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Many factors can influence herbicide degradation, namely precipitation and temperature. But, regardless of the environmental conditions, herbicides require time to break down in the soil. When drought, hail, or other situations change crop rotation plans, it can result in concerns about herbicide injury due to inadequate time for a potentially injurious herbicide to break down. A bioassay is one of the simplest things to do to determine the potential for herbicide residues to injure a subsequent crop. A bioassay is an easy at-home test to see how your seeds will grow in the field soil. There are three steps to conducting a bioassay.
- Collect soil. You need to collect both treated soil from the field you are concerned about and similar, nontreated soil. The non-treated soil can come from a neighboring field that is being planted to the same crop that you are doing the bioassay for. The soil sample should include the top 2 to 4 inches of the soil profile. You’ll want to collect enough soil to fill two or three pots for each field.
- Plant your crop seeds in the soil you collected. Within a day or two of collecting soil, place soil in pots and plant the seeds. Depending on the pot size and seed quality, consider planting 25 to 50 seeds per pot. Another consideration is to plant in rows or another pattern that will make it easy to determine if plants have not germinated.
- Monitor crop growth. Put the pots in a sunny place and water them as needed. Monitor seedling emergence over two to three weeks and evaluate seedlings for herbicide injury symptoms. Having the soil from both fields allows you to compare the seedlings that emerged for any injury symptoms easily. A guide to herbicide injury symptoms is available in the KSRE Bookstore.
Sarah Lancaster, Extension Weed Science Specialist
slancaster@ksu.edu
Jeanne Falk Jones, Multi-County Agronomist
jfalkjones@ksu.edu
Tags:
herbicide carryover soil bioassays