How do dogs sniff out powdery mildew, the enemy of grapes?
Dogs have an excellent sense of smell, and they work in cooperation with humans as police dogs and drug detection dogs. However, it was not clear how dogs can detect the smell of powdery mildew, a disease that is the enemy of grapes. A research team from Texas Tech University has come up with a hypothesis about this mystery.
Guardians of the vineyard: Canines and chemistry team up to combat powdery mildew - American Chemical Society
Powdery mildew is a plant disease caused by powdery mildew, and gets its name from the white spots that appear on the leaves, as if they have been sprinkled with powdery powder.
Powdery mildew is particularly susceptible to infection on grape vines, and is avoided by grape growers because it stunts plant growth. The only way to identify an infection is to check the leaves of the plant for signs of white cloudiness, but once the symptoms are visible to the human eye, it is already too late and large amounts of fungicides are required to eradicate them.
That's where dogs come in handy. Past research has shown that dogs can detect powdery mildew-infected grape vines with their sense of smell, and research is being conducted based on the idea that by identifying grape vines in the early stages of symptoms using their smell, it may be possible to take early action. However, the crucial question of 'why dogs can smell powdery mildew' is not exactly clear.
Paola Prada-Tiedemann of Texas Tech University and her colleagues decided to identify the volatile organic compounds, or 'smells,' given off by mildew-infected trees.
The team tested healthy and mildew-infected grapevine leaves using solid-phase microextraction-gas chromatography-mass spectrometry to determine what odors were emanating from the leaves. To do so, they placed the leaves in a vial, inserted a very thin absorbent fiber into it to absorb chemicals in the air above the leaves, and then inserted the fiber into a gas chromatography-mass spectrometer.
They found that diseased grapevine leaves released high concentrations of aldehydes and terpenes , and that while healthy leaves emitted less steam over time, diseased leaves emitted increasing amounts of volatile organic compounds as the infection progressed, suggesting that these scents may be detected by dogs.
In future studies, Prada-Tiedemann and her team plan to test whether dogs respond to a specific compound or a mixture of compounds. If they can identify such compounds, they hope that dogs might be able to be trained to sniff out the early signs of powdery mildew.
'The ultimate goal is to move away from visual diagnosis and towards smell-based diagnosis - think of a dog telling you, 'that ivy is starting to die.' After all, we all want to drink good wine,' says Prada-Tiedemann.
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