Biological and mechanical control of Japanese stiltgrass (Microstegium vimineum)
Date
2016
Authors
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Publisher
University of Delaware
Abstract
Japanese stiltgrass (Microstegium vimineum) is an invasive grass that poses a major threat to native biodiversity and restoration efforts in invaded areas. Preliminary research suggests that there may be potential biological control agents that can be used in a classical biological control program in the United States. We compiled a test plant list for submission to Technical Advisory Group for Biological Control Agents of Weeds. Using a phylogenetic approach, we chose 59 plants species that will help to determine the host specificity of any potential biological control agents for Japanese stiltgrass. We will submit this test plant list to TAG-BCAW for review and comment.
We also investigated non-chemical control methods for Japanese stiltgrass. Several studies suggest that mowing can be an effective control method, but none have explicitly explored the effects of mowing height. Additionally, no studies have assessed the effectiveness of leaf mulch as a management strategy. We explored the effects of mowing timing, mowing height, and leaf mulch addition on Japanese stiltgrass in White Clay Creek State Park in Newark, DE. In 2014, we established small plots at two sites: secondary forest understory and early successional field. Plots were mowed at one of three heights (10 cm, 5 cm, 0 cm) in late August before seed set. In 2015, we established small plots in secondary forest understory. Treatments included leaf mulch addition in April (3 cm or 8 cm), mowing in July (0 cm or 10 cm), and mowing in September (0 cm or 10 cm). Treatments were compared to untreated plots. Vegetation surveys were conducted prior to treatment and at the end of the season. Aboveground biomass was harvested and sorted into Japanese stiltgrass vegetation and all other vegetation before drying and weighing. Seed spikelets were counted, dried, and weighed. All treatments except the 3-cm leaf mulch addition reduced cover and biomass of Japanese stiltgrass. Mowing at ground level in July or September were the most effective treatments, reducing Japanese stiltgrass cover, biomass, and seed production by as much as 99%. The 8-cm leaf mulch addition also reduced Japanese stiltgrass cover, biomass, and seed production, but not as effectively. However, mowing at ground level also significantly reduced the cover and biomass of the resident plant community, which implies that land managers should consider the composition and desirability of the resident plant community when choosing their management strategy.
Lastly, we explored the effect of cutting at different internodal regions on Japanese stiltgrass growth in the field and stem cutting growth in the greenhouse. No studies have investigated the effectiveness or viability of Japanese stiltgrass stem cuttings, which could be useful for large-scale production for a biological control program or future experiments. In July 2014, we established samples at two sites in the White Clay Creek State Park System: a secondary forest understory and an early successional field. Each sample had ten stems of Japanese stiltgrass that were all cut at the same internodal region: below the first node, below the second node, below the third node, below the fourth node, or below the fifth node. Treatments were compared to uncut samples. Maximum height and seed spikelet presence data were collected weekly. The stem remnants from the Japanese stiltgrass that was cut were planted in the greenhouse and monitored for stem survival, maximum height, and date of first seed emergence. At the end of the season, aboveground biomass from field and greenhouse plants was harvested and seed spikelets were sorted into chasmogamous (CH) and cleistogamous (CL) seed spikelets before drying and weighing. In the field experiment, all cutting treatments reduced Japanese stiltgrass biomass and seed production. However, stems cut at higher nodes recovered better than stems cut at lower nodes and had greater height, biomass, and seed production at the end of the season. Additionally, Japanese stiltgrass height and biomass were greater at the sunnier site. These results suggest that mowing height is important and effects may vary by light conditions. In the greenhouse experiment, >99% of stem cuttings survived and produced seed. Biomass and seed production did not differ among treatments, but stem cuttings from higher nodes produced seed more quickly. These results suggest that stem cuttings are an efficient and viable method for propagating Japanese stiltgrass.