Voles. The little Oregon Vole can also be troublesome. It is much smaller than the Townsend Vole, but other than that looks quite similar.

Transcription

1 Voles Slide 1 Voles are another fury pest we sometimes have to deal with. These are another kind of rodent. And they can be very troublesome when populations are at peak levels. Slide 2 There are several species of voles in western Washington. On the west side of the mountains, the Townsend Meadow Vole and the Creeping Vole are the most troublesome. East of the mountains the Montane Meadow Vole, Microtus montanus, causes the most damage. Slide 3 The Townsend s Vole is one of our larger species, as you can see. These animals are largely fossorial, they mostly live underground, as you can tell by the small ears and small eyes. Note that the tail is considerably shorter than the head and the body, and this holds true for most of the voles. Slide 4 The little Oregon Vole can also be troublesome. It is much smaller than the Townsend Vole, but other than that looks quite similar. Slide 5 Just a little bit of biology on these animals. As you can see, they have several litters per year and several in a litter. So, they are quite prolific. Over the course of several years, these populations can grow to huge numbers, up to several hundred per acre. Slide 6 This is pretty typical of vole damage to root crops and flower bulbs. With their sharp little incisor teeth they hollow out bulbs and root crops. They will also come aboveground though and graze on grass, cut down vegetables, damage of that sort. Slide 7 Voles are also notorious for girdling apple trees, and actually they will eat the entire root system. This was Dr. Leonard Askum up in the Bellingham area in 1988 when we checked out a commercial orchard up there. That s all that is left of the root ball of that apple tree. Slide 8 Voles will damage not only apple roots but a wide variety of plants. The hybrid poplars are very common in their diet. They will feed on a wide variety of ornamental plants also. I have even seen them damage juniper. Page 1 of 5

2 Slide 9 If you are in an area where there is snow on the ground for extended lengths of time, these little rodents will tunnel through the snow and girdle plants quite a ways up above the ground level. Slide 10 During the summer if you look out in the fields, you can see their obvious trails through the grass. They make established runways throughout their territory so they can move quickly. Slide 11 They also do a lot of travel underground, though. During the winter when the grass is knocked down, you will often see their tunnel openings. These can be anywhere between three quarter inch to roughly one and half inches in diameter. Slide 12 The tunnels are usually quite shallow, and if you stick your finger into a hole, you can sometimes just unzip the entire trail system. Slide 13 Here we have girdling damage on an apple tree just a little bit below ground level. As you can see, this is pretty complete girdling and this tree won t survive. Slide 14 So, how do you tell if you have a vole problem? You certainly don t want to wait until you see your plants wither up and keel over. If you want to monitor for these rodents, it should be done in the fall. Most of the damage underground is done during the winter when other food resources are at a minimum. Slide 15 To tell if you are going to have possible damage over the winter from these rodents, you can utilize what is called the apple activity index. To do this, pick several places out in your garden and cut slices of apple. These can be placed preferably in vole tunnels or at least in places where you think voles might be active. Cover them with a sheet of cardboard, or plywood, or something of that sort. Leave them for a day or so. That will encourage voles to find these areas if they are out there. Then place a bait in there; again, after 24 hours check it, and see how many are damaged. Take the number of damaged slices divided by the total number of stations and that will give you your activity index. A rule of thumb says, if it is 20-25%, that indicates the potential for damage over the coming winter. If it is 40% or more it is pretty sure that there is going to be damage in that area. Page 2 of 5

3 Slide 16 Here we have some typical damaged apple slices. If you look closely, you can see the parallel grooves that are indicative of rodent damage. Slide 17 So, what do we have for control options? Well one would think that there would be some rodenticides available for the home gardener. But, there are none registered home use only in the state of Washington, so Master Gardeners may not recommend them. The public may of course legally purchase a number of these in the garden stores and use them if they wish, but we cannot recommend them. Even if it doesn t say vole on the label, as long as the site is on the label of the pesticide, it can legally be used in that situation. For instance, there are many mole and gopher baits that are grain based and contain zinc phosphide as active ingredient. If these are placed in underground tunnels, generally the voles will eat them and die some place underground. Slide 18 Trapping is the usual option for home gardeners, and we can legally use common rat and mouse traps for this. Slide 19 As you can see, these can be quite effective on this little creeping meadow vole anyway. Slide 20 There are several ways these can be used but generally they are placed in the voles runway. If it is done aboveground, it has to be covered with a box or something. I have often used them around my apple trees by excavating down to the tunnels and placing the trap crosswise so that the vole will run over the trigger, even if he doesn t catch the bait. I like to use apple as a bait. A lot of people use peanut butter, but by using that material you will also catch a lot of beneficial shrews which are always down there eating slugs and various arthropods in the soil. It is a good idea to tie your traps down in case a coyote comes by. If a trap isn t tied down, and there is a vole in it he will run off with the whole thing. Slide 21 Even if you trap is in an underground runway, it needs to be covered with a box or a piece of cardboard. Something to keep birds away from it. Slide 22 Also with traps, as with rats and mice, you need to check the traps constantly. Once or twice a day is ideal. Again, as we talked about with previous rodents, wear gloves, drop the carcass into sealable plastic bags for disposal, or just bury them out in the garden, ornamental garden, back fields, something of that sort. Page 3 of 5

4 Slide 23 You can also use the pitfall traps for voles as we discussed when we talked about moles. For voles though, these don t have to be really buried underground to intersect an underground tunnel. Although you can certainly do that. With voles it is quite effective burying these level with the surface of the soil and then covering with a tarp or a piece of board. I like to put some hay and a piece o f apple in the bottom of the pit fall so the vole can be comfortable if he gets caught in one of these. However, keep in mind that you may not legally transport these animals off the property to release them. So, you either have to release them elsewhere on the property or euthanize them. Slide 24 Cultural management is often sufficient for dealing with these animals, though. You need to deal with the vegetation. This is not only the hiding place for voles but it is also their food source. Slide 25 As far as orchards go, it is a good idea to keep at least a three foot area clear around the base of the trees. Voles love cover, whether it is turf or any other kind of plants on the ground. So, clear away the vegetation and that will really go a long way to reducing vole damage. If you like to use organic mulch, don t use too much. Just a couple of inches is all you need. If you use a very thick layer, that gives voles a really easy material to dig through and they can become a very big problem in those situations. I have talked to some orchardists that actually use coarse crushed rock around their trees. That kind of mulch makes it very difficult for voles to tunnel. Slide 26 You can use quarter-inch hardware cloth as a barrier around orchard trees, but remember that these rodents do dig. So, you need to have these go deep enough in the soil so that they will protect the crown of the tree. Slide 27 Wrap around guards are not very good for voles because most of the damage takes place underground. And these little rodents can even crawl up underneath of these guards and damage the plants up there. Slide 28 The underground barrier such as we talked about when discussing moles also works very well on these little rodents. You usually don t have to go as deeply with them but you do need to be sure that six inch above ground fence is there because the voles do spend a lot more time above ground than moles do. Page 4 of 5

5 Slide 29 Encouraging raptors and other small predators will also help control vole numbers. Do keep in mind though that predators will not eliminate a vole problem. Slide 30 If you would like to improve your raptor habitat, Washington State University has a publication, Attracting Birds of Prey, that is available online. Page 5 of 5