The Clatsop County Public Works Department is enacting a more environmentally friendly spray program for weed-control along county roads.

After a lengthy review the department is switching to chemical herbicides that are less potentially harmful to streams and wetlands and making other changes to its methods of clearing roadsides of unwanted vegetation. The proposed changes will be presented to the county commissioners at a work session today.

The review was prompted by an incident last August when a public works crew accidentally sprayed a roadside in Arch Cape that had been designated and marked as a no-spray area.

The crew was applying the common weed-killer Garlon on East Shingle Lane when a local resident pointed out that the area, near the local water treatment plant, had been designated a no-spray zone and even posted by the public works department itself.

The employee in charge of the spraying was reprimanded, and the department contacted a poison control center to ensure that the chemical posed no risk to local residents. But the entire spraying program was temporarily put on hold while the department took a broader look, according to Public Works Director Ed Wegner.

The department is responsible for controlling weeds and vegetation on 185 miles of roads around the county. It uses a combination of mowing and chemical sprays to knock down everything from dandelions to blackberries and any vegetation that would otherwise fill in drainage ditches, cover signs and block motorists’ view of the roadway, Wegner said.

The department tries to maintain a balance between citizens concerned about the possible harmful effects of the chemicals used and others who want more aggressive weed-control spraying, he said.

“We think we’ve got a pretty good program,” he said.

Property owners can request that the roadsides along their land not be sprayed, but in return must agree to handle the vegetation control themselves. There are about two dozen designated no-spray areas in the county, Wegner said.

In the aftermath of the Arch Cape mishap, the department hired a consultant to review the entire program, including the chemicals used and the costs of alternative weed-control methods.

The consultant, Pacific Habitat Services Inc., found that the county does not use any herbicides currently restricted by the Environmental Protection Agency, but it recommended that the county switch to chemicals deemed safe by the EPA for aquatic areas. It suggested restrictions on spraying around water, including hand-spraying in riparian areas, and tagging sprayed areas. Blackberry bushes should only be sprayed when there is no ripe fruit on the vine, to eliminate the chance that people might eat sprayed berries.

The cost analysis found that switching to the aquatic-friendly chemicals would cost an additional $5,000 on top of the $27,000 the department spends each year on its existing spray program. Switching exclusively to mowing, on the other hand, would cost an estimated $129,000 a year, because mowing is slower and requires that areas be tackled more often. There is also the wear-and-tear on equipment, Wegner said.

“We think it’s well worth our investment” to adopt the aquatic-sensitive approach, he said.

Chemical herbicides are the only workable tool for eliminating some of the most troublesome weed species, according to Dave Ambrose, director of the Clatsop Soil and Water Conservation District, which works with the county from time to time on targeted weed removal.

For example, the county was removing purple loosestrife, an invasive weed, by mowing it but that method only exacerbates its spread, Ambrose said, since not only the roots remain intact, but the cut stems can themselves send down new roots. At the conservation district’s suggestion, the county switched to herbicides to control the plant.

The No. 1 problem plant for Clatsop County is probably Japanese knotweed, a particularly destructive weed that has already choked out sections of riverbank along the Nehalem River, Ambrose said. The invasive species shades out and eliminates other vegetation, and spreads easily during high-water periods when sections of root are washed downstream.

The Nature Conservancy conducted an exhaustive study into methods of controlling the tenacious weed, and concluded that only chemical herbicides were effective. The local watershed council uses a spray protocol drawn up by the organization in its fight against knotweed, Ambrose said.