This week it’s time for the third and last installment on insects in our gardens and landscapes. We’ve looked at the types of damage these insects do, how to scout for them and the clues in finding them. So now, we need to talk about how to control them.
Let’s start with the understanding that simply because you have found a bug in the garden, that doesn’t mean that you have to buy gallons of poisons and kill every living organism to ensure that you have a nice rose, a great apple or a wonderful tomato. I recently visited a garden where the owner spotted a problem with her lilies and immediately sprayed with Sevin. I literally went berserk. Not just because she used Sevin, but because she had no idea what she was spraying for and what the effects of Sevin could be.
I’m sure you’re more thoughtful.
Of course, we have to deal with insects that chew our plants, suck the life out of them and rasp the foliage and buds. Essentially we are dealing with chewers, suckers and raspers—each can require a different treatment.
Thirty years ago we used chemicals that were essentially neurotoxins and stomach poisons. These days we’re much more creative. Now we use biologicals, botanicals, soaps and oils, with the stronger stuff held back as a last resort.
Oils, such as dormant oils, have been used for years to smother scale and insect eggs on fruit trees early in the spring. A variant on the theme is a much more refined oil, called a light horticultural oil, that can be used throughout the season as an effective control on scale insects.
Light horticultural oil acts to smother the scale and has little to no effect on other insects so it’s considered somewhat benign. It can’t be used in very hot weather though, and some plants are very sensitive to it. But for most scale control, it can be very effective when used correctly.
Insecticidal soaps are very effective for controlling certain insects, such as aphids. The soaps are derived from a number of sources and you can even make your own soap sprays based on recipes you can find online.
Keep in mind though that soaps are only effective against a very narrow range of insects, and when used incorrectly, such as on a very hot day or in very bright sunlight, soaps can kill bugs but plants as well.
And like with oils, some plants are sensitive to soaps.
One of the newer insecticides is neem oil. It’s derived from the neem tree, which grows in India. It’s been in use for about 15 years in this country.
The active ingredient in neem oil acts as both an insect repellent and as a feeding disruptor. It may also have a side benefit of controlling some plant diseases.
Neem oil also seems to disrupt insect reproduction. But, this insecticide, while organic, takes time to work and is probably best used as a prophylactic insecticide than as a product that will actually knock down an insect and kill it.
The best formulation of neem oil is 70-percent neem and the label will state that. It will not kill bees as long as it is not applied directly on them.
Spinosad is one insecticide that most interests me. It’s a broad-spectrum insecticide, meaning that it kills a wide range of insects, but it doesn’t harm beneficial bugs such as lady beetles, parasitic wasps, lacewings, spiders and predaceous mites and bugs. It is toxic to bees when wet but once it dries it won’t harm them.
Spinosad was discovered in an abandoned sugar mill in the Caribbean quite by accident. It’s a biological that is considered an organic pesticide.
It’s very effective on chewing insects—such as beetles, caterpillars and thrips—but it doesn’t work well on aphids. Sorry.
This biologic acts as both a stomach- and nerve poison. When a feeding insect ingests it, feeding stops within minutes and death takes place within 48 hours.
I think this is probably the most promising pesticide that home gardeners have had a chance to use since the 1950s and it’s a whole lot safer than what we used in the last part of the 20th century. I can’t wait to try it this year to see if it will be effective on Japanese beetles.
When you read the ingredients on some pesticides, you’ll see the name “acetamiprid,” another relatively new pesticide. This one is systemic, meaning that it’s absorbed by the plant, making the entire plant toxic.
While considered by some as being safe, this product is not without its controversy. It falls into the insecticide classification of nicotinoids—neuro-active insecticides chemically related to nicotine. There are those who believe that this class of pesticides may be at the root, or at least a contributing factor, to the collapse of our honey bee populations.
Acetamiprid is effective on sucking insects, such as aphids, and is used on leafy vegetables, including: grapes, cole crops (vegetables in the mustard family, including broccoli, Brussels sprouts, cabbage, cauliflower, collards, kale, and kohlrabi), apples and ornamental plants. I haven’t used it so I can’t make any recommendation but as noted it does have its detractors.
There are also a number of products that have essential oils of other plants in them, including peppermint, spearmint and clove oil. For hard-core organic folks, these may be fine, but before you use them make sure you read up on what they are effective on and what plants not to use them on.
Lastly, there’s Sevin and Malathion. I consider these “the dirty duo.” Both are holdovers from the 1950s and both are controversial. Neither can be used in an organic garden and both have environmental issues.
Sevin is chemically known as “cabaryl.” It’s very effective against Japanese beetles and mosquitoes but it’s also highly toxic to honeybees and crustaceans. Therefore you never want to use this product near bees or anywhere near ponds, lakes, streams, bays, etc.
I would probably never use Sevin out here because of the environmental consequences. Anywhere else, I would only use it as a pesticide of last resort. I haven’t used it in at least 25 years.
Then there’s Malathion. This is the only organophosphate pesticide that’s left for home garden use. It’s effective against chewing and sucking insects but is broad spectrum and will kill bees, as well as most beneficial insects.
Malathion was used as an aerial spray in the 198os in California to combat the Mediterranean fruit fly. In 1999 and 2000, it was sprayed in New York City and Long Island to combat the mosquitoes that carried the West Nile virus.
Organophosphate pesticides, such as Malathion, are quite controversial and have been in dramatic decline for many years. This is another product that I haven’t used in over 30 years. It’s hard to find a reason why you’d use it when safer products are easier to use.
When it comes to bug control, these are pretty much the choices. You can read much more about each and every product online and the product labels are quite informative as well. You may not immediately know what is in any given insecticide but the label on the front will be quite clear, though you’ll need good reading glasses to see the fine print.
Always follow the label directions EXACTLY. If it says 1 ounce to 1 gallon of water, then that’s what you should use.
Changing the formula by doubling the dosage doesn’t kill the bugs twice as fast or for twice as long. But it may kill your plants.
Make sure the pesticide is matched to the pest and the plant. The label will tell you if you’ve got a match.
Use the wrong pesticide to control mites and you’ll end up with more mites, not dead mites. Also remember that water works wonders as a spray, but it doesn’t work on everything.