how do insecticides work
I don’t know about you, but insects seem to love my tomato plants. Some seasons the insects aren’t too bad – mainly a few tomato hornworms here and there. Other seasons make me think that a biblical plague has descended upon my garden!
I do try to garden without using insecticides as much as possible, but sometimes I have to throw in the towel and reach for my sprayer. I thought I’d share an “Insecticide 101” post with you. 🙂
Insecticides – What Are They?
It may seem kind of obvious, but these exist to hopefully get rid of the bad bugs (i.e. the ones that want to eat your veggies) and leave the good ones (the ones that pollinate and that eat the bad bugs). They can do it by any of several methods:
- Contact: Some pesticides kill on contact, so when the bugs get sprayed or walk onto it — bye-bye! This generally works on the insect’s nervous system.
- Mechanical: These are the ones that scratch the bug’s outer casing and thereby cause it to dehydrate. This also includes things like sticky traps.
- Ingestion: When the pest chomps on the plant where the insecticide is spread, it ingests it. The bug doesn’t die immediately, but rather within a day or two.
- Reproductive: This doesn’t necessarily kill the insect, but rather interrupts the reproductive cycle so that the they can’t multiply.
There are others, but the above are the main categories.
Organic Versus Chemical Pesticides
First, when you get down to it, everything is a chemical. However, for the purpose of this post, “chemical” refers to synthetic chemical pesticides. These are typically created in a lab, as opposed to existing in nature “as is”. Examples are things like DDT, organophosphates, parathion and chlorinated hydrocarbons.
Organic refers to those insecticides that are extracts of naturally occurring ingredients. Examples include pyrethrum, rotenone, neem and Bacillus thuringiensis (Bt).
****Very Important: Whether synthetic or organic, by their nature the vast majority of what we consider insecticides/pesticides are toxic, in varying degrees, to people and pets. Always, always, always read and follow the instructions on the label of whatever you purchase.
There are some like diatomaceous earth which are safe to ingest (if you get the food-grade version) and to use around pets, but by and large, treat all insecticides carefully.
I am the first to admit — when it comes to the fire ants that invade my garden, I do use synthetic pesticides — I’ve tried all kinds of organic versions, and they just don’t work. My only defense is to keep the fire ants as far away from my garden as possible, and to use as little synthetic pesticide as possible.
But when it comes to all other pests — my organic insecticides of choice are neem oil and Bt.
One Size Doesn’t Fit All
Unless you only have a specific kind of insect invader, you may need more than one type of pesticide at various points in the gardening season. For example:
- Rotenone is very effective on most types of beetles, but not as much on soft insects like caterpillars and worms. It is quite toxic to fish.
- Neem doesn’t kill directly, but is more of a repellent. It also works to inhibit insect eggs from hatching. Neem is one of the least toxic of the pesticides, but you should still use care when handling it. Interestingly, neem oil can also act as a mild fungicide.
- Pyrethrum is made from chrysanthemums, and it works by attacking the nervous system of insects. It also works as a repellant. It biodegrades quickly and is also among the least toxic to mammals and people – but quite toxic to fish.
- Bt is a bacteria that when ingested by insects, disrupts their digestive tracts. It’s typically used as a spray or a powder, and is most effective on soft-bodied insects — primarily worms and caterpillars that like to feast on your plants.
- Diatomaceous earth works mechanically, by abrading the insect’s exoskeleton. The bug then dies from dehydration. It also works as a flea powder around pets.
These aren’t the only organic insecticides that are out there, but they are the ones that you will come across most often in stores and online.
Which One Should You Use?
You should use what is best for your particular insect problem. You need to know your enemy (which bugs are bugging you), and then choose the insecticide that will be effective against those insects.
Also keep in mind that some insecticides are not made to be used around vegetable plants — they don’t biodegrade well, and you could potentially ingest their residue. Others are safe to use in a vegetable garden, up to the day of harvest. Once again, read the label and follow the instructions — don’t guess!
I hope this has been helpful to you. Now excuse me while I go check my tomatoes to make sure I haven’t had a caterpillar or hornworm invasion and need to get out the Bt!