For the month of June, we are focusing on mile a minute (Persicaria perfoliata), an herbaceous annual vine also known as devil’s tearthumb. The name “mile a minute” fits the characteristics of the plant, as its quick spreading nature allows it to cover ground very rapidly - it can grow up to six inches a day in the proper environment. Mile a minute (MAM) readily colonizes disturbed areas along forest edges, wetlands, stream banks and roadsides, preferring high soil moisture. MAM arrived in the United States in the late 1800s and is found in highest numbers in northeastern states.
Figure 1A and 1B: MAM distribution by state and in the Northeast, respectively (www.eddmaps.org)
The leaves of MAM are light green and have a triangular shape. They grow in an alternating pattern, with each leaf isolated along the vine, rather than being paired with another leaf immediately opposite it. Its vines have a green color and smooth texture when young, but become red and hardier over time. Distinctive, cup shaped ocreae surround the stems from which flowers and fruit bud. Once pollinated, the small white flowers form clusters of berry-like fruit that contain a singular black seed called an achene. The seeds of this plant usually germinate in the early spring and flower in early June. The process of flowering and fruiting continues until late October, when the plant dies. Mile a minute is self-pollinating so one seed can lead to the formation of an entire colony, allowing it to grow quickly and take over ecosystems. Small, curved barbs line the stem and underside of the leaves which allows it to climb over other plants and grow up to 25 feet tall in a single season.
Mile a Minute grows over trees, shrubs, and other herbaceous plants, covering them in thick, dense mats. This physically weakens them due to smothering, and hinders their ability to receive nourishment from the environment. Due to its smothering coverage, impacted plants struggle to receive sunlight and can be unable to photosynthesize at sustainable rates, essentially choking out neighboring plants. In addition, the weight and pressure of the vine destroys growth of branches and leaves. Due to the speed at which MAM grows and the process by which it suffocates other plants, this vine can negatively impact native biodiversity in ecosystems it becomes established in.
Figure 2A and B: Key identifying characteristics and appearance of MAM (bugwood.org)
Biocontrol and remediation measures are underway by PRISM staff and partners to limit the spread and damage of MAM in the Lower Hudson region and greater metropolitan area. If no berries (which contain the seeds of the plant) are present along the vine, then simply pulling the plant and its roots out of the ground and leaving it in the sun to dry out will suffice. If berries are already present, however, slightly more extensive measures must be taken to ensure containment. The plant must similarly be pulled out of the ground along with its roots, but then must be contained in a black plastic bag, along with all seeds and left in the sun for up to 4 weeks before it can be disposed. It is highly advised that this disposal be done at a designated LH-PRISM collection site, as home composting and other plant disposal sites typically do not reach the required heat to kill the seeds of the plant and thus prevent it from spreading. The location where it was pulled from must be monitored over the following years to ensure no new plants have begun to grow from any seeds that may have been missed.
A special and more widespread method of biocontrol was approved in the United States in 2004, through the release of a small insect, a 2 millimeter long, stem-boring weevil (Rhinocomimus latipes L.). These weevils feed exclusively on MAM, completely colonizing it and defoliating it, causing the plant to stress and release fewer seeds. Presence of these weevils within the plant can be observed through noticeable feeding damage to the leaves, with small holes covering the foliage where the weevils have been eating. While the introduction of these insects has proven to be quite successful in limiting the spread of the plant, it will not completely remove it, and thus must be paired with manual methods of removal. Combined, not only can the spread of MAM be contained, but its numbers can also slowly be reduced—a large step in the eradication of this damaging, invasive plant in our fragile ecosystem.