Using essential oils in the fight to protect vegetable crops in Jamaica
The organic farming movement is huge and its impact has been felt around the world. Common sense supports it, as we all know that people farmed vegetables successfully for thousands of years before the invention of modern toxic pesticides. As the earth becomes more polluted and cancer rates rise, more people become concerned about the poisons they use in their daily life and consume in their diet.
In most countries, the market is flooded with natural and safe pesticides that protect against every imaginable pest. Most of these reduced risk pesticides have essential oils as one of the main ingredients. Plants produce essential oils to protect themselves from pests. These powerful, concentrated oils contain the very essence of the plants they come from and have many uses.
Unfortunately, here in Jamaica, despite support for organic farming from government and non-profit agencies, commercial organic pesticides are not available in most stores, and farmers who want to avoid toxic pesticides rely on word of mouth to learn what they might do to protect their plants. Garlic tea? Laundry soap mixed in their spray pan? Many times, nothing works, and farmers who have their heart set on protecting their plants organically have to watch as their plants are devoured by pests, or resort to using small amounts of toxic pesticides.
This past summer, five college students volunteered to work on our north coast farm, Yerba Buena Farm in Strawberry Fields, distilling the essential oils of many native plants and trees. The goal of our project was to test these essential oils to see if they could act as effective pesticides, protecting some of our main vegetable crops. We wanted something that would repel pests and kill the ones already on the plant.
Conor Lally, Armelle Mauss and Marisa Schwarz, three of the five interns who volunteered to find a natural pesticide for Jamaica.
We chose plants that we knew were or that promised to be insecticidal, and tried around thirty plants. Pimento, sour orange leaf and fevergrass produced the most oil and were the ones that we tested in the garden. When we distill essential oil from plants, the main byproduct is hydrosol, the condensed steam that contains essential oil, but in less of a concentration. In our tests, we used the essential oil and hydrosol mixed in a spray pan.
We planted eggplant, broccoli, callaloo and watermelon, and tested the sprays’ effectiveness against thrips (Thrips palmi, Frankiniella occidentalis), Fall armyworm (Spodoptera frugiperda), Southern armyworm (Spodoptera eridania), Beet armyworm (Spodoptera exigua), Flea Beetle (Disonyca laevigata), the melon aphid (Cerosipha gossypii).
At this point, Armelle Mauss from France took over the project. She made so many valuable contributions and worked so diligently during her three months with us that this project became her own. Her academic training and attention to detail ensured that the study would be done in a scientific way.
We compared our essential oil plots to a control plot, which was not sprayed, and to a plot sprayed with laundry soap mixed into water, which we had used before as a pesticide. We sprayed all of the plots every three days for five weeks. Armelle took pictures of every plant as she sprayed to document the effect of the sprays.
The sour orange leaf hydrosol was effective on eggplant and callaloo. The pimento hydrosol burned all of the young eggplant and callaloo plants, but was as effective as sour orange leaf on large, established plants. The lemongrass hydrosol seemed to work initially, but after several weeks it was clear that it was burning all the plants, both young and old.
The eggplants in the unsprayed control plot were destroyed by a virus causing tomato spotted wilt, which is transmitted by thrips. Pests also devoured the callaloo in the control plot. The plants treated with the laundry soap were not destroyed, but enough pests lived that the yield was seriously affected. However, laundry soap worked very well against aphids on watermelon.
Following this first series of tests, we selected the sour orange leaf hydrosol for further testing because it was the most effective and had the broadest spectrum. We carried out new tests to find the smallest effective dilution of sour orange leaf hydrosol. We used seedlings and young callaloo and watermelons plants that were already affected by pests. We tested three dilutions: 100ml, 200ml and 400 ml per one liter of water. After four weeks of tests, the results were very good for all dilutions.
As not everyone has an essential oil distiller in their yard, we tested what we called “kitchen recipes”, natural pesticides anyone could make with what they have in their kitchen. We tested them on callaloo and watermelon.
1) 3 bulbs of garlic, finely ground, add some kerosene, keep for 2 days. Add 1 tablespoon of soap powder, stir and add 15-20 liters of water.
2) 100g basil leaves dipped in to 1 liter of water. This should be soaked overnight in water. Filter the mixture, add 1 ml of liquid soap and stir. Dilute with 10-15 liters of water.
3) 500 grams of soursop leaves boiled in 2-1/2 liters of water until only 1 / 4 of the original water left. Dilute this mixture with 15-20 liters of water.
Excellent results were obtained with the all recipes. Unfortunately, as the first recipe has a small concentration of kerosene, it is not organic.
Our next step will be to experiment with extracts of the plants that did not produce essential oil. We will also experiment with making insecticidal soap.
This project was a wonderful way for the students to literally get their hands dirty while working on a worthwhile project. Struggling to care for garden plants under harsh tropical conditions made them have more understanding for farmers who turn to chemical fertilizers and pesticides to feed and protect their crops. As their dinner menu depended on what they could produce in the garden, they felt the importance of creating an effective and safe (for humans) pesticide in an immediate and real way. Being tested by having to adjust to unexpected problems in a real-world situation that is totally foreign to them, being immersed in a rural Jamaican environment for the summer, meeting people with such a different perspective that it changes how these students see the world – all of these experiences will hopefully add to the creativity, sensitivity and resilience that the students already had when they came.
Hopefully, with the resources that Jamaica has, and the interest on a grassroots level to farm in a less toxic way, more studies will be done to find natural pest repellents and insecticides that are effective in a tropical environment. Perhaps the Ministry of Agriculture could eventually make a brochure available that gives farmers a list of natural homemade pesticides that work against different pests?
We hope that the work we did this past summer can be of use to people on our island and in other tropical places. Jamaica, LAND WE LOVE!
Agape and Kwao Adams, with Armelle Mauss