Non-synthetic post-harvest pest management

Essential oil from Eucalyptus grandis leaves has been proved by various scholars and researchers to possess anti-insecticidal, anti-bacterial, anti-fungal and anti-nematicidal properties. I would like to undertake a research on the applicability and suitability of the different forms of essential oil from Eucalyptus grandis as post-harvest treatments against post-harvest pests and diseases in beans, maize grains, cow peas and soya beans. I would like to find out whether essential oil is suitable when applied as fumigant (gaseous form) or liquid (direct contact with the oil) at different concentrations. I would also like to establish whether exposure of the seeds and grain to essential oils alters their integrity.

One of the prerequisites for graduation from my course at Makerere University was undertaking a final year project and submitting a dissertation. As I pondered which area to explore, I remembered that during my childhood, I used to observe my grandmother place eucalyptus leaves on the ground, below the granaries. She said the leaves would ward off pests.

As I carried out research about this, I realized her assertion tallied with that of researchers and scholars. More research revealed that essential oil producing companies in Uganda extract oil from Eucalyptus citriodora, whose main active ingredient is citronellal and is employed in perfume and cosmetic industries, which have an extensive market in the country. However, Eucalyptus grandis leaves, rich in Cineole, the pharmaceutical ingredient, were either burnt or left to rot in the fields after the harvest of trees for timber. This is because, aside from ignorance of the tree plantation owners, there was no market for cineole rich essential oil.

I thought to myself that in order to persuade investors to extract cineole rich essential oil, there needed to be evidence that the leaves of Eucalyptus grandis trees planted in Uganda could generate a substantial amount of essential oil (yield of essential oil varies with geographical location according to literature). I therefore decided to undertake a final project with the title: comparing the yield of essential oils extracted from leaves of eucalyptus grandis trees at different age brackets. My results indicated that older trees, 17-25 years yielded significant amounts as compared to younger trees.

It is against this background that I have applied for this opportunity. I would like to complete my research with significant contribution to crop protection. The process is not that cumbersome.

The variables are:

  • 2 sacks (or an equivalent in other package) each of beans, cow peas, maize and soya beans.
  • 5 smooth walled small to medium copies of locally fabricated metallic silo-like structures.
  • 1 porous net,
  • 1000 liters of Eucalyptus grandis essential oil,
  • a culture of bean and maize weevils,
  • a smooth plastic pail of about 1m3 in volume and a mixer,
  • a metallic carrier in form of a porous plate fitted with a metallic handle of 1.3 meters,
  • large plastic polythene bags of 1m3 about 4 pairs of plastic gloves and 4 overalls.
Extraction of essential oil using a modified clevenger apparatus

Step 1: The 5 smooth walled silo-like structures are placed on a well-drained, gently sloping area, preferable near gardens, to avoid high transport costs.

Seeds/grain to be treated with essential oil in liquid form.

Step 2: 20% of the bean seeds are infested with pests for a period of 24 hours and then mixed with the rest of the beans.

Step 3: 1 sack of beans is divided into 4 parts and each part placed in an essential oil bath at concentrations of 25%, 50%, 75% and 100% v/v for 10 minutes.

Step 4: the seeds are then placed in the silo and closely monitored for a period of 2 months.

Step 5: Experiment is repeated for a sack of cow peas, maize, and soya beans.

Seeds/grain to be treated with essential oil in gaseous form

Step 2: 20% of the bean seeds are infested with pests for a period of 24 hours and then mixed with the rest of the beans .

Step 3: A porous net, capable of holding at least half a sack of the beans is suspended.

Step 4: Beans are poured on the net so that they are suspended in the air.

Step 5: A cylinder containing concentrated essential oil is placed at the bottom of the net so that its fumes pass through the beans for a period of 2 months. The experiment is then repeated for remaining sack of cow peas, maize and soya beans.

Proposed outcomes:

a) Essential oil is effective against pests in both liquid and gaseous forms
b) Oil concentrations of 75% and 100% are equally effective against pests
c) Soaked beans and grain had a glossy appearance and were not appreciated by consumers as compared to those which were treated with vapour.

I have decided to undertake this research so as to add to the types of organic based solutions to crop pests as opposed to synthetic chemicals, which are costly and harmful to both humans and the environment if disposed of inappropriately.

Success of this project would also encourage Ugandans to venture into essential oil production for pharmaceutical purposes, which will create more jobs along the entire production chain.

Lastly, increased market for cineole rich essential oils would also encourage afforestation, which is an important factor in mitigating climate change.

Mark Lazarus Oketch , Uganda

73 comments

  1. This is quite interesting especially since I have always thought of plant eucalyptus trees, Hope your proposal is considered . Best of luck

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  2. Wait. Hold up. Eucalyptus oil has been proven to serve very many purposes in the pharmaceutical sector. A number of pain balms and flu remedies contain Eucalyptus extracts. But boy I have seen how eucalyptus leaves get wasted. They cannot be used to even warm bathing water let alone half cook a meal. I think that if you prove that indeed they are that helpful, You will have solved a big challenge for the world and rural Africa.

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