Research Looks at Drones to Detect Water Stress

In the near future, blueberry growers may have a better idea of their irrigation needs because of a research project being conducted by scientists in Oregon and Washington.

The researchers are studying the use of drones and thermal imaging to depict water stress in blueberry and raspberry plants with the goal of helping farmers maximize their irrigation supplies by applying exactly what is needed.

Scott Orr, a biological research technician at USDA, left, operates a drone with David Bryla, right, a research horticulturalist with USDA, looking on at the 2019 Oregon Blueberry Field Day in Aurora. Bryla and Orr are working on an app that growers can download that delivers real-time data on crop conditions to phones.

The project involves estimating the water requirements in blueberries and raspberries, which involves measuring evapotranspiration, plant canopy and other factors, and analyzing thermal images to determine water stress.

“When plants become stressed, they close their stomates, and when the stomates close, the canopy heats up, which we are able to detect,” said David Bryla, a research horticulturalist with the USDA Agricultural Research Service in Corvallis.

Bryla is working with Lisa DeVetter, an associate professor with Washington State University, and Chris Benedict, a Whatcom County Extension agent. The project is funded in large part by a Washington State Department of Agriculture Specialty Crop Block Grant. The researchers are using specialized cameras mounted on a drone that collect infrared and multispectral images to determine plant stress levels.

To date, researchers have quantified that plants project different images when they are stressed, Bryla said. In one field, for example, plants in an area where a drip line was plugged portrayed quite differently than plants in other areas.

“You could easily see where the plants were water stressed,” Bryla said, “and we could make good estimates of canopy cover.

“So, now we are tying to relate that information to the water requirements of the plants over the course of a season to get better estimates of how much irrigation growers should be using,” he said.

“If we can dial that in a little better, we can figure out exactly how much water (irrigators) should be putting on over the course of a growing season,” he said.

Drones also can be used to look for Phytophthora root rot and other plant diseases, Bryla said.

“We are looking to see if (drones) are also useful for looking at plant diseases, such as shock virus and silver leaf, to quantify the percentage of plants in fields that have it and how that changes over time,” Bryla said. The work on plant diseases is being conducted in collaboration with Jason Myer from the Northwest Berry Foundation.

“I think there is a lot of potential for drone technology,” he said. “A lot of different commodities are using drones now and you can collect a lot of information with drones. The problem is, we need to learn how to interpret this information.”

Bryla plans to continue the research after the block grant funding expires this year. Among future plans, he hopes to obtain a hyperspectral camera, which can collect many times more wavelengths than the multispectral module the researchers currently are using.

“The more wavelengths you get, and if you understand what that information means, we can start looking at other issues,” he said. “For example, we might be able to assess what the nitrogen status of the plants are.

“This is the type of work we plan to continue in the near future,” he said.

Bryla also is working with Scott Orr, a biological research technician at USDA, to develop an app that farmers will be able to download on their phones that will be able to deliver real-time data from the drone to the farmer.

The two hope to have that ready by 2022.