Precision Sensors: An Innovative Future for Agriculture

Electronics & Sensors INSIDER

In the summer of 2022, growers in North Carolina were alarmed to find a new variant of the Tomato Spotted Wilt Virus (TSWV). Transmitted by insects called thrips and resistant to existing treatments, TSWV is difficult to eliminate and can ruin an entire crop. With one of the widest ranges among plant diseases, it also infects peppers, tobacco, potatoes, eggplants, squashes, lettuce, onions, spinach, and herbs like peppermint.

Diseases caused by pathogens like TSWV are only one of many challenges today’s farmers face as they navigate an industry with little room for error. Crops require time and ideal conditions to reach their peak for harvest. Finding an infection of TSWV too late is expensive, risking growers not only their entire crops but also the cost of resources and labor they’ve invested. Recouping costs even by next year’s harvest can be difficult.

These tough odds are one reason the North Carolina Plant Sciences Initiative (N.C. PSI), headquartered at NC State, is developing tools to help with a common conundrum: If growers had a way to detect a problem sooner, they could intervene before it became pervasive.

Researchers at N.C. PSI are innovating advanced sensor technology to aid in early detection. These smart sensors can detect diseases before visible signs appear, measure plant health more accurately, and alert for harmful crop conditions — saving growers time and costly resources.

WolfSens, an ongoing N.C. PSI research project, has developed two sensors that can help growers facing challenges such as the blight-like effects of TSWV and similar pathogens.

“The earlier growers can identify plant diseases or fungal infections, the better able they will be to limit the spread of the disease and preserve their crop,” said Qingshan Wei, associate professor of chemical and biomolecular engineering and leader of the interdisciplinary WolfSens research team.

An ode to NC State’s mascot, WolfSens is also shorthand for “Wearable Olfactory Sensing.” These two advanced sensors can alert growers to the presence of disease by detecting — or ‘sniffing’ — the gasses plants naturally emit called volatile organic compounds (VOCs). Farmers can determine which disease a plant has by measuring the type and concentration of VOCs the plant releases.

Wei and the WolfSens research team built a wearable electronic patch that provides continuous, real-time detection of a plant’s health. When attached to the underside of a leaf, the patches can detect the VOCs of viral and fungal infections. The patches can also alert growers to other stresses, such as overwatering, drought conditions, lack of light, or high salt concentrations in irrigation water.

During tests, WolfSens researchers found the patch detected a viral infection in tomatoes more than a week before any symptoms of TSWV became visible.

The WolfSens team also created a portable sensor that uses a colorimetric strip of paper that measures VOCs and changes color depending on the presence of disease. The sensor utilizes a handheld device plugged into a smartphone, making it a convenient option for use in the field and greenhouses alike.

In proof-of-concept testing, the portable sensor detected and distinguished tomato late blight from two other important fungal pathogens that produce similar symptoms. In addition, the researchers showed they could detect the pathogen Phytophthora infestans in tomato leaves with greater than 95% accuracy.

Historically, testing plants for disease has been an invasive procedure that requires destroying crop tissues to get a sample. That process often requires hours or days in a lab, delaying disease identification by days or weeks.

The WolfSens team created these two sensors to work together. The current versions of the patch and the portable strip sensor are designed for use in greenhouses with wireless internet access. Ultimately, WolfSens plans to develop the sensors to the point where they could be used in outdoor fields, so farmers could apply them to a much wider variety of crops. Compared to the patch, the portable sensor — which works with any smartphone — could be priced lower, and therefore be even more attractive and accessible to farmers and growers of many different crops.

Another NC State researcher at N.C. PSI is also furthering sensor technology to help growers. Michael Kudenov, a professor of electrical and computer engineering, specializes in the application of light polarization — the use of light waves for measuring biological structures. He and his team are exploring using polarized light in agriculture and have developed software to assist imaging sensors in overcoming the sun’s glare.

Sensors used in agriculture are typically programmed to determine a plant’s well-being based on the color of its leaves or stems. However, bright sunlight can distort the colors the sensors perceive, leading to an inaccurate determination of a plant’s health.

With Kudenov’s software, the imaging sensors can capture a plant’s color and measure how polarized the light is. The software’s algorithm estimates the true color of a leaf based on two variables: the color that the imaging sensor perceives and how polarized the darkest wavelength of light is in the image. Kudenov’s team has developed this algorithm to simplify the technology and use less computational power than previous tools.

“The software we’ve developed essentially acts like an incredibly dynamic pair of polarized sunglasses, able to account for whatever polarization challenges are present in order to accurately capture the color of a leaf, regardless of the glare,” said Daniel Krafft, a Ph.D. student at NC State who was first author of a paper published on the imaging sensor software research.

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