Garlic on broccoli may keep pests away

Strong flavours such as garlic, thyme and cinnamon are a good way to hide the flavours of vegetables you don’t like.

Thanks to their odours, they may also be a good way to ensure you have plentiful supplies of the ones you do like, research suggests. 

But in the field, as in the kitchen, you have to make the right matches.

A study by the University of Vermont, in the US, suggests that agricultural pests can be kept away from vulnerable plants by spraying around the odours of other plants – with the most repellent being those that are more distantly related to the host plant. 

It’s not exactly a new approach to pest management, they acknowledge, but until now people have tended to adopt a “trial by error approach”. 

“People often think more aromatic plant oils, like mint, basil and lavender will repel insects, but usually there is no rhyme or reason for choosing,” says senior author Yolanda Chen. 

“It turns out that as we go along the family tree, plants that are more distantly related from the host plant are generally more repellent.”

Chen and colleagues studied the swede midge (Contarinia nasturtii), a tiny fly that is becoming a big problem for growers of broccoli, kale and other crops in the northeast of the US.

It’s a good case study of a broader problem, and possible solution. Midge larvae must feed on the brassica plant family to survive – and as they thrive, the plants often don’t. But if eggs are laid on the wrong plants, the larvae won’t survive.

The researchers observed the behaviour of female midges when presented with broccoli plants that had been sprayed with essential oils from 18 different plants that varied in their degree of relatedness to the host crops. 

They found that oils from plants that are are more distantly related to the host crop were more repellent that those that weren’t. The same was also shown for odours that were more chemically different. 

They suggest that this study can lead to a new sustainable solution for pest management strategies across other species, which can be used across a variety of different crops. 

“It’s hard to get away from using insecticides because they’re good at killing insects,” says lead author Chase Stratton. 

“But plants have been naturally defending against insect herbivores for millions of years. Why are we so arrogant to think we can do it better than plants?”

The paper is published in the journal Scientific Reports.