Buoyancy and survival of weed seeds in container nursery irrigation ponds

Authors: RAY, ALISHA - North Carolina State University; LEBUDE, ANTHONY - North Carolina State University; Altland, James; HARLOW, CHRISTOPHER - North Carolina State University; NEAL, JOSEPH - North Carolina State University

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/2026
Publication Date: 4/23/2026
Citation: Ray, A., Lebude, A., Altland, J.E., Harlow, C., Neal, J. 2026. Buoyancy and survival of weed seeds in container nursery irrigation ponds. Weed Technology. 40. Article E27. https://doi.org/10.1017/wet.2026.10101.
DOI: https://doi.org/10.1017/wet.2026.10101

Interpretive Summary: In container plant nurseries, weeds continue to appear despite efforts to prevent them. Although several sources of weed infestations are known—such as wind, reused containers, and nearby mature plants—growers have long suspected that irrigation water might also move weed seeds around. However, little information has been available on whether weed seeds can float in water or survive long enough underwater to be spread by irrigation. To address this problem, a study was conducted to determine how easily common nursery weed seeds float and how long they stay alive when submerged in irrigation ponds. Thirteen weed species were tested for buoyancy, and four species were tested for their ability to survive underwater for up to a full year. It was found that some weed seeds, such as eclipta and marsh yellowcress, floated almost perfectly, remaining on the water surface for the entire seven day test. Others, like yellow woodsorrel and flexuous bittercress, sank quickly. Seeds with fluffy attachments (called a pappus), such as those of common groundsel and dogfennel, floated much better when the pappus was present. This showed that seed structures can greatly influence whether seeds stay afloat and potentially move with irrigation water. In addition, seeds from several weed species were submerged in real nursery irrigation ponds for up to 360 days. All species were able to germinate after 240 days underwater, and many remained alive even after a full year. Flexuous bittercress and eclipta, in particular, maintained high germination rates after long periods of submergence. Even species with low buoyancy, which would normally sink, were found to remain alive and were detected in irrigation water samples in earlier nursery studies. With this information, nursery managers can take practical steps, such as managing weeds near pond edges, avoiding irrigation during heavy rain, or improving water capture and filtration areas. These actions can help limit weed seed movement and reduce the chances that irrigation water will carry new weeds into nursery crops.

Technical Abstract: Weed seed buoyancy and survival in irrigation ponds were investigated as part of a larger study evaluating the potential for weed seed spread via overhead irrigation in container nurseries. Seed buoyancy was assessed for thirteen weed species common to container nurseries. Two of the thirteen species were tested with the pappus intact and removed. Seeds were placed in water, and seed settling was recorded each day for 168 h. Among the species tested, seed buoyancy ranged from 0% to 100%. Eclipta and marsh yellowcress maintained 100% and 99% buoyancy. In contrast, flexuous bittercress and yellow woodsorrel had 2% and 0% buoyancy. An attached pappus significantly increased seed buoyancy for both common groundsel and dogfennel. To test seed survival in irrigation ponds, seeds of spotted spurge, eclipta, flexuous bittercress, and yellow woodsorrel were placed in mesh bags and submerged at a depth of 60 cm in irrigation ponds at four nurseries. Seeds were collected from each location at 7, 15, 21, 30, 60, 90, 120, 240, and 360 days after submergence then germinated. All weed species germinated following 240 days of submergence. Flexuous bittercress and eclipta maintained over 80% germination following 360 days of submergence in three of four locations. In contrast, yellow woodsorrel seed germination was less than 15% following 240 days of submergence and less than 5% after 360 days in three of four locations. Spotted spurge seed germination declined over time but remained greater than 15% following 360 days of submergence. Results of these experiments show that seeds of several common nursery weeds are buoyant and remain viable in irrigation ponds for extended periods of time. Seeds that are both buoyant and survive in water may have greater potential for distribution by irrigation systems.