This report was splits into seven sections of which a quick summary of each is provided here. If you want to read the full report see the links at the bottom of this article. Note that all information is correct at the time of publication.
1. Key non-target plants of farmland
- 40 species of non-crop flora were identified as key species associated with agricultural systems including a range of trees, weed species, grassland, herbs and woodland flora.
- Species were chosen to be representative of various habitat types, taxonomic groups, functional groups and soil types.
- These species were then used in the following sections to identify the non-target effects of pesticide use.
2. Life Histories and Ecology of key non-target plants of farmland
- The biology and ecology of plant species (e.g timing of growth and flowering) can affect their susceptibility to pesticides and influence their exposure to pesticides in farmland environments.
- The habitats, life forms, flowering and seed biology of the chosen species were summarised - from this it was shown that the species displayed a variety of adaptations to survival and reproduction.
3. Assessing the importance of each plant species identified as a food source/habitat for vertebrate and invertebrate wildlife
- Herbicides affect not only plants, but can also have direct and indirect effects on non-plant species too. This section assessed the routes of such effects on 3 major animal groups (invertebrates, birds and mammals) and highlighted how the original 40 plant species interact with these groups. Some of the main findings are highlighted here:
- Many insects rely on pollen and nectar as food sources (and many plants including crops in turn depend on insect pollination). Several plants on the selected list including Leguminosae (Lotus, Trifolium, Vicia) and Umbelliferae (Daucus, Heracleum) were identified as important nectar/pollen plants.
- The most important herbivore plants were also identified from the selected list and included Lotus, Cirsium, Carduus, and Taraxicum. Their leaves are likely to be browsed on by herbivores.
- Many of the selected plants were identified as providing important overwintering shelters and habitats for insects, such as predatory beetles.
- Loss of plant diversity due to herbicide drift through its effects on invertebrate populations, also affect invertebrate-predatory birds
- Several plant families were identified as bring the most important food sources for birds including Compositae (daisies and allies) and grasses. Importantly these families were critical in the diet of priority birds outlined in UK biodiversity action plans.
- Plants provide important nesting habitats - especially trees, shrubs and hedges, as well as grass species for ground nesting birds. These ground cover species likely to suffer more damage from herbicides.
- Mammals are highly regulated by their food supply. Insectivores (e.g shrews) may have indirect associations with plants (via the indirect impacts of herbicides on their insect food sources). Several mammals also feed on soil invertebrates - there is little information of the effect of herbicides on such invertebrates, like earthworms.
- A variety of the listed species were identified as key food sources for omnivorous mammals (e.g hedgrow fruits and berries - Crataegus monogyna) and for lagomorphs such as rabbits, grasses (e.g Festuca) are important parts of their diet.
- Hedgerows can provide not only food, but also cover. High populations of species like voles and shrews encourage diverse populations of mammal predators in these areas as well.
4. National and within-field distributions of key non-target plants of farmland
- Location of non-crop flora is important in determining pesticide exposure. Species within arable fields will be directly exposed to pesticide treatments, hedgerow species are liable to drift, and species in adjacent semi-natural habitats will have variable exposure.
- In this section the national distributions of the key plant species were tabulated as well as their within-field distributions
- The majority of species are ubiquitous, whilst some have a Southern/South-eastern UK distribution (eg Daucus carota and Dipsacus fullonum).
- Data confirmed that all identified target species occur throughout England and Wales in suitable habitats whilst a few are less common in Scotland.
- In terms of within-field distributions, the majority of the key plants species inhabit the field boundary (non-cropped habitat), though annual arable weeds are typical of cultivated ground. Thus suggests that arable weeds are exposed directly to the pesticide, whilst others may be more effected by non-target drift.
5. Pesticide impacts on non-target plants
- Likely methods of pesticide drift during application include: spray and evaporated droplets, vapour and leaching into soil water. Droplet movement is most common form of drift and usually occurs as a result of technical errors (eg wrong sprayer adjustment).
- Secondary movement of pesticides following application can include rainfall, pesticide leaching through soil profile and vapour redistribution.
- Distance travelled depends on factors such as: equipment and settings used, wind speed and direction, field shape.
- Impacts of pesticide drift on plants can be both direct (via toxicity of the pesticide) or indirect (mediated by the responses of other pants).
- The amount of herbicide reaching non-target plants can often be predicted but the biological effect at species and community level is uncertain. One hypothesis is that in non-target habitats next to intensively sprayed fields, the community becomes adapted to irregular disturbance events and become dominated by species-poor assemblages dominated by resilient plants.
- Gaps in the literature are identified including insufficient dose-response experimentation and a lack of testing of newly commercialised herbicides on non-target species. As such the non-target effects of many compounds are unknown.
- A recurring feature in research is the susceptibility of a wide-range of plant species to broad spectrum herbicides (particularly glyphosate). These products likely pose the greatest risk to non-target species. As such GM approaches of incorporating broad-spectrum herbicide resistance genes into crops may increase the use of these compounds and increase risk of non-target effects.
6. Options for testing and risk assessment
- It is impractical to test all susceptible plant species for non-target effects - need to identify and test a limited number and extrapolate findings. However, the most common species should be given particular consideration in the risk assessment as well as species such as ferns, mosses and conifers.
- Options include toxicity testing and conducting species-specific risk assessments.
- Risk assessments should consider species both inside the target area as well as outside. They should also consider how to take account of cumulative exposure from repeated pesticide applications.
- Combining factors of plant location (in/out of crop) and life stage (seed, young plant) implies the need to consider a total of 4 exposure scenarios (6 if mature plants are included).
- See the full report for more information on testing and risk assessments.
7. Risk management to protect key species
- Most of the risk to non-target plants is posed by herbicides (not fungicides or insecticides). Spray drift represents greatest threat of pesticide movement.
- Types of risk management can be grouped into four main categories
- Application methods - related to composition of spray solution and equipment used. Precision of pesticide delivery onto the target is essential. Factors such as sprayer design, weed mapping, patch spraying and incorporating mechanical weeding into control methods can help reduce risk of drift.
- Timing methods - relating to when in the season the pesticides are applied. Need to fully understand the agronomy, target and precision control operations to manipulating timings effectively.
- Spatial methods - relating to separation of the non-target organisms from the crop by buffer zones (e.g unsprayed crop edges, conservation headlands). Buffer zones can not only reduce drift to non-target areas but also have positive effects on on-farm biodiversity.
- Area methods - if used in small amounts over small areas some pesticides may present greatly minimised risk. Landscape-scale application events pose high risk.
- Each of these management methods have both advantages and disadvantages. A combination of approaches may be used. Adoption of these techniques will depend on both effectiveness and cost/
- This report has highlighted an approach of assessing risks to non-target organisms by identifying species of plants which could become targets during pesticide application. It then evaluated the effects of non-target pesticides on those species, which have important interactions with animal groups such as insects, birds and mammals.
- 40 species of wild plants were selected and evaluated in their importance and options for management and risk assessments given.
Read more about the Government's biodiversity plans at: https://www.gov.uk/government/speeches/2022-is-a-critical-year-for-biod…
And you can read the full report summarised here at: https://sciencesearch.defra.gov.uk/ProjectDetails?ProjectId=7499