Weed Wisdom April 2020
Stinkweed (Thlaspi arvense L.)
By: Nicole Vincent and Charles Geddes
Stinkweed (Thlaspi arvense L.) is an annual or winter annual herb most prevalent in the prairie provinces. It came from Europe and Asia and reduces crop quality by stealing moisture and nutrients before seeding and by contaminating seed. It can be particularly harmful to yields in Alberta oilseed crops or less-competitive crops like pulses. If eaten by livestock, stinkweed can taint meat and milk with an undesirable odor.
Stinkweed has two ecotypes, early and late flowering, that can vary in appearance based on growing conditions. It is very adaptive and acts as a colonizer in disturbed soils. It appears throughout field crops.
Stinkweed has a distinct turnip-garlic odor Its hairless stems and leaves distinguish it from field peppergrass. Stinkweed starts as a rosette then matures to 5 to 60cm tall with smooth branched stems. Clusters of small white flowers elongate to stems tipped with broad, flat silicle. Seed pods have distinct halves containing 5 to 8 seeds each. Each plant can produce up to 15,000 seeds that remain viable for 6 to 20 years, creating a moderately-persistent seed bank in the soil.
Land managers can minimize stinkweed, but not eliminate it, with a competitive crop rotation. Tillage is rather ineffective because seeds continue to mature on the stalk following physical disturbance. Stinkweed is susceptible to phenoxy herbicides like 2,4-D and MCPA (See your provincial Guide to Crop Protection).
Spray winter annuals before first frost because plants quickly mature and bolt in spring often before the first herbicide application. Summer annuals germinate in spring and early summer; which allows for control with pre-seeding herbicide application. In-crop herbicide is often ineffective because stinkweed matures before application. Growing an herbicide-resistant crop, like canola, soybean, lentil, or others, could help eliminate stinkweed, but apply herbicide early when the plants are small.
According to the 2017 Alberta Weed Survey, stinkweed populations are declining in relative abundance compared with other weed species (Leeson et al. 2019; Figure 1), but research identified a Group 2 herbicide-resistant biotype in 16% of sampled fields (Beckie et al. 2019; Figure 2). This ecotype wasn’t identified in the 2007 survey, so herbicide resistance in stinkweed in Alberta is relatively new. Crop rotation can help control herbicide resistance when combined with other practices like rotating herbicide site of action. Field scouting after herbicide application is also an important practice to ensure effective application and catch resistance early. Apply herbicide when it will be most effective for the target weed. This means an early spring or late fall application for stinkweed.
Beckie, H.J., S.W. Shirriff, J.Y. Leeson, L.M. Hall, and K.N. Harker. 2019. Alberta weed survey of herbicide-resistant weeds in 2017. Weed Survey Series Publ. 19-2. Agriculture and Agri-Food Canada, Saskatoon, SK. 39 p.
Best, K.F., and G.I. Mcintyre. 1975. The biology of Canadian weeds. 9. Thlaspi arvense L. Canadian Journal of Plant Science 55:279-292.
Leeson, J.Y., L. Hall, C. Neeser, B. Tideman, and K.N. Harker. 2019. Alberta weed survey of annual crops in 2017. Weed Survey Series Publ. 19-1. Agriculture and Agri-Food Canada, Saskatoon, SK. 275 p.