Herbicide Bioassay

Woods End’s plant-response bioassay methods have been carefully developed over decades and can detect low levels of plant-active auxinic herbicides in soil and compost that may be relevant to practical plant culture. This is a different class of environmental toxicology which is focused on practical protection of producers and growers.

Test Procedure is based on a GLP process-documentation protocol at each step of the process. Seeds may be germinated in a Standard Soil (CEN control soil) or equivalent Standard Grow-Media to which is added specific volumes of test material (compost or soil with suspected contaminant) to establish dose-rate response. After a suitable growth interval under controlled conditions, the plants are statistically ranked on a bioassay scale using appropriate bio-indicators determined from previous calibration assays. Results are keyed into a computer program that interpolates injury-index potential (PIRM) and predict damage thresholds. In many if not most cases, apparent damage is found at a minimal risk level.

REGULATORY INFRASTRUCTURE: Residues of pesticides used in lawn, garden and farm occur frequently in organic residues but may not pose any risk depending on molecular composition. Characterizing the decay kinetics (“fate”) and potential phyto-toxicity (“Effect”) is important for proper product registration and consumer protection. The occasion that these residues become troublesome when recycling via composting or soil application  may be rare but must always be characterized.

HERBICIDES FOCUS: A wide category of herbicides are used in agriculture and horticulture. The types most likely to influence plants when organic matter is recycled are those known to have carryover potential in crop rotations, already well characterized. Farmers have learned how to manage post-application damage by choosing which crops follow in a rotation. However, this context is challenged by composting  which presents a novel “fate pathway”.

VEGETABLES AFFECTED: Consumer impact is also evident. Certain common vegetables are variously sensitive to herbicide carryover outside label guidelines, posing a unique challenge for manufacturers and applicators. Auxins for example are not labeled for tomatoes and there is no tolerance limit. However, auxins present in compost will affect tomato growth sometimes leading to epinasty.

LAB ANALYSIS: Laboratory testing using quantitative measures is often warranted to pinpoint molecules present, but it cannot determine bioactivity-injury potential. Thus lab data alone which implies a danger may be misleading  if growing plants are not affected.

PLANTS AS BIOASSAY: Woods End has worked carefully over two decades to develop effective plant herbicide detection methods that are relevant to what a grower will experience. The bioassay technique distinguishes plant sensitivity groups. The test predicts the probable level of bioactive herbicide calibrated to a known molecule.

Plant Injury Risk Management: The final result of Woods End herbicide bioassay test is “PIRM” – Plant Injury Risk Management. With this tool the likelihood of passing on risk to customers is largely obviated.

Contact us: if you have concerns about chemical compost residues: we’ll help you manage it.