Emptying the Bank, the Weed Seedbank

Jesse Fulbright, MSU Liberty County Extension

As a teenager on a farm in south-eastern Washington, I was involved in some spring farm work.  For me, that meant rogueing rye out of wheat fields.  For us, that involved getting into the fields early enough to clip the heads of the rye before the seeds were mature and viable.  I didn’t realize that now, but that simple task each year was giving me valuable insight into parts of my job now.

Weed seedbanks, which we were trying to diminish by clipping the rye, are reserves of viable weed seeds present on the soil surface and scattered in the soil profile.  It consists of both new weed seeds recently shed and older seeds that have persisted in the soil for different periods of time.  So, how do we manage the weed seedbank? 

According to an MSU Extension MontGuide, titled, “Weed Seedbank Dynamics and Integrated Management of Agricultural Weeds,” seedbanks can be managed in one of several ways.  The most efficient approach is prevention.  Care can be taken to avoid bringing new weed seeds into a field by washing equipment before bringing it into the field.  It would also include visual and physical inspections of equipment.

Reduction is another approach as it not only minimizes future weed problems, it also reduces the speed at which weed patches expand across fields.  Increasing crop interference by increasing seeding rates and filling empty niches with cover crops helps minimize weed seeds into the seedbank.  Other approaches include mowing weeds prior to seed production and control of weeds through chemical means or cultivation.

Rotation of crops, say from a cereal to a pulse crop, or vice versa, can also cause a shift in weed species composition.  This also allows existing weeds in a cereal crop to be worked out, for example if you went into a pulse crop system.  Just be careful of residual spray if spraying broadleaf weeds in a cereal system and you plan on rotating into a pulse crop system. 

Many of these tips today can also be applied to a garden setting in one’s garden.  The principles of prevention, reduction and rotation can be valuable tools in our fight against weeds in gardens and cropping systems.