Ah, spring! It’s the time of year when the days brighten, the weather warms, and wildflowers flaunt their petals. But it’s also when invasive plants begin encroaching on the native ecosystems throughout the Tualatin River watershed. Each spring, Tualatin SWCD’s Invasive Species Program gears up to take on one of our watershed’s greatest foes, garlic mustard.
Garlic mustard (Alliaria petiolata) is biennial, meaning each plant lives its life over two growing seasons. Seedlings emerge in early March, forming a rosette with kidney-shaped leaves the first year. During its second year, the plant produces white, four-petaled flowers with triangular-shaped, serrated leaves. Seed pods, also called siliques, burst open, sending seeds flying up to 20 feet away! Each plant can produce up to 5,000 seeds that can remain viable for ten or more years in the soil! These seeds are then spread by humans or animals who unintentionally pick them up on shoes, clothing, fur, or equipment. And that’s not even garlic mustard’s most concerning characteristic …
Once established, garlic mustard emits chemicals from its roots that prevent other plants from growing nearby. This prevents forest regeneration and displaces native understory and ecologically important wildlife. Without natural predators in the Pacific Northwest, infestations quickly spread. Garlic mustard is also self-fertile, meaning that a single flowering plant can start an infestation. You can see why garlic mustard is one of our watershed’s weeds of greatest concern.
Over the last decade, partners across the Tualatin River watershed have made tremendous strides in controlling garlic mustard. The weed can be treated one of two ways: hand-pulling small infestations or carefully treating larger infestations with herbicide. Read our Weed of the Month article to find out more about treating garlic mustard. This spring, Tualatin SWCD staff and contracted crews have hand-pulled or applied herbicide to 3,056 patches of garlic mustard covering 2.8 net acres. We’ve also surveyed 62 stream miles along 10 different creeks to identify and treat new outbreaks before they grow out of control.
Trevor Norman, one of our Invasive Species Technicians, describes what it’s like searching for garlic mustard:
It is 8:00 am and you’re already drenched. Rubber boots might help keep water out, but you’ve already taken a dip in the creek and there is still another mile left to go. No use in emptying your boots, you’ll just get them soaked again. Every step you take has potential. Look around, closely. What do you see? Lots of green. Snowberry, Indian plum, fringecup, large-leaved avens, the occasional oceanspray showing off its cream-colored blooms. These are all pleasant to witness, a sign that nature is resilient, but these are not the plants you are looking for.
And then you see it. Just one rosette at first. You lean down to pull it up. Grab the base … be careful not to snap the root! Nice. You got the whole root. No chance of it growing back. You toss it in your garbage bag and get ready to keep trekking. However, when you look up you notice a carpet of kidney-shaped leaves hovering just a few inches above the ground. In the center of that carpet are taller versions of the same plant covered in seed pods ready to pop. Looks like you are going to be here awhile …
Chasing and treating garlic mustard in the Tualatin River watershed can feel overwhelming. Nearly every Tualatin River tributary maintains a population of this pesky mustard. No matter how hard we try, it comes back each year with a vengeance. Seeds wait just beneath the soil’s surface – sometimes for 10 years! – just to sprout and start the cycle over again. But there is hope! Slowly and steadily, the seed bank is becoming depleted throughout the Tualatin Basin. Data show that there is less garlic mustard now than when we started. Although this downward trend is promising, our ability to slow its spread depends on the cooperation of the community. The majority of streamside properties in our watershed are privately owned, meaning permission must be given prior to any garlic mustard surveys or treatment. Although we have made progress in community outreach and education to identify and control garlic mustard, there is still a long way to go in terms of surveying entire stream systems. For every patch of garlic mustard we find, there is another one lurking in an unseen stretch of the creek.
If you think you’ve spotted a patch of garlic mustard, report it to the Oregon Invasive Species Hotline! This early response tool connects Oregonians with local natural resource managers, like the Tualatin Soil and Water Conservation District. When filling out a report, you’ll be asked for your contact information, approximate location of your sighting, and a description or photo if you’re able to capture one.
If you think you’ve accidentally trekked through a patch of garlic mustard – it happens to the best of us! – there are a few simple steps you can take to reduce the spread. Play, Clean, Go has put together a few #ProTips to help stop the spread of invasive species like garlic mustard.