Pest management by smallholders

Barn owl shot by farmers; an unfortunate action showing farmers' lack of knowledge

Barn owl shot by farmers; an unfortunate action showing an unfortunate lack of knowledge

After a few weeks without a post, it was about time to write a new story from the field. I visited Bah Lias Research Station, part of London Sumatra Bioscience, one of the oldest plantation companies in Sumatra. A lot of fascinating oil palm research is carried out on that station, and it is also a very pleasant place to be. People often complain about palm oil being a monoculture and all that, but still, plantations can be very charming places to visit. Cool, quiet, with lots of insects and birds humming and flapping and buzzing around; it’s rural life but with plenty of comforts. I’ve visited Bah Lias two times before, and I’ve always been welcomed very warmly and kindly by the researchers and other staff. It’s definitely one of my favourite places in Indonesia!

My story is not really about Bah Lias, but more about two people I met there, who were both oil palm researchers as well. We had such interesting conversations about pests in oil palm, and what I really liked is that they knew especially much about biological control of important pests. So I’ll start with a short discussion on environmental pressure caused by the use of fertilisers and pesticides in oil palm plantations, and then I’ll move on to the alternatives for using pesticides, and why these alternatives are important for smallholders.

Fertilisers in oil palm plantations

Fertilisers from oil palm plantations can cause environmental damage if used in the wrong way. Nitrogen, potassium and magnesium easily dissolve in rain water and then flow down through the soil towards the ground water. Leaching is the process where the nutrients enter the ground water instead of being taken up by the plant. It is impossible to prevent all leaching, especially in tropical countries where the rainfall is so intense. But it can be reduced in several ways, for example by applying the fertilisers in small amounts at a time, rather than all at once, and by applying them at the place where the plant roots are most dense. Nitrogen can also evaporate into the atmosphere, contributing to air pollution and global warming. This can be prevented by applying the fertilisers just before rain, so that the nitrogen dissolves into the water and enters the soil right away. Phosphorus, which causes algal blooms (eutrophication) in water, can easily be lost through surface runoff, when large amounts of rainfall wash the top soil with freshly applied fertilisers away from the plantation and into rivers, streams or canals.

A good soil cover, erosion control measures, and a balanced use of fertilisers are all important ways to protect the environment and improve the profitability of the plantation. Smallholders can learn, with the right training, to create a soil cover and to follow good fertilisation practices, as it is not rocket science at all. But to really get the right fertiliser balance, it is common practice to collect leaf samples and check for the nutrient concentration in the plant. Bah Lias Research Station has a laboratory for the analysis of soil and leave samples, and there are also a number of long-term fertiliser trials being carried out. These trials provide important information about the optimum fertiliser balance for oil palm.

Drying soil samples; note the variety of colours!

Drying soil samples; note the variety of colours!

Pesticides in oil palm

Pesticides used in oil palm can cause very severe contamination of waterways, and several rivers in Indonesia are now seriously affected. It is considered good practice in plantations to wait for a while with spraying when an outbreak of pests is observed, but nevertheless pesticides are a big environmental problem. For me, the use of pesticides by smallholders is a difficult issue. On the one hand, I would be sad to see farmers lose their source of income because of an uncontrolled pest. In the area where I was last week, for example, the plantations are well maintained but a caterpillar plague has been causing damage over the last three months, and it may get worse unless the smallholders take action. On the other hand, I have observed again and again that the farmers are not interested in taking proper safety measures, even when they know it is important to use a mask, gloves, etc. When using herbicides, this can already be a problem, as it seems that even glyphosate may be more harmful than previously thought. But pesticides are usually far more toxic, and in addition, the application is more complicated. Luckily pest outbreaks in mature oil palm plantations in Indonesia are uncommon. For now I am happy not to train my farmers in the use of pesticides, and I would like to stick to that approach, but in case of an outbreak such as I observed last week, I am hesitating. It’s a difficult issue!

