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Controlling Pests Without Harming Good Bugs


Q. I want to spray the aphids feasting on my columbine and crepe myrtle with Pyola, but I'm afraid it will hurt the few ladybug larvae amongst them. Will Pyola hurt them? Thank you,
    ---Elen in Albuquerque, NM
A. Thank YOU for asking a very important question, Elen! People often assume that alternative pesticides like Pyola only harm pest insects and leave pollinators and beneficial insects alone, but the reality is much more complicated.

Let's begin by discussing one natural pest control that is 100% targeted: Bt, the poster child for safe insect killers. Each strain of Bt (there are several) affects only one type of 'target' pest. The Bt that's specific to Colorado potato beetles only affects those bad beetles. The incredibly popular one known by the initials BTI only affects mosquitoes, black flies, fungus gnats and other members of the fly family that breed in water. And the oldest strain, BTK (which almost everyone just calls "Bt" for short), only affects pest caterpillars (which are often referred to as 'worms' in their common names, which is 100% incorrect).

Spray that old, original form of Bt on a plant that's being munched on by pest caterpillars and any caterpillars that eat the sprayed leaves will soon be unable to eat any more. Then they die. But if a bird swoops down and devours some of those caterpillars after they ingest the Bt, the bird only gets a good meal. Same with hungry toads and other helpful predators. Bt won't harm them, you, your pets or even any non-caterpillar pests (like annoying aphids); even if those pests immediately eat the sprayed leaves.

Some people consider this a drawback. They {quote} "want something they can spray on their plants to kill everything". But since 'everything' would include pollinators and beneficial insects, I find targeted controls like Bt to be vastly superior.

OK—now to actually answer your question. (And yes, this might be a personal best of procrastination; I'd have to go back and count words.)

Pyola is a popular low-toxicity pesticide that contains two organically-approved ingredients. The bulk of the product is refined canola oil—which I use for cooking when I need to heat something up to a temperature that's too high for my preferred extra virgin organic Spanish olive oil. The other ingredient is a scant one half of one percent concentration (0.5%) of the botanical insecticide Pyrethrin, which is isolated from the dried flowers of a specific variety of chrysanthemum that has been cultivated for centuries for use against insect pests

Pyrethrin is technically a "broad-spectrum" insecticide; that is, it has the potential to harm any insect—good, bad or just hanging around. But the concentration in Pyola is very low, and unlike its synthetic cousins, Pyrethrin degrades rapidly when exposed to air and sunlight. I suspect that the vast majority of Pyola's effectiveness comes from the canola oil alone. Oil sprays—generally known as 'horticultural oils'—are some of the earliest known insecticides, and work by smothering pests.

Dormant oil sprays are refined petroleum products that are pretty much only used on trees in the wintertime (the 'dormant' period) to smother and kill overwintering pests. (You should never spray dormant oil on a non-dormant plant.)

Light horticultural oils—often called 'summer sprays'—are refined vegetable oils that are much gentler on plants and can be used at any time of the year.

BUT—and this is a big 'but'—oil sprays only work when you spray them directly ON pests. This makes dormant oils an 'act of faith'; you can't see the pest eggs on the trees in the winter, but research and experience have shown us that they are there, and that a well-timed spray can eliminate quite a few future troublemakers.

But the light horticultural oils must be sprayed directly onto visible pests to work. You can't prevent damage by spraying plant leaves with them in advance. Same with insecticidal soap—you must hit the pest. This makes oil sprays a PERFECT weapon of choice against bold and brazen creatures like Japanese beetles. Same with Pyola, which would both smother and expose them to a little Pyrethrin. (Just try and be careful not to get any on plant flowers—to protect bees from ingesting even a miniscule amount of anything that might harm them when they gather pollen.)

Yellowjackets are another perfect target for oil sprays. Those nasty aggressive stinging wasps once built a nest in one of my compost piles, so I sprayed the hovering guard wasps as I approached, and the rest as they flew out in anger. Very satisfying; I'm smiling now just thinking about it.

Note: the folks at GA have just informed me that Pyola is not 'labeled' (that means officially approved by the EPA) for use against these stinging monsters. It should be! Somebody pay the EPA fee and get that nasty name added to the label!

Ahem.

But both components of Pyola—the oil and the Pyrethrin—have the same capacity to harm wonderful ladybug larvae as they do (non-wonderful) aphids. Same with a spray of horticultural oil alone; even without the Pyrethrin, it would smother good and bad creatures alike. So use water on this problem instead. Cradle the aphid-covered plant parts with one hand while you blast the rats off with sharp streams of water from a nozzle in the other. No, the baby ladybugs won't enjoy the ride, but they should survive. Research studies show that the aphids will not.

In general, when you have a nasty pest and potential beneficials or pollinators nearby, be careful not to smother any good bugs with oil or soap or use anything with residual effectiveness. Look for solutions that solve the specific problem without any collateral damage.

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