By Amy Grotta, OSU Foresty & Natural Resources Extension – Columbia, Washington & Yamhill Counties
Rid your land of English holly
Tis the season to spot holly
When all the other leaves are gone
Fa-la-la, la-la-la, la-la-la
Holly’s deep green stands out strong
Ok, there’s a good reason I didn’t become a songwriter. The point I want to make, though, is that this is a great time of year to scout your woodland for a common and nefarious invasive plant: English holly. It stays green all year long, so now that herbaceous plants have died back and other shrubs have lost their leaves, it’s easier to spot.
You will typically find holly in mixed hardwood or hardwood/conifer stands, especially those that have been disturbed or are on the fringes of populated areas. It gets spread around by birds who consume the bright red berries, and it thrives in the shade. It has the tendency to form many sucker sprouts around the base of an established plant, resulting in a thicket that is difficult to remove.
English holly is an invasive plant, and one that is worth your time to control if you wish to promote a healthy forest with native biodiversity. Even if you are a bird lover, I would argue that there are winter berry-producing native plants that you might rather have them spread for you: common snowberry is one example.
You can pull up small (pencil-thickness) plants by hand when the ground is soft, but once holly becomes a shrub or tree, a properly-applied, targeted herbicide to the base of the tree or cut stump is necessary for control. Cutting the plant down and not treating the stump with herbicide will only result in many resprouts – not just from the stump, but also from the roots and even at times from branches of the felled tree that come into contact with the ground and re-root.
Recommendations for treating holly with herbicides largely come from the restoration community, since holly is abundant in natural areas and public greenspaces. One common tactic is to use the hack-and-squirt (or frilling) method with imazapyr (Arsenal) or triclopyr (Garlon 4). With a small axe, make small hacks every couple of inches around the base of the tree and use a squirt bottle to apply a small amount of chemical into the cuts. Or, for larger trees that you don’t want to leave standing, cut the tree down and immediately apply triclopyr with your squirt bottle to the outer tissue of the cut stump (see photo).
Another method is to use triclopyr in a basal bark application. Here, you are using a backpack with a low-pressure nozzle to wet the bark all around the base of the stem. In this case it’s important to use an oil-based solution for bark penetration. Apply when it’s cool out to reduce the chemical volatilizing and affecting nearby desired plants; and clear away leaves and woody debris from the base so as to hit all the way to the root collar.
To read up more about all of these different basal application techniques, refer to this very useful primer from the PNW Weed Management Handbook. As always, read the product label for specifics on concentration rates and timing (and see our Pesticide Disclaimers).
These herbicide treatments can be done at various times during the year – so in winter, you can scout and flag holly infestations to come back to later for treatment. Because holly is everywhere – from holly farms to cultivated specimens in backyards – new holly introductions will likely continue even after you have eradicated it from your woodland. So it’s important to stay vigilant. Pull up new plants when they are small and the soil is moist – now is also a great time for that.
While holly is a festive component of our holiday decorations, we don’t want it taking over our forests. So chant some Christmas carols while you go out and collect some wreath making material – and bring along some flagging tape.
Some further reading:
English Holly: Garden and Wildlife Favorite or Invasive Foe?
Earthcorps (Seattle) English Holly Treatment Executive Summary