Assessing the Presence of Weed Seeds in Surface Irrigation Water in Container Nurseries

Abstract Nursery crop producers in the Southeastern U.S. use open ponds of captured water for irrigating container-grown plants, often without filtration. Many growers perceive irrigation water as a source of weed seed dispersal, but data on the presence of weed seeds in nursery irrigation ponds are lacking. The presence and diversity of viable weed seeds in irrigation pond water samples from six commercial container nurseries in central and eastern North Carolina, U.S.A., were documented in the spring, summer, and late summer for two consecutive years. Irrigation pond water was filtered in 75,708-L increments using a custom-fabricated filtration system. The sample volume was chosen to approximate daily irrigation for 0.405 ha. A total of 216 filtrate samples were collected, six for each location, season, and year. Filtrates were spread on soilless substrate in plastic trays, and seedling emergence was recorded every seven days for twelve weeks. Irrigation samples from all locations, seasons, and years contained viable seeds. A total of 75 different taxa were present in the irrigation filtrates, including 28 weed species common to container nurseries. The average number of seeds collected at each location ranged from 9 to 35 per 75,708-L sample. Averaged across years and locations, there were 12.5, 24.8, and 18.2 germinable seeds 75,708 L -1 in spring, summer, and late summer collections, respectively. Some common weed species, such as eclipta, marsh yellowcress, large crabgrass, flexuous bittercress, and spotted spurge, were present in samples from each season’s collections, while other species were unique to a single season. Although irrigation water introduced weed seeds, the number of weed seeds was small compared to other potential sources of weed seed dispersal within the nursery environment.