Burdock is an invasive plant that causes problems for livestock and crops, and is generally considered a noxious weed. The tall burdock plant, a native of Eurasia, is a biennial, which means it lives for two growing seasons. The first year, it merely grows leaves and accumulates food reserves in its roots, like a carrot. The second it grows a long, deep taproot, and a tall stalk, producing flowers that become burrs that spread the seed by latching onto the hair of livestock and other animals or in baled hay or straw.
Burdock flowers in late summer, producing a composite seed head that matures by mid-August in southern areas and later in northern climates. Ripe burrs consist of hundreds of tiny hooked slivers, and if these get into an animal’s eye they cause severe irritation — especially if caught under an eyelid where they continually scrape the eyeball every time the animal blinks.
Eye problems often occur in fall and winter when the burrs are ripe and dry, whereas pink eye is more common in summer fly season. But dry burrs remaining on old plants can cause problems any time of year.
- The hooks on the tiny burr slivers attach like hook fasteners.
“This is one of the concerns we hear from cattle producers when cattle are off the home ranch, grazing outer areas where they are not seen daily, says Dave Ralph, project manager of the Invasive Species Council of British Columbia. “The ranchers may not have an opportunity to see their animals for long periods of time. When you have to bring an animal off the range pasture to do any veterinary work it becomes a big inconvenience and an extra expense.”
Of approximately 30 different regional districts in B.C., nine list burdock as a noxious weed. In Alberta it is listed under the Schedule 2 list of noxious weeds.
“They can also affect sale price of animals if a producer is unable to remove them prior to putting them on the market,” adds Ralph. “In some instances buyers refuse to take animals with burrs. No one wants to bring burdock seeds to their ranch.”
Even in areas where there are no agricultural operations, burdock is a concern for wildlife, particularly birds and bats that get tangled up in old burrs.
“This has contributed to a reduction in bat populations,” he says.
“In B.C. burdock may not be as much of a priority as some of the agencies or industry would like to see it, but we deal with a lot of weeds. In certain areas and certain times, resources are sometimes unavailable to manage burdock. On Crown lands the provincial government is the landowner/occupier and does allow a certain amount of its budget for contractors to control burdock, but primarily burdock control is carried out on private lands,” Ralph explains.
“In areas that are not along riparian zones or water courses, we can use residual broadleaf herbicides, but in areas adjacent to lakes, streams or creeks, we have a pesticide moratorium for 10 metres (30 feet) above high water mark. There is almost no use of herbicides in those zones and we have to rely on manual or mechanical control.” In these locations the plants can be chopped, mowed or pulled up.
“Burdock has a large root, however, and unless the soil is very moist so you can pull or dig it up, you only get the top growth and it will come up again from the root. Some producers repeatedly cut the plants, to keep them from going to seed. In a biennial like burdock, this just extends its life, but eventually the plants will die off in three or four years. The people who have success digging it up say you have to get at least two or more inches of the root to have a chance of killing the plant.
The seeds remain viable for two to 10 years, however, so even if you keep chopping down or digging up the current plants new plants may keep coming up for several years. This can be a long-term battle.
Burdock can invade new forage seedings, and establish faster than more desirable species. Its thick fibrous stalk can also create problems for harvesting equipment.
It pays to try to prevent getting it in your fields and pastures in the first place. “People buying forage or livestock should always check for any noxious weed seeds or structures — in case it might have been baled up in hay or straw. Check the source of your feed and any new animals you bring onto your place,” he says.
The tenacious burrs are a very effective means of spreading seed. If you look at the tiny burr slivers with magnification, their hooks are almost identical to a Velcro fastener.
“It’s very hard to remove them from clothing or fur and hair. I’ve heard that if you wet down the animal, the burrs come loose easier, but I am not sure about that. A person could try it, however, if burrs are stuck to their cattle, horses or pets,” Ralph says.
“The good thing about burdock is that it is a plant that people can remove,” says Gail Wallin, executive director of the council. “You can actually hand pull it out if the soil is moist, and this is often a good approach,” she says. “Community groups will often take action on it.”
B.C. has two species of burdock: Arctium lappa, great burdock, typically found in the northern regions of the province, up around the Peace region, and Arctium minus or common burdock in the southern and coastal regions.
Dr. Don Morishita, University of Idaho professor of weed science, says several broadleaf herbicides will kill burdock,if applied properly. Burdock plants are easiest to kill in the first year of their life cycle when they remain in a rosette stage.
“Apply spray at a time when the plant is putting food into the root, since you have to get herbicide into the root to kill the plant. Use a broadleaf herbicide that can move down into the root. If you spray early in the spring you generally kill new young sprouts and last year’s rosettes (plants that are trying to create more food reserves in their root for their big push to complete second- year growth and make burrs). You have to spray very early to get the second- year plant. After the stalk comes up it is harder to kill with herbicides because the plant is sending food up from the roots instead of down,” he says.
When using herbicides to kill burdock or other biennial and perennial weeds, don’t overdo it.
“If you use too much, it quickly kills the top-growth leaves and doesn’t get down into the taproot. The root survives, to regrow. You want a slower kill so the leaves survive long enough to transfer the herbicide down into the root, to kill the whole plant.”
He also cautions against using anything other than broadleaf herbicides. “Burdock is a bare-ground plant; it doesn’t grow well where there’s a lot of grass cover or competing plants. Don’t use anything that would kill the grass, because grass tends to inhibit regrowth of burdock.”
Chopping is also effective, but you must do it at the right time or the plant will regrow from the root. “The best time to chop it is after the stalk is budding but before burrs are ripe. At that point the food reserves are so low in the root that it cannot regrow,” says Morishita.