The City of Portland hires licensed contractors to survey and spot-spray garlic mustard plants along roads and stream corridors in Portland during the spring and summer. The best time to spray is when the plant has white flowers in late April and early May. City staff and partners are waiting for rosettes to lengthen and flower (or 'bolt'). When most plants are in flower, treatment will begin. Meanwhile, now is an excellent time to pull rosettes, but sure you have the right plant!
Areas treated by Environmental Services will be listed here.
Garlic Mustard Phases
|Current Phase (in bold)||
Description of Garlic Mustard In Each Phase
Like many plants, garlic mustard changes form several times over its lifetime. A typical garlic mustard plant forms as a seedling in the spring and overwinters as a rosette, a low-growing cluster of leaves typically one to six inches tall. The rosette form is easily confused with several native species, and is often hard to find under winter's leaf litter.
With longer days in March and April, garlic mustard rosettes undergo a change called bolting. The stems lengthen and leaves go from round to triangular. Buds form at the top of the building cluster of leaves.
After a sufficient number of warm, light days in April or May, the buds atop bolting plants will open into garlic mustard's characteristic four-petaled white flowers. The flowering stage of garlic mustard typically lasts three to four weeks. Herbicide treatment is most effective during this phase. Roots not removed during pulling will likely form a new flowering plant in a few weeks.
Seed formation occurs over the course of two to three weeks. Many plants will display flowers at one end of the bud cluster and new seed pods at the other end. By the time all flowers have formed seeds, it is typically early June in the Portland area. Herbicide treatment can be done on a limited and considered basis. Pulling should still attempt to remove all roots. All pulled plants should be bagged and disposed of in the trash, to prevent spread in yard debris.
Seed ripening goes on for four to six weeks until the plants begin to dry out, typically in early to mid-July. Pulling can be done in this phase, without regard for root re-growth, but MUST stop when plants begin drying. No herbicide treatment should be attempted in this phase.
|Seeds Ripe Don't pull!||
Newly-dry seedpods will explode at the slightest touch, depositing seeds in clothes and hair and making the well-meaning puller an ideal vector for infesting new areas.
(updated 3/4/14; MRB)