Butterfly gardening is a rewarding hobby. With a fair amount of research and some hard work, you can transform an area of your yard into a happy place for the neighborhood butterflies to stop in and enjoy. If you are lucky enough, they’ll soon call your garden home and produce further generations for you to marvel at and enjoy.
Besides planting the right flowers to serve as nectar and host plants, it is important not to use pesticides in the butterfly garden. Pesticides are harmful to beneficial insects like butterflies, butterfly larvae (caterpillars) and bees – the pollinators you are attempting to attract to your garden.
So what happens when mother nature sends a marauding army of caterpillars to munch down your prized plumbago or a battalion of flea beetles to bite through your hibiscus?
I use a few methods of organic control described here and they have worked well, but this year has been productive for those little pests in my garden, especially the caterpillars. While away for a week on vacation, the caterpillars tore through the herb garden, chowing down on the sage. Webworms have moved in as well on the thyme plants and rosemary. I usually have success just handpicking them, as with loopers, but with webworms it is a little more complicated.
Looking online, I find many references to the use of Bt (Bacillus thuringiensis) as an organic pesticide in the garden. Bt is a soil-dwelling bacterium and is, therefore, all natural. It has been used since the 1920’s as a pesticide (Bt-dusting), and, as Wikipedia points out, it is also a naturally occuring bacterium found “in the gut of caterpillars of various types of moths and butterflies, as well as on the dark surface of plants”. (1)
Recently, however, Bt has become quite a buzzword in environmental debates because agricultural companies have been producing genetically modified crops that express the Bt genes and proteins as a means of pest control since the mid nineties. Some speculate that this use of GMO/Bt crops is the reason for dwindling numbers of beneficial pollinators as well as Colony Collapse Disorder in the last decade.
The reason for this speculation is because, as a pesticide, Bt is an excellent larvicide and performs its work indiscriminately against beneficial insects and pests. Since adult butterflies/pollinators begin their life as larvae, GMO crops expressing the Bt genes may have a negative environmental impact on them. That seems to make sense to me.
So this leads me to the specific question, “In a butterfly garden, do I or do I not use Bt?” That is a question you’ll have to weigh the answer out for yourself. In my garden, the answer is not to use Bt. I want a healthy environment for our winged friends to live within. Even though Bt is natural, it is not fair. It will harm all caterpillars that come into contact with it. Introducing large quantities of bacteria to an area is not even really natural, if you ask me, but then neither is adding fertilizer using the same rationale …
Regardless, other butterfly gardening websites I’ve consulted say no to Bt. The ButterflyWebSite says that Bt “kills butterfly larvae” so it warns against its use. (2). Likewise, Jeff Schalau of the University of Arizona Cooperative Extension writes, “pesticides should not be used in or near butterfly gardens. This includes Bacillus thuringiensis (Bt) which is a toxin to caterpillars.” (3). In a news release from the University of Illinois Extension on 4/5/10, Jennifer Schultz Nelson, Unit Educator of Horticulture is quoted as saying, “Many gardeners prefer to use the more ‘natural’ insecticide produced by the bacterium Bacillus thuringiensis (Bt) … This insecticide kills all kinds of caterpillars, even those that later become the butterflies you are trying to attract.” (4).
I’ll heed the warnings and keep Bt out for the meantime. I’ll continue to do battle with those pesky webworms by handpicking, water-hosing and soap spraying.
Still, if I find myself unable to surmount the webworm problem, I may ask myself again, “To Bt, or Not to Bt?”