Variability in cogongrass seed viability across Alabama and the Southeast
Nancy Loewenstein, Research Fellow III
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Cogongrass (Imperata cylindrica) is a growing threat as it continues its rapid spread across the Southeast, reducing forest and pasture productivity, destroying wildlife habitat, impacting rights-of-ways and presenting an extreme fire hazard. Dispersal of this aggressive non-native weed occurs both vegetatively and by seed. However, reports on variability in seed viability have led to questions regarding the relative role of seed production in cogongrass spread within different regions of the Southeast. Under optimal conditions, an individual plant can reportedly produce as many as 3000 seeds. Production of unfilled florets is not uncommon though, as cogongrass is an obligate outcrosser, requiring pollen from distinct genotypes for the production of viable seed. Consequently, low seed production is expected in areas consisting primarily of clonal plants established vegetatively and/or in areas with small, isolated populations. The presence or absence of viable seed and the genotypic variation within infestations have several major implications on regional control for cogongrass. Use of spring applications of herbicides to reduce seed production is on the rise, while these are believed to have little impact on overall plant control. These could be wasted applications if the population is not producing significant quantities of viable seed in the first place. Also, if outlier populations are clonal and essentially infertile, then their treatment is less urgent than if they were heterogeneous and capable of producing viable seed. The primary objective of this study is to determine if anecdotal reports of seed viability differences are correct and if regional strategies for cogongrass control need to take differences in seed viability into account.
