As gardeners, when we encounter insects in the garden there is often a tendency to assume that the insect must be killed before it damages our plants.  If there are holes in the leaves of our plant, it must certainly be the fault of the insect we saw on the leaf of that plant.  While there are thousands of insect species that can damage plants, not all insects are bad for the garden, and some are actually very helpful. These good insects may eat other bad insects, or help to pollinate flowers and vegetable crops. Most pesticides are not selective in killing only bad insects and leaving the good ones unharmed, they’ll kill everything.  Learning which insects are good and which are bad will save you time and money in the garden, and help create a natural environment that will enhance plant growth. 

Advertisement

Ladybugs are the most recognizable beneficial (“good”) insect, as most everyone knows what a ladybug looks like and they are large enough to be easily spotted.  Ladybugs are round insects with black spots.  They eat many harmful insects such as aphids, mealy bugs, whiteflies, thrips and others. 

Praying mantids are another easily recognizable insect that has some benefits to the garden.  Praying mantids can be up to about 4 inches long, with modified front legs that they use to grab their prey (and they rest in a way resembling prayer, thus the name Praying mantis).  Praying mantids eat all kinds of insects, including some good ones and even other Praying mantids, but can be beneficial because they eat many insects that are harmful. 

In addition to these two, and spiders that eat all kinds of insects, there are many beneficial insects that are in the garden, but may be harder to identify.  These include insects such as assassin bugs, green lacewing, ground beetles, pirate bugs and many types of wasps.  The best way to identify these insects is through an insect identification book or field guide.  We also have some pamphlets at the extension office that can help you recognize beneficial insects, or visit cipm.ncsu.edu/ent/biocontrol/goodbugs/tachinid.htm which is the Web site of the N.C. State entomology department biological control information center. 

While using pesticides will not solve all pest problems, beneficial insects may not always be the answer either.  Still it is important to be able to recognize these insects, as they will help you determine the best course of action for controlling a certain pest.  For instance, if you have a few plants that are covered in aphids, but you know you have ladybugs all over the garden, the ladybugs will probably eat the aphids before they cause major damage.  If you don't have ladybugs, spraying maybe necessary. 

When possible, consider using pesticides like Bt (often sold under the trade name Dipel), horticultural oils, or insecticidal soaps.  These types of pesticides will only kill specific bugs, and only those that you spray directly.  By using these pesticides, you can kill undesired pests without causing much damage to beneficial insects. 

Diverse plantings also helps encourage beneficial insect populations.  Try to avoid planting large groups of a single plant type, and mix in flowers like marigolds, sunflowers, cosmos, tansy, bee balm, fennel and yarrow into landscape beds and vegetable gardens to provide habitat for beneficial insects.

The Roanoke Valley Farmers Market will have its annual Strawberry Day on Saturday, May 16.  Stop by from 8 a.m. to 2 p.m. for fresh local strawberries and other produce and goodies, including rain barrels. At 10:30 a.m.,  I will be teaching a class on growing strawberries in your home garden, so come prepared to ask questions.

Matthew Stevens is the horticulture extension agent for Halifax County Cooperative Extension.  If you have any questions about this article or other aspects of your home gardening, please contact Matthew at 583-5161 or matt_stevens@ncsu.edu.