I recently overheard a woman in a local store asking for a spray to kill the little green worms on her lettuce. I had to restrain myself from offering her unsolicited advice. I, too, had just found little green worms on my lettuce, but I recognized them as syrphid fly larvae.
Syrphid flies are also known as hover flies, or flower flies, because they are usually noticed when hovering over flowers. They may cause alarm because they have a black and yellow striped body, resembling a bee or wasp. However, syrphid flies are benign and do not sting or bite.
The adult flies eat flower pollen and nectar. They are also valuable pollinators. You should not be afraid when you see a syrphid fly, but any aphids present should be afraid. That is because many types of syrphid flies are predacious. These syrphid flies lay their eggs near colonies of aphids. The eggs hatch into hungry larvae that will eat hundreds of aphids in a month.
If you see a "little green worm" on a plant infested with aphids, take a close look. Syrphid fly larvae have a tapered body with no legs. They blindly move over the leaf surface searching for aphids to eat. When they find one, they use their piercing mouth to suck out its bodily fluids.
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So if you find a little green worm on your lettuce or see a bee-like fly hovering around your flowers, it is likely a syrphid fly larva or adult. Syrphid flies are beneficial insects that do double duty, eating aphids and helping with pollination. Encourage them instead of buying a spray to kill them.
For more information, read about "Beneficial Insects, Spiders, and other Mini-Creatures in Your Garden -- Who They Are and How to Get Them to Stay" by going to http://tinyurl.com/beneficial-insects for your free downloadable copy written by Dr. David G. James, Associate Professor, WSU Department of Entomology.
-- Powdery mildew
Several gardeners have come to me recently because they were worried about the silvery patches on the leaves of their zucchini plants. They wondered if it was powdery mildew, a fungus disease that is fairly common in area gardens. It first shows up as small white powdery spots on squash leaves. These spots grow larger until the fungus covers the entire leaf and stem, killing the infected tissues. It typically shows up on squash late in the growing season, about the time the plants are finished producing fruit.
Luckily, what these gardeners have encountered is the natural silvery blotchy variegation characteristic of some zucchini cultivars (varieties). It is not a problem, and the plants are healthy for now, but it is advisable to watch for signs of powdery mildew on squash, cukes and melons.
Avoid powdery mildew by doing a few simple things:
-- When possible, plant cultivars that indicate they are resistant to powdery mildew.
-- Don't plant your squash or other cucurbits where they will be in the shade of other plants or structures for part of the day.
-- Provide good air circulation by not crowding the plants.
-- Finally, rotate your crops so cucurbits are not planted in the same location for at least two years.
For more information, go to WSU's Hortsense website at http://pep.wsu.edu/hortsense.
-- Marianne C. Ophardt is a horticulturist for Washington State University Benton County Extension.