LSU AgCenter researchers and extension agents conducting research using unmanned aerial vehicles (UAVs) are learning when to fly, what to fly and how to use this technology to increase soybean profits.

After some experience with UAVs — commonly called drones — researchers and agents have modified their technique, using the vehicles to spot-check crop conditions rather than take time-consuming photos of entire fields, said Dennis Burns, AgCenter agent in Tensas Parish.

By flying a random path 10 to 50 feet above the field, the UAV can mimic how a scout would walk through and record images that can be evaluated while still on-site.

“We can fly the UAV to scout the crop from the turnrow, so if there is a site we need to look at more closely, we can walk that part of the field and compare data while we are still at the field,” Burns said.

The shift to spot checking in crop scouting allows for a smaller number of photos and some video, while whole-field images require more sophisticated computer programs and at least two to three hours to run the software.

“It goes back to time and purpose, whether it is flying 10 feet off the ground trying to get a plant stand count or flying 400 feet to monitor irrigation efficiency,” Burns said.

Previously, researchers used whole-field imaging in Madison, Tensas and East Carroll parishes to detect insects, weeds and diseases and evaluate nematicide trials and irrigation efficiency.

Projects for 2017 include imaging a nematicide trial in Morehouse Parish, an irrigation efficiency site in East Carroll Parish and other northeast Louisiana soybean fields for diseases and insects.

Using the UAVs for Normalized Difference Vegetation Index (NDVI) photography allows for improved evaluation of overall plant health, said Donnie Miller, AgCenter Northeast Research Station coordinator. The NDVI photography shows reflectance differences of the plants and compares crop response.

“A normally healthy plant may reflect at one level, while one under stress will reflect at a lower level. So the UAVs are not actually going in looking for insects or weeds,” he said.

NDVI photos can detect differences as early as two weeks before they can be detected with the naked eye, providing valuable information and allowing for improved decision making, which ultimately translates to increased profitability, Miller said.

“UAV technology is just another tool in the toolbox,” said R.L. Frazier, AgCenter agent in Madison Parish.

The images point out the difference in crop health, but often they create more questions than answers, he said.

“The NDVI will show the stressed and non-stressed plants in the field, but you still have to put boots on the ground to find out why,” Frazier said.

For whole-field imaging of a 100-acre field, Burns recommends using a plane that can stay in the air up to an hour and capture more than 600 images. For crop scouting, multi-rotor copters work better.

Cameras vary in quality and expense, he said. More expensive cameras with NDVI capability are typically used for whole-field imaging, while crop scouting can use either NDVI or RGB (red, green, blue) cameras, depending on the purpose of the image.

“Each time we fly, our image analysis improves, and the comparisons from walking the field make better sense with what we’ve seen in the images or, in some cases, what we didn’t see in the image,” Burns said.

Images taken in a Madison Parish field last year, for example, gave no indication that the field had treatable levels of the redbanded stink bugs feeding on plant pods.

“When we walked it, we found them,” Burns said. “These are some of the things we are learning, and it all goes back to purpose.”

Researchers plan to fly intervals once a week beginning in late July or early August on late-planted soybean fields to collect images and then walk the fields to compare data.

“There is still a place for whole-field imaging but not on a weekly basis,” Burns said.

Both the 2017 nematicide and irrigation efficiency trials will utilize whole-field imaging, while the crop-scouting trial will focus on regular intervals of spot-checking and physically walking the field for comparison.

“It all ties together,” Burns said.

By learning more about what type of image is needed according to crop stage and purpose, producers can make better decisions on whether to just fly a crop scout or fly a whole field image, he said.

Karol Osborne