Late blight is a common disease of plants such as tomatoes and potatoes, capable of wiping out entire crops on commercial-scale fields. Caused by a fungus-like pathogen, it first appears as black or brown lesions on leaves, stems, fruit or tubers. If conditions are favorable, it can quickly spread to other plants through wet soil and as wind-scattered spores.

In the mid-nineteenth century, late blight famously caused the Irish potato famine. Today it still causes more than 6.7 billion dollars in annual losses worldwide. Small farms and organic growers are often the hardest hit, because they have fewer resources to identify and treat the disease.

But farmers may have a new weapon to add to the arsenal. The technology, designed by researchers at North Carolina State University, relies on the science of subtle plant odors, and it can recognize sick plants early by employing a simple test strip that plugs into a reader on a smartphone.

Plants emit signaling chemicals from their leaves, not unlike the pheromones released by humans. “If a plant is diseased, the type and concentration of these volatile organic compounds changes,” said Qingshan Wei, a biomolecular engineer at NC State University. By sampling a plant’s emission profile, a farmer can assess whether or not a sample of their crop is infected, Dr. Wei said.