The Winter Harvest Handbook

Consider the little mouse, how sagacious an animal it is which never entrusts its life to one hole only.

We have often joked that our worst pests in the winter harvest are our devoted customers who pester us on those occasions when our supply is unable to meet their demand. It may not be quite that perfect, but pests in the form of insects and diseases have not been a real consideration, and we have found little new to report since I discussed this topic in The New Organic Grower. The major pest that has developed is not a bug or a microbe but a mammal. We are engaged in a battle of wits with the meadow vole.

Meadow voles (Microtus pennsylvanicus) look like chubby, extra-furry mice. All of their qualities make them difficult to control on the small farm:

• They are serious pests for the fruit-tree grower as well as for us because they girdle the bark of young trees.

• They are vegetarians and seem to like our crops as much as our customers do.

• They need to eat their weight in plant food every day because their metabolism is so high.

• They can breed at thirty-five to forty days old, they can breed year-round, and they can have up to ten litters a year with three to six young each time.

• They live in underground burrows, and they like to line their nests with chewed-up shreds of row-cover fabric.

Not surprisingly, they consider our greenhouses an idyllic place to spend the winter.

Our first response to any problem is prevention rather than cure. That would seem to be the obvious course of action in this case. However, the mobile-greenhouse concept makes prevention more difficult. We have tried mobile-greenhouse designs with more deeply buried edges to keep voles from burrowing under. We have worked diligently to block any and all small holes that might allow vole ingress. But even after we have taken all precautions, the forces created by winter freezing and thawing can open new holes. In short, we have not been successful at keeping them out. In many cases they are already surreptitiously established before we even move the houses to their winter sites.

Although I am a mild-mannered sort and show great kindness and respect to wild creatures in general, I admit to a strong aversion to voles in the winter greenhouse. My efforts are not yet quite as manic as those of Bill Murray in Caddyshack, but I notice a fleeting resemblance on occasions. I have considered any and all options short of bombs, poisons, or chemicals. At present, I rely on snap traps and I use a lot of them. I know from my records that one year I trapped over fifty voles in the vicinity of the greenhouses during August and September, and a neighbor’s cat probably got almost that many. Come winter it didn’t seem as if we had even made a dent. The only effective method we’ve found is to keep trapping year-round.

The usual rat and mouse baits like cheese don’t work for these fruit and vegetable eaters. Besides, there is just too much delicious food available in the greenhouses. In addition to the recommended slices of raw fruit, we found a few other baits that often produced good initial results. We even baited some of our traps with wild-strawberry flavored bubble gum. Whatever devious ingenuity went into concocting that flavor to tempt little children, it appeared effective at tempting voles in midwinter when fruit has been scarce in the vole diet. Macadamia-nut butter from the health food store seemed to work better than peanut butter. Then we added carob powder to the macadamia-nut butter and that was momentarily successful. But we eventually realized the flaw with all baits and why we had to keep changing them. The voles became wise to what we were doing. We could imagine the third vole that approached a baited trap thinking, “Uh-oh, the last time I smelled that Uncle Harry bought the farm,” and shying away. We then learned to place the traps so as to intercept the voles’ lines of travel. That meant, for example, at the entrances to their burrows, across the surface runs they use when moving from one burrow to another, and up against walls, since they like to scurry along edges. When successful, these traps seemed to catch voles simply because of accurate placement.

Many wild predators consider voles little furry snacks and we make every effort to help them find dinner. We keep the grass mowed very closely around fields and greenhouses so that foxes, coyotes, skunks, and owls and other raptors can easily spot the scurrying vole. According to wildlife studies, a pair of barn owls with chicks will dispatch up to 3,000 rodents in one breeding season. Owl nest boxes and raptor perches are useful additions to the farm landscape. Foxes, coyotes, and bobcats can be effective vole deterrents even if they never come around the farm. Scent pellets containing urine from these predators are available, and fear alone will effectively keep voles from entering a scented area. See appendix C.

Based on that experience our next strategic development was to do away with baits completely and take advantage of another common vole behavior—the tendency to enter small dark holes. This was the key to success. We built wooden boxes about 12 inches long, 8 inches wide, and 6 inches deep with a bottom attached but with a removable top. At one corner of each of the 8-inch ends we drilled a rough mouse-sized hole at floor level. We place an un-baited trap inside each entrance hole. When voles do what voles do, darting into small dark holes, the traps get them. After the first vole enters the box it smells like vole and they seem to have no aversion to it. Every morning we lift the top, empty the traps, and reset them. This solution has been, and continues to be, impressively effective.