Rodents—particularly voles, ground squirrels, and gophers—can have a big economic impact on orchard and vineyard production costs.
Rodents cause obvious damage to orchards and vineyards, especially to young trees that have yet to establish a large root mass. They also can girdle adult trees when they chew on the trunk. Examples of girdled trees and young trees that can be easily pulled out the ground are the obvious costs to orchard management, says Mike Omeg, a cherry grower from The Dalles, Oregon.
But then there are the hidden costs. That’s when the gopher or squirrel eats some—but not all—of the root system. “The tree lives, but it’s never healthy and never produces normal yields,” Omeg said.
He believes growers spend more on annual rodent control than they think they do. Oregon State University Extension estimated that growers spend an average of $95 per acre for rodent control, according to the 2012 Enterprise Budget for high-density, sweet cherry production. The budget is based on actual orchard management costs of a cross-section of commercial growers.
“Ninety-five dollars per acre is a lot of money, and that doesn’t even reflect the damage done to the trees,” said Omeg.
Based on figures contained in the enterprise budget, Omeg calculates that if 0.5 percent of new trees are lost to rodent damage in a 20-acre high-density planting with 340 trees per acre (at a planting cost of $17 per tree), a grower will lose about $580 per year in lost trees (34 dead trees). Three years of losing 0.5 percent of the planted trees results in a loss of nearly $1,750, and that’s not counting the replanting costs and lost time.
Barn owl economics
For a 20-acre block, two barn owl nesting boxes for rodent control could be commercially built and installed for around $250 each—even less if the boxes are homemade.
“Young orchards are perfect for barn owls because the tree canopy is not too big,” he said, though young orchards also provide perfect conditions for voles and gophers.
“Raptors, including hawks, owls, and kestrels, were designed by Mother Nature to be rodent killing machines,” Omeg said. “Barn owls live to eat voles and gophers.”
Studies have shown that a family of barn owls will eat 10 to 12 gophers per night during the brood period from April through July, according to Omeg. In a year, that equates to more than 3,000 gophers. For voles, a barn owl family will consume about 120 per night during the brood months. Single barn owl adults eat at least one gopher or up to ten voles per night for the rest of the year.
He estimated that with a cost of $5 to $7.50 per acre for bait material, treating 5 percent of a 200-acre block, twice a year, would cost $100 to $150 per year, not including cost of the equipment or labor.
“Once occupied, barn owl boxes (two costing $500 total) will pay for themselves in saved rodenticide costs in three to five years,” he said. “And even less time if you figure your equipment and labor costs.”
At one time, Omeg used trapping to supplement his pocket gopher control efforts. Trapping gophers is effective if populations are high enough and workers are motivated, he said, adding that orchardists often pay their workers a bounty for trapped gophers as a way to earn extra money.
Omeg used to pay $2.50 per gopher (growers in the Hood River-Parkdale area were paying $3.50), and he provided the traps at no cost. “Several of my guys were making an extra $400 to $500 every month during the spring and summer for their trapping efforts. It was pretty good money to them. But now, I have such few gophers that no one wants to do it. Traps just aren’t practical for me anymore because I’d have to pay by the hour.”
He attributes the reduced gopher population to the raptors that have moved into his orchard.
Omeg has placed 75 barn owl and kestrel nesting boxes in Omeg Orchards in the last three years. The boxes also have raptor perches attached to them.
Today, his rodent control program consists of raptors, bait stations in high population areas (4-inch diameter ABS corrugated plastic drain tubing), and he uses the Verminator, a burrow-building implement pulled behind a tractor.
The Verminator, manufactured by Inventive Products of Mountain Home, Idaho, is pulled through the orchard rows when the ground is still moist enough to allow the machine to build a burrow. The newly made burrows intersect or are near gopher burrows, and the gophers enter the new tunnel out of curiosity or to search for food. A bait hopper allows bait to be laid in the burrow by the machine every three feet.
Omeg has had such good results with the Verminator that he purchased two so he could get through the orchard in a timely manner.
“You only have a certain window of time when the soil is moist but not too wet,” he said. He likes to put two different types of bait in the hopper, believing that he increases his odds of getting gophers to eat the bait. “At certain times of the year, they seem to prefer one bait over another.”
The Verminator comes in two sizes: one for a tractor with 35 to 200 horsepower and the junior model for smaller acreages (30 to 60 hp tractor). The large model retails for around $5,000.
Omeg no longer uses zinc phosphide because it doesn’t fit his operation. If the ground is wet, the zinc phosphide deactivates, and it can be dangerous to workers when applying.
In the past, Omeg used what he calls the “gopher bomb.” The Rodenator injects a controlled mixture of propane and oxygen into a rodent burrow. A self-contained ignition system creates an underground shock wave or concussion that instantly eliminates rodents and collapses the burrow.
Because his rodent populations are now reduced, he no longer traps or uses the Rodenator.