One of the longest-running weed seed longevity studies (Beal Seed Experiment at Michigan State University) has shown that some weed seeds may survive in the soil for more than 140 years (Figure 2)! That’s right, one-hundred-and-forty years. The experiment is still ongoing with the next batch of seeds scheduled to be unearthed in 2040 (stay tuned!). To read more about the Beal Seed Experiment, please visit their website.
The non-dormant weed seeds will germinate and emerge every year. Some of the seedlings may die through various means: competition, tillage, and herbicide application, among others. Some may survive and produce seeds to add to the weed seedbank (Figure 1). The cycle continues every single season.
You might be thinking, why don’t we just kill all the seeds in the soil? If it was that simple, I (and many weed scientists) probably won’t have a job. The closest we have come to killing weed seeds in the field is through the use of preemergence herbicides. However, preemergence herbicides only kill germinating (non-dormant) weed seeds.
Yes, there’s fumigation, but it is not very effective and not commonly used in most cropping systems because of toxicity concerns. Put differently, we currently have no practical way of controlling dormant weed seeds in the soil. This leaves us with nature–we rely on seed-eating bugs, rodents, and pathogens to do this for us.
All hope is not lost. As part of the Pacific Northwest Herbicide Resistance Initiative, we are devoting a lot of resources to studying the weed seedbank and how we can better manage these in our cropping systems. I will leave you with this: effective long-term management requires preventing weeds from going to seed and the exhaustion of seeds in the soil. This is an uphill task, but maybe, we will win someday. If you are interested in estimating how your weed control practices may impact your seedbank over time, Dr. Andrew Kniss from the University of Wyoming developed a model that can provide some insight.