An important component of managing weeds in field crops is preventing the seeds released by weeds each autumn from becoming new plants. Nature assists in the loss of weed seed through predation, decay, and loss of viability. Integrated weed management strategies that facilitate these processes can lead to high levels of weed seed loss.
The journal Weed Science presents results of field experiments conducted at two locations in Arkansas between November 2010 and October 2011. Researchers studied post-dispersal seed loss of five of the most problematic weeds in the midsouthern United States—barnyardgrass, johnsongrass, pitted morningglory, Palmer amaranth and red rice.
After harvest, weed seeds left on the ground are vulnerable, and biological interventions can keep them from becoming seedlings and the next season’s weeds. The seeds provide food sources for ants, rodents, and birds. Pathogenic microorganisms can attack seeds, causing decay. In addition, physiological aging can affect the longevity and viability of seeds.
The authors of the study estimated total seed loss through predation, decay, germination, and loss of viability, and they examined the influence of residue level and seed burial depth, both near the surface and at 5-centimeter depth. All five species in both locations showed a reduction in the percentage of the active seedbank present between the spring, 5 months after dispersal, and the next fall, 1 year after dispersal.
With these forces of nature working against weed seeds, greater seed loss can be achieved with a little encouragement. Techniques such as no-till planting can allow seeds to remain on top of the soil, making it easier for predators to find them. Additionally, this study indicated that practices to increase soil temperature, organic matter, and moisture content could help promote microbial activity and therefore seed decay. Planting a cover crop after harvest of the main crop, however, was not found to assist predation of the seeds.
Biological seedbank management is a tool of sustainable weed management. Incorporating this as one of many diverse strategies is important for achieving sustainable weed management, particularly with the spread of herbicide-resistant weeds.
Full text of the article, “Postdispersal Loss of Important Arable Weed Seeds in the Midsouthern United States,” Weed Science, Vol. 61, No. 4, October-December 2013, is available.