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A Simple and Effective Insecticide

By Noe Smith

We have never been overly fond of using insecticides more than is absolutely necessary, or of using the more toxic types indiscriminately if at all, so we were happy to try a recipe passed on to us some 15 years ago by another orchid grower. Since that time we've used this recipe exclusively and have found it to be very effective at wiping out scale, mealy bug, red spider, and any other undesirable insects which have invaded out orchid houses from time to time.

Drums of hazardous chemicals
Spraying insecticide

I'm sure this particular recipe has been passed around among orchid growers for a very long time and many of you reading this may know it or use it. However, for those of you who don't know it, the recipe is as follows:

To make up 500ml of the mixture, add 10ml of White Oil and 40ml of 4gm-per-litre Pyrethrum to 450ml of water and shake to combine. For larger quantities simply multiply the ingredient amounts for the desired quantity.

We have found the most effective method of treating any infestations is to spray the plants twice at 10-12 day intervals, to both kill the active insects with the first treatment and then to clean up any new insects which may hatch from eggs that survive the first spraying. If we find an outbreak of pest insects on our plants we spray the whole collection using a pressure sprayer and making sure that we spray the undersides of the leaves and down around the bulbs so the insecticide penetrates between the leave bases where insects often hide.

We also keep a small 500ml pump pack of the mixture on hand when repotting or potting up new orchids from any source as a matter of course.

Using insecticide

Over the years we have found this brew to be most effective without being fatal to the frog population, which lives in our orchid houses and in and on our plants. Likewise, the many jumping spiders which also inhabit our orchid houses also seem to survive the spray. The spiders don't much like it and can be seen jumping off the orchids while spraying is going on, but all or most of them do seem to be back "at home" on the plants in a day or two.

The spray doesn't damage any orchid genera we grow besides Cymbidiums, including Paphiopedilums, Cattleyas, Dendrobiums, Masdevallias, Oncidiums, Odontoglossums, Sarcochilus and Zygopetalums, nor does it seem to affect the flowers if sprayed on plants in bud – although we don't use it on open flowers. Still, we don't spray plants in spike unless absolutely necessary either as you can never be totally sure of the results under particular conditions. We also avoid spraying during periods of extreme heat and strong sunlight, usually spraying in the evening if we have to during summer months.

We spray when the plant foliage is dry to avoid dilution of the mixture and always well before the plants will be watered again. As our watering system turns on at 5am during all but the dead of winter, spraying the day before watering seems to work well.

Spray bottle

While Pyrethrum may be a "natural" insecticide, being extracted from Pyrethrum daisies, it doesn't mean it isn't poisonous. However, diluted in this formula, it presents little risk to people or pets (although it is toxic to fish so avoid getting it in any fish ponds), but precautions should always be taken when spraying any insecticides, fungicides, or the like. We'd recommend following a standardised routine for spraying all potentially harmful substances and believe it's only commonsense to do so.

Noe Smith

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