Pesticides? You decide.

It is time to redress the balance on pesticides. For too long pesticide manufacturers have controlled the information and hence the debate; they pay for the research, select what is published, and have too loud a voice in legislation and too much influence over the direction food production has taken. We believe there is no ‘safe’ level of pesticide; they are designed to kill at very low doses. The debate shouldn’t be whether they are safe, but rather do they pose a risk which is acceptable given the benefits, and are there better alternatives.

In this series of blogs by Guy Watson we hope to raise questions and provide balanced information and, for those with the time, references. We will leave you to decide.

When I was at agricultural college in the early ‘80s, my favourite lectures were on integrated pest management (IPM). IPM relies on understanding the ecological interactions of crop, pest, predator and the wider environment, before making intelligent interventions based on an awareness of their wider impact. An ‘intervention’ could be a pesticide (ideally well-targeted and short-lived) but could equally be, in theory at least, introducing the pest’s predators, planting a hedge to encourage pest predators, or timing sowing to avoid peak pest egg-laying.

Why can’t many pesticides just be washed off?

That was 40 years ago; people are still talking about IPM but there’s been no real challenge to the ignorant kill-them-dead approach that seems the norm in non-organic farming. Outside horticultural cropping in glasshouses/polytunnels and organic farming, there has been almost no progress in turning theory into reality. Most pesticides are applied with almost no understanding of their impact beyond killing their target pest; the disruption and damage caused by the 99.9% that misses the target receives scant attention. Effective application of IPM requires a level of observation and learning, an understanding of ecology and, as diversity is normally part of the answer, a level of farm habitat complexity that is beyond most commercial UK farms. Perhaps the lack of progress beyond application of the latest chemical comes as no surprise given that farmers receive the huge majority of information on pests and their management from pesticide suppliers.

“Most pesticides are applied with almost no understanding of their impact beyond killing their target pest”

An extrapolation of the progress anticipated by my lecturer and I as a young farmer would by now see non-organic farmers using minimal highly targeted sprays with selective toxicity. But we were wrong; farming didn’t get that smart, it just found more sophisticated, powerful ways of being stupid. Threatening bee and other pollinator populations with systemic neonicotinoid seed treatments is the latest manifestation of what seems to be a never-ending cycle.

Contact pesticides kill the pests that they touch, be that a weed, a fungus or an insect. The challenge for pesticide manufacturers and farmers is making enough ‘contact’ to kill most of the target pests; difficult if the pest is under the leaf, in crevices, underground or has not yet arrived. Predictably only a tiny proportion of contact pesticides reach the target (typically less than 0.1%); 99.9% ends up on the crop, in the soil or being dispersed in air and water. The advantage of contact pesticides is that, for the most part, they stay on the surface of the plant, giving you a slightly better chance of removing them by washing or peeling – though scientific research suggests washing can have a limited effect at removing pesticides.

Systemic pesticides are absorbed through the leaves or roots and translocated to every part of the plant. In the case of herbicides (weed killers) like glyphosate, this gives the great advantage of killing all parts of the plant rather than just the leaves, so it can’t regenerate from the roots. In the case of insecticides (like neonicotinoids) and fungicides (like thiophanate methyl) it means direct contact is unnecessary; so long as the pest eats or is in contact with enough of the crop, it will die. The downside of systemics is that the pesticide is inside the plant, including the parts that are eaten, giving you no chance of washing or peeling it off.

Contact pesticides kill the pests that they touch, be that a weed, a fungus or an insect. The challenge for pesticide manufacturers and farmers is making enough ‘contact’ to kill most of the target pests; difficult if the pest is under the leaf, in crevices, underground or has not yet arrived. Predictably only a tiny proportion of contact pesticides reach the target (typically less than 0.1%); 99.9% ends up on the crop, in the soil or being dispersed in air and water. The advantage of contact pesticides is that, for the most part, they stay on the surface of the plant, giving you a slightly better chance of removing them by washing or peeling – though scientific research suggests washing can have a limited effect at removing pesticides.

