Banana is the number four food crop in the world after wheat, maize and rice. Only 15 percent of global production (75 percent produced in Latin America and the Carribean) is exported, showing its importance to local communities and domestic food consumption.

Plantations around the world have been hit by black Sigatoka, an airborne fungus. In addition to this destructive disease, Asian countries and three South American countries are affected by Panama disease (Fusarium oxysporum f.sp. cubense tropical race 4, abbrev. TR4), a Fusarium fungus that can destroy plantations and contaminate soils, rendering them unsuitable for banana production for at least 20 years.

Farmers have increasingly reached for more chemical products to combat these diseases, but biocontrol products could offer a solution as well as providing longer term benefit in building resilience in soils.

New AG International spoke to Lieselot Van der Veken of Pro Terra-Agro, who has spent the last 20 years of her career studying this vital crop, building an in-depth knowledge of Central and South America.

New AG International (NAI): To begin with, please tell us a little bit more about the problem – what are the main diseases banana growers face globally, have there been new diseases in recent years and how do they spread?

Lieselot Van der Veken (LVdV): The main disease globally in banana is black Sigatoka a fungal leaf disease. It’s an airborne disease that attacks the leaves and then renders the leaves insufficiently productive to photosynthesize, so you have a yield loss attached to it and premature ripening, which is huge problem in transport. This is the most widespread disease where in terms of pesticide budgets, it’s the biggest cost to farmers. It’s present almost everywhere in the world, except for Peru for now, because it’s a desert area and quite dry.

The pressure of black Sigatoka is very much linked with rainfall conditions. That means that to be able to produce organic bananas, you must go to areas where the rainfall is less than 400 millimetres on a yearly basis to be able to control your black Sigatoka in an organic way. That’s how the organic banana production is actually situated around the world, just through the precipitation levels.

Then there is the Panama disease, tropical race 4 (TR4). That’s the Panama disease, Fusarium, so that’s a vascular disease, which is very devastating. The growers in the east of the world, India and all the eastern parts of the world, Philippines, which is of course the centre of origin of banana, have been suffering from that for many years. Since it’s a vascular xylem blocker, it just terminates the plantation when there is not enough soil biology present. It causes a wilting of the plant, through the blocking of the vascular system of the plant. The progressive wilting and other symptoms don’t allow you to produce anymore in the field. Also, the spores stay around for 15 to 20 years in your soil. So that means a huge loss of investment in capital in terms of banana production, unless you have some management strategy in place, which involve creating “living soils” to prevent this disease from having its own party in what we might call “dead soils” in conventional systems.

So, they are the main two diseases, and then there are some insect pests that are more specific to areas and periods, so bit more punctual in the banana growing season and climate related.

NAI: How do those fungal diseases spread? What added long-term problems can they cause?

LVdV: Black Sigatoka spreads by ascospores carried on the wind. The disease has an asexual-sexual cycle, so growers tend to cut off the affected leaves. The leaf material that stays on the ground can also carry the spores. But since it’s so labour intensive to remove all those leaves, they tend not to do this.

Some have tried to find a business model for these old leaves. They provide organic fibre, but they are also a source of this foliar fungus.

The Fusarium spreads in a different way, by its spores in soil and infected plant material and attaching itself to animals, or even equipment. This has been the case in spreading the disease from Asia to Central America and then Latin America. When we had the first report in Colombia and then Peru, it apparently had something to do with a bulldozer that came from Asia to do some farming works. There’s a lot of pathways, so that makes it really hard to contain, and if you go to banana producing countries, in the airport you will see signs asking for help in preventing TR4. Even shoes can be a source of contamination.

NAI: So why is TR4 difficult to treat?

LVdV: It’s a vascular disease, meaning that it gets inside the plants. Why does it get easily inside of the plants? It doesn’t have its own equipment to do so, so the fungus enters via damaged roots. Damaged roots can be caused by weevils or by nematodes. Or by equipment causing damage to the roots by aerating the soil, which is not so often done.

