Not all insects are harmful to plants

When most gardeners think about insects, fungi or bacteria in the garden, bad things normally come to mind.

//

But not all insects, fungi and bacteria in a garden are bad. Many of these organisms provide benefits for our gardens.

As we lose pesticides from regulation issues or pest resistance, we need to use more biologically based pest management systems.

Some of the natural control systems include the use of pest-resistant plants or the use of pheromone traps. The most commonly used biological controls are the use of predators, parasites and pathogens.

Predators are insects, spiders and mites that find and kill other insects. Sometimes these insects look very similar to insects that attack our plants.

I was looking at the plants in my vegetable garden recently when I spied a stink bug. Stink bugs are one of the hardest insects to kill in a vegetable garden, and they can do serious damage to tomatoes and beans.

However, upon closer inspection, I was not looking at a bad stink bug. It was a predaceous stink bug called a spiny soldier bug. The spiny soldier bug is a known predator of more than 100 pest species.

So how do you tell the difference between a stink bug that is a pest and a predaceous stink bug? The plant feeders have rounded shoulders, and the predaceous stink bugs have spines on their shoulders. So, I left the spiny soldier bug alone.

There are many other predator insects. Lady beetles are among the most famous of these. They are also one of the best predators that we have in the garden. The adult and larva stage eat insects. They are great predators of aphids, scale insects, mites, mealybugs other soft-bodied insects and their eggs.

Another famous predator is the praying mantis. They are fun to watch, but they are not the best at suppressing insect populations. They will feed on larger insects, but are not suited for feeding on the small insects such as aphids. Some of the better predators are green lace wings, paper wasps, earwigs, ground beetles and assassin bugs.

There are a number of parasitic wasps and flies that attack other insects. The parasitic wasps are very small, and unless you know what you are looking for, you will rarely see them. There are parasitic wasps that attack aphids. They are the size of or smaller than the aphid. The wasps lay eggs on the aphids, and the young wasps develop inside of the aphid. They kill the aphid as they develop. If you look closely, you will see the tail end of the aphid missing. This is where the young wasp emerged.

If you grow tomatoes, you have seen tomato horn worms. These are large caterpillars that can devour your tomatoes overnight. Sometimes, you find the horn worms with white egg looking things attached to their backs. These are the larval stage of a parasitic wasp. Leave these on the tomato plants. The caterpillar at this stage is not eating your tomatoes; it is being eaten by the wasp larva. If you leave them in the garden, you will have more parasitic wasp to control more worms.

There are pathogens in the garden as well. If you find caterpillars or insects that have a moldy growth on them, leave them alone. These insects died from a fungus. Leave them in the garden so spores from the fungus can attack other insects.

So, how do you increase the number of beneficial insects in your landscape or garden? The first step to increasing the number of insects is to avoid the use of broad-spectrum, highly toxic pesticides. These not only kill the crop pest, but the beneficial insects as well. If possible, use an insecticide that has quick knockdown of insects, but it doesn't persist in the environment long.

The second practice is to plant flowers that bloom for the entire season in the area. Many of the predators and parasitic wasps and flies feed on pollen and nectar. Some of the plants that are attractive to beneficial insects are daisies, Queen Anne's Lace, yarrow, goldenrod and clover. I use clover in my garden as a winter cover crop.

Aphids will feed on the clover during the winter, and I had lady beetles in the clover feeding on the aphids. The next spring, I had some aphids on my tomatoes, but there where so many lady beetles that they cleaned up the aphids in two days.

Beneficial insects can reduce the number of insect problems in your landscape and gardens, but you need to monitor the pest to see if they are being attacked by predators. If they are, let the beneficial insects do the work for you.

Columbia County Extension agent Charles Phillips can be reached at (706) 868-3413 or by e-mail at charlesp@uga.edu. The Extension Web address is www.ugaextension.com/columbia.