By Edward R. Ricciuti
Unmanned aerial vehicles, better known as drones, are constantly being used for new purposes. They help locate lost people, deliver packages, and now have proven their worth at detecting when agricultural crops are being stressed by insect pests, according a paper published in the Journal of Economic Entomology.
The research turns on the fact that plants under stress reflect light waves differently than normal plants. Red reflectance from vegetation, for example, indicates chlorophyll content of the plant canopy and active photosynthesis, and near-infrared reflectance provides information about the cellular structure and intracellular air spaces within leaves, overall canopy coverage, and above-ground biomass.
The study found that that stress to soybean crops caused by the soybean aphid (Aphis glycines) can be detected by drone-based multispectral imagery, which photographs reflected light of several electromagnetic wavelengths in the same image. It can paint a high-resolution picture in wavelengths visible as well as invisible to the human eye and has potential for scouting the presence of not only the soybean aphid but other field crop pests. Combined in an index, the wavelengths detected provide a measure of overall plant health, which often correlates to crop yield.
A New Remote-Sensing Option
Satellites and piloted aircraft have been used for remote sensing of crops but are expensive, low-resolution, and limited by atmospheric conditions and orbital periods. More recently, changes in reflectance indicating stress caused by the aphid have been detected by ground-based measurements, with hand-held sensors, for example.
“Ground-based sensing is a recent development and provides far less coverage than from a drone,” says lead author Zachary Marston, PhD, of the University of Minnesota’s Department of Entomology. “Detecting soybean aphid-induced stress from a drone is the big win.”
Introduced from Asia in 2000, the soybean aphid has hit hard at the soybean-growing heartland of the north-central United States, which produces 75% of the nation’s crop. The United States leads the world in production of soybean, and it is the nation’s most widely grown field crop.
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