Tag Archives: avoidance

Ethephon, the ‘good guy’ organophosphate?

14 Mar
Ball-and-stick model of the ethephon molecule,...

Ball-and-stick model of the ethephon molecule, the most widely used plant growth regulator. Colour code (click to show) : Black: Carbon, C : White: Hydrogen, H : Red: Oxygen, O : Orange: Phosphorus, P : Green: Chlorine, Cl (Photo credit: Wikipedia)

Have you ever tried putting an unripe pear in a paper bag with a ripe banana to ripen the pear more quickly? Go ahead! It works. The reason this works is because many ripe fruits give off ethylene, a gaseous growth hormone, when they are ripe, and ethylene triggers the generation of more ethylene, in a cascading, snowball effect within these ‘climacteric’ fruits. Ethylene also triggers stems and leaves to senesce, or turn yellow and mobilize their valuable photosynthesis machinery to other parts of the plant. In the original example, if you put a head of broccoli in the paper bag with the ripe banana, the broccoli will yellow and then brown. Pest managers have learned that you can use this hormone to good advantage in an integrated pest management plan by hastening the ripening of fruits to avoid late-season pest pressures such as walnut husk fly in walnuts. But how can you target the application of a gas like ethylene to the fruits of a tree in an orchard at high enough concentrations to ripen the husk (fruit) of the walnut tree? The answer might surprise you: spray an organophosphate pesticide such as ethephon that breaks down into ethylene and phosphonic acid. This stuff is now only registered in the USA as a plant growth hormone, but in fact it was originally registered in the 1970’s as a pesticide and has pesticidal properties, acting upon the nervous systems of insects, crustaceans and humans. It is a lousy pesticide, since it is not very toxic to insects and breaks down quickly in the environment, so nobody uses it as a pesticide on purpose any more. Instead, it is used exclusively as a growth regulator. http://1.usa.gov/16w8BO7

Avoidance by changing the timing of harvest is a wonderful strategy for preventing the need for ‘real’ pesticides which have serious insecticidal properties in the late season. I think it is important, however, to be aware that this stuff is actually an organophosphate pesticide as well, and to take proper precautions when applying and storing it, just as you would if you were spraying diazinon or chlorpyrifos or any other major organophosphate pesticide, which everyone knows are neurotoxins by means of inhibiting the enzyme cholinesterase in the brain. We can toy with the idea that we are using a safer material, but safer is a relative term.
Also, please note that ethephon acts upon plants as a growth regulator and upon insects and mammals as a neurotoxin, so let that be a lesson to ya not to assume, as I did, that plant growth regulators are as safe as water for human handling and for beneficial insects.
In my amateur opinion, then, ethephon is an undercover organophosphate playing the ‘good guy’ in today’s orchard crops because of the small concentrations and low toxicities applied and because these applications allow farmers to avoid rather than treat late-season pests through early ripening, but it is important to remember that this stuff is still a neurotoxin and to take proper precautions when handling it.

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