Dyers woad is no respecter of boundaries, wildflowers or wilderness.
The weed, traditionally considered a threat to agricultural land and rangeland, could eventually infest almost 99 percent of the land in the Logan District of the Cache National Forest.Many areas most susceptible to infestation are in the Mount Naomi wilderness area, according to Utah State University researchers who used satellite images to predict the weed's spread.
Some people oppose the use of herbicides in national forests and wilderness areas, claiming dyers woad poses a very limited threat to these areas.
That does not appear to be the case, says Steve Dewey, USU weed scientist who conducted the Utah Agricultural Experiment Station-funded study with geographer Kevin Price.
The researchers compared currently infested sites in the Cache National Forest near Logan with satellite images of the same area. They used spectral components to divide the satellite images of the same area into 60 types of cover. They found 55 of them, representing 98.8 percent of the forest, were similar to sites now infested by the weed.
Conditions in 10 types of cover representing 17 percent of the forest were similar to those in areas already seriously infested.
"We were extremely conservative in our approach," Dewey says. "Dyers woad is a lot more versatile than the results of our study indicate."
Dewey says dyers woad is relatively easy to control with herbicides. However, delaying control until the weed has infested large areas would mean the loss of many desirable plants, including those used by deer as winter range, and would make it much more difficult to control without damaging native vegetation.
"We definitely should try to eradicate small infestations, and perhaps spray the perimeters of existing large infestations to keep the weed from spreading," he says.
There are now scattered infestations of dyers woad in the Mount Naomi wilderness area. However, conditions in the area seem to favor a rapid spread of the weed, Dewey added.