We have noticed increasing interest and discussion, both locally and internationally, about clopyralid — a herbicide used to control broadleaf weeds in turf and lawns.

Clopyralid can only be used in New Zealand by qualified ‘approved handlers’. Although it breaks down quickly on lawns and turf, it doesn’t break down through composting and can impact on some plants, such as tomatoes and potatoes, at very low concentrations.

Composters across New Zealand use unwanted materials (such as garden waste, bark, food scraps, and chicken manure) to make great composts and soil conditioners.

With a strong focus on quality product, good producers regularly test their composts to make sure they are fit for purpose. Composters also carefully manage the materials used for compost manufacturing to avoid contamination.

Compost is an important part of the push to decrease New Zealand’s carbon footprint. It reduces landfill emissions while also providing a valuable product for home gardens and agriculture.

Any contamination can undermine the benefits of using compost. That’s why WasteMINZ’s organic materials sector group surveyed commercial composters and greenwaste processors about clopyralid testing in 2014.

The survey showed testing was being carried out at many facilities. To reinforce the importance of the issue, the sector group produced a guidance document on how to test for clopyralid and how to manage grass clippings as an input into compost.

WasteMINZ has also raised the issue of increasing restrictions on the use of clopyralid several times with the Environmental Protection Authority (EPA). These discussions are ongoing.

The group’s chair, Chris Purchas, says the composting sector has been working on the issue for many years, and will continue to do so in 2021.

“Last month we reminded greenwaste processors and composters of the importance of testing for clopyralid residue in compost batches, using one of the methods outlined in our guidance document. We know the sector is aware of the issue, and has measures in place. We have also contacted the EPA again to continue our discussions about regulatory measures to control the use of clopyralid.”