May 20, 2025
When Laurel Williams thinks of soursop, she thinks of ice cream. Not just any ice cream, but the one made from the soursop she grows on her farm in Grenada, a small island nation in the Caribbean Sea.
“I have this real affection for soursop,” she says. “You have all the medical side of it, there is so much goodness that comes out of soursop … for me, it’s ice cream.”
Soursop, a tropical fruit with a spiky exterior and sweet white flesh, is a culinary treasure for Grenadians. As well as for ice cream, they use it for cakes, juices, smoothies, even tea and margaritas. But it is also a profitable and heavily exported commodity.
Laurel Williams working in her field in Grenada, where she grows soursop and other fruits. Credit: Noah Friedman-Rudovsky / CABI
Grenada is the only country in the Caribbean authorised to export fresh soursop to the United States, where demand is increasing due its nutritional benefits.
According to the UN’s Food and Agriculture Organization, the fruit has become the largest source of foreign agricultural earnings for Grenada, valued at US$ 2.6 million.
However, the export potential of soursop hinges on it remaining free of pests, especially the Annona fruit borer and the soursop seed borer.
And in recent years, a new species has sparked concern among farmers and pest control authorities — a sucking insect known as croton scale that weakens the host plant by sucking sap.
Also known as the croton bug or croton beetle, the insect’s main host is the croton plant, but it also infests the shoots, leaves and fruits of mango, guava, plums, and soursop.
Williams is one of the Grenadian farmers who have lately seen this unwelcome visitor on their soursop trees.
“Less than a month ago, we identified five trees with the croton scale,” she says. “When we saw it, we immediately cut the branches off, bagged them and burnt them.”
Williams had heard about the pest in the last couple of years but says: “We had never seen it on our farm. It was something new to us.”
Hundreds of trees
In 2022 a number of other small-scale farmers reported that the pest had damaged hundreds of their trees.
One of them, Ryan Hall, says the appearance of croton scale on his farm was extremely worrying.
“I was wondering if it’s going to take over the farm and destroy it,” he says.
Croton scale, seen here on a soursop fruit in Grenada, can easily return after spraying with pesticides. Credit: Noah Friedman-Rudovsky / CABI
Within a few months, the bug had spread to about 500 of his 1,200 soursop trees, affecting the development of the fruit.
Grenada’s Ministry of Agriculture sought assistance and resources to study the pest and control it, without the need for chemical pesticides.
The programme is led by the Ministry of Agriculture along with the agricultural research organisation CABI (the parent organisation of SciDev.Net), through its PlantwisePlus programme, in collaboration with the Sandals Foundation, a non-profit linked to the Sandals holiday resorts.
It is part of a planned long-term project to help Caribbean countries act quickly and prevent pests from damaging biodiversity and farmers’ livelihoods.
No one knows exactly how the croton scale arrived in Grenada. Since it was first detected in Florida, US, in 2008, it has been reported in different Caribbean islands such as Barbados, Guadeloupe, Puerto Rico and The Bahamas.
Thaddeus Peters, the chief agricultural officer at the Ministry of Agriculture in Grenada, suspects it would have come in plant imports out of Florida.
But when they first saw the pest, in May 2020, Peters and his technical staff were not sure what it was. So they sent some samples to the Florida Department of Agriculture and a few days later they got confirmation — croton scale had arrived in the country.
Black soot
They quickly noticed that the scale spreads quickly. Females can live 60 days and lay up to 400 eggs. Once it lands on its preferred host, it reproduces rapidly and infests the younger part of the plant, the shoots and the softer tissues.
Females also produce large amounts of a sugary liquid known as honeydew, which creates an ideal home for a sticky, black fungus called sooty mold, which covers the surface of the plant.
“The quality of the plant deteriorates,” says Peters. “The fruit is not marketable and all you see is this black soot on your plant.”
This happened to Noreen Francique, a Grenadian farmer who grows aubergine, beans, cucumber, cabbage, sweet potatoes, and soursop to sell on the roadside outside her home.
“When the buyers come for it, it is being rejected,” she says.
Grenadian soursop farmers like Joy Pelius, pictured, are turning to natural solutions to tackle destructive pests. Credit: Noah Friedman-Rudovsky / CABI
“If we usually sell something like 500 pounds, sometimes it was 300 pounds because of the black spots.”
During 2020 and 2021, Grenada’s Pest Management Unit received multiple reports of croton scale, especially in the southern part of the island where almost every household was affected.
Pest control technicians initially used pesticides and oils extracted from the seeds of neem trees, which can destroy the insect by suffocating or desiccating its skin.
They used different products but found that the neem products were the quickest at removing the sooty mold. So they pushed the spray and most of the affected farmers saw a reduction of the pest.
“The control management came, they sprayed and they pruned and [the croton scale] gradually disappeared,” says Francique.
However, the challenge when it comes to pests is not only killing them but avoiding reinfestation or regrowth of the population.
Within a few months of the initial spraying, many farmers were calling pest control again because the croton scale had returned.
Another generation
Peters explains that regrowth happens because of the reproduction of the insect. The body of the adult usually covers the younger ones. So when sprayed, the adult will die but the younger ones will emerge and start another generation almost immediately.
“This means that once you kill the adults, in a few days you need to go back quickly to attack the new ones that were initially protected,” he says.