Systemic pesticides are absorbed through the leaves or roots and translocated to every part of the plant. In the case of herbicides like glyphosate, this gives the great advantage of killing all parts of the plant rather than just the leaves, so it can’t regenerate from the roots. In the case of insecticides (like neonicotinoids) and fungicides (like thiophanate methyl) it means direct contact is unnecessary; so long as the pest eats or is in contact with enough of the crop, it will die. The downside of systemics is that the pesticide is inside the plant, including the parts that are eaten, giving you no chance of washing or peeling it off.

The reality is that most neonicotinoids are fairly persistent in the environment (half-lives typically range between 200 and 1000 days). They are toxic to all insects, and harmful to most other animals through toxicity or disruption to food sources. Despite being systemic, 95% of those neonicotinoid seed treatments are dispersed into the wider environment, where they disrupt soil life or get carried in dust to other crops nearby. As a student I would have never believed such toxic reach was possible, but the evidence is overwhelming. History has taught us that there is no safe pesticide; as their power comes from disrupting fundamental life processes, there are only degrees of risk.

“We were wrong; farming didn’t get that smart, it just found more sophisticated, powerful ways of being stupid”

We have a regulatory regime which is overly dependent on information provided by pesticide suppliers. Though it is probably reasonably effective at identifying simple, acute and short-term effects, where the impacts are chronic, long-lasting and complicated by interaction with other environmental factors, it repeatedly fails. Too often ‘no evidence’ doesn’t mean no risk; it just means the experiment hasn’t been done, wasn’t long enough, or occasionally wasn’t published for commercial reasons. It turns out that just because neonicotinoids passed the ‘toxicity to honey bees’ test at the appropriate levels, we didn’t anticipate that the pesticides reduce their ability to find their way back to the hive or have negative effects on wild bee fitness and their ability to forage; that was just too complex for the methodology.

“There is no safe pesticide; as their power comes from disrupting fundamental life processes, there are only degrees of risk”

A few years ago I visited Charles, a Ugandan smallholder who Riverford had helped to train in farming through the charity Send a Cow. Charles grows a multitude of crops on his two acres, including a small medicinal garden. Some plants were to treat his family and livestock, while some were for making his own crop sprays. He described mixtures of ash, urine, plant and compost teas used to control various insects. I noticed some tobacco growing and asked him if he used nicotine. He said it was there ‘just in case’, but he had never used it; he would consider it a mark of his failure as a farmer to resort to such a strong and unselective insecticide. I was stopped in my tracks; here was IPM being used with subtlety, sophistication and good effect. First-world farmers could learn a great deal from him.

Guy Watson

Systemic pesticides - the facts

  • There are 2 main types of pesticide: contact and systemic. Contact pesticides sit on the surface of plants. Systemic pesticides are designed to be absorbed through the roots or leaves into every part, including the bits you eat.
  • Washing many modern pesticide residues off your food simply isn’t possible.
  • Systemic neonicotinoids (or ‘neonics’) are the most widely used insecticides in the world.
  • It has been argued that because systemic pesticides are absorbed into the very tissue of the crop, there is no need for farmers to keep reapplying, thus reducing the total volume of chemicals released into the atmosphere. But in practice, application of systemic pesticides does nothing to reduce overall volumes of pesticide use, as shown by upward trends in use data in UK arable crops.
  • The toxins are persistent as well as powerful, lasting for the entire life of the plant and for years after that in the soil.
  • Neonicotinoids have been proven to damage bees’ ability to navigate, learn, and reproduce, and linked to drastic declines in butterfly and bird populations.
  • Two neonicotinoids have also been linked with damage to the human nervous system, especially brain areas associated with learning and memory.
  • Pesticide residues are found in 58% of all UK fruit and veg, with many containing multiple residues, and 5% exceeding the maximum residue level (MRL) legally tolerated by the EU. Traces of non-organic pesticides are sometimes found on organic produce because of cross-contamination.

Were you aware that washing and peeling fruit and veg doesn’t get rid of all the chemical nasties? Let us know in the comments, or join in the conversation on Facebook and Twitter.