Vegetation management

This flyer pertains to report 2019RIC09, Best Practices for Boulevard Turf Design and Maintenance.

This Technical Summary pertains to Report 2023-20, “Turfgrass Seed Variety Evaluation Process,” published June 2023.

Our project addresses two critical needs: to update existing MnDOT turfgrass recommendation lists and to develop a new process to keep lists continually updated in a fair manner with data-driven recommendations. We evaluated the current list of MnDOT-approved turfgrass varieties and found underperforming varieties that should be removed. We then found new, improved varieties that should be considered for inclusion on the MnDOT lists. To facilitate a process to keep lists updated for the future, we first conducted a survey of seed distributors. Using their input, we developed a new process that MnDOT can use to approve turfgrass varieties for inclusion as official seed mixtures. Ultimately, this will lead to a more nimble, consistent, and clear process so that existing and new seed vendors can have complete confidence in data-driven decision making by MnDOT.

This report presents the results of a four-year study on techniques for revegetation of native sedges in created basins. Although often the dominant genus in shallow wetlands, sedges (Carex spp.) do not readily recolonize after restoration or creation of the water table. It is unlikely that sedges will naturally establish in created wetlands. The results of seed germination studies on five Carex species suggest the highest germination rates in fresh seeds - with one exception. Wet/cold storage also can prolong seed viability for at least two-and-a-half years. Dry storage is not recommended for wetland sedge seeds. Short-term wet/cold treatment after prolonged dry storage does not improve germination rates. Sensitive to deep water, rising water levels, and competition during the establishment year, seedlings grew well across a wide range of water depths in subsequent growing seasons. Both species outcompeted annual weeds within two to three growing seasons, but not Phalaris arundinacea (reed canary grass). The study recommends weed control during the establishment year to prevent the invasion of P. arundinacea. Wetland soil promotes seedling growth relative to other soils, but does not affect germination rates. Because of the potential for the introduction of undesirable weeds, the study does not recommend the use of donor wetland soil. Instead, study results suggest the potential for the use of organic top-dressings.

This research project investigated the effects of seeding date on native prairie grasses. Specific objectives included determining * the effects of seeding date on first-season establishment * the effects of seeding date on second-season establishment * whether dormant seedings are as successful as seedings done during the main growing season * whether increasing the percentage of cool-season grass seed in a mix improves stand establishment In 1996 and 1997, native prairie grasses were seeded in field plots at the University of Minnesota's St. Paul campus. Seeding was done 10 times during each growing season, at two- to four-week intervals. Species included Schizachyrium scoparium (little bluestem), Bouteloua curtipendula (sideoats grama), Elymus canadensis (Canada wildrye ), and Bromus kalmii (Kalm's brome ), a 'cool-season' and a 'warm-season' mix. Mixes with a higher percentage of cool-season grass seed performed better than mixes containing more warm season grass seed. However, the cool-season mixes produced very few warm-season grass plants.

In this project, researchers used extensive laboratory, greenhouse, and field studies to determine the relative salt tolerance of select native grasses and forbs used to re-vegetate rights-of-ways within four meters of the pavement edge. The studies found that grasses prove relatively tolerant to salt, but show poor survivability in the field during over-wintering. In contrast, forbs generally are sensitive to salt in their environment. Planting success of monocultures and mixtures of grasses near the pavement edge was poor. Observed percent coverage after two years ranged from about 10 to 20 percent over all tested species. Monitoring of longer established sites also shows that native species do not increase as a stand ages. Soil amendments including gypsum, potash, and potassium nitrate were only minimally effective in alleviating salt stress in sodic soils, although gypsum may have some promise in further field testing. The application of salt during winter salting operations also permanently and negatively impacts soil chemistry, which in concert with other plant stress factors such as soil compaction and infertile roadside soils, will continue to limit the success of establishing desirable vegetation on the inslopes of heavily salted roadways in Minnesota.

The Minnesota Department of Transportation (Mn/DOT) has been active in developing the best technology for roadside vegetation control. One method, herbicide spraying, helps eliminate unwanted vegetation. Treatment of unwanted weeds often requires the use of different herbicides. Sprayers must have the capacity to spray more than one chemical at a time, negotiate rough terrains, and apply herbicides safely and in a way that preserves the environment. This report presents the results from testing and evaluating four automated sprayers: The B&B Ditch Sprayer 300 Prototype, a Wanner Innovative Sprayer, the Micro-Track Spray System, and the SCS 750. All four tested sprayers are more economically feasible than the traditional sprayer. The B&B Ditch Sprayer has the lowest net annual savings of the four tested sprayers. The Wanner Sprayer is more economical for use in large districts or in areas with extensive road miles. The Micro-Track Sprayer has the highest rate of return, and also reduces annual costs. The SCS Sprayer has the highest net annual savings and also can monitor, tabulate, and print all vital statistics. The report details product features, testing, and results.

A study was performed to assess the use of perennial native grasses in the control of leafy spurge and Canada thistle and also to evaluate the effects of herbicides applied during the fall to leafy spurge crown buds. As part of an integrated vegetation management program, grass treatments containing the native prairie grass little bluestem established well and were effective at reducing the cover of leafy spurge. Paramount to the success of using native grass species is getting adequate grass establishment which necessitates the careful selection of grass species adapted to the specific site conditions. A fall application of the herbicide picloram at 0.5 and 1.0 lb ai/acre was very effective at controlling leafy spurge and may be mediated via the direct absorption of picloram by the elongated crown buds at this time. The report contains an extensive literature review of the biology and weed control efforts of both leafy spurge and Canada thistle.

This project sought to examine whether it was possible to re-introduce naturally occurring soil fungi called vesicular arbuscular (VA) mycorrhizae back into disturbed soils as part of a normal seeding operation for restoring a prairie. The project consisted of three phases; 1) a survey to determine the types of VA mycorrhizae occurring in different soils and vegetation types (i.e. general roadside, prairie remnant, prairie planting); 2) collect from the wild and then grow prairie VA mycorrhizae species in a greenhouse at the University of Minnesota; 3) install the VA mycorrhizae along with seed from a conventional native seed drill and monitor whether the cultured VA mycorrhizae formed mycotrophic associations with prairie species in the field. This project was a preliminary feasibility study and was not intended to answer long term questions regarding the possible benefits VA mycorrhizae may confer to roadside plantings or other prairie restorations. All phases of the project were successful. The survey indicated that differences in VA mycorrhizae composition exist between different sites. It is possible to produce VA mycorrhizae in a greenhouse by culturing on living plant hosts. The VA mycorrhizae produced was successfully installed along with seed into field plots and did form mycotrophic associations with newly planted prairie species. Preliminary results obtained from this project indicate that further investigation is warranted.

This preliminary study focused on a) surveying the concentrations of sodium and other metals along the rights-of-way of several of the most heavily traveled and salted roadways, b) development of a selection and screening method for salt tolerance in 6 species of native warm season grasses, and c) establishment of outdoor garden plots and field sites to further test the ability of native warm season grasses to grow under highly saline conditions. Salt levels along roadways were found to vary from very low to very high concentrations during the winter months but were found to decrease to levels that probably will allow germination and growth of tolerant grasses. Two species of grasses, blue grama and buffalo grass, were found to be tolerant of saline environments. Two roadside prairie restoration sites were established to further test the ability of mixtures of grasses to tolerate highly saline soils.