Even organic products can be harmful to bees, other beneficial bugs

By Rebecca Jepsen
For the Mercury News
May 15, 2010

So you've rid your shed of all those nasty pesticides, chemicals and fertilizers (and, of course, you took them to your local hazardous-waste recycling center) and replaced them with only organic varieties. Is it now safe for you, your pets and your "good bugs" to be out and about in the backyard?

Well, it all depends.

Organic products are derived from natural sources instead of synthetically manufactured ones. Therefore, they generally wreak much less havoc on our environment but need to be used sparingly and with caution.

One of the most common garden foes is the aphid. There are more than 4,000 species of aphids. They come in colors that include black, brown, red, green, yellow, pink and purple. We spend lots of time, money and energy trying to get rid of them, without much success. Some species do very little damage while others, in large quantities, can be a serious threat to their host plant. They weaken a plant by cutting off its nutritional supply, which can lead to stunting and distortion.

There are many organic insecticidal soaps and products containing pyrethrum that help in the control of aphids. However, these products do not just take out the bad guys — they will annihilate your bees and beneficial insects as well.

I have roses in both my backyard and my side yard. The roses in the back don't have a single aphid (that I can see). However, the ones on the side that divide my property line were recently so infested with aphids that you could barely see the leaves covering the buds. Upon further inspection, I saw several green lacewings (Chrysoperla) on the buds as well. Lacewings are among the most beneficial tools in our garden bag. They are bright green, about three-fourth of an inch long, and have translucent, slightly iridescent wings. The larvae, often called "aphid lions," are shaped like tiny alligators and can range in color from gray to brown. The larvae are the true "work horses"; their estimated life cycle is about six weeks, and each larva can eat approximately 600 aphids in its lifetime.

I didn't want to disturb my beneficial buddies, so I gently shook the bushes to get the lacewings to fly off and then wiped off and squished large quantities of aphids in order to give the lacewings a fighting chance. A few days later, there were virtually no aphids on any of the roses. Now, if you don't find pleasure in bug-squishing, a blast of water from the hose would have done the trick as well.

And, according to Nancy Garrison, one of our veteran Master Gardeners, if you just wait a few weeks and let nature take its course, the good guys will usually overpower the bad guys without any human or chemical intervention.

Another product frequently used by organic gardeners is neem oil. This is a vegetable oil pressed from the fruits and seeds of neem (Azadirachta indica), an evergreen tree found in India and the tropics. It repels a wide variety of pests, including cabbage worms, mealy bugs, whiteflies, beetles, leaf miners, caterpillars and aphids. It has also been known to control powdery mildew, anthracnose, black spot and rust. Neem oil works by suffocating the insects it is sprayed on, as do other horticultural oils. Although some studies show that neem has been used successfully without significantly affecting bee colonies, other reports indicate that is has had negative effects on honeybee populations.

There are situations that require chemical intervention (peach leaf curl on peach trees, invasive plant species, etc.). But before you jump to the gun "... er, spray bottle, remember that bees are essential for pollination of most of the foods that we eat. By choosing plants that require minimal input (water, fertilization) and putting them in the right location at the right time of year, you can cut down on the money and labor required to try to make something work that doesn't.

It's best to step back, assess the situation, weigh all the options and then make a decision that works for you, your habitat and the planet.

Master Gardeners Ann Northrop and Nancy Garrison contributed to this column. Have a question? Call the UC Cooperative Extension Master Gardener hot line, 408-282-3105, 9:30 a.m.-12:30 p.m. Mondays through Fridays. Details: www.mastergardeners.org.