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Ashes to aphids October 15th, 2017 by

Anyone interested in organic farming will eventually come across the use of ash to protect crops from pests and diseases. The internet has made it easy for people to consult, and to copy each other’s training materials. But one has to be cautious when borrowing ideas, as we recently learned during a script writing workshop in Bangladesh.

During the first day of the course, the 13 trainees from Bangladesh and Nepal laid out their key ideas to write a fact sheet and a script on a particular problem.

All of our script ideas were hot topics, that is, they are problems that occur widely across developing countries, requiring good training materials with ideas that are both feasible for smallholders and environmentally friendly.

One of the selected topics was how to manage shoot and fruit borer in eggplant, a pest for which many farmers in South Asia spray pesticides twice a week, or more. Just knowing this makes you frown when this tasty vegetable is presented to you in one of the delightful Bangladeshi dishes.

Another group worked on aphids in vegetables and suggested using ash to manage these pervasive pests. When Jeff and I asked why ash is useful, the group gave us various reasons: because it is acidic; it contains sulphur; it is a poison; the ash creates a physical barrier which prevents the aphids from sucking the sap of the plant. These all sound like plausible answers yet some are incorrect. Ash is rich in calcium, like lime, and therefore not acidic, for example.

We do know that ash makes the leaves unpalatable to insects and corrodes their waxy skin, making them vulnerable to desiccation. The FAO’s website on applied technologies (TECA) suggests controlling aphids by applying wood ash after plants are watered. If not, the sun may cause the leaves to burn. Our simple question about using ash reminded me that the scientific basis for many local innovations is poorly understood. There are too few researchers to validate each technology and limited resources often focus on high-tech solutions (e.g. plant breeding) rather than low-tech farmer innovations.

We may not always know why local innovations work, which is all the more reason to be cautious when recommending substitutions. During this workshop, for instance, I learned that not all ashes are the same. Shamiran Biswas, an extensionist with a rich experience working with farmers across the country, explained: “When one field officer told farmers to sprinkle ash on his crop, a farmer who followed this advice saw his entire bean field destroyed within half an hour. We were shocked and tried to figure out what went wrong. It seemed that the farmer had used ash from mustard leaves, which some rural women add to their cooking fires when they are short of wood. But leaf ash from mango, mustard, bamboo and other plants may also be harmful when sprinkled on crops. The only ash that is fully safe to recommend is ash from rice straw or rice bran,” Shamiran concluded. He added that “ the ash should be cold and sprinkled on the crop when the leaves are still wet from the morning dew.”

Experienced extension agents like Shamiran are experts at explaining farmers’ ideas to outsiders, as well as explaining scientific ideas to rural people.

When people give advice to farmers, or develop farmer training materials, it is easy to copy ideas from the Internet. It is easy to assume that because ash is natural that it must be harmless. In fact, tree leaves are often full of toxic chemicals, to deter herbivorous insects; it stands to reason that the ash of the leaves may also be poisonous.

A natural solution can go wrong, even one as simple as applying ash.

To develop good farmer training videos, solid interaction with farmers is crucial. And collaboration with a seasoned, open-minded extensionist helps to orient us in the right direction.

Related blogs

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A spoonful of molasses

Further viewing

To watch videos that merge scientific knowledge with farmer knowledge, visit the Access Agriculture video-sharing platform. All videos are developed by people who value local innovations, and feature technologies that are validated by real farmers.

Acknowledgement

Shamiran Biswas works for the Christian Commission for Development in Bangladesh, an NGO working on food security and non-formal education.

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