Teaching a sweet potato self-defense

Sweetpotato farmer.jpg

By Max Johnston

Here in the states we like our sweet potatoes fried, sweetened and tater-totted. But the nutritious sweet potato is more than just a side dish. Sweet potato is also a cheap and resilient crop.

While it’s a popular food here, it can be a livelihood for low-income farmers. Especially in sub-Saharan Africa.

But there’s a small problem, or should I say a big problem in a small package. We may enjoy sweet potatoes, but so does the weevil–a small brown beetle that resembles an ant.

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Brooke Bissinger is an entomologist at AgBiome, a biotech company in North Carolina. She says the weevil loves the taste of sweet potato.

“Weevil is the most devastating pest to the sweet potato worldwide,” Bissinger said.

Bissinger says the weevil likes to eat and live in sweet potatoes. But in the process, they ruin them for everyone else.

“The insect lays its eggs in the sweet potato itself and then the larvae or the immature weevils, feeds on the potato,” Bissinger said. “It also causes the potato to make chemicals that are both bad tasting and toxic to people and animals.”

Weevils can be especially devastating to African farmers because sweet potato is a ‘low value’ crop that doesn’t fetch much cash in the open market.

Here in the states farmers spray pesticides to kill weevils. While that’s effective here it’s not really an option for farmers in sub-Saharan Africa.

“It’s a very low-value crop they’re growing to feed their families,” Bissinger said. “So the cost for them to use insecticides in these African countries is much more than the crop itself.”

Because there are so many farmers in the region it’s very easy for weevils to spread and devastate other crops. There are certain cultural practices to stop the spread of weevils, like rotating your crops and burning infested sweet potatoes. But those require a lot of work and time that those farmers might not have.

So Bissinger and her team at AgBiome are looking for cheap and effective ways to protect the sweet potato from weevils. They’re doing this by studying micro-organisms and bacteria that are already present in the sweet potato and the surrounding soil that can fight off the pest.

This isn’t an entirely new concept. There’s good bacteria all over the place. There’s good bacteria in your stomach to help with digestion. Even yogurt is made from healthy bacteria that ferments milk.

“So there are good bacteria that can control bad bacteria, or even other organisms. So there are good bacteria that can control insects,” Bissinger said.

Using good bacteria to fight pests has been done before. Bt, short for Bacillus thuringiensis, is a common bacteria in soil that kills insects.

“It’s super commonly used in agriculture and insect control, but Bt isn’t the only microbe that’s out there,” Bissinger said. “So we’re really interested in looking around sweet potatoes to see if there are other bacteria that are beneficial that could kill the weevil.”

If AgBiome finds bacteria that fight weevils in sweet potatoes and their soil, it could be used to give African farmers cheap and easy access to an effective weevil pesticide.

For the next three years AgBiome, with a grant from The Bill and Melinda Gates Foundation, will be identifying microbes and bacteria in sweet potatoes and soil from sub-Saharan Africa.

“Hopefully once we find something, we’ll go over to Africa and test it against the species they’ve got and work with partners over there to get it out to the growers,” Bissinger said.

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