Managing vegetation along roadsides is a task faced by every county in Washington.  While most counties rely on regular herbicide sprays to manage roadside vegetation, more and more counties are successfully managing roadsides without the use of herbicides.  Jefferson County has set a very strong example by managing their roadside vegetation without chemicals for 23 years. Jefferson County has been extremely thorough in researching and implementing the most appropriate techniques to replace herbicides. All the hard work has paid off over the years, making Jefferson’s program an excellent model for counties throughout the state.
The “No Spray” Program

In the late 1970’s, many Jefferson County residents became concerned about the hazards of herbicides for humans and aquatic life.  Community groups asked the county commissioners to investigate the use of alternatives to pesticides.  As a result, a moratorium was put in place, and the county commissioners asked the road maintenance division to develop a plan to manage roadsides without herbicides.  Based on this request, the crew accepted the challenge and began a two-year transition that resulted in a mechanical weed-management program that is still going strong today.

The Science of the Road

The Jefferson County road crew maintains approximately 400 miles of roads within the county, which equates to about 800 miles of shoulders.  The responsibilities of the crew include pavement-crack sealing, road-shoulder maintenance, roadway sweeping, culvert cleaning and repair, storm-drain systems maintenance, slope repair, litter pickup, control of vegetation, bridge-deck repair, and snow and ice control.

Most of Jefferson County has high rainfall, creating an ideal ecosystem for woody trees and shrubs.  In the drier regions, annual broadleaf weeds pose an additional challenge.  Before the no-spray program was created, the county performed yearly sprayings along the roadsides.  Today, the county uses no herbicides at all, but instead employs an aggressive mechanical program based on a vegetation study done by Dr. Roger del Moral of the University of Washington’s Department of Botany.  This study, conducted in 1979, was conducted to identify plant communities with the low-growing, spreading characteristics that are the most desirable for low maintenance, and to find ways to encourage their survival through continued mowing and other mechanical controls.

Dr. del Moral found that the most common problem plants were common horsetail (Equisetum arvense), Douglas-fir (Pseudotsuga menziesii) red alder (Alnus rubra), and salmonberry (Rubus spectabilis).  To address the problems, the report outlined a non-chemical approach to control based on manipulation of natural plant succession.  The goal of this manipulation was to keep plants at the successional stage that would provide for relatively easy roadside maintenance and road safety.  Thus, Jefferson County adopted a strategy that replaced routine herbicide spraying with selective actions based on extensive knowledge of the ecology of common species.

Success Today

The primary goal suggested by Dr. del Moral was to produce relatively stable plant communities that require little maintenance and possess other desirable traits.  The roadside program elaborated upon this general philosophy to establish the following goals:

1. To economically insure the efficient and safe operation of roads;
2. To produce naturalized vegetation on the right-of-way that is self-sustaining and which blends into the surrounding vegetation;
3. To control erosion from slopes and cutbanks;
4. To produce an aesthetically pleasing right-of-way;
5. To provide cover for desirable species of wildlife; and
6. To reduce the opportunities for the migration and distribution of undesirable weeds.

To achieve these goals, the road crew uses a number of different methods. Machine mowing is a key tool to control grasses, broadleaf weeds, and immature woody vegetation. The mowing height is set at six to eight inches to favor plants such as salal (Gaultheria shallon) and Oregon grape (Berberis nervosa), which have a low-growing growth habit that allows good visibility while keeping out weeds.  The road crew generally mows from April to September, skipping sections where desirable low-growing native vegetation already dominates.

The mowers are often followed by mechanical brooms, which in addition to cleaning the pavement can remove soil and vegetation at the edge of the pavement and thus allow for better water drainage.   Machine brush cutting is conducted approximately annually where woody plants need to be controlled to maintain visibility along the roadsides. Other techniques include manual control of weeds, tree trimming with a pneumatic saw, periodic grading of roadside shoulders, annual clearing of ditches, and hydroseeding grasses and wildflowers in bare and disturbed soils to discourage the establishment of problem vegetation, prevent erosion, and add to the aesthetics of the roadside.  

All of the above methods require an alternative base of knowledge for the crew to match the philosophy of the program.  This has given the machine operators an added degree of respect for the precision and care that they employ in using IPM methods.  Crew members are also encouraged to continue to develop non-chemical methods to control any new problem that might develop.

Future Plans

Ultimately, the IPM program for vegetation management along roadsides in Jefferson County took a long time to evolve to what it is today, but it is an incredibly inspiring and encouraging model for other counties and jurisdictions. Aubrey Palmer, Operations Manager for the Maintenance Division, sums it all up: “It took a major change of an ingrained mindset for our maintenance crews to initiate and support a non-chemical vegetation-management program.  However, we consider it to be extremely successful.  Vegetation control without chemicals is doable.”