CORVALLIS, Ore. — Christy Tanner crouches on a dirt road next to a grass seed field, with a drone to her right and a calibration control panel sitting directly in front of her.
Tanner, an Oregon State University Extension seed production agronomist, takes a photo of the calibration panel with the drone camera. A few minutes later and after some more preparation, the drone takes off.
It flies in a grid pattern over the grass seed field — covering a trial area in 20 minutes. The drone takes a picture every second that will eventually be connected into a map of the plot and surveyed for indicators of vole damage. Voles are members of the rodent family and are commonly found in Western Oregon grasslands. They can cause significant damage to crops, orchards, vineyards and pastures.
Tanner, an assistant professor of practice based in the Willamette Valley, uses the drone and its two cameras to measure the damage voles are doing to the grass seed crop. The multispectral camera allows her to calculate a value called Normalized Difference Vegetation Index (NDVI), which predicts the amount of green healthy plant tissue.
“With the regular camera and some software, I can create a 3D map of the crop, which tells me how tall the crop is,” Tanner said. “Voles eat the grass, which makes it shorter, and reduces the amount of plant tissue.”
That plant tissue is critical to a grass seed grower’s success.
Vole populations are characterized by a peak and a crash over a four- to eight-year cycle. Though voles live in small tunnels, they spend time above ground eating grass and nibbling on other plants. The mouse-sized voles leave many burrows and connecting runways through the damaged grass they’ve been dining on.
“We have general idea of what damage voles can do, we want to document it and quantify it,” Tanner said.
In addition to measuring crop damage, Tanner is using aerial imagery from the drone as a research tool to test new management practices. In this trial she is testing whether tamper proof-boxes with rodenticide baits can help protect the crop.
Bait boxes
The study was done in one field last year and was expanded to three fields this year. The bait boxes were placed next to vole burrows, in areas where there are clear signs of vole damage. Tanner is using bait boxes that have sensors inside that record when a vole or other small creature enters the box. Sprout Mahoney, an Extension student employee, adds to the project by collecting data from sensors inside the bait boxes.
“There aren’t many options, so bait boxes are something new growers might be able to use,” Tanner said.
