NEIGHBORHOOD GARDEN FOR AUGUST 15, 2009

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DON ’T KILL YOUR BENEFICIAL INSECTS PART #3

BY GEORGE EDGAR

          Did you know that there are over 1,000,000 insect species that have been described by entomologists? Do you know how many of these are actually garden pests? According to a University of Wisconsin Extension Horticulture Educator , less than 100 are actually garden pests. Three years ago I wrote a series of articles “Only 3% Of the Insects in Your Yard and Garden Are Destructive”. I decided to recycle this series of articles when I heard recently of a person who saw a black bug on her plant and grabbed the only insecticide she had in the house. A couple days later the leaves started to turn brown and then dropped off. This insecticide had an oil base and when applied outside in 90 degree weather, the leaves burned. Her plant will probably not survive. She did not know what the bug was or if it was destructive. All she knew was the bug was on her plant.

          So if only 3% of the insects are destructive, what about the other 97%? One entomologist told me that the other 97% of the insects can probably be classified as follows:

·        Nuisance insects

·        Neutral or incidental insects

·        Beneficial insects

1.       A good example of a nuisance insect is the Boxelder Bug. This bug does not eat your plants, it does not bite you. When it gets into your home it does not eat clothes, drapes, or furniture. These bugs are just a nuisance and can be best cleaned up with a vacuum. Mini-vacs are a tremendous advance in household pest control technology. And no chemicals are needed. Many do not like these nuisance insects but they are not destructive.

2.       Neutral or incidental bugs are just that. They exist in our environment but are not chewing on our plants, they do not transmit diseases, nor do they bite us or our pets. Some, like butterflies, can be very pretty and are prized for their aesthetic value.

3.       The beneficial insects can be further classified as

·        Decomposers, that break down organic matter, help turn yard and kitchen scraps into compost, and are necessary for the health of the soil in our yard and garden;

·        Pollinators, such as bees, flies, beetles, and other flower-visiting insects;

·        Predators and parasites, including lady beetles, green lacewings, syrphid flies, ground beetles, parasitoid wasps, and other insects that eat aphids, grubs, caterpillars, as well as other yard and garden pests. The parasitoids lay their eggs in, on, or near many undesirable insects, their eggs eventually hatching and the larva feeding on the host, soon killing it.

         Fred Birdsall , a Colorado Master Gardener, and Carl Wilson , a horticulturist at Colorado State University Cooperative Extension, have written an article on “Growing Plants to Attract Beneficial Insects”. In this they say a gardener can grow plants in their garden that attract beneficial insects. “Adult lacewings, flower (syrphid) flies and parasitic wasps, for example, feed on flower nectar and pollen. Their young devour many of the insect pests that can make a gardener’s life miserable. Maintaining this workforce however means providing food for the beneficials AND tolerating a few insect pests.” (“Growing Plants to Attract Beneficial Insects” by Fred Birdsall , Colorado Master Gardener , and Carl Wilson , horticulturist, Colorado State University Cooperative Extension. Copyright by CSU /Denver Cooperative Extension Master Gardener 1999-2006.) Whitney Cranshaw , Colorado State University entomologist updated the article in February 2009 and includes a list of plants that have high visitation by beneficial insects. This list is contained in an article entitled “Beneficial Insects and Other Arthropods”. For a copy go on the internet to “http://www.ext.colostate.edu/pubs/insect/05550.html”. He has also written an article on “Managing Nuisance Household Invaders”.

          It really bothers me when people get out the bug spray whenever they see any kind of insect. Or when people buy a 4-step, 5-step, or 6-step lawn program and put the insecticide step on their lawn even though they do not have and never have had an insect problem. Or when homeowners sign a contract with a lawn care company for an insect application when they do not need it.

          I overheard a man tell a store clerk that he had just finished mowing his lawn and had many moths fly up as he mowed. He was sure they were laying eggs and they would destroy his grass. He asked for an insecticide that would take them all out. He had no idea what the moths were, if they were really laying eggs, and if they would injure his lawn. The clerk in the box store did not know anymore than the homeowner and sold him a granular insecticide for his lawn. For years the only insecticide I have put on my lawn is “imadicloprid” (Merit) for grubs. The more insecticides you use the more you kill the beneficials and predators that keep the bad bugs under control.

          If you use a general purpose insecticide like Sevin, Eight, Malathion or Bifenthrin every time you see a bug, or every year put a general insecticide on your lawn just because you think you should, you may be doing more harm than good. Make sure the insects you see are actually hurting your lawn or your plant before taking action. Not all the holes in the leaves of plants are caused by insects.

          Use the right insecticide, at the right rate , at the right time, on the right insect.

Copyright 2009