What is the species?
- Alliaria petiolata (garlic mustard)
- ODA “B” rank
Garlic mustard, a native to Eurasia, has been introduced in North America and locally as a garden herb. In general, it is considered a biennial, needing two growing seasons to produce seed, though area land managers have seen numerous exceptions.
Why are we concerned?
Garlic mustard is known to form dense patches that begin in disturbed areas (trails, streams) and expand into undisturbed areas. It dominates and displaces most native understory species, reduces plant diversity and decreases forage for native wildlife, such as the Columbian black-tailed deer. In addition, the roots of garlic mustard are thought to produce a toxin that kills the soil fungi many plants depend on. Garlic mustard infestations can lead to:
- Reduced plant and animal diversity as other plant species are displaced
- Reduced vitality of forests as seedlings fail to grow up and replace old trees
How does it spread?
Garlic mustard is spread primarily by seed, although buried root fragments can grow new plants. Garlic mustard seeds are moved around by:
- Tires and machinery
- Hiking boots
- Running water
What does it look like?
Garlic mustard has different forms throughout its life. It has a low form with round, scalloped leaves in the first year, and an elongated flower stalk in the second year. Its triangular leaves are alternate on the smooth stem and sharply toothed (see life cycle diagram).
Garlic mustard flowers between April and May and forms seeds in early June, which ripen after several weeks. Plants can have several flowering stems with numerous four-petaled white flowers. Crushed leaves and roots often smell like garlic. Plants typically range from 12 to 48 inches tall, though plants as short as 1 inch or as tall as 72 inches are not unusual. The black, oblong seeds are in rows within a long, narrow pod and can survive in the soil for at least five years.
Are there lookalikes?
There are dozens of mustard species in the Willamette Valley, many of which are confused with garlic mustard, but other native species also have similarites.
In its rosette form, garlic mustard looks these native plants:
- fringecup, Tellima grandiflora – look for hairy leaves and stems
- piggy-back plant, Tolmiea menziesii – look for hairy leaves and stems
In its flowering form, garlic mustard might look like:
- hairy bittercress, Cardamine hirsuta – look for short (6-8” or less) plants, and compound or deeply-lobed leaves
In its mature form with ripe seedpods, garlic mustard looks like many mustard cousins, including:
- black mustard, Brassica nigra – look for longer pods with very pronounced seedbumps
How do we deal with it?
- Manual: Digging up garlic mustard on private property can be effective, but requires weekly attention to catch new plants.
- Herbicide: On patches of more than a few plants, herbicides are used in combination with the manual methods described above.
Clean your shoes after walking in areas of known garlic mustard infestations so you don’t spread seed to your neighborhood yards and parks.
How can folks help?
If you suspect you’ve found garlic mustard on your own property, feel free to report it to the city, which may be able to assist you. Management and proper disposal on private property are strongly encouraged.
Garlic mustard in public areas, such as in parks or along roads, is probably already on the city’s treatment plan for April and May. In those cases, reports made after Memorial Day are more effective.
Dig deeper ...
Have a look at on-line maps for more information about what’s being done in your neighborhood....