Category Archives: Weeds

Garlic Mustard: Early Detection and Rapid Response

arlic mustard is a pervasive weed problem throughout most of the Northern US.  This invader is a cool weather biennial native to Europe that immigrants brought with them for an early season edible green and medicinal herb.  It has since flourished, taking over understory ground cover in forests and disturbed sites.  According to ODA, this weed is in limited distribution in Hood River, Clackamas, Columbia, Polk and Tillamook counties and abundant in Multnomah County.  Unfortunately, its spread in Yamhill County seems inevitable.

This weed is an early bloomer and usually begins flowering in April and May.  The plant has a 2 year life cycle with a first year rosette stage and a second year flowering stage.  It can thrive in both sun and shade and is usually found in disturbed understory forest habitats.  Garlic mustard only spreads through seed distribution and seed viability is estimated to last around 5-7 years.  It has allelopathic traits, poisoning the soil around it, which depresses growth of surrounding competition.   In fact, it has been estimated that Garlic Mustard patches can grow in size about 20 ft a year.  First year rosettes are usually low to the ground with 3-4 kidney shaped, scallop edged leaves that resemble the native fringecup.   In its second year it can grow to be 1-4 ft tall in maturity with little white flowers with 4 separate petals that form a distinct cross.  True to its name, its leaves and stems smell like garlic when crushed.

Garlic mustard can be hand pulled if seen, but should be disposed of in bags because seeds can continue to ripen after plants are pulled.  Any root fragments left behind will most likely resprout, which means sites will need to be monitored after weeds have been pulled.  Mowing is NOT an effective control of Garlic Mustard because this will encourage the plant to bolt and may lead to additional seed head creation.  This is especially true after seeds are present (May – September) and will actually lead to greater infestations.  Chemical application is encouraged in April or May when the plant is bolting or beginning to flower which can be problematic if there is wet spring weather.

If spotted in Yamhill County, we urge you to report it immediately to the Invasive Species Hotline (1-866-INVADER).  Early detection and rpaid response is critical in limiting this weeds spread into Yamhill county.  Please also be aware this summer, especially if you are returning from areas such as Portland or the Columbia River Gorge hiking trails, that this plant is spread by seed.  Use trail head boot brushes if they are provided.  Please help us keep Yamhill County free of Garlic Mustard!

Garlic Mustard in the first year rosette stage

Garlic Mustard in the first year rosette stage

Garlic Mustard second year flowers

Knotweed Spraying to Commence

For the past few years the District has been battling Japanese knotweed in the county.  There are a number of sites, mostly along riparian or drainage areas, that the District sprays in order to stay ahead of this weed.  The District has been providing this service to landowners in order to prevent the spread of this class “A” noxious weed.  Fall is usually the best time of year to spray this weed because it is beginning to send its energy to the rhizomes to prepare for winter.

Japanese Knotweed is a incredibly invasive weed that has become a problem in the counties surrounding Yamhill County.  It resembles bamboo and can grow to 8-10 ft in height.  It’s leaves are heart shaped and it can be easily recognized by its showy white flowers in the fall.  It’s commonly found along riparian or disturbed areas and can spread from rhizome fragments.  It grows quickly and will out compete native vegetation, as well as other weeds, and quickly creates a monoculture environment.  Diligence and long term planning is required when dealing with knotweed removal.

If you are aware of Knotweed populations within Yamhill County please contact the District in order to be added to the list of areas receiving spray treatment.

Mowing to begin on Cozine Creek


The area behind the McMinnville Police department is going to be looking a bit different after tomorrow.  We are working in conjunction with the City to remove the blackberry briars and japanese knotweed that is along northeast bank of Cozine Creek and replant with native trees and shrubs.  Since the bank is so steep, the mowing will be followed up with hand crews to clear the whole bank. The plant material will be left to act as ground cover and suppress weeds.

After the bank has been mowed, we will follow up with a spray of the regrowth this fall.  Next summer we will remow the area and spray it again.  Planting will occur in spring of 2013.

A big challenge with this project is going to be the planting.  The bank is mostly fill material, not ideal for growing trees.  Our planting list includes: Oregon Ash, Oregon White Oak, Doug Fir, Big Leaf Maple, Red Flowering Current, Nootka Rose, Oregon Grape, Spirea and Pacific Ninebark. We will also be planting blue wild rye for grass cover.

Be ready for the Cozine’s new look!


I went to a training this morning on a new web tool that is being rolled out to monitor invasive species in Oregon.  This site allows members of the public to browse the occurrence of weeds across the state as well as create a account to add their own weed observations that they are encountering in their backyard.

Click here to go to the site:

The weeds that the District has been actively working on Spurge Laurel and Japanese Knotweed.  This data has not been uploaded into the ImapInvasives website yet, but we will be working on that in the upcoming months.