Date of Award
Master of Science
Crop Production and Physiology
Bob G. Hartzler
The monarch butterfly’s (Danaus plexippus Linnaeus) vibrant orange color with contrasting black veins and white spots make it recognizable to many. Unfortunately, the remarkable migration made by the eastern monarch population is at risk due to the recent decline in this cohort of the species. Many factors are said to have caused the decline, including overwintering habitat destruction, increased dependence on herbicide-tolerant crops, extreme climatic events, predation, loss of breeding habitat, etc.
Two studies were conducted to: 1) determine the impact of sub-lethal herbicides on growth of common milkweed and utilization by monarchs and 2) investigate simple methods for establishing common milkweed and three additional forbs (golden alexanders (Zizia aurea L.), wild bergamot (Monarda fistulosa L.), and New England aster (Symphyotrichum novae angliae L.), into an existing sod landscape.
In the first study, fomesafen caused rapid damage to leaves contacted by the spray, resulting in the loss of many leaves. However, plants recovered rapidly and ovipositing by monarchs was not affected. Additional herbicides commonly used in Iowa crop production were evaluated for their effect on common milkweed in greenhouse experiments. Glufosinate was more injurious to common milkweed than either imazethapyr or mesotrione, but as with fomesafen, treated plants showed signs of recovery from all three herbicides within two weeks of application.
The second study investigated the effects of mowing and sub-lethal rates of glyphosate on the establishment of common milkweed and three forbs in an established stand of smooth brome (Bromus inermis Leyss). In general, suppression of smooth brome sod with sub-lethal rates of glyphosate increased recruitment of seedlings, but there was a low probability of permanent establishment of common milkweed and other forbs. Establishment of golden alexanders and wild bergamot was greater than either common milkweed or New England aster.
Lizotte-Hall, Sydney, "Investigations into the function of common milkweed (Asclepias syriaca) in the agricultural landscape" (2018). Graduate Theses and Dissertations. 16623.