Naturally, organics can be effective in anti-pest arsenal
By Becky Barclay
Published in News on July 3, 2009 1:46 PM
After you've put in hours and hours of time making sure your flower garden is the prettiest in town or tending your garden so it will yield the freshest produce possible, you notice that something is eating away at your plants.
Your first thought might be to turn to chemical pesticides for help. But they could adversely affect the environment.
Another option is to try natural pesticides.
The three most common categories of natural pesticides are organic, oils and insecticidal soaps, said Karen Blaedow, extension horticulture agent. She said organic ones contain organisms such as bacteria. Oils can be vegetable or petroleum based.
Natural pesticides can be broken down into even further categories depending on what organism they kill or control -- insecticides, fungicides and others.
But all of them are all natural and can be purchased at any garden center, Ms. Blaedow said.
Oils and soaps work well on ornamental plants.
"The way the oils work is they coat the outside of the insect and plug up the holes where they breathe," Ms. Blaedow said. "They have little holes on the sides of their bodies. That's their version of lungs. When you spray that oil on them, it clogs those holes and they suffocate."
But she cautioned that the oils work only if they come into contact with the bug. That's one of the downsides. You have to spray that whole plant, underside the leaves and top, to make sure you get the bug.
Oils work best on soft-bodied insects, like aphids or spider mites, which are usually a huge problem on ornamentals, according to Ms. Blaedow.
Soaps, too, have to come into contact with the insects in order to kill them. So, once again, you have to spray the plants thoroughly.
"Soaps break down cells and kill the bugs that way," Ms. Blaedow said.
If you decide to go with an oil or a soap spray, you'll probably have to spray more than once. They are not like chemical pesticides, which last so long in the environment that if you spray one day and a week later a bug moves onto that plant and ingests the toxin, it will still kill the insect. This type of pesticide works longer because of its chemical makeup, said Ms. Blaedow.
Also, with chemical pesticides, sometimes they are taken up by the plant itself and become part of it. They can stay in the plant for up to three to four weeks.
"Anything that comes in contact with that plant and eats it is going to die," Ms. Blaedow said.
She said natural pesticides don't last long, which is a plus for the environment. But that also means they don't control pests for very long either.
"So you might have to reapply a couple of times," she said. "The organic pesticides usually break down pretty fast in the light and heat. They're safe because they don't stick around in the environment for very long."
Another advantage to using oil and soap sprays are that they are less likely to run off into the waterways. And often they are not toxic to other mammals and aquatic life.
"If you take an organic pesticide and put it next to a chemical one and looked at the dangers, the organic would be a lot safer," Ms. Blaedow said.
In addition to oils and soaps, there are also botanical organic insecticides, the most common being pyrethrums or pyrethrins.
"They are natural botanical insecticides that come from chrysanthemums," Ms. Blaedow explained. "The insecticide has been extracted from the plant."
They work well on various kinds of insects.
Ms. Blaedow said another botanical is neem oil, which is also extracted from plants.
"Plants are the source that they're getting a lot of the organic pesticides from," she said.
Bacterial pesticides are microbial-derived insecticides. The most commonly-used one is bacillus thuringiensis or BT.
"The bacteria produce proteins that are toxic to different insects," Ms. Blaedow said. "Basically, you want to use BT when you're trying to control a chewing bug, one that chews on the leaves. A good example is the caterpillar."
She said that for it to work, the bug has to actually ingest the BT, which is a poison. But then a lot of poisons are proteins.
BT is safe enough to use on your vegetables as well as on your ornamental plants, according to Ms. Blaedow. And you can use BT right up to harvest time.
"The thing that I would be cautious about is if you're trying to conserve some beneficial bugs, it may kill them, too," she said. "For example, if you really like butterflies and have a butterfly garden and a vegetable garden, the BT is going to kill your butterflies. So you have to be careful about what you're trying to target. Just know what bug you're trying to get rid of and be cautious of what you don't want to kill."
She suggested always reading the label on any pesticide, even natural ones.
"All products will tell what it will kill and what not to use it on," Ms. Blaedow said. "The label will also give the rate for using the product, how to use it, health and environmental hazards and what to wear when using it."
When you shop, be sure to look at the label to see what the product controls. And look at its toxicity.
"Keep in mind that some plants might be sensitive to some of the pesticides and the label will give you that information," Ms. Blaedow said. "The oils and soaps are going to have an effect on the plants as well as the bugs."
And just because it's organic, or natural, doesn't mean it's not harmful in some ways to people.
"It's killing something so obviously it has some properties that you need to be cautious of," Ms. Blaedow said.
She does caution that one organic pesticide -- rotenone -- is pretty toxic. It's extracted from a plant and is a stomach poison to insects. But it can be just as toxic to people or the environment as a chemical pesticide, even though it's organic.
There are advantages to using natural pesticides.
"I think if you want to try to protect beneficial organisms in your garden, keeping some of the good ones that attack bad bugs, then the organic can help you select the ones to kill," Ms. Blaedow said.
"Also, the organic pesticides don't stick around in your garden very long, which is a plus for a lot of people. Especially with your food. If you're up to a week before harvest and have a problem, you could spray a soap on and still harvest them. That's another benefit.
"And they're usually not as toxic to people as chemical pesticides."