Garden Tips from Marianne Oprahdt: Newer pyrethroids less toxic

Marianne Ophardt, Garden TipsJuly 25, 2013 

I created a challenge for area gardeners a couple of weeks ago when I mentioned that the newer synthetic pyrethrins, also known as pyrethroids, are one of the few options for controlling tobacco budworm and sunflower moth in garden flowers.

Just what are these “newer synthetic pyrethrins?” Before answering that question, let’s first talk a little about the origin of pyrethroids.

One of the first botanical- or plant-derived insecticides was pyrethrum. It was made by drying and crushing the flowers of two types of daisies, Chrysanthemum cinerariifolium and Chrysanthemum coccineum. When purified, this mix was called pyrethrin. Pyrethrum and pyrethrin were desirable because they were “natural,” had a relatively low toxicity and a short period of residual activity. While a lack of persistence is valuable in protecting beneficial insects, it also made them less effective in controlling insect pests. 

Another obstacle to their use was that the pyrethrum was expensive, and supplies were limited. This prompted the pesticide industry to seek a way to create a synthetic pyrethrin. This was done in 1949 when the first synthetic pyrethrin, allethrin, was developed. The next generation of pyrethroids came in 1960 with the introduction of tetramethrin, resmethrin, bioallethrin and phenothrin. The second generation was more toxic than the natural.

Chemists did not stop there. They have continued to develop new pyrethroids that are more toxic, and most also have longer residual activity. These are the “newer” pyrethroids I referred to a couple of weeks ago. They include esfenvalerate, permethrin, cyfluthrin and bifenthrin.

Home gardeners with insect pest problems have been frustrated because a number of insecticides they used successfully in their gardens for pest control were taken off the market because of health and environmental concerns. These newer pyrethroids are effective against a range of garden insect pests, especially chewing insects, and have helped replace materials, such as diazinon, that no longer are available.

As a group, the newer pyrethroids generally are low in toxicity to mammals and birds, but highly toxic to fish and beneficial insects. They are fast-acting and kill insects by contact and ingestion.

How do you know if a product contains one of these newer pyrethroids? I found out it was not easy to find in local stores. Product names don’t give hints. You have to check the label for active ingredients. There will usually be a common name, such as esfenvalerate, along with its long chemical name in parentheses. Check the label to make sure it includes the crop, such as flowers, on which you plan to use the material. Also note any precautions you should take to protect yourself and wildlife. By the way, I was able to find several Bayer, Ortho and other brands of home garden products that contain at least one of these newer pyrethroids. - Marianne C. Ophardt is a horticulturist for Washington State University Benton County Extension.

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