Forest fires a factor in spread of noxious hawkweed in Alberta

Colourful weeds are a potential problem for producers

INDUS, Alta. — An explosion of hawkweeds has been discovered in southwestern Alberta.


Inspections in the Crowsnest Pass region found dense patches of orange, yellow, tall, meadow and a new type, yellow devil hawkweed in remote areas where people would not normally travel.


Last year, weed inspector Mike Kirby travelled about 800 kilometres of trails where he estimates 16 percent had hawkweeds. 


Most cropped up in former forest fire sites where they are spreading and could eventually end up on grazing land, said Kirby, an invasive plants co-ordinator with Alberta Environment and Sustainable Resource Development.


He figures 25 percent of the trails around the burn areas had hawkweed.


The Lost Creek and Race Horse Creek fires in 2003 burned thousands of acres and were about 40 km apart, yet both areas have infestations. 


He is not sure where the weeds came from, but one theory suggests they may have travelled with fire fighting equipment from British Columbia, he said at a weed school sponsored by Rocky View County in Indus, Alta., June 4. 


“We had equipment coming in here from all over the place, especially from B.C., where we know we have this hawkweed,” he said. 


In the United States, equipment cleaning is required before travelling to a new fire, but that’s not the case in Alberta. That policy should be considered, he said. 


The weeds may also have been in the soil for a long time and when the fires burned away the tree canopies, the sun loving plants had room to grow. 


“I believe they are hybridizing as well in spots where they have features of more than one species,” he said. 


Most types spread through rhizomes, but the yellow devil type spreads by seed. 


“It is like someone took a giant pepper shaker full of weeds and spread it all over the area. Its seed must be extremely viable because we are finding weeds in the weirdest places,” he said.


It is also one of Canada’s windiest regions and the seeds could have blown in, he said.


All varieties seem easy to kill but there are no registered products for hawkweed in Canada.


Researchers experimented with different chemical treatments including Milestone and 2,4-D and the following year the sprayed spots appeared dead. These sites will be checked again this year.


Another problem is working in the rough, rocky terrain. Spraying equipment can be damaged and there may not be a nearby water supply to mix with the chemicals.


Hawkweed is a prohibited noxious weed in Alberta where the policy is to eradicate it, but Kirby said that may not be possible because there is so much of it. 


Provincial weed specialist Nicole Kimmel said the yellow devil hawkweed has also been found near Edmonton. 


“It just jumped out of nowhere so it is concerning that it might be elsewhere in the province,” she said.