May 20, 2019

What Is Witches’ Broom & How Does It Affect Cacao?


Like any other plant, cacao is vulnerable to pests and diseases. One of the most damaging infections is witches’ broom, an aggressive fungus that can kill the tree and wipe out whole farms. In the 1980s, the disease devastated Brazil’s cacao production and it’s never far from producers’ minds.

Let’s take a look at what witches’ broom is and how cacao farmers can handle it.

Lee este artículo en español ¿Qué es la Escoba de Bruja y Cómo Afecta al Cacao?

Arataca, Bahía, Brazil, one of the areas hit hard by witches’ broom in the 1990s. Credit: Tuta Aquino

A Brief History of Witches’ Broom

Today, most of the world’s cacao is produced in Côte d’Ivoire and Ghana. But as recently as the early 1990s, Brazil was also a major producer. Then a fungus ran rampant through the nation’s cacao plantations and the industry was decimated. The fungus responsible was Moniliopthora perniciosa, more commonly known as witches’ broom (or, sometimes, witch’s broom).

Cacao producers were familiar with the fungus, which is indigenous to the Amazon basin. But the outbreak in the Bahía region spread more rapidly than ever seen before. It’s reported that cacao output fell from 390,000 metric tons in 1988 to 123,000 metric tons in 2000.

There is some evidence that the outbreak of witches’ broom in Bahía was intentional. Some have even termed it bioterrorism. Tuta Aquino is a cacao farmer at Vale Potumuju in Bahía. He says, “I’m convinced it was brought to the region and deliberately spread in our plantations.”

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Cacao pods spoiled by witches’ broom. Credit: Tuta Aquino

How Witches’ Broom Attacks

Witches’ broom is a hemibiotrophic fungus, meaning that it functions in two stages. In the biotrophic stage, the tiny fungus spores enter healthy cacao trees through surface wounds or small gaps.

The fungus extends tendril-like mycelia in between the cells of the plant and it feeds on the living tissue. The infected shoots morph into swollen spindly stalks, or the “brooms” that the fungus is named for. The fungus diverts the plant’s energy away from effective growth and eventually causes cell death.

The necrotrophic phase takes place two to three months after infection. The mycelia start to feed on the dead plant cells and the brooms change from green to brown, commonly known as dry brooms. Infected pods show rotten spots and they’re likely useless for consumption or to grow new trees.

Finally, when temperature and humidity levels are at the right point, dramatic pink basidiocarps (mushroom fruiting bodies) form and release new spores. In the humid Amazonian climates, conditions are perfect for them to flourish and spread quickly.

The broom shaped stalks of an infected tree. Credit: Tuta Aquino

Tackling Witches’ Broom

When witches’ broom broke out in Bahía in the early 1990s, Brazilian cacao agency CEPLAC advised producers to raze their crops. Entire forests were destroyed to prevent the spread of the fungus, and farmers took out loans to cover the losses of their crops. This left many in deep debt. The Financial Times reports that the collapse of the industry cost an estimated 200,000 jobs.

Because there is no cure or effective treatment for witches’ broom, producers must focus on prevention. Tuta tells me that “the pruning is the main thing you have to do… All the dead leaves, all the new sprouting of the brooms, you clip them out.”

Cacao pods infected by witches’ broom. Credit: Tuta Aquino

Many producers treat pruned material with Tricovab, a competitor fungus formulated by CEPLAC and released in 2013. But some producers are cautious about the effectiveness of the product. Tuta says that “[CEPLAC]’s research is done at their farm with 500 plants… that’s not real life.”

Witches’ broom has proved resistant to copper-based fungicides, though there is some evidence that these fungicides reduce the number of affected pods.

Using Tricovab and taking on labour to effectively monitor and prune trees adds to the cost of cacao production. And even if a producer is vigilant, the spores spread so easily that crops can quickly become reinfected. Tuta says, “If across the river your neighbor doesn’t do it, the wind blows it over, and all of your work [is ruined].”

Cacao beans drying. Credit: Miguel Regalado

Genetic Resistance

So what can producers do to protect their crops from witches’ broom? For farmers starting from scratch, choosing varieties with genetic resistance is an important consideration. In the 1970s, a high-yield strain of cacao resistant to witches broom was developed in Ecuador. The problem is that this CCN-51 strain has a reputation for subpar flavour. For producers looking to sell to specialty chocolate-makers, this is a real concern.

But Nicaraguan cacao producer and exporter Gustavo Cerna pushes back against the reputation. He tells me, “If you don’t have good post-harvest practices, quality isn’t there” but that “as with coffee, you can bring out good attributes with good post-harvest practices”.

