Fighting a “New” Non-Native Invasive in Town: Reports from the Front Line on Removing Italian Arum

Text by Kit Britton; photos by Jim Bly, unless otherwise noted. 

The February 26 Italian arum eradication event at the grounds of Culpepper Garden senior living community was the kickoff of a stewardship activity to last one year. A plant that was likely spread to the site as an escaped houseplant, in the root ball of a purchased plant, or by bird transmission of seed has turned into an ecological nightmare.

What is Italian Arum and Why is it a Problem?

Italian arum (Arum italica) is an ornamental plant that was brought to North America because of its attractive winter foliage and orange berries. It has been listed as a “dirty dozen” plant in Virginia can spread quickly to nearby areas and can outcompete native plants. It can be spread further by birds that eat and disperse its seeds. Arum has orange-red berries that grow in oblong clusters and can be toxic to both humans and wildlife. Its flowers emit an unpleasant odor, and its oils are a known skin irritant. Even with all these negatives, it is still commonly sold in the horticulture trade as both a houseplant and a landscaping plant.

Sightings of this plant in Arlington vary. Some are found on the margins of parks near houses and gardens and in backyards and neighborhood vacant lots, but they also appear in parks far from potential backyard origination points. Unfortunately, once Italian arum takes root, it can become quite dense. 

At Culpepper Garden, staff and residents were horrified to discover the potential damage this spreading invasive could do to this iconic 5-acre site. As a resident of the community and ARMN member, I suggested that we contact Jennifer Soles, Invasive Species Coordinator of Arlington’s Department of Parks and Recreation. Once she investigated the situation, she developed a protocol for eradicating the Italian arum from the location.

At Culpepper Garden, the Italian arum plants were more widely spaced than in many places, making their removal easier. Using Jennifer Soles’ directions, we dug up each plant with its surrounding soil, lifted the whole mass carefully into bags, and marked the holes from which the plants had been removed with red flags for a one-year measurement of outcomes included in the project design. It took 11 volunteer Master Naturalists, community volunteers, and resident volunteers about three hours to dig up and bag 36 plants found in four distinct areas of infestation. 

Later, Culpepper Garden grounds maintenance staff picked up the tied bags and carefully transported them to the trash dumpster for treatment as trash (not compost, which could spread their seeds).

This project is coming at the right time because it may add information about control options at a time when Italian arum infestations are on the rise—not only at Culpepper Garden but in area private properties and public spaces where ARMN park stewards work. (Park stewards are Adopt-a-Park leaders who oversee volunteer stewardship work in Arlington, Alexandria, and Falls Church parks and engage with neighboring park communities.) And there is still time to dig up the plants prior to their 2023 seed production.

How Does the Italian Arum Spread?

Arum italica has two methods by which it propagates and spreads. First, the above ground foliage grows from an underground tuber or bulb; the tubers propagate by forming multiple bulblets or daughter tubers, which separate and produce new stems. As the tubers spread laterally, Italian arum spreads. Sometimes, small plants can be eradicated by digging out all plant parts and tubers.  

The second method of propagation occurs when the plant flowers in the spring and summer and produces heavy seeds that drop onto the ground below or not far away. Wind cannot carry these seeds, but water flow can. And birds eat and spread the seeds.

The seeds themselves form a “transient” seed bank with less than one year of viability; not a “persistent” seed bank with seeds viable for more than one growing season.  Despite the transitory nature of the seeds, the next step in the reproductive cycle from seed is formation of a tuber that stays dormant for two years. So, there is effectively a three-year lurking danger from underground: one year as viable seeds and two years afterwards as dormant tubers. On the Culpepper site, seeds dropped by plants in summer 2022—as well as seeds up to two years older than that—can germinate plants now.

So, How Can We Get Rid of Italian Arum Once and For All?

In January, Master Naturalists exchanged strategies to eradicate Italian arum from their parks and neighborhoods, and after spirited discussion, the consensus was that digging and removing all plant material and more dirt than one might think necessary is needed to dispense with both dormant bulblets and the stubborn seedbank lurking in the soil. 

In addition, for resilient plants like this Italian arum, Master Naturalists wondered if chemical treatment would be an effective long-term solution. The problem is that only complicated chemical mixes may work, and these are beyond the reach of typical homeowners. This solution was also nixed by the Washington State Noxious Weed Control Board (a state where this invasive plant is rampant). There has been no consistently reported success with any chemical mix. With that, the Noxious Weed Control Board confirmed that manual methods including deep digging are the way to go. So, the Master Naturalists are sticking with manual removal, too.

The Plan for Culpepper Garden

We decided to monitor the holes left behind from which the arum was pulled and the broader infestation areas on a weekly basis and note any new growth. Italian arum plants found will be removed immediately. Weekly removals will ensure that we get the plants out when they’re very small. Removals at or near the holes will hopefully provide data to evaluate and refine the eradication protocol. The admittedly optimistic scenario of no regrowth in and around the holes would indicate that we successfully removed dormant seeds and tubers. Some regrowth but less than at a distance in the broader infestation areas could indicate that we need to dig deeper. Also, if the plant doesn’t appear at or near the holes but does show up at a distance in the broader infestation areas, perhaps we are dealing with bird transmission or other forms of transmission.

The project will end on Feb 16, 2024, when the one-year monitoring period is over, after which we will use the data we gathered to refine protocols for future Italian arum eradication. 

Normally, ARMN volunteers only work in parks or other natural areas rather than private properties. While Culpepper Garden is private property, it has been designated as “Private Property of Special Ecological Significance.”  As such, ARMN volunteers may work here on invasive plant removal projects.