Garlic Mustard (Alliaria petiolata)
Appearance: Biennial herbaceous plant with weak single stems 12 - 36" high in its second and flowering year. Only plant of this height blooming white in wooded environments in May.
Leaves: Round, scallop-edged, dark green; first year, rosettes of 3 or 4 leaves; second year plants have alternate stem leaves. Leaves and stems smell like onion or garlic when crushed.
Flowers: White, small and numerous, with four separate petals. Each plant has one or two flowering stems on second year plants.
Seeds: Slender capsules 1-2 1⁄2" long, containing a single row of oblong black seeds. Seeds are viable in the soil for 5 years.
Roots: White, slender taproot, "S"-shaped at the top.
Reasons Garlic Mustard is a Problem:
- Garlic mustard spreads into high quality woodlands, both upland and floodplain, not just into disturbed areas.
- Garlic Mustard sprouts very early in the spring and forms a blanket shade cover. This early start allows it to out-compete native wildflowers and invaded sites undergo a sharp decline in native herbaceous cover.
- Garlic mustard alters habitat suitability for native insects and thereby birds and mammals.
- Seeds can survive for 5 years and thus form a very resilient seed bank.
- Tiny seeds are easily spread by human activity, including walking and driving.
Because Garlic Mustard requires shade it is not a direct threat to prairie ecosystems, but can destroy entire woodlands and once established spreads very rapidly. Floodplains such as the one along the Cannon River would be especially at risk. It has become an increasingly large problem in the region; 27 Midwestern and Northeastern states as well as Canada now report serious infestations. Because the seeds are so easily spread by human activities, such as walking (via the soles of shoes) garlic mustard often shows up first around roads and heavily used trails. Indeed, the only report of garlic mustard in the arboretum occurred around the trails near the entrance gate on the east-central side by Canada Ave. in the spring of 2006. Plants were sprayed with herbicide in their first year of growth and thus far no mature seeds have been noticed. This area will continue to be monitored and receive spraying in subsequent years.
Cowling Arboretum Procedures for Removal:
Groups of lants are sprayed with herbicide immediately upon discovery to prevent any possible seeding, and sprayed again in subsequent years to suppress the long-lived seed bank. Individual plants are pulled, with special attention paid to removal of the entire root.