Fusarium is a secondary disease – it comes into the plant by openings that are already there. Its origin was as an endophytic fungus, meaning there are Fusarium strains that actually provide profit to plants in terms of growth promotion. I’ve seen it in trials. Originally it must have been a co-evolution between the plants and the fungus. That’s why the plant lets it enter and once it enters the vascular system, it is able to grow there.

Under the pressure of pesticides and systemic fungicides to treat black Sigatoka, our hypothesis is that this fungus has been under a lot of stress chemically and it has switched on its pathogenicity genes. The plant is tricked in a way because it’s a fungus that is adapted to growing in the vascular system. Once it’s in the vascular system, it is hard to treat the fungus chemically because you won’t be injecting your plants with chemicals.

It’s really a kind of an endpoint in our conventional programs in treating Fusarium. It’s not only a problem in banana, you see it in most of the intensively grown crops.

We see lettuce or fruiting vegetables like a tomato and sweet pepper coping with Fusarium but it’s usually a bit of an endpoint in the sense when your soil is really in a bad condition and not a lot of life anymore around, then the crop becomes sensitive and under pressure from your fungicide. You get yourself a strain that is pathogenic instead of helping your plant out.

Biologically speaking, this fungus doesn’t even have the apparatus that other pathogenic fungi have in order to penetrate the roots. This means that it has always been able to enter the roots through existing holes and that the plant has allowed it. It never switched on its defense system and has benefited from growth promotion.

NAI: What are other aspects of fertilization can encourage pests and diseases?

LVdV: If we talk black Sigatoka, so a foliar fungus growing on your leaf tissue, the usual fungal pathogens or insects come and feed on a plant because they are in search for nitrogen, for example. But they have to find it in a digestible way for them. So, with our current fertilizer systems being nitrate and urea being applied, we get a very incomplete amino acid incorporated into our leaves, which makes it highly digestible for pest and diseases.

It’s known with big agro producers in banana that they have to be careful with their nitrate fertilizer because otherwise they know that the black Sigatoka really gets out of control, so it’s something that has been observed for years in the field and the people know.

NAI: Tell us about biocontrol treatments that you have either worked with or researched, and how effective have those biocontrol treatments been?

LVdV: Typically when we have foliar diseases, we look for a mycoparasitic organism, which can be a Trichoderma that’s used in grape on fungal diseases, or botanical that eradicates bacteria or diseases, such as neem or tea tree oil.

Among the disinfectant, oily substances that can be used against black Sigatoka today, the biggest product is paraffinic oil that is allowed in organic agriculture. It has a fungistatic effect, and that’s how they rotate with biologicals, like for example the botanicals. Or, if you go for something living in an organic system, that might be a Bacillus bacteria. Some Bacillus species produce lepidopeptides that induce the plant’s resistance and also kill off the fungal disease on your leaf surface.

These products are applied by air over the plantation. Depending on the pressure, it’s sometimes twice a week, such as in Costa Rica, where there are high levels of precipitation. Usually it’s every 10 days or every two weeks, depending on precipitation levels.

NAI: Can you clarify the importance of precipitation levels?

LVdV: The germination of the fungus goes faster and you get a faster disease cycle and thus a higher disease pressure at higher precipitation levels.

Another approach that we’ve seen in the field involves biological nitrogen. The workers in the plantation came to see me to discuss what I had used because they had observed that in the plots where we had used free-living, nitrogen bacteria, the plots were much less affected by the black Sigatoka.

This confirmed my hypothesis, and it’s also not only my hypothesis, but we start to see that if we feed simple nitrogen to plants, then they become very prone to pests and diseases. And we get into a vicious cycle because then you need the chemical pesticides to treat the pests and diseases.

NAI: Do you see a place for integrated pest management (IPM) that uses chemistry and biocontrol?

LVdV: I’m convinced that it’s a transition that needs to happen towards more resilient, more biodiverse banana cropping systems, and it’s a stepwise approach. I’m sure that there will be a stepwise approach to first botanicals, which are easy transition products because basically they are from natural origin. They also eradicate just like we are used to with chemicals in a farmer’s mindset.

