Can vinca survive and conceal a mole infestation? Better to remove dirt or tamp it down?

Asked July 6, 2020, 5:14 PM EDT

Hi!
Our front yard is a west facing slope of clay and seasonal runoff. Many years ago it was landscaped with juniper and laurel. Some of those have clung to life, but most have perished. Originally I was replacing the laurels, but gave up about 10 years ago. At some point I realized it was the winter water, not the summer dryness which was killing the plants. So, I have been working to establish vinca, with some red twig dogwood to anchor the steepest places. That seems to have worked.

Recently, a mole has tunneled under a walkway and started to colonize our hillside. There are exploratory runs around the edges, and hills popping up all over, especially at the bottom, along the sidewalk/street edge. I've removed some of the dirt, hoping to give the vinca underneath a chance to recover, but that's getting old and I don't know if I'm just enabling the mole to dig more in those locations. My husband would be willing to 'take measures' against the mole, but if the vinca can cover most of the activity, I'd rather not escalate. My questions:
1. Will the vinca survive having the tunnels underneath?
2. Should I haul away the visible excess, or try to push it back down into the hole?
3. Would regular irrigation discourage the digging or change the location of hills?
4. Some of runs have pushed up sand from the original drainage installation. Will the tunnels affect the drain field?
5. Will the mole ever be satisfied and just live there, or will it dig under the street and infest my neighbors?
6. What else should I do to support and encourage the vinca in the meantime?
Many thanks in advance! Bonnie
PS: see pictures. In the second photo, 'bottom looking up', there are about 4 molehills where I've removed the dirt, running up diagonally from bottom left to the forlorn laurel, and two untouched hills farther away above it.

Washington County Oregon

1 Response

The mole(s) is there because it dispersed from somewhere else, made it into your landscape, and found enough earthworms and grubs to keep it happy. It is almost impossible to kill Vinca so I don't expect the moles to have much of an impact on that plant. The mounds are a result of the tunneling which creates the grocery aisles for the mole. Here is where it gets complicated. Field mice (also known as voles) will use mole tunnels and they do feed directly on plant roots and lower crowns. So it is possible that the voles might damage the red osier dogwood but probably not the Vinca. In addition, mole tunnels alter drainage patterns in a landscape. It is unlikely that they would physically impact the drainage system already there but could divert water in some unpredictable ways, thus altering the existing drain lines effectiveness (either for better or worse). So what to do? The moles will stay there until they run out of earthworms or until they are caught by a predator or dealt with by the home owner. Trapping is the most consistently effective mole management tool but it takes some skill from past experience to locate the best places to trap. I think it is quite possible that you have only one mole. Moles are quite territorial and don't allow other moles to encroach on their feed sources. One mole can make a lot of mounds as they create their grocery aisles. So removinmg one mole might solve your concerns until another finally shows up. I hope this helps. If you have more questions, you can email me directly at chip.bubl@oregonstate.edu Chip Bubl OSU Extension Agent/Columbia County