Warmer winters are contributing to a dangerous build-up of crop pests in the cassava-producing region of southern Brazil, according to scientists at CIAT.
Potentially devastating pests such as the cassava mealybug, whitefly, lacebug and green mite – which were normally kept in check by occasional frosts and crop management practices – are now reported to be on the rise.
Cassava is a multi-million dollar industrial crop in Southern Brazil. Starch from the roots is used to supply industries from mining and cosmetics to food processing and textiles. Around 70 per cent of the crop is produced by smallholder farmers in the region, and processing factories employ thousands of people in rural areas.
CIAT research shows that average temperatures in south-central Brazil – encompassing the states of Mato Grosso Del Sur, Paraná, and Sao Paolo – have increased by 1.5 degrees Celsius since 1950, and continue to rise.
“That might not sound like much, but it can be the difference between having a frost or not,” explained CIAT entomologist and cassava pest expert Tony Bellotti, at the second meeting of the Global Cassava Partnership for the 21st Century (GCP21-II) in Kampala, Uganda, this week.
“Frosts help to break pest cycles, but without them the pests can survive through to the spring.”
According to Bellotti, there are other factors contributing to the increased vulnerability of cassava in Southern Brazil to pest outbreaks.
“With the year-round demand for starch, you increasingly see different generations of cassava being grown in overlapping cycles, often right next to each other in the field. This allows pests to pass from one generation of plants to another. You also see planting material – stakes cut from older cassava plants – being stored right next to plants growing in the field. Unless treated, these stakes can harbour the pests – meaning they’re just waiting to pounce.
“A common response to higher pest populations is the increased use of pesticides. But these are indiscriminate, often killing off the beneficial insects – the natural enemies of cassava pests, like certain spiders and parasitic wasps,” he continued. This can just make the situation more precarious.”
While cassava has been shown to be able to tough it out in difficult conditions that would kill other food crops – it can only survive up to a point.
“As warmer conditions begin to favour cassava production in new areas, farmers and industry need to be on the lookout for increased pest problems. This doesn’t just apply to South America, but also the present and potential future cassava zones of southern Africa and Asia.”