Bishops Weed - Control Options

What is Bishops weed?  
Aegopodium has several common names including Bishops weed, Goutweed and Snow on the Mountain.  Bishops weed can be found in the variegated form or a solid lighter color green plant. It prefers moisture and can tolerate sun or shade conditions.

Common Bishops weed grows to 10-12" in
height, shading out other plants in the garden.

It is aggressive and considered invasive, spreading from underground rhizomes and from seed, creating dense patches of ground cover that will crowd out other more desirable plants in the landscape.

Bishops weed can be used as a ground cover where it is contained by defined landscape elements like pavement boundaries or well defined and maintained beds. Incorporating Bishops weed into a mixed use garden or bed will invite a constant challenge of keeping the bishops weed from invading and taking over other plants.

Control Options: 
Control options are varied and you may need to use several strategies to successfully eradicate Bishops weed. An open bed area can be managed differently than a ground cover bed or even perennial bed.  The more attached you are to saving existing plants in an infested bed will limit your options. Even with aggressive control it can take a year or more for you to overcome bishops weed.

Simply weeding a garden bed may not be enough. The Bishop weed plant stem will snap off readily from the root or rhizome leaving the remaining plant part in the soil allowing new tissue to emerge. Keep in mind that plants create food or energy through photosynthesis which requires sunlight. Bishops weed is tenacious and will keeping coming back even with aggressive weeding. The plat spends energy producing new growth in an effort to collect sunlight - but if you can starve the plant of sunlight with timely weeding you can rob the plant of its energy and new growth will slow and ultimately stop.  Allowing a plant to grow back in and capture sunlight is giving the weed a second lease on life.

Bishops weed in two forms: the light green
small plant are newly emerged plants while
the dark green taller plants in flower have been
allowed to mature and will soon produce seed. 

Forking: Using a digging fork, you can lift and separate the soil just enough to pick the roots and rhizome plant parts from the soil. You are effectively hand weeding the garden, but you're not just taking out the top growth, but also the part of the plant that stores energy producing new growth.  This can be tedious and challenging in a dense planting, but can be effective at thinning the crop and getting areas of the bed under control.

Mechanical removal: This is a fancy way of saying weeding, removing the top growth from the bed by hand weeding, hoeing or even using a line trimmer in larger open bed areas. The goal is to remove the leaves that can photosynthesize to create energy for the plant. Regular and consistent weeding is an option, particularly in beds that are dense with desirable plants.

Block Sunlight: Open bed areas can be covered with black plastic to prevent sunlight from reaching the plants. Black plastic will absorb the sun's heat, deflect water and essentially bake the underlying plants. It may take a full season before the plant is successfully killed in this manner. Pin or weight the plastic sheeting down, but do not mulch over it.  You'll want the sunlight to reach the plastic and if you do mulch over the plastic it will hamper your ability to remove the black plastic when the time is right.

Chemical control: Spraying a non-selective herbicide like glyphosate (i.e. Round-Up) is an option in open bed areas and where collateral damage to surrounding desirable plants is not an issue. Glyphosate is designed to be absorbed through the leaf tissue and will systemically kill the plant. You could alternatively use an organic product like Burn Out, but this essentially only scorches the leaves - which helps to prevent the plant from photosynthesizing, but it won't kill the plant right away requiring repeated applications.

In our experience spraying small, less mature plants is more successful in knocking back Bishops weed than spraying larger mature plants. If possible, we may line trim taller and mature plants first and then return to spray when the new plants are relatively small and likely to simply disappear after dying off. Large dead plants don't just disappear and are unsightly in the meantime.  Repeat applications will be necessary as new plants reappear.

Heartache 
The slow, methodical and tedious process of removing the plant by hand can be enough to get even the most persistent gardener to call it quits. Alternatively, while it may cause heartache in the short term, a heavy handed approach of removing everything from the bed may be more efficient and prudent in certain circumstances. Heavily infested beds can be cleaned up, managed and allowed to remain fallow until you are certain the bed is clear. You can then plant with confidence and know that your investment will not be overrun by Bishops weed.

If you do decide to clear out a bed, a word of caution. Saving certain plants from the bed which are transplanted to new locations or temporary holding areas can carry Bishops weed into other areas of the yard, compounding your problem. Sometimes it is better to simply start over and not try to save any of the plants so you can be certain of your success.

Regardless of the method used, it will take patience, time and the will to win this battle. Persistence is the key.