Herbicide Bioassay A bioassay involves growing sensitive plants in a sample of growing media, such as compost, under controlled environmental conditions and observing the growth of the plant for indications of stress. There have been a number of reported incidents internationally indicating the potential for persistent herbicides, in particular clopyralid and picloram, contaminating recycled organics products.

No incidents of contamination in Australia have been reported, however a risk management approach has been adopted to manage potential risk whilst longer term and sustainable resolution of this issue can be addressed.

The ROU has directly consulted the developers and practitioners of various bioassays for these persistent herbicides and has adapted and documented a bioassay that:

• Assesses the growth of clover which is highly sensitive to these herbicides with observable effects at 1 to 2 ppb;
• Provides observable results within 14 days
• Provides readily observable plant response; and
• Is cheap to conduct.

This poster is freely available from:

Red Clover Response

The reference photos of red clover response to various concentrations of auxin-like herbicide that accompany this bioassay method are also provided for reference at:

• Auxin-Like Herbicide Bioassay reference photos

When conducting the bioassay method, we advise that a copy of the poster be used for comparison of red clover response. The distinguishing features of herbicide damage are provided in fine detail on the poster resource.The poster is freely available.