Wild mustard plants have from 10-18 seeds per pod and from 2,000-3,500 seeds per plant. During harvesting operations, shattering may result in large quantities of seed being left on the ground, or seeds may be transported into other fields by harvesting machinery or as impurities in crop and forage seed. Some wild mustard seed is capable of germination as soon as it is mature. However, these seeds may also remain viable in the soil for as long as 60 years, particularly those that are buried at considerable depths. Due to the longevity of wild mustard seed in the soil it is important to control this weed and reduce the amount of seed returned to the soil. This minimizes potential economic losses in current as well as future years.
Wild mustard can represent a serious weed problem in canola and spring cereals. Germination of wild mustard seed, and rapid early seedling growth under cool spring and fall temperatures, allow wild mustard to compete effectively with crop plants for light, water and nutrients. Populations of wild mustard left uncontrolled throughout the growing season can reduce potential yield and seed quality of the harvested crop.
Since wild mustard is an annual plant that reproduces only by seed, this weed can be controlled by mechanical cultivation of emerged seedlings. However, cultivation of infested land is often impossible since wild mustard seed germinates at about the same time as spring planted annual crops. If cultivation is not possible or if chemical control is desired, select a control practice from the Ontario Ministry of Agriculture and Food Publication 75, Guide to Weed Control.
Chemical control of wild mustard can be achieved with sulfonylurea herbicides (chlorimuron, ethametsulfuron, nicosulfuron, thifensulfuron-methyl), imidazolinone herbicides (imazethapyr, imazamox), triazolopyrimidines (flumetsulam), members of the triazine family of herbicides (atrazine, cyanazine, simazine, metribuzin), with phenoxy type compounds (2,4-D, MCPA, MCPB), substituted ureas (linuron, monolinuron, metobromuron), bentazon, and benzonitriles (bromoxynil), or with tank-mixes including any of the preceding chemicals. Refer to Publication 75 for specific herbicide doses, registered tank mixes, timing and method of application. If wild mustard is a problem in spring canola, use either ethametsulfuron-methyl or varieties of canola that are triazine tolerant. Because these tolerant varieties are not injured by recommended doses of the triazine herbicides, wild mustard can be selectively controlled within the crop.
Wild mustard is regarded as palatable in young stages, but seeds may cause serious illness in livestock if ingested in large quantities. Wild mustard seed poisoning has the symptoms of severe gastroenteritis due to toxic compounds including Allylisothiocyanate, Sinapine, and Sinalbin. Symptoms such as severe pain, salivation, diarrhea and irritation of the mouth may appear soon after ingestion of a toxic amount and could eventually result in death.
Wild mustard is a serious weed of cultivated land. It is responsible for reductions in crop yields, dockage losses, and for costly chemical and cultural controls. In spring rapeseed, for example, wild mustard densities as low as 10 plants per square metre can reduce rapeseed yield by 20%. The presence of wild mustard seeds in the harvested canola seed results in an undesirable loss of quality of the canola oil and meal. Since wild mustard seed is similar in size and shape to canola seed it is impossible to separate the seeds using conventional methods. This can result in a significantly reduced price received by the grower. Canola seed is graded as Canada Number 1, 2, 3 or Sample Reject depending on its overall level of quality and amount of contamination in the harvested seed. A 12% reduction in price occurs if the harvested seed is downgraded from 1 to 2, an additional 22% reduction occurs from a downgrading of 2 to 3. If it is downgraded to Sample Reject there is another reduction of 19%. Contamination of delivered seed with only 5% wild mustard seed results in a grade of Sample Reject, which would represent a total price reduction of 53% to the producer. This level corresponds to a weed infestation of approximately 20 plants per square metre. In spring cereals, dense wild mustard infestations reduce yields by as much as 53% in wheat, 63% in oats, and 69% in barley.
Figure 2. Wild mustard seedling. Notice the broad kidney-shaped cotyledons indented at the tip.
Herbicides can also be effective in controlling wild mustard. There are several different types of herbicides that will work against wild mustard, but there are some that the weeds have grown resistant to and that will no longer work.
Unfortunately, there are no other cultural or biological control methods for wild mustard. Burning does not help, nor does allowing animals to forage. The seeds of wild mustard can actually be toxic to livestock.
Wild mustard control can be a challenge because this is a tough weed that tends to grow and create dense patches that out-compete other plants. Wild mustard is a pain, but it is a bigger problem for farmers than for home gardeners. You can use both physical and chemical strategies to manage or eliminate wild mustard in your yard or garden.
Controlling Wild Mustard Plants
Because it’s so tough, getting rid of wild mustard can be a real project. If you do not want to use chemicals in your garden, the only way to eliminate this weed is to pull it out. The best time to pull mustard weeds is when they are young. This is because they will be easier to pull out, roots and all, but also because removing them before they produce seeds will help limit future growth.
Wild mustard (Sinapis arvensis) is an aggressive weed native to Europe and Asia, but one which was brought to North America and has now taken root. It is an annual that grows to about three to five feet (1 to 1.5 meters) and produces yellow flowers. You will often see these plants growing densely by the roadside and in abandoned areas. They are mostly problematic in cultivated fields, but wild mustard plants can take over your garden too.
If you have too many to pull, you can mow down wild mustard before seed production, during the bud to bloom stages. This will limit seed production.
There are different varieties of wild mustard, so first determine which type you have and then ask your local nursery or university agricultural department to help you select the right chemical.
Foraging North America is a 12-week online course designed to arm you with a functional working knowledge of botany and taxonomy that you can take with you out onto the land to fast-track the ID process and boost your confidence when gathering wild foods for the first (or five-hundredth!) time.
If you are interested in cultivating your own patch of wild mustard, it couldn’t be simpler: just gather seeds after the pods mature, then broadcast them in a bare patch of soil. You’ll have your own self-sowing crop in no time – just be careful to only plant it in places where you won’t mind it taking over.
B. rapa is one of a few species we might call “the quintessential mustards” along with the closely related B. nigra (black mustard) and B. oleracea (whose cultivars include broccoli, cabbage, kale, collard greens, Brussels sprouts, and just about every other cruciferous vegetable). B. juncea (brown mustard) is also an important commercial crop, as is B. napus (rapeseed, canola).
If you’ve ever been out for a drive in the country in April or May and thought, “I wonder what all those little yellow flowers are?” chances are good that they were wild mustard.
Brassica rapa, Brassica nigra, others
In terms of human ecology, we can group wild mustards in with the chickweeds and the dandelions – they’ve already followed us humans everywhere we can go, and they certainly don’t need our help to grow.
Because wild mustards are so closely related to our cultivated cole crops, you will quickly notice the shared traits that are reminiscent of these vegetables: leaves like collard greens or kale, flower buds like broccoli, flower stalks and seed pods like all of the above. (By the way: the ‘cole’ in cole crops derives from the Latin caulis, translated as ‘stem,’ alluding to the mustard family’s characteristic flower stalk – now you know!)