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How much of an impact do herbicides and pesticides have on biodiversity?

How much of an impact do herbicides and pesticides have on biodiversity?

Submitted by: Hileaeyesus Solomon


Expert response from Steve Savage

Consultant, Savage & Associates

Tuesday, 24/04/2018 15:00

While biodiversity is an important issue, the relationship to agriculture and to agricultural crop protection chemicals is a bit complex.  First of all, since its beginnings 10,000 or more years ago, farming has been quite intentionally an effort to make one plant species dominant in any given tended area or field.  From the plant biodiversity side, the struggle has always been with other plant species that are particularly “weedy” which means they are well adapted to being competitive with the crop under the artificial conditions of farming. This has been true long before there were any chemical crop protection tools and weed control involved hand labor or later mechanical tillage. Not all biodiversity is good, particularly when it involves invasive and highly competitive weeds. To make efficient use of land, water and other finite resources really requires limiting the plant biodiversity in a field. 

In a farming setting the best way to encourage overall plant biodiversity is to encourage the growth of less weedy species on field boundaries, wind breaks, buffers along waterways or “prairie strips,” because then that kind of biodiversity provides environmental services and often a base from which pollinators and beneficial insects can flourish. In annual cropping systems there can be the opportunity to grow additional “cover crops” after the main season and these can be diverse mixtures of species that stabilize and feed the soil. Chemical herbicides are very helpful for transitioning from the cover crop to the “cash crop” then next season and so that is a case where herbicides are a plus for a plant biodiversity strategy. In perennial crops like orchards or vineyards, plant biodiversity can be encouraged in the “middles” while managing the vine or tree row with herbicides to reduce weed competition for fertilizer and water.

Chemical herbicides are also very helpful for allowing farmers to grow crops with minimal mechanical disturbance of the soil. Herbicide tolerant “GMO” crops make this kind of system even easier to implement. These no-till or minimum-tillage systems are very good for “soil health” which is really all about the biodiversity of the fungi, bacteria, earthworms, and beneficial nematodes – a kind of biodiversity that is seriously compromised by tillage. So, when it comes to the biodiversity of a healthy soil – herbicides are a major plus because they can obviate the need to till.

Biodiversity in terms of insects and mites is something that can be quite positive for a farm because even pests have pests and if that kind of diversity is encouraged then the insects or mites that damage the crop can be better kept in check. Many of the older classes of insecticides were “broad spectrum” and would kill off beneficials and pollinators as well as pests. There are now many more selective chemicals for pest control and between their use and care about timing, farmers can encourage helpful biodiversity and still limit pest damage. The Bt-based insect resistant GMO crops are an excellent example of a more selective, biodiversity-encouraging way to farm. In this case the pesticide is an extremely specific agent which really only effects a pest that actually eats the crop. There is no impact of that on pollinators or beneficials.

Finally, any of the technologies that allow more efficient crop production on farmed land help to reduce the pressure for converting more natural areas to farming. Those undisturbed forests, grasslands etc. are incredibly important for global biodiversity and so allowing humanity to be fed without disturbing such areas is a very positive outcome, at least partially enabled by crop protection agents like herbicides, insecticides and fungicides.