Potato pest in Peru

Potatoes filled with Andean potato weevil larvae. Image: Jesus Alcazar

The potato is one of the most important staple crops in the world. Pest damage can be devastating.

'In Peru the Andean potato weevil is a pest – it can cause serious damage. Up to 40% of potatoes can be infested at harvesting, even when the farmers use pesticides. Sometimes fields are abandoned because of high infestations,' says Jürgen Kroschel, a potato pest expert at the International Potato Centre.

But how can farmers get rid of the weevils?

Hold the chemicals

Farmers also use plastic barriers around their fields to stop weevils getting in. Image: Jesus Alcazar

Farmers can use harsh chemicals to control weevils. But many prefer to use a range of different methods – integrated pest management – that doesn't involve chemicals.

Weevils are pretty persistent pests, Kroschel explains: 'The weevil hibernates in the soil. When the new crop is planted the adult weevils emerge and lay their eggs. These hatch into larvae and attack the potatoes.'

But chickens kept in the fields after the harvest will reduce the number of weevils. The chickens scratch around in the soil and eat any weevil larvae before they get the chance to grow into adults.

Rice crisis

Scientists study rice in an effort to fight blast. Image: IRRI

In parts of China, farmers have a huge problem with rice blast, a disease that can destroy up to 20% of each year's rice harvest. Spraying harsh chemicals is one way to control rice blast, but it's not good for the environment, or for the farmers' health.

Scientists at Yunnan Agricultural University in China and the International Rice Research Institute (IRRI) have shown that there is another way.

'In China farmers grow different rice varieties in alternate lines instead of using chemicals to fight the devastating rice blast disease,' says Hei Leung, a plant expert at the IRRI.

Blast rice disease!

Different rice varieties planted in rows help stop the spread of disease. Image: IRRI

Rice blast evolves very quickly, but farmers can reduce its impact by planting different varieties of rice with different levels of resistance. The chances of rice blast evolving into a type which can overcome all these different varieties is very small. So farmers won't lose their whole crop if rice blast does appear.

Planting different types of rice in rows is easy and simple. The success of this idea has allowed poor rice growers not only to protect the environment but also to increase their incomes.

But rice isn't the only crop to benefit from careful selection of varieties.

Late blight

Spot the difference between blight-infected potato plants and the resistant ones. Image: David Shaw

Potatoes cost £40 million in Great Britain alone and several billions worldwide. To develop a range of blight-resistant potatoes using conventional breeding is tricky – but not impossible...

David Shaw, potato expert at the Sárvári Research Trust, explains how it's done: 'Researchers select the best blight-resistant potatoes from their screening programme. These promising potatoes are cloned and the clones undergo several years of field trials. Those that survive blight attack consistently, grow well and have no major defects can then be sold in shops.'

Tasty tatties

David Shaw, potato breeder, Sárvári Research Trust. Image: David Shaw

Breeding potatoes which are resistant to blight isn't the only tricky task. 'The problem is developing a potato which is resistant to blight and also looks good and tastes the way people want it to,' says Shaw.

'In the future people may have to learn to be less fussy about what their potatoes look like to make sure we can grow enough.'