MICE AN' MEN
The best laid schemes o' Mice an' Men, Gang aft agley." Those words, immortalized by novelist John Steinbeck, were first penned in 1765 by Scottish farmer and poet Robert Burns. Plans go awry, he was saying, especially in nature. Though sentimental, his 18th century prose reveals the struggle between field mouse and farmer. 240 seasons later mice and men are still ...
at odds in Union County.
Last month Phil Hassinger was in the field when he noticed the wild antics of his four dogs running behind the tractor.
"They were going crazy eating, chasing and playing with dozens of mice. It's an infestation one I've never seen the likes of before," he says.
Hassinger, in talking with other farmers, says the Grande Ronde Valley's acres of perennial grass fields and alfalfa are populated with "mice by the hundreds" this year.
"A guy over near Island City is really havin' trouble," he says.
Commonly known as meadow mice, the creatures infesting the fields are actually voles. Both are members of the rodent family, but voles are classified as a different species.
Physically, voles are much bigger than a house mouse fully grown voles may reach 8 inches in length. Voles have heavier bodies, shorter legs and tails, and smaller ears. Their coats are usually grayish or blackish brown in color.
Craig McNeal has been a field man with Blue Mountain Seeds for more than 10 years and says vole populations cover the entire Pacific Northwest.
He's talked to orchardists in Yakima and grass seed growers in Wenatchee with big vole problems.
Although meadow mice have always been a factor in agriculture, McNeal says this year's infestation is the worst he's ever seen.
"Some fields have always had problems, but this year every field is bad. Voles usually tend to die off after harvest because their food source and cover is gone. But this year with the mild winter and early green-up I don't know, maybe that's had something to do with it." McNeal shakes his head in a combination of frustration and amazement.
The region's mild winter and early spring may have come at a peak in the voles' natural population cycles, providing optimum living conditions in the alfalfa and grass fields. McNeal says their reproduction rate is staggering.
The furious courting of cottontails cannot out-nest this especially productive pest. Voles have been known to breed any time of year, though spring and summer are their peak mating seasons.
With an abundant food supply, females will become pregnant as early as four weeks followed by a gestation period of just 21 days.
In the field, voles average up to five litters per year, but University of California-Davis lab experiments indicate they are capable of producing up to 17 litters a year under optimum conditions. Litter size may be as high as 11, but the average is usually 3 to 6.
So, let's say a single female in late February has an average litter of four, of which two are females. That means a single female is capable of tripling reproductive units within two months.
Gee, that's just three little meadow mice, you say.
Well, translate that lone female into a conservative estimate that 10,000 reproductive female units were living in Union County at the end of February and do the math to the end of harvest. That's a ton of meadow mice, but still not exactly mind-boggling.
Prepare to be boggled.
Both Hassinger and McNeal say they've never in all their years on the ground seen so many voles, McNeal saying every field is bad.
So, consider this estimate.
The Forage Information System on Oregon State University's Web site states that heavily infested fields will support as many as 1,000 to 3,000 voles per acre.
In 2003, there were about 97,000 acres in crop production in Union County. Split the difference and say a mere half of those fields are heavily infested this year at another split-difference of 2,000 voles per acre. That figures out to 97 million mice living and breeding in Union County.
That is mind boggling.
Admittedly, mental exercises in population estimation are guesses only there is no way to actually count the hundreds, thousands or even millions of voles scurrying beneath hay fields, fruit orchards or under the back yard tool shed.
What is known, is that there is a population boom of voles and farmers are having to deal with it more aggressively than usual.
Besides being good at making more of themselves, voles are very good at causing extensive damage to field crops, row crops, vines and trees. They will spend the summer in grass fields eating the seed heads but leaving the stems. Severe gnawing around the base of smaller trees and vines can kill them. For orchardists, vintners and home gardeners preventative measures may have some success in controlling voles that creep into a garden or lawn.
Burying wire fencing with a mesh size of at least one-quarter inch or less at least 6 inches underground with a height of 12 inches above, will help keep voles out of a garden.
Placing protective covering around the trunks of small trees will also help, as voles are not good at climbing higher than a few inches. Maintaining a buffer zone of cover-free earth around trees and vines and frequent mowing to expose tunnels are also good suggestions.
For those small landowners without a dog or cat, trapping and baiting with pesticides are other options. Or consider adopting a dog or cat or encouraging predator birds.
Some research has shown that building predator platforms for hawks next to farm fields may prove successful in keeping vole populations down.
Other natural predators also include foxes, coyotes, skunks, owls, eagles, ravens and believe it or not the great blue heron.
"Most people think of them only as a water bird," says Scott Findholdt with the U.S. Fish and Wildlife Service. Whenever the long-legged fowl are standing out in the middle of an alfalfa field, he says the chances are they're catching mice.
In the past, some farmers have flooded fields to drown rodents, but in a water shortage year for dryland farmers, flooding is not a practical solution.
It has also been suggested that a byproduct of open burning, once a widespread practice in Union County, was the asphyxiation of rodents in burrows due to the extraction of oxygen that occurs during a quick, intense burn. Since the decline of open burning in favor of propane, there is not enough oxygen-depriving heat generated.
The most practical method left for farmers for controlling rodents by the hundreds is with the use of a pesticide.
The pesticide of choice, McNeal says, is zinc phosphide a restricted use pesticide, or RUP. That classification means you must be a certified applicator to purchase and use zinc phosphide.
Zinc phosphide is marketed under several different trade names including Arrex, Commando, Denkarin Grains, Gopha-Rid, Phosvin, Pollux, Ridall, Ratol, Rodenticide AG, Zinc-Tox and ZP. Depending on the chemical formulation, labeling ranges from highly toxic (DANGER: POISON) to slightly toxic (WARNING or CAUTION.)
However, McNeal says zinc phosphide does not stay in the muscle tissue of the voles after they ingest it like a coagulant would, which makes it less likely to harm other animals.
County field crops Extension agent Darrin Walenta concurs, saying there is little tendency for residual zinc phosphide in tissue.
"Besides, chances are they're going to die underground," he says.
Walenta says there are several ways to apply the zinc phosphide bait hand-baiting heavily infested areas in the field, injecting the pellets into the tunnels, inserting metal rods into the ground that dribble the bait into the tunnels, or using a gopher plow.
A gopher plow hooks onto the tractor and has a hopper for the pesticide. As the tractor moves over the field, Walenta says the gopher plow digs a tunnel underground while dispensing the poison into the tunnel.
However it's done, whatever is used, applying another chemical to the ground this spring means more expense pesticide costs, labor costs, fuel costs, time costs as every pass through the filed affects the bottom line.
Adding to the severe water shortage and current weed expansion, an exploding vole population is just one more shake of the head in dealing with nature.
For more information on voles, visit the University of California's Integrated Pest Management Web site at ttp://www.ipm.ucdavis.edu, or check out Oregon State's Web page on vole control at http://forages.oregonstate.edu/voles.html
For information on zinc phosphide, go to OSU's Web site, http://npic.orst.edu