Lindsay Shupert, a graduate student with Dr. David Gibson at Southern Illinois University conducted a research project on sericea lespedeza (Lespedeza cuneata) in the Crab Orchard National Wildlife Refuge. The refuge is located near Marion, Illinois between the Mississippi River and Ohio River, in Williamson County.
The goal of the study was to explore a comprehensive approach to reducing the abundance of sericea lespedeza. Primary objectives of the research were to: (1) Measure the level of sericea lespedeza control and forb tolerance to varying rates of Garlon® 4 Ultra specialty herbicide and PastureGard® HL herbicide applied in spring and summer; (2) compare effectiveness of summer-applied to spring-applied herbicide treatments; and (3) determine how supplemental seeding of native grasses and forbs enhance restoration success following herbicide treatment. The hypothesis was that the combination of herbicides and seeding would allow an increase in native plant diversity and reduce regrowth and reinvasion of sericea lespedeza.
Field studies were established at three sites within Crab Orchard Wildlife Refuge on infestations of sericea lespedeza. A split-plot design was used, where half of the summer herbicide-treated plot received a spring seeding of desirable prairie species, and the other half did not receive seeding (Figure 1).
Two herbicides at multiple rates were applied in August 2012 and two herbicides at one rate each were applied in May 2013 (Tables 1, 2). Herbicides included Garlon 4 Ultra* (triclopyr) and Pasturegard HL (triclopyr plus fluroxypyr), which have been shown to provide effective control in reducing sericea lespedeza. A native seed mix designed for Conservation Reserve Program lands (Table 3) was seeded in February 2013 to half of the August herbicide-treated plots. Plots were hand raked prior to seeding to remove litter and allow seed contact with the soil. The seed mix was distributed at an approximate density of 300 seeds per square meter. Plots receiving the May herbicide treatments were not seeded.
Vegetation was assessed prior to or immediately after herbicide application, and post-application in June and August 2013. Density of sericea lespedeza were measured using stem counts to quantify density, and a visual estimation of canopy cover according to the modified Daubenmire scale. Cover and richness of exotic and native plants on the August-treated herbicide plots were also measured. These steps allowed for comparison of the effectiveness of herbicides with and without reseeding, and applied in spring and in summer.
Mixed Model analysis by site was performed to test the effect of herbicide and seeding treatments on sericea lespedeza. The August herbicide-treated plots were also tested for effects on other plant groups. Statistical analysis was performed to assess community composition response to seeding and herbicide treatments.
Herbicide treatments applied in August significantly reduced sericea lespedeza stem density (Figure 2) and cover compared to non-treated plots 10 months after application at all three locations. Evaluations taken 12 months after application showed Sites 1 and 3 responded similarly to herbicide treatments, which provided effective control of sericea lespedeza; however, only PastureGard HL at 2.2 pints/acre significantly reduced sericea stem density at Site 2 compared to non-treated plots. Site 2 had less intensive management than sites 1 and 3, soil compaction, and the lowest cover of native species, which may have affected herbicide efficacy and regeneration of sericea lespedeza. There was no significant difference in sericea lespedeza stem density or cover between various herbicide treatments except at Site 2. Supplemental seeding in the August herbicide-treated plots did not reduce the abundance of sericea lespedeza consistently across plots or sites.
Both Garlon 4 Ultra and PastureGard HL applied in May (spring) significantly reduced sericea cover three months following application similar to the August treatments. Comparisons between summer and spring treatments were difficult to assess since evaluation intervals were only four months for the spring application, and 10 to 12 months for the summer application.
Herbicide effects on native plant species were variable, and cover and richness of native plants was not correlated to herbicide treatment in the spring plots. Similarly, in the summer plots the richness of native plants fluctuated by sampling date, but was not correlated to herbicide treatment.
Good to excellent short-term control of sericea lespedeza was achieved in both the August (summer) and May (spring) herbicide treated plots. However, data from the herbicide treatments suggest that sericea lespedeza will regrow or reinvade on some sites and follow-up control will be necessary.
There was insufficient evidence to determine if supplemental seeding at the applied rate had an effect on restoration success following herbicide application, at least in the short term that this study was conducted. Data showed that supplemental seeding of native species did not significantly reduce regrowth of sericea lespedeza. This poor response of supplemental seedling may be due to the persistent soil seed bank created by sericea lespedeza, or ecological changes occurring in infested sites such as changes in fungal or bacterial communities or allelopathic tendencies of sericea lespedeza. These factors may allow sericea lespedeza to re-establish faster than the desirable seedlings can establish. In addition, the six-month time period that measurements were taken may have been too short for native seedling establishment or the ability of seedlings to compete with sericea lespedeza. Native species richness and cover were not consistently higher in seeded plots compared to non-seeded plots suggesting poor establishment of seed mix species.
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Active ingredients for products mentioned in this article. Product (active ingredient):
Garlon 4 Ultra (triclopyr), PastureGard HL (triclopyr and fluroxypyr).