Ah, those dandelions!
Personally, I am not a total zealot when it comes to using chemicals in the garden. I cannot imagine not using Roundup (glyphosate) for troublesome weeds – digging them up and composting them is better, but cannot always be done.
And those of us who love a green lawn, more-or-less free of dandelions, will often use something like 2,4-D, which is the least worst of the lawn broadleaved weed killers.
However, I never use pesticides (insecticides) except the mosquito killer Bacillus thuringiensis. There seems very little point indeed trying to encourage birds and snakes and bees and butterflies and toads and foxes and dragonflies…..if we are either going to wipe out their food or poison them directly.
2,4-D is the commonest weed killer on lawns, and in fact one of the most-used herbicides in the world. It is a ‘growth hormone’ that causes any plant that absorbs it (except grasses, which are immune) to go into a crazy, fatal growth spurt…and seed like mad if it is a dandelion. It is usually used mixed with other weed killers to achieve a more powerful product – often mecoprop and dicamba. Mecoprop (MCPP) is very like 2,4-D, but is more persistent – and dicamba is similar. Unfortunately, because these chemicals are designed to hang around in the environment and keep on poisoning your plantains and dandelions and clover, they are often found in ‘groundwater’ – the water that a lot of people end up drinking. How dangerous is that? Well, it is difficult to say – pesticides on the market have to jump through a lot of hoops in terms of testing, but it is very difficult to prove long-term safety, particularly in combination with other chemicals. 2,4-D always has a trace of a dioxin contaminant (2,7-dichlorodibenzo-p-dioxin); this, like all dioxins, is a very powerful toxin affecting the immune system as well as cell division. It is completely unknown whether – and how – the levels of dioxins caused by the 2,4-D lawn deluge are affecting us.
Glyphosate (“Roundup”) is the weed killer most gardeners use to keep weeds under control in flower beds. It is absorbed through leaves (a ‘systemic’ herbicide) and kills all types of plant, by interfering with the way plants make amino acids for proteins. For this reason, it only works on actively growing weeds (well, any plant, ‘weed’ or not!)
Happily, the herbicide itself, when diluted and ready for use, is almost completely non-poisonous if you swallow it (although please do not try to prove me wrong, as it is mixed with detergents that CAN harm you), and the same good news applies to all mammals. It does not build up in animal tissue and seems to have a clean bill of health in terms of cancer risk…. as is well-described here.
Alas, we are looking afresh at these chemicals and their ability to affect reproduction – so-called gender benders or (posh name) endocrine disruptors. Studies in the lab suggest that glyphosate might interfere with the making of testosterone. This does not necessarily translate into real environmental effects.
This herbicide is tightly ‘sequestered’ (grabbed hold of and kept) by soil, and, although it hangs around in the soil for a while, especially in cold areas, it seems to be broken down by soil bacteria. There is some evidence that useful bacteria that turn atmospheric nitrogen into fertilizer (‘nitrogen fixers’) are negatively affected by glyphosate…and – somewhat perversely – crops seem more susceptible to disease if glyphosate is in the soil.
In the form that we gardeners use, glyphosate is quite poisonous for aquatic life. It persists for some months and affects fish and other water-living animals. Ironically, there are versions especially formulated for aquatic use that are less dangerous, but of course they are not the ones that will wash into waterways from our yards.
Bacillus thuringiensis. Often called “B.T,” this is a biological insecticide, that is, a disease that affects moths and butterflies – and is also used against mosquito larvae in water – and you can buy the BT “rings” to drop into your ponds and fountains. It leaves other things like fish and frogs alone. Cool!
Other pesticide information can be found at….
Questions? Comments? E-mail me on firstname.lastname@example.org