Personally, I do not like the term “pest” very much, as it reflects our narrow perspective on things. At the Center for Sustainable Development Studies, we have about 2.5 hectares of land dominated by 2 exotic tree species (oranges and mangoes, both originally from Asia). Both are fairly well adapted to the seasonal tropical climate, but without human intervention, the surrounding semi-deciduous tropical forest would take over the place in a few years. What is nature supposed to do? Of course it will send us “pests and diseases” in the form of fruit flies, rust mites, leaf cutter ants, scale bugs, beetles, caterpillars, and all sorts of fungi to make room for a far more diverse, productive, and native vegetation. On the other hand, fresh orange juice and ripe mangoes picked right from the tree are really great. And besides that, these fruits are an important source of income in this area, because they do in fact grow well and tasty here.
The common response to pressure from “pests and diseases” is chemical warfare. Until a couple of years ago, commercial insecticides and fungicides were commonly used on the Center’s farm by external contractors managing our orchard and by our own maintenance staff. There is a long list of very convenient and effective products. But improper handling or long-term exposure to pesticides can cause a similarly long list of severe toxicological effects, such as skin and eye irritation, nausea, headaches, cramps, vomiting or diarrhea. Chronic effects include potential damage to the liver and reproductive organs, birth defects, and cancer. Effects on the environment may include large scale kills of birds or fish and toxicity for honeybees, among others. Globally, tens of thousands of people die every year of pesticide poisoning, and externalities from negative impacts of pesticide use on human health and the environment amount to billions of dollars.
When we started our certification process with the Rainforest Alliance, we decided to go beyond the regular requirements and transition right away into organic farming. We took farm management into our own hands and got seriously involved with integrated pest management (IPM). IPM basically consists of three steps that help to minimize the application of agrochemicals: prevention, monitoring, and control. In the case of organic farming, there is a strong emphasis on prevention and monitoring, because the options to control a massive pest outbreak are limited.
About two years ago, we hardly knew anything about the management of tropical fruit orchards. With the help from our local staff and students we now have identified the most important “pests and diseases” at our site and have gained a substantial understanding of their ecology, life cycles, and their potential weak spots. Most importantly, we are dealing with leaf cutter ants (Atta sp.), formerly kept at unperceivable levels by chemicals, fruit flies (e.g. Anastrepha ludens) and fungal infections such as gummosis (Phytophthora spp.) on orange trees and anthracnose (Colletotrichum gloeosporioides) in mangoes. In addition, we have learned some important lessons that may help us to get closer to our goal: grow healthy oranges and mangoes organically.
Lesson 1: First surprise – organic agriculture does in fact use some chemical inputs. The Costa Rican Ministry of Agriculture, as well as the USDA National Organic Program refer to a list of allowed substances. Fungal diseases for instance can be reduced by a combination of prevention (e.g. pruning trees) and control with copper sulfate. Subsequently beneficial fungi of the genus Trichoderma can be introduced to help us avoiding new infections.
Lesson 2: Organic agriculture requires a lot of work and research. This is a good thing, because that is exactly what we are doing here. Fortunately, we do not really rely on selling our fruits. While we are currently losing a substantial part of our production to “pests and diseases,” the farm has a higher value now as an outdoor laboratory and classroom for our students and faculty.
Lesson 3: Leaf cutter ants are really hard to beat. They form a super-organism buried deep down in huge underground nests where they feed the leaves of our fruit trees, vegetables, tree nursery and ornamental plants to a fungus that in turn feeds their exploding populations. They can kill a tree by defoliating it repeatedly. We have tried several organic remedies – all failed. We need to become more systematic in our efforts to get the ants down to a level that will allow co-existence. As a first step, we are now building physical barriers to protect our trees individually. As a next step we try to decrease their numbers either by attacking them directly (e.g. by using a non-toxic mineral, Diatomite, which dehydrates their bodies on contact) or their fungus, by trying to introduce other fungi into their nest.
Lesson 4: Fruit flies are rather easy to beat. They can ruin a whole harvest, but they have a weak spot. The larvae need to get out of the fallen fruits and into the ground, in order to complete their life cycle. So we pick up the fallen fruits and that’s it. These fruits are turned into organic fertilizer.
Lesson 5: Other “pests,” such as scale bugs or rust mites are bizarre and amazing little creatures that we never would even have heard of without studying our trees more closely. They can get massive, but are easy to control, e.g. by washing them off the branches.
After 2 years we cannot say that we are there yet. We are still struggling to get things under control. Is it worth all the extra hours of work and demolished orange trees? In my opinion – yes, absolutely. Finally we are making a true connection to our farm. The benefits of teaching and learning by doing are obvious. Understanding the challenges of organic farming in the tropics is an eye-opening experience. Hopefully we will soon be able to produce high quality oranges and mangoes and become an example for other growers in the area.