Friday, October 19, 2012


Well, the JBs have found their way into my lawn as grubs, chewing as they went; the spider mites have hopefully gone dormant after our first hard frost here in Minneapolis; and the deer can't do too much more damage, after the roses go dormant.  So, there's nothing else to worry about except winter-protecting the roses, right?  Not!  Now it's time to start protecting the roses from winter's nastiest pest: Voles!

These voracious little rodents are also known as meadow mice, which is a much kinder name than they deserve.  What they do, if you haven't experienced them, is burrow around in the mulch and winter-cover in your rose beds and eat the bark off the roses, right down to the cambium, which, of course, girdles the canes and kills them.  It has happened to me and I had to cut all the plants in one of my beds right to the ground and, in some cases, below ground level to save them.  Thankfully all of my roses grow on their own roots, because otherwise they would not have survived.

Here are a few facts about voles from a North Carolina State University article: 

Characteristics: "Voles are small mammals, commonly called meadow mice, that live in field and shrub habitats. In the wild, voles forage on native vegetation and provide a valuable food source for predators such as weasels, hawks, and snakes. In horticultural plantings, including flower and shrub plantings and home orchards, however, voles can cause damage by eating flower bulbs, girdling the stems of woody plants, and gnawing roots. Plants not killed outright may be invaded by diseases or die from water stress during periods of drought."

Reproduction: "Female voles have a gestation period of 24 days, have an average litter size of 2.8, and produce four to six litters per year. They reach sexual maturity at 37 to 38 days and have a reproductive life span of 15 to 18 months."

That's a pretty amazing, geometric, reproduction rate so it's easy to see how they become an infestation in and around your garden, requiring yearly control, as they have in mine.

Here's the address of the NCSU article if you'd like to read more:

And here's what voles look like:

Vole Control

Fortunately, there are several things you can do to protect your roses from voles. 

Castor Oil: This is the most effective solution I have found.  Voles really don't like castor oil; apparently, from what I have read, it makes them sick, and they avoid an area on which it has been applied.  Mix one or two teaspoons of castor oil (I use more rather than less) and one teaspoon of liquid detergent, per gallon of water, and apply it liberally around the bases of your roses and generally around your rose beds, where the voles might travel/burrow in the winter.  The best time to do this is in late Fall, when the ground is lightly frozen, just before putting your final mulch or leaf cover around your roses. Around here, that would be in mid to late-November.  I mix it in a 30-gallon trash container, pump it out with a sump pump, and apply it with a hose and watering wand, exactly like I do liquid fertilizers and potassium. You can also use a sprinkling can to apply it, if your garden isn't too big. You'll also get a good idea of how castor oil clings to anything on which it is applied if you run your hand around the inside of the trash container or sprinkling can, after you're finished.  It's still clinging to mine, after a full year of using the can to apply other mixtures.

The article below suggests using a hose-end fertilizer applicator and I think that might be a good idea.  The article describes the success a commercial hosta grower in New Hampshire has had with castor oil to protect his hosta fields.

(P.S. There's also an interesting article about controlling slugs on hostas on his website.)

So, my immediate question, after reading the article, was: Where the heck do I get castor oil?  I did some research on-line and found that you can order large quantities of castor oil, enough to last you for many years, relatively inexpensively, but I also found that buying more than you need for one year at a time is a mistake, because castor oil has a very short shelf-life once its container has been opened.  So, the best place I have found to buy just the right quantity of castor oil is Wal-Mart, in their health and beauty area.  Look in the laxative section, because that's what it's used for and, come to think of it, that's probably why it works on the voles! 

Rodent Baits:  Killing voles is desirable, before they over-run you, but this is a touchy subject because rodent baits can also affect other animals, like neighborhood cats and dogs.  The common rodent bait that you find in most stores is an anti-coagulant poison, which, when eaten a couple of times, stays in the intestines, causes massive internal bleeding and kills the animal.  I used it in my rose beds for years, without thinking, until about five years ago when we got a new kitten and he managed to find a mouse or vole that had eaten it, in among the winter-protected roses.  I will save you the terrible details, but it resulted in a very large emergency veterinary bill to save this humane society kitty and, fortunately, he is still with us (but he used two or three of his nine lives on that one).

After that experience, I went to work researching what other non-coagulant rodent baits might be on the market, and I found one.  The brand name is "Eraze", made by Motomco, the same company that makes the anti-coagulant baits.  The active ingredient in this one is Zinc Phosphide, which is nonetheless a poison, but acts in a different way, killing small animals immediately after ingestion.  There are conflicting opinions on this, but an article by Michigan State University indicates that it is less lethal to larger animals, such as cats and dogs, because their normal reaction after ingesting it would be to regurgitate it rather than digest it.  There is no question that it would kill any animal if eaten in sufficient quantity, but it apparently is less dangerous because it kills the rodent and dissipates rather than staying in the animal as the anti-coagulant does, thus potentially transferring to another animal or predatory bird (owl or hawk) that might eat the dead or dying rodent, as we believe our kitten did.  Note that Motomco also makes a similar product labeled as mole bait that uses Zinc Phosphide, so if you can't find Eraze, you can use the mole bait (check the label to be sure).  Other companies also offer Zinc Phosphide under different brand names.

Most important is how you use the bait.  The most common way of putting it in the rose beds is to use a tin can lying on its side alongside or between the rose bushes.  The can should be covered with leaves and/or protected in other ways (such as fencing) so that neighborhood animals can't get at it.  I also use the large, black, "Tomcat" poison dispensers that are usually found in warehouses or barns.  I put a couple of bricks or heavy stones on top of each container because animals like raccoons try to get the bait out of them by tipping them on their sides.  I also put a securely anchored cylinder of  24" fencing around each container to keep other animals away.

There is another device for dispensing rodent poisons that is made of L or T-shaped PVC piping buried in the winter protective leaf and mulch cover.  This method is used extensively in the University of Minnesota Landscape Arboretum rose gardens and is discussed in detail in the following article from the University of Missouri.  The article also deals specifically with Zinc Phosphide as the vole bait of choice and displays a graphic of the PVC dispenser, right at the end of the article.  I will leave you with that article for your perusal:

Bottom line is that in every winter I have either used rodent baits, applied castor oil, or both (as last winter), I have not had vole damage to any of my roses.  The one winter that I did nothing I had severe damage.  So, lesson learned: you need to do something to protect your roses from voles.

E-mail if you have any questions to: .

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