That’s the first phase of our transition, and by the time the farmers get the confidence and the experience with our biologicals, our system can be more conducive to life stepwise as well. Since we have less harsh chemicals, all the biocontrol agents you insert or you bring into the system have a higher chance to actually proliferate and do their job properly.

For sure it won’t be overnight; let’s say a switch from conventional chemical inputs to all of a sudden a regenerative approach, or organic system at the other end of the spectrum.

NAI: Is it likely that chemistry will be required along with biocontrol in the near future?

LVdV: I’ve worked for seven years alongside some organic banana farmers and they actually reached the same production potential as they would reach conventionally, being 3,000 boxes per hectare, which is a good production if we talk about the Caribbean area.

You can actually do the job and do it in a way that is profitable for the farmers, reducing their input costs. So, it’s no longer an argument to say we have to keep doing it the way we do it, because otherwise it’s not profitable.

NAI: The organic farmers that you mentioned, are they using manure from local farms?

LVdV: The farm I was talking about is 200 hectares, so it’s not a small farm. What they basically do is the same management principles of a conventional farm but replace the input for an organic one and manage it that way. That means if you go with biofertilizer instead of mineral fertilizer, that means applying your fertilizer a bit earlier because it’s a slow release.

Typically, organic fertilizer is slow release, so it requires some adaptations of your management in terms of timing of application, and you feed your soil microbes, which in turn feed your plant.

They substitute their inputs with organic inputs where possible, but not everybody has access to that.

NAI: In terms of phosphorus and potash potassium, is that coming from manure as such?

LVdV: The farms I was working with had an organic fertilizer – an NPK from organic origins, and from what I understand it includes animal origins, such as feather, bloodmeal, the bones, so all the waste of animal slaughtering.

And also cocoa pods. Let’s say waste streams that you put into a granule, just as if it were a mineral granule.

NAI: What’s in the pipeline for biocontrol products, and what innovation are you seeing that excites you?

LVdV: What I am seeing is that biocontrol companies have become aware of the outdoors, because historically we were born in greenhouses as a biocontrol industry in terms of natural enemies, and then microbials are being used. If I talk about Latin America, there is more of a history of using microbials than macrobials.

More and more companies are becoming aware of better formulations. There is, for example, better Bacillus species or strains coming on the market, and a combination of Bacilli that are coming on the market for leaf application where we see very good results against black Sigatoka comparable with chemicals.

Not only the soil has a microbiome, but also the leaves have a phyllo sphere microbiome. So, if we can work with living preparates, adding biodiversity that is functional for a system in eradicating pathogens, then we have a gain in biodiversity and a control or management of our disease, which is a double win compared to something that eradicates the disease and maybe has a lot of collateral damage around it as well.

As a first step, I would see these botanicals being a transition product for these fungal leaf diseases in a rotation, and stepwise we can go towards a more biological system where also a Bacillus would grow well or Trichoderma can grow well and actually make sure that your leave surface gets covered again with a good microbiome to protect itself.

Drone Use in Banana Plantations

NAI: Do have you had any experience using drones for either broadcasting a biocontrol product or possibly surveying the health of a crop?

LVdV: Yes, we do. We are thankful for this technology advancing because banana farms can be 200 to 900 hectares.

In Central America, a drone is developed where we can spread predatory mites against the banana rust thrips, which is attacking very heavily there and damages the fruit.

It does not damage the nutritional value of the fruit, but due to aesthetical damage there is no market acceptance. The rust thrips produce brownish blemish on the fruits, which is not accepted. To control these thrips, we can just add predatory mites at a rate of one hectare a minute by drone, so that makes it very feasible also to apply biocontrol in these outdoor crops. The nice thing is that we see our predatory mites establishing in the crop when not too many chemicals are being used.

NAI: And microbials you can apply by drone as well and what?

LVdV: Yes, there has been some examples of microbials being applied as a powder since they drop on the leaf and the leaf surface is moist. It’s tropical humid conditions.

When it’s a liquid that you want to apply, you usually use an airplane and that’s really the way to do it. It’s a kind of ultra-low volume. You create a mist.

This article was featured in our March/April 2024 issue of New AG International.