Milkweed Establishment in Restored Central Missouri Prairie

Abstract

The decline of the Eastern North American monarch butterfly (Danaus plexippus) population continues to be a major concern among conservationists. Numerous publications and organizations suggest that establishing milkweed (Asclepias spp.), at a landscape scale, is necessary to increase the monarch population. The translocation of commercially grown containerized plugs is commonly recommended to establish milkweed. During 2017, we used a split-plot design to examine the factors of age of prairie restoration, plant type, and land preparation method on survival of translocated milkweed in restored prairie in central Missouri, USA. Milkweeds were translocated to 16 0.81-ha sites, half classified as young (<8 yr) and half as old (>9 yr) prairie restorations. We randomly selected 8 sites to establish bare-root milkweed seedlings and 8 sites were planted with milkweed seedling plugs. Each site contained paired 0.4-ha plots. At the plot level we tested 2 land preparation techniques, disking with the application of pre-emergent herbicide and application of a grass herbicide. Milkweeds were planted at the density of 200 milkweeds/ 0.40 ha as suggested by the Missouri Monarch and Pollinator Conservation Plan. We conducted a census to determine milkweed survival 2 growing seasons after establishment. Two-year survival of translocated bareroot milkweed (x = 0.26, 95% CI = 0.12-0.49) was nearly 5 times greater than that of milkweed seedling plugs (x = 0.05, 95% CI = 0.02-0.13). Milkweed in disked plots had greater survival (x = 0.18, 95% CI = 0.10-0.31) than in plots treated with grass herbicide (x = 0.08, 95% CI = 0.04-0.16). Milkweed survival in older restored prairies (x = 0.07, 95% CI = 0.03-0.18) was lower than that in newer prairie plantings (x = 0.21, 95% CI = 0.09-0.41). Our results suggest translocation of bare-root milkweed seedlings, combined with disking and application of pre-emergent herbicide, is the preferred alternative. We suggest translocation of milkweed may be a feasible method of enhancing monarch habitat. However, meeting the challenge of restoring milkweed at recommended densities in established grasslands may be limited if milkweed seedling plugs are used.