Thursday, May 15, 2014

Voles or pocket gophers -- what's eating your garden? By Irene Shonle

I get a lot of calls and questions about critters in the garden.  People almost always think that voles are the ones wreaking havoc in their gardens, when often pocket gophers are the actual culprits. The confusion arises when both species are present -- the vole spends much of its time above ground, and so is often seen (and therefore gets the blame), but the pocket gopher, which almost never emerges, usually causes far more destruction.

Here's how you can figure out what's eating your garden:

1.  Look at the holes/tunnels.

Voles have small, oval,open holes - about 1-2" wide.  These are never plugged with soil, and there is often a "runway" in front of the hole.  This can be easiest to see when the snow melts and the grass is not too high, or in the winter.

Vole holes - note that they are open.  The winter picture shows the runway clearly.

Northern Pocket Gophers' holes are about 2-3.5 inches wide, but are almost always plugged with soil.  In the summer, the holes are surrounded by large fan-shaped mounds of dirt  that are 12 to 18 inches wide and 4 to 6 inches high.

Pocket gopher hole -- note that it is plugged, and the fan of dirt.  The "hole" is not always this obvious.
In the spring time, just after the snow melts, if you see long tubes of solid soil  (eskers) snaking about on the surface , that is a definite sign of pocket gopher.  This is due to ongoing excavation of burrows during the winter -- they pack the excavated dirt into the snow, which shapes them into the eskers, rather than the fan-shaped mounds when there is no snow.

2. Look at the damage - is it above-ground or below-ground?
The most common voles we have are meadow voles and montane voles, and these two species mostly eat above-ground parts of plants, including  leaves of flowers, grasses and sedges and fungi  in the summer.  Dried grasses, bark, and twigs are winter staples.

Voles are of most concern when their winter bark-chewing girdles trees and shrubs (they are also problematic in lawns, but lawns less common in the mountains):
During the winter, a vole girdled this lilac by chewing the bark off all the way around the shrub

Pocket gophers mostly eat the roots of plants (below-ground).   They only rarely come above-ground to eat, and then only a very short distance from their burrow.  They use their sense of smell to locate the roots of plants, and then will eat the entire root system.  This causes a sudden and unexpected "wilt" of the plant.  They can even pull an entire plant underground -- sometimes even under the astonished eyes of a gardener!
The middle columbine's roots were eaten by a pocket gopher -- look for sudden, unusual "wilting"

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