He makes a comparison with the coffee variety Catimor, which is known for its resistance to coffee leaf rust more than its cup quality. He points out that in the 2017 Nicaragua Cup of Excellence auctions, a Catimor scored 90.5 points.

Gustavo says that it’s too early to conclude that CCN-51 can’t taste good, telling me, “I don’t think we should be gauging the quality of the product because we haven’t tested or experimented with any of the harvesting or post-harvest practices.”

Cacao beans in a fermentation box. Credit: Tuta Aquino

Even if a producer chooses to plant a resistant variety, maintaining genetic purity is a difficult task. Cacao is “self-incompatible”, meaning that it requires cross-pollination from a different cacao plant to produce fertilised seeds. This is good for genetic diversity, but bad for farmers who want to maintain genetics for quality, productivity, or resistance purposes. Therefore, some producers choose to use cloning to ensure genetic traceability.

Farmers can spend less money upfront by planting cacao seeds, but will quickly lose control of the genetic purity of their orchard because of cross-pollination. Or they can spend more money for certified clones which will provide stability over the long run.

Gustavo tells me that a standardised orchard simplifies life for the farmer. “You will be able to have uniform pruning and uniform fertiliser management,” he says. This means production and processing is more consistent and the final product is more uniform.

Cacao trees that have cross-pollinated will grow at different rates and sizes and mature at different times. “If you have a salad mix of different varieties, it just becomes harder and more expensive, and it’s not productive in the long term,” Gustavo says. And of course, any genetic resistance to witches’ broom and other diseases is likely to be reduced.

A view from Tuta Aquino’s farm, Vale Potumuju, in Bahía, Brazil. Credit: Tuta Aquino

Good Practices For Prevention

In Brazil, many producers used the traditional cabruca system, which recreates the natural conditions of the Amazon basin. “The cabruca system is where you plant the cacao trees under the shade of forest trees,” Tuta tells me.

It’s ideal for cacao and beneficial for biodiversity. But what is good for cacao is also good for witches’ broom. When the fungus took hold in Bahía, the cabruca system was seen as a liability.

Today, cacao producers are adapting their cultivation practices. Gustavo tells me that in the eastern parts of Nicaragua, where land is cheap and rainfall plentiful, farmers are planting with more space between trees to mitigate the risk of infection and spread. “They’re not allowing the plants to interlapse with one another,” he says, “so there is always a dry environment around them. The main drawback is that you cover more land.”

Healthy cacao pods on a tree. Credit: Miguel Regalado

Gustavo is taking a different approach. “We’re looking to plant cacao in the driest area we can find in Nicaragua. As long as the soil’s good and we have cheap access to water, we’ll plant cacao there,” he says.

This method reduces risk because fungus spores germinate in humidity. Witches’ broom may still be present, but will stay dormant without the right level of moisture. Irrigation allows farmers more control over the amount of water the plants receive.

Gustavo tells me that small-scale farmers need to cooperate since one mismanaged farm can infect all nearby ones. He also says that governments or other agencies need to provide technological innovation and support to producers to tackle witches’ broom, and these agencies and farmers need financial support.

A cacao tree affected by witches’ broom. Credit: Tuta Aquino

Preparing For Future Outbreaks

Preventative methods add costs to production. In relation to this, Gustavo tells me that the world’s top cacao-producing region, West Africa, is at risk of an outbreak of witches’ broom. “The risk is high. You have a lot of smallholder farmers that are not following good practices, with very, very old trees… There’s not a lot of innovation happening, so the risk is huge,” he says.

Producers in Côte d’Ivoire and Ghana don’t have the resources to invest in new crops and implement best practices. Gustavo acknowledges this, saying that “the return to farmer percentage of the FOB [price] is really low in West Africa. It’s extremely low.” This means that the producers who are already seeing the least return on their work are the most vulnerable to devastation by witches’ broom.

“We’re preparing for disaster,” Gustavo says, meaning that Nicaragua is readying its production to fill the gap that a collapse in the West African cocoa industry would bring.

Cacao is also making a resurgence in Brazil. Tuta tells me that it simply isn’t profitable to grow cacao for commodity, but that with a growth in bean-to-bar chocolate-makers as well as new focus on quality genetics and post-harvest practices, there is hope.

“Brazil has the opportunity now to really turn this horrible page and now introduce not only resistant but productive and good flavour profile varieties,” he says. “That’s the only way I see to survive as a [cacao] farmer.”

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Written by Zach Latimore.

PDG Cacao

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