Seedbank Management

For a production system to remain sustainable, the soil weed seedbank must be static or declining. An increasing seedbank is evidence of a weed that is escaping the current management regime through herbicide resistance or some other adaptation. Furthermore, the risk of resistance evolution is shown to be positively associated with the initial seedbank size; therefore, keeping the soil seedbank at low levels reduces the risk of future evolution of herbicide resistance.

The concept of what constitutes an acceptable level of weed seed production must be abandoned in favor of a zero or near-zero threshold to slow the rate of herbicide-resistance evolution. Weed management programs must aim to eliminate weed seed production from the most competitive, resistance-prone weeds in a field.

In particular, knowledge of the earliest time in the growing season when viable seed are produced is vital for timing late-season applications. Some nonherbicidal approaches to weed-seed prevention create additional management challenges. For example, weeds must be removed mechanically or physically before seed maturity.

After Harvest

After crop harvest, producers often allow weeds to grow uncontrolled. Such lapses in weed management can lead to increases in the soil seedbank if sufficient time elapses between harvest and a weed-killing frost, even if a high level of weed control was achieved during crop production. Post-harvest weed-seed production must be prevented to effectively manage soil seedbanks for the long term. In some weeds, such as Common Waterhemp, viable seed production can occur as early as seven days after pollination, meaning that these weeds are capable of producing seed after crop harvest, especially in southern climates.