Broad-leaf weed killers that contain the pyridine herbicides have caused widespread damage to many gardens in New Zealand, the UK and the US in recent years, and these herbicides are now being sold in Australia.
Pyridine herbicides include aminopyralid, clopyralid, fluroxypyr, picloram, and triclopyr. They are only effective on broad-leaf plants, but the chemicals remain active in mulch cut from sprayed pastures and in manure from animals that have grazed on sprayed pastures until the chemicals are broken down by soil microbes. Of particular concern to home gardeners and councils that recycle waste into compost for agricultural and domestic use are the products containing aminopyralid, clopyralid and picloram because they are quite persistent in compost (particularly anaerobic compost), and residue from these herbicides can damage crops for up to 24 months.
Is it just me, or do other people think it is crazy that there is widespread concern about the future of food production in Australia, and all levels of government are advising us to recycle and store carbon, yet the Australian Pesticide and Veterinary Medicines Authority (APVMA) continues to register more and more of these herbicides that damage food crops, and little if anything is being done to warn the public of the risk in using mulches, composts or manures contaminated by these herbicides.
Although there are only two pyridine herbicides containing aminopyralid (Hotshot and Grazon Extra), the APVMA has registered 59 herbicides containing clopyralid, 54 containing picloram, 27 containing fluroxypyr, and 77 containing triclorpyr, and there are several more of these herbicides awaiting approval – an impossible list to remember when purchasing mulches, manures or compost.
The problem with Australian regulating authorities is that they regard the person who sprays the herbicide as the ‘end user of the product’ and any warnings are limited to product labels without any regard for the unsuspecting gardeners who, in good faith, purchase mulch, compost or manures contaminated with the herbicide, and who may not recognise the cause of the damage to their crops because they have not personally used any herbicides.
I am very grateful to Jo T. who has sent me a link to photos of damage to vegetable plants caused by aminopyralid. These may help readers identify this herbicide problem in their gardens.
You can find Australian product names of these herbicides by going to APVMA’s Public Chemical Registration Information System page. Select herbicide and then type aminopyralid, clopyralid or picloram in the active constituent panel.
The NSW Government has been aware of the problems with these herbicides in Australia since 2005:http://www.environment.nsw.gov.au/resources/warr/SPD_ORG_ReduceRiskHerbCompost_FS.pdf
Jo has also provided a link to UK information about aminopyralid problems.