates
The variety must be suited to soil and climate conditions and where possible pest-resistant varieties should be used. The choice of a variety is closely linked to the choice of the date and density of seeding, which also have consequences in terms of development of parasites, diseases and adventive species. Direct-seeding mulch-based cropping systems (reducing weed emergence) limit the appeal of cereal crops for aphids, by an indirectly repulsive effect of mulch but also by the more direct impact of many polyphagous predators present in mulch which probably give rise to many semiochemical signals (Schmidt et al., 2004). Mulch provides shelter for auxiliaries, ensuring their presence in greater numbers. Use of mechanical weeding techniques on plots with low adventive specie pressure is recommended after tillage (seeds buried (5-10 cm) so that no other germination wave can be triggered by tillage.
Some physical processes make it possible to reduce pest populations:
- physical barriers: vertical nets, insect-proof plastic film, trenches, trap strips, inert silica-based powders with abrasive and drying properties
- solarisation: this technique consists of using solar energy to “heat” soils and destroy or weaken pathogens and stimulate antagonistic organisms (used in vegetable gardens).
- mechanical weeding makes it possible to reduce the use of plant protection products. Weeding and hoeing destroy weeds by cutting them at shallow depths. Weeding using hoes is a very effective technique in spaces between rows. Harrowing makes it possible to tackle young weeds, while aerating soil on the surface with limited damage to crops. Ridging makes it possible to smother adventive species in rows. The ridging technique is widespread in some crops such as potato and leek.
- the stale seedbed technique: to prepare the soil mechanically or chemically so as to ensure weed germination and destroy weeds immediately afterwards. For field crops, it consists of one or several stubble ploughing operations with compaction. This process favours microorganisms in the soil.
- integrated weed control: consists of chemical weeding on the row when the crop is sowed followed by hoeing after emergence. This technique can be used on all plots with a wide space between rows (ideal from 45 cm). The greater the space, the more the farmer can reduce the quantity of herbicides. Integrated weed control is quite effective as long as hoeing is undertaken early and in good conditions, i.e. in sufficiently dry soil with young adventive species.
- Biological control
Biological control is defined as follows by the United States National Academy of Sciences: "the use of natural or modified organisms, genes or genetic products to reduce the effects of undesirable organisms (pests) and to favour desirable organisms such as crops, trees, animals, beneficial insects and microorganisms.”
In all ecosystems, there are organisms known as “auxiliaries” which are the natural enemies of “pests”. There are predators such as ladybirds and lacewings that devour or empty their prey. We could also mention Phytoseiulus persimilis phytoseiid mites against other spider mites, entomopathogenic nematodes against certain insects...
There are those that use pests to grow, thereby causing death of the host. These are called parasitoids: microscopic plant-eating worms, hymenoptera and diptera or other small wasps and flies.
There are also viruses, bacteria and very infectious fungi that cause epidemics which totally destroy pest populations. These are called pathogens.
Biological control helps to favour auxiliary populations by means of release or creation of environments conducive to their development. Flower strips, grass cover and hedges offer shelter to auxiliaries such as syrphid flies and ground beetles. This organisation could make it possible to control pest populations. >>> Promoting biodiversity areas
A well-known example of successful use of parasitoids is the use of Trichogramma against European corn borers. Other marketed natural predators include ladybirds, plant bugs and lacewing against certain aphids.
Study: sowing rapeseed under plant cover
Sowing rapeseed with pulse crops as cover makes it possible to reduce doses of fertiliser, herbicides and insecticides.
Rapeseed crops are rather demanding in terms of input. To reduce inputs, an innovative approach has been tested over the last few years: sowing rapeseed with pulse crops as cover.
Two types of interaction are sought between rapeseed and the plant cover:
- improving nitrogen use in order to reduce the dose of mineral fertiliser (nitrogen fixation by pulses and greater effectiveness for rapeseed);
- competition between plant cover and adventive species to reduce herbicides.
Moreover, it is presumed that autumn insect cycles will be disturbed, which would make it possible to reduce insecticide use.
To avoid competition between rapeseed and its cover crop and to hope to stabilise and even improve yields while reducing inputs, the cover crop used with rapeseed should be combined with the crop in autumn without too much competition, and be totally destroyed by frost at the beginning of winter, to allow normal development of rapeseed in the spring. Only a few pulse species appear to be good choices here, namely horse bean, lentil, chickling pea, certain types of vetch and Egyptian clover. Not all varieties of a given species are suitable, because there are different sensitivities to frost and growth rates within the same species.
To allow optimal development of the rapeseed and cover crop, the combination should be sowed early, around 20 August. This will ensure optimal development of the pulse which will allow good nitrogen use and increased sensitivity of the plants to frost. Seeding after 1st September will not allow the pulses to develop and compete with adventive species.
Mild weeding. On a specific plot, farmers can skip weeding at the time of seeding and use only post-emergence grass or broadleaf herbicides. But to avoid contamination that would be difficult to control at a later date, a half-dose of herbicide before emergence makes it possible to have clean plots so as to use smaller doses of herbicide.
Determine the appropriate dose of nitrogen. At the end of winter, biomass in rapeseed associated with a cover crop is often lower than for rapeseed alone. However, if the pulse cover crop is well developed at the beginning of winter, the nitrogen it contains is degraded when it is destroyed by frost and can be reused by the rapeseed in the spring. It is therefore possible to decrease the dose of nitrogen by 20 to 30 units, calculated by weighing rapeseed at the end of the winter.
The indicators linked to these BMPs are the following:
- Production costs
- Treatment frequency index
- Nitrate levels
- Energy balance
- Greenhouse gas balance
- Nitrogen balance
- Biological activity