The weather patterns this year in the Intermountain Region of Northern Nevada has been different from what we have seen the previous 4 years. In most years, high pressure usually moves in periodically sending Pacific cold fronts farther north and giving us periods of warm dry weather. However, this winter and so far, this spring high pressure has not dominated and we have been continually bombarded by cold fronts.
The frequent rains/snow this winter and spring has resulted in changes in the weed spectrum. One weed we have seen a lot more of in this area is bur buttercup. Bur buttercup (Ranunculus testiculatus) has been widespread this spring and in some cases dense populations have been observed. It germinates early, prefers high moisture and cool temperatures and can be seen as early as February and into April or May in this environment.
This plant is extremely aggressive. It spreads rapidly, reducing plant diversity and wildlife habitat. It uses water that would otherwise be available to native species. It can produce two seed crops in one year. When crushed and eaten, it is highly toxic to animals, including horses. If the plants are near a roadside, the seeds can be spread far and wide by the tires of cars and bicycles. When dried out, it poses a serious fire risk to communities and the environment. Its range is spreading rapidly in arid and semiarid areas. Its populations can quickly become so large that eradication is difficult, if not impossible.
The “burs” that give this flower its common name are often what drive inquiries to the Extension office about this plant. Research shows, however, that prickly seed heads are just one of the ways this plant can be frustrating. The life cycle, growth habits, and reproductive strategies of this introduced plant have enabled it to invade the US northwest. Insights into these same features- life cycle, growth habits, and reproductive strategies- are also key to its management.
Bur buttercup starts actively growing as soon as temperatures reach the 40’s and 50’s. The plant begins flowering within three weeks of emerging from the soil- much more quickly than most familiar ornamental plants. Seed development begins within days of flowering. This goes largely unnoticed, as the plants grow only up to about five inches tall, and are easily hidden within grass or other plants.
Each flower develops into a swollen “bur”, complete with prickles, and containing anywhere from five to eighty seeds. As the seeds mature, the burs dry into a tough protective package that floats in water, blows in the wind, and irritates tender feet. The seeds remain viable for at least a few years: some sources suggest as many as twenty. The combination of early growing plants and high seed production can lead to large, dense patches of Bur buttercup that become difficult to manage.
Like small hooks, the seed-containing burs that give this plant its name attach to shoes, pets, livestock, and camping equipment. In the eastern US, where the plant is far less frequently encountered, patches of Bur buttercup are usually associated with campsites. It’s also possible that some seed is distributed via feeding by birds.
In well managed pastures, Bur buttercup doesn’t usually become a problem: it prefers dry, disturbed sites, and doesn’t compete well against pasture crops. However, Bur buttercup is highly toxic to cattle, sheep and horses and can affect humans by irritating skin and causing blisters. The plant contains ranunculin, which turns into a toxic compound protoanemonin when the plant is crushed for example by chewing. This toxin is not a threat in baled hay and the plant is so small it is not likely to be present in hay.
Usually it is not a problem in pastures because livestock generally avoid the plant due to its acrid or pungent taste and because the poison causes blisters in the mouth. However, when forced to eat it because there is a lack of other more palatable forage, bur buttercup can be a problem.
There are little data indicating the consumption rate needed to affect livestock. One experiment showed that sheep died after exposure exceeded 1.1% of their body weight. How this relates to toxicity levels in cattle is unknown. However, assuming similar toxicity in cattle, if you have an 800 lb. heifer, for example, the animal would need to consume about 9 pounds of the green plant. Fortunately, this is not easily done because other range plants are more prevalent and palatable. We don't know how much of an issue bur buttercup may be with cattle grazing in infested rangeland or pasture in the intermountain area this year, but exercise caution if you see significant amounts of this weed in your fields without much other more palatable plants.
Control strategies:
First and foremost, never let the plants flower or go to seed. Pull, hoe, or dig the entire plant out of the ground and bag it to keep flowers and seeds out of the soil.
Planting competitive grasses may help to control Bur buttercup.
A number of chemical options are available that provide excellent control (>95%) and include the herbicides chlorsulfuron (Glean, Telar), aminocyclopyrachlor + chlorsulfuron (Perspective), dicamba (Banvel, Clarity), metsulfuron (Escort, Ally), picloram (Tordon, Grazon), sulfometuron (Oust) and triclopyr (Gardon, Remedy), glufosinate-ammonium (Finale, Liberty) and dicamba + 2,4-D.
For those who do not have a restricted pesticide licenses the following chemicals will work; glyphosate (Roundup) 2,4-D.
Remember, when using any pesticides, always read and follow the label instructions.
Sources:
High Prevalence of Bur Buttercup, Cari Koopmann Rivers, Steve Orloff, UCANR.
Five reasons Bur buttercup is so annoying, Nicole Sanchez, Horticulture, OSU Extension Service, Klamath County