Either way, in the guest house of Bah Lias Research Station, I met with two visiting phytopathologists. They are the people who specialise in plant diseases, and, in this case, also in plant pests. Oil palms rarely die from pest attacks once they are mature (say, more than three years old) but the young trees are actually quite vulnerable, especially to rhinoceros beetle (Oryctes rhinoceros) and rats (Rattus spp.). Both of these pests can really destroy young plantations.

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Oryctes rhinoceros

The rhinoceros beetle is a big black or dark brown beetle with a horn on its ‘nose’ (hence the name). It likes to eat developing leaves of oil palms and coconut palms. The beetle digs a way into the heart of the palm and then just sits there, eating holes. When the palms are older, the leaves are usually large and strong enough to survive, and, even if one leaf dies, the next one will still be okay. But in young trees the beetles can eat through the entire growing point, and without that the palm dies. Actually, most plants have multiple growing points, so if one growing point is destroyed, the others just keep developing, or new growing points are formed. In an oak tree for example, if one branch breaks off, other branches grow from different places. But monocotyledons, such as palms and grasses, have only one above-ground growing point, located safely in the middle of all the surrounding leaves. If that one is killed, the plant can no longer produce new leaves and it will die. To deal with this, many grasses and also banana palms grow new shoots from underground, which then appear around the ‘mother plant’, but oil palm cannot do this. In that sense it is quite vulnerable.

Rats do the same thing as rhinoceros beetles: they eat the fresh shoot of the young oil palm and can easily kill the tree. In older plantations, they mostly eat the fruits, so the yield is reduced but the palms aren’t damaged.

The easiest way to kill rats is by using toxic baits. In some oil palm plantations, this is normal practice, but it needs to be done every half a year in order to really keep the rat population under control. That’s because rats can double their population every eight weeks, which is really fast! So, it is no use baiting rats in a smallholder field: as soon as most of the rats are dead, a few families from the surrounding plots will move in, and two months later the population is back to normal. Unless all the farmers in a large area work together, it is quite pointless. In addition, there are goats, cows, dogs, cats, children and workers going in and out the plantation, so putting toxic baits all around is quite risky. It’s not something I would recommend, but I can see that the rats do a lot of damage. What to do?

The answer is: barn owls. One of the two researchers I met had done several barn owl introduction projects with smallholders and he was able to give me some useful tips. For example, it is necessary to build breeding boxes for the owls, and he knew a relatively easy design which we could use. He also suggested to start with a larger number of boxes than is usually recommended, which is nice because it means many farmers can have their own box, and feel more ‘involved’ with their owls. This is important because currently the farmers are still hunting the owls, not realising that they are the one animal that can effectively help them to control the rat plagues that are causing so much damage.
Barn owls are fascinatingly beautiful creatures, and I think it really adds something to integrate these great predators in the oil palm agro-ecosystem. They are also very functional, 100% organic, and quite cuddly as well, especially the chicks. Perfect!


Barn owl chicks :). Source:

The rhino beetle can also be controlled without pesticides, and there are actually several methods. The beetles fly at night and are attracted to light, so one way to control them is to place traps around lights, which work a bit like wasp traps. The beetles are attracted to the light and fall into a bucket under the light, from which they can’t get out again; voila! Similarly, it is possible to use pheromones to attract the beetles to traps. Or, nets can be placed in strategic ways, for example between the trees and a light, and the beetles will fly into the nets and get stuck. Sad for the beetles, but good for the farmers. If the methods above are combined with the removal of all rotting wood, where the beetles like to breed, then it is possible in many cases to manage the rhinoceros beetle without using chemical pesticides.

For control of other oil palm pests and diseases, biological control measures are also being developed, often by research departments of plantation companies. It would be really interesting to visit some more companies and find the practices that are most suitable for implementation in smallholder plantations.

I’m looking forward to a chance to start introducing owls in the areas where I work!


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2 Responses to Pest management by smallholders

  1. WoWt!er says:

    Bah Lias, those were the days.
    Pay them my warmest regards next time you visit them again.

  2. Lycke says:

    Interesting story again sis :)!

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