Patrick Burch, Travis Rogers, William F. Brunson, J. Parker Hill, and Randal S. Osteen 
Managing incompatible woody vegetation  along utility and transportation rights-of-way (ROW) requires careful planning, consistent budgets, and judicious allocation of time and resources. When budgets or resources are inadequate, planned vegetation maintenance may be postponed to the following growing season or beyond. While delaying maintenance for even one year allows woody vegetation to increase in density and height, the actual increase in time and material to control the vegetation after one or more years of delayed treatment has not been determined.
Dow AgroSciences initiated a research study on a utility ROW in cooperation with Santee Cooper, a South Carolina public-owned utility.
Goals of the study were to:
- Gather data on the amount of time and material needed to control incompatible woody shrubs/trees associated with skipping vegetation management for a year or more;
- Assist ROW managers in making informed decisions that would support consistent vegetation management budgets;
- Determine viable alternatives to delayed maintenance.
The study was initiated on a stretch of Santee Cooper transmission ROW at a site in the coastal plain region of South Carolina. Woody vegetation growing on the site—primarily red maple (Acer rubrum), water oak (Quercus nigra), loblolly pine (Pinus taeda) and American sweetgum (Liquidambar styraciflua)—had been historically managed using a continuous mowing program. The last mowing date was May 2014, and subsequent management was not conducted prior to initiation of the study in 2016.
The study area was divided into three replicated plots (1, 2 and 3), each approximately 150 feet wide and 300 feet long. Woody plant stems were counted in each replicated plot, and the average tree/shrub height estimated (Table 1).
Simulated herbicide applications over each plot were made with a backpack sprayer and again with a hydraulic sprayer mounted on a utility terrain vehicle (UTV) (Figure 2). Water alone (no herbicide included) was applied to target woody plants with each application method.
FIG 1. Study plot 1 showing the ROW transmission line and size of woody vegetation in September 2016 at the time of simulated foliar herbicide treatment.
FIG 2. Plot layout showing two types of equipment used for the simulated herbicide application along a utility rights-of-way. Individual plot size was about 150 feet by 300 feet (ft).
TABLE 1. Number of woody plant stems calculated on a per-acre basis and estimated tree height in 2016 for each study plot.
Simulated herbicide applications occurred as follows:
- 1st – Foliar application in September 2016
- 2nd – Dormant-stem application in January 2017 (Figures 3 and 4)
- 3rd – Foliar application in June 2017 (Figure 5)
The amount of time and volume of water applied to treat woody vegetation in each of the three study plots were recorded for each application technique and date. In late June 2017, a visual assessment was conducted to estimate increased growth of target woody plants since the previous growing season.
FIG 3. Simulated hydraulic dormant stem application in Plot 1 with a hydraulic sprayer mounted on a UTV.
FIG 4. Simulated backpack dormant stem application in Plot 2.
FIG 5. Date and description of each treatment by year in the study area.
The amount of time and gallons of solution needed to apply a foliar treatment to incompatible woody vegetation more than doubled between 2016 and 2017, when vegetation maintenance was delayed on the ROW (Table 2). The additional woody growth required an average of 108 and 111 percent more time and volume of material when applied with a backpack sprayer and hydraulic sprayer, respectively.
TABLE 2. Total gallons of solution and number of minutes to treat woody plants with a simulated foliar application in 2016 compared to 2017*.
The dormant-stem treatments took fewer gallons of solution and less time to apply, compared to the 2016 foliar treatments. Delaying treatment to the following growing season, rather than making a dormant-stem treatment, significantly increased foliar application time and volume of material in 2017 (Table 3).
TABLE 3. Total gallons of solution and number of minutes to treat woody plants with a simulated dormant-stem application, compared to a foliar application applied in September 2016 and June 2017*.
ROW company field observations of dormant-stem treatments to woody brush indicate that foliar applications are generally more effective than dormant-stem applications; however, dormant-stem applications still provide 85 percent or more control. Effective results are closely aligned to proper application methods, spray tips, and herbicide mixing. Furthermore, training in dormant-stem application techniques is highly recommended.
Dormant-stem applications can be used on sites with low to high woody stem densities, and on woody brush with basal diameters smaller than 3 inches. Sites with woody stem densities less than 500 per acre, and woody brush with basal diameters up to 6 inches are best suited for low-volume, basal bark applications.
Advantages of dormant-stem treatments:
- Expands the application season for woody brush control from leaf-drop in fall to early leaf-emergence in spring.
- Offers an opportunity to better align maintenance budgets and work schedules over a longer period of time.
- Minimizes browning of brush compared to foliar herbicide applications made during the growing season. Although there is eventual browning of treated conifer foliage, an overall reduction in browning lessens public scrutiny and potential complaints.
- Minimizes impacts on desirable non-target vegetation—which are dormant during treatment cycles—when applied with selective herbicides.
It is important to remember that results may vary among ROW based on several factors, including previous methods of maintenance, weather, stem densities, brush species present, and more. Converting ROW from a mow-only approach to a more integrated vegetation management program using herbicide treatments may result in higher initial cost increases based on brush density. As stem densities decline with herbicide application, time and material to maintain those ROW will decrease over time.
A similar ROW study has been initiated at a new site and data will be collected over a three-year period. Dow AgroSciences will publish final results from this study in cooperation with participating partners.
For detailed information on dormant stem applications including recommended herbicides, appropriate tank mixes, and herbicide rates go to [ https://www.dowagro.com/en-us/vm/evistas/december-2017/are-dormant-stem-applications-right-for-my-program ]. Note herbicide rates will vary by target vegetation and brush density, so contact your local Dow AgroSciences territory manager for more comprehensive training and customized solutions, and always read and follow all labeled rate restrictions.
 Patrick Burch (Field Scientist) and Travis Rogers (Market Development Specialist) with DowDuPont; and William F. Brunson (Superintendent), J. Parker Hill (Supervisor), and Randal S. Osteen (Supervisor) with Santee Cooper.
 In this document, the term “incompatible” woody vegetation indicates tall-growing trees that are not compatible with management objectives for right-of-way function.