Keeping clopyralid out of composts

30.04.24 10:24 AM By WasteMINZ

The name Clopyralid sounds like a sci fi monster – if you are a gardener or compost manufacturer it can be your worst nightmare. Clopyralid is a herbicide belonging to a family of herbicides called pyridines. It came onto the market in the late 1970s for the control of annual and perennial broadleaf weeds in certain crops and lawn turf. In New Zealand it is still widely used in the management of broadleaf weeds in turf, playing fields, parks and is also used by lawn management contractors to control broadleaf weeds in their clients’ lawns.

If lawn clippings or weeds with Clopyralid on them find their way into home or commercial composts, it can create contaminated compost. Clopyralid residues in compost are damaging at very low levels (1-3 parts per billion) and the residues can persist for more than 12 months. Contaminated compost can be very damaging to a range of garden plants and vegetables such as Fabaceae - peas, beans, sweet peas; Solanaceae - tomatoes, potatoes, eggplants, capsicums etc; and other plants in the genus; Asteraceae – Dahlias and many other flowers, lettuce, artichokeRosaceae -  roses, loganberry and raspberry; Vitaceae – grapes and Umbelliferae - carrots, celery, parsley, etc. 

Plants may be stunted, distorted, or may not germinate at all if planted from seed.

Plants affected by clopyralid - photo supplied by Minette Tonoli
Since it started being used in Aotearoa, there have been problems with Clopyralid contamination of composts - both home and commercial.

The Organic Sector Group of WasteMINZ, who represent compost manufacturers in NZ at all scales, appeals to commercial turf and lawn managers and product suppliers to follow the Environmental Protection Authority (EPA) guidelines rigorously.

Compost companies can and do test their product for Clopyralid. However, this adds considerable extra costs to the production process and is not fail safe due to the very low levels of contamination that can cause problems for end users.

The EPA (Te Mana Rauhī Taiao) is the regulatory body for this issue and requires the registration of products containing Clopyralid. Now no longer available through retail outlets, pyridine herbicides, including Clopyralid, are only available through registered outlets to customers who are registered as certified safe handlers. Most commonly,  products containing Clopyralid are classified only for use ‘in the workplace’ and operators must have up-to-date safe handling certification.

There are 27 products containing Clopyralid approved for sale in NZ, and rules have been developed to prevent residues getting into commercially made composts. There are labelling laws and restrictions on the sale and use of products containing these chemicals. If anyone along the supply chain does not follow the rules, then Clopyralid contamination can cause immense damage. It can render large batches of compost unsellable – or, worse still, reach end-users and cause havoc in their gardens and loss of faith in compost products.

Growsafe and Adroit Solutions both offer Certified Handler Courses, which any Clopyralid suppliers requires. These qualifications are valid for five years. Suppliers are required to:

  • keep a register of purchasers, and
  • ensure commercial operators sign the register and show their safe handling certification at point of purchase.


Operators can find out more about certification on the WorkSafe website.


Different products have different uses so they can also have different rules. Operators must follow the rules for use and disposal of the specific product they  are using. Products containing Clopyralid should never be shared with non-registered users.

Check the EPA website to make sure your operators can comply with the rules for the product that you want to use. You should also follow the instructions on the label and safety data sheets.

Most importantly plants and grass clippings treated with clopyralid must not be put into compost, mulch, or council green waste. The only safe way to dispose of Clopyralid-treated organic waste is to send it to landfill.

About the author

Liz Stanway is a member of the WasteMINZ Organic Materials Sector Group Steering Committee, which aims to minimise the generation of residual organic materials, and to maximise the value of residual organic materials, ensuring they are re-used beneficially.