When I think about insects, fungi or bacteria in the garden, bad things normally come to mind. I hate the sight of plants that have been eaten; leaves turning brown or plants dying.
But not all insects, fungi and bacteria in a garden are bad. There are many of these organisms that 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-resistance 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 plants. The other afternoon, I was looking at the plants in my vegetable garden 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 plant feeding stink bug but at a predaceous stink bug called a spiny soldier bug. The spiny soldier bug is a known predator of more than 100 pest species.
So, what is the difference between a pest stink bug 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 insects. They are also one of the best predators that we have in the garden. They are great predators of aphids, scale insects, mites, mealybugs, other soft-bodied insects and their eggs.
Another famous predator is the praying mantids. 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, wheel bugs and assassin bugs.
There are a number of parasitic wasps and flies that attack other insects. The parasitic wasps are very small, and mostly go unnoticed in the garden. 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. The wasp larva will kill the aphid as they develop. An aphid that has been killed by the wasp will have a golden color and the tail end of the aphid will be missing where the young wasp emerged.
One of the major pest of tomatoes is the tomato hornworm. These are large caterpillars that can devour tomatoes overnight. Sometimes, the horn worms will have white egg-looking things attached to their backs. These are the larval stage of a parasitic wasp. These caterpillars need to be left on the tomato plants. The caterpillar at this stage is not eating your tomatoes; the caterpillar is being eaten by the wasp larva. If you leave them in the garden, there will be more parasitic wasps to control more worms.
There are pathogens in the garden as well. Dead caterpillars or insects that have a moldy growth on them need to be left alone. These insects died from a fungus. If they are left in the garden, spores from the fungus can attack other insects.
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 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 over 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 were so many lady beetles that they cleaned up the aphids in two days.
Charles Phillips is a retired Columbia County Extension Service agent and operates Hort Consulting. He can be reached at cphillipshort@ comcast.net.
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