Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2008
Publication Date: 7/11/2008
Citation: Davis, A.S. 2008. Weed seed pools concurrent with corn and soybean harvest in Illinois. Weed Science. 56(4):503-508. Interpretive Summary: Uncontrolled weed seed production is the primary source of ongoing weed problems in midwestern field crops, yet few commercially viable methods of reducing inputs to the weed seedbank exist. A survey of conventionally managed corn and soybean fields in central Illinois in 2004 and 2005 revealed that weed seedbank management failures (seed additions resulting in replenishment or augmentation of the weed seedbank) were common even in apparently clean fields. For several species, including giant foxtail, velvetleaf, ivyleaf morningglory, prickly sida and cocklebur, the majority of new seeds remained undispersed at the time of harvest, indicating good potential for capturing these seeds with modified harvesting machinery. Other species, such as common lambsquarters and common waterhemp,however, had dispersed most of their seeds by harvest time, suggesting that measures aimed at reducing plant growth and survival, or at increasing the number of seeds eaten by seed predators, may be more effective seedbank management approaches for these species.
Technical Abstract: At the time of grain harvest, weed seeds may be classed into one of four pools based on dispersal status and location: 1) undispersed, remaining on the mother plant, 2) dispersed in the current year, on the soil surface, 3) dispersed in the current year, and collected by harvest machinery, and 4) dispersed in a previous year, and persisting within the soil seedbank. Knowledge of the relative sizes of these seed pools for different weed species under different crop environments will be useful for determining the best way to reduce the size of inputs to the soil seedbank. In fall of 2004 and 2005, four randomly selected commercially-managed corn and soybean fields in east-central Illinois were sampled to quantify weed seed pools at time of crop harvest. Thirty randomly-located 0.125 square meter quadrats were placed within each field, the four seed pools mentioned above were sampled for each quadrat, and the species composition and abundance of each seed pool was determined. The magnitude of the weed seed rain varied among species, and between years and crops. Twenty four weed species were found to contribute to at least one of the four seed pools. However, the weed seed pools were consistently dominated by six species: velvetleaf, Amaranthus species (redroot pigweed and waterhemp), ivyleaf morningglory, giant foxtail, prickly sida and common cocklebur. For each of these species, the ratio of undispersed seeds to seeds in the soil seedbank at harvest time was greater or equal to 1 in at least one crop during one of the two experimental years, indicating that the soil seedbank was completely replenished or augmented by that year’s seed rain. This analysis demonstrates the urgent need for techniques to limit weed seed inputs to the soil seedbank at the end of the growing season.