IPM scientists combat pest of highly prized cacao in Ecuador

Rachel Melnick learned one thing about spending long days in Ecuadoran cacao orchards: do not work past 4:00 pm. “Once, we made the mistake of working past 4 pm in the field. We quickly realized why no one did this – that is when all of the mosquitoes come out!”

Rachel Melnick working in Ecuadoran cacao orchards.
Rachel Melnick working in Ecuadoran cacao orchards.

Working with Penn State plant pathologist Paul Backman, Melnick, a graduate student, is studying how to use beneficial bacteria to fight diseases that attack the cacao trees. The program is part of the IPM IL, funded by USAID and managed by the Office of International Research, Education and Development at Virginia Tech.

The cacao tree, of course, is the plant from which we get cocoa, the foundational component of chocolate. And chocolate is big business in Ecuador and becoming more so by the day.

In 2009, Ecuadoran President Raphael Correa began an initiative to expand the production of cacao in the country by having 50,000 additional hectares – the equivalent of 123,550 acres – planted with cacao. This venture alone will require the planting of at least 50 million new cacao shoots, according to Backman.

However, a serious pest has wreaked havoc on cocoa production in Ecuador in recent years. Witches’ broom, a fungus disease caused by Moniliophthora perniciosa, has devastated the cacao industry in Latin America. Witches’ broom arrived in Ecuador in 1918, and since then has catastrophically affected the cacao production – reducing output by 50 to 90 percent.

Melnick and Backman sprayed bacterial treatments on developing cacao pods as biological control agents, an environmentally effective way to reduce pests through the use of natural enemies. “I sprayed the bacteria onto the cacao trees with an adjuvant – a connecting agent – that allowed the bacteria to colonize the internal tissue of the tree. From there, it could be a natural enemy to the fungal diseases,” Melnick said.

The bacteria is robust; it was applied a few hours before a rainfall and survived after the rainfall both on the surface and inside the cacao pods. These results are encouraging because they indicate that the bacteria will be able to persist through Ecuador’s rainy season.

Although none of the trials reduced pod disease for a whole season, there was significant suppression and delay in the development of infections that lasted through mid-season. “We were really excited the day we learned it reduced the disease,” Melnick said. “It had never been reduced before.” For the struggling cacao, the news was even better: Application of one of the bacteria reduced witches’ broom on the leaves and stems throughout the entire rainy season.

The researchers have been very successful so far. They have developed methods to reproduce cacao that can be used by both large and small scale production facilities and allows for the use of materials and technologies that are available to farmers. Furthermore, interesting results have surfaced from other IPM trials showing that intercropping cacao with plantain reduced diseases on both crops, and also reduced nematodes (microscopic roundworms) that were attacking plantain. One of the trials also indicated suppression of black pod rot, which is a disease that is responsible for the most significant losses in cacao worldwide.

Melnick, the key researcher for this project, has completed her Ph.D. and accepted a post-doctoral position at the United States Department of Agriculture, Agricultural Research Service, Sustainable Perennial Crops Lab in Beltsville, Maryland, where she plans to continue her work on cacao disease control.

Melnick worked long hours while in the field in Ecuador. In addition to not staying out past 4:00 pm, she also learned to bring lots of sun block!

IPM scientists combat pest of highly prized cacao in Ecuador