The treatment became a real challenge for the Pest Management Unit, which only had four people spraying each day. There were around 30 farms growing soursop, and at least half of them were asking for assistance.
“Most farmers relied on us to visit their farms and spray their soursops,” says Francis Noel, pest management officer at Grenada’s Ministry of Agriculture.
“It’s always difficult because farms are all over the island.”
Peters adds: “What we had, in terms of people and time, wasn’t enough. We always knew we had to get into biological control.”
Grenadian farmer Noreen Francique sells fruit and vegetables on the roadside outside her home. Credit: Noah Friedman-Rudovsky / CABI
Biological control means using natural enemies of pests to manage invasive species populations without relying on chemical pesticides.
They can be predators that feed on other animals for survival, parasitoids that lay eggs on a host and then kill the host, leaving their eggs inside, or entomopathogens, which invade and reproduce in insects, spreading to infect other insects.
Mealybug
In the mid-1990s, a pest known as the pink hibiscus mealybug had a devastating impact on the agriculture, biodiversity and tourism of Grenada.
The total reported losses of the outbreak for the Caribbean came US$138 million, excluding pest control costs and lost exports.
So, the Grenadian Ministry of Agriculture teamed up with CABI to find natural enemies. They used wasps, and imported 25,000 ladybird beetles, which turned out to be very skilled at eating the mealybug. The pink hibiscus mealybug was controlled.
Thirty years after that outbreak, staff from the Pest Management Unit suspected there were natural enemies controlling the croton scale.
“We needed to make sure they were there, because if you don’t know then you’re just walking in the dark,” Noel says.
Surprisingly, one of the confirmed natural enemies of croton scale was the same ladybird beetle that was used to reduce the pink hibiscus mealybug.
Naitram Ramnanan, CABI’s regional representative for the Caribbean, explains that natural enemies can remain in the environment and persist for decades. “The … beetle is still there and working to control this new pest,” he says.
But the ladybird was not the only biological control. The CABI technicians that visited Grenada helped to collect and identify other natural enemies like parasitic wasps and even a moth.
Knowing the specific species that work as natural enemies of croton scale has been crucial.
Now, the Pest Management Unit can help to spread them quickly either by moving them from one field to the next one, or by collecting samples, waiting for them to emerge in the lab and taking them back to the farms.
It also saves on resources because technicians don’t have to go to the farms to spray every three months.
Microscope
As the pest management officer, Noel visits lots of farms in Grenada. He hears from farmers about how their crops are doing, how much they have been pruned or sprayed, and how they have assessed the presence of pests.
“Whenever I see something that I’m not familiar with, I pick up the phone and call him immediately,” says Williams.
Francis says it’s about building communication and confidence. “When we come to a farm, we usually engage [farmers] in discussions and let them know what is going on and why we don’t want to overdo the treatments.”
One of the key points that both technicians and farmers have learned is that biological control only works if there is a pest. The natural enemies don’t eradicate a pest, they just keep it under control.
“So you still need to maintain a certain level of infestation in the field, because that is how natural enemies work,” says Noel.
“So we explain to them that if they see an infestation, not to panic.”
The recommendation is also not to use toxic pesticides, which could kill the natural enemies. “We don’t want to destroy what is working for us”, he adds.
The programme has helped train farmers about biological controls and rational pesticide use, so they can monitor their own farms, check on the presence of natural enemies in their own farms, and ask for technical assistance only when they see a major problem.
Peters acknowledges that one of the main challenges in talking about natural enemies is that some of them — like the parasitic wasps, which can be less than 1mm in length — are so tiny that people wouldn’t believe they really exist.
Last year officials met with farmers so that they could finally see them. “We brought the samples, the microscopes and the magnifiers, so people could see them. People were amazed,” Peters adds.
Trust Fund
CABI’s next step is to attract donor support for a Caribbean Invasive Species Trust Fund to independently mobilise and manage financial resources for invasive species management and to strengthen capacity for developing strategies.
Noel Francis (right), from the Ministry of Agriculture in Grenada, with a local farmer who is battling croton scale with assistance from CABI. Credit: Noah Friedman-Rudovsky / CABI
In the current conditions, with weak biosecurity and surveillance “inevitably once a species gets introduced to any one of the Caribbean islands, they will spread to others”, Ramnanan warns.
And even when invasive species are controlled, sites need to be constantly monitored. “We can’t start a great [pest management] project today and then walk away from it. It has to be continuous,” adds Arica Hill, former executive director of the Environmental Awareness Group (EAG) in Antigua and Barbuda and current Caribbean lead for conservation charity Fauna & Flora.
Ramnanan adds: “We’ve seen repeatedly that once the project stops and the sustained funding goes out, the problems reoccur.”
It is hoped the trust fund could help the Caribbean have a quick and sustained response to any new invasive species outbreak.
Ramnanan says it could also allow Caribbean countries to train and keep technicians monitoring vulnerable sites, or to employ scientists to look for biological control solutions.
“We can do much more,” he adds. “We can make a huge difference in managing the invasive species problem in the Caribbean.”
This article is supported by PlantwisePlus, a CABI-led global programme to help countries predict, prevent and prepare themselves for plant health threats – thereby ensuring farmers reduce their crop losses and produce the quantity of food required and also to improve the quality of food grown, in the face of a changing climate.
This piece was produced by SciDev.Net’s Latin America and the Caribbean desk.
