This article from the Agricultural Research Service (ARS) is a good answer to that question. There are a number of beneficial insects that prey upon the insects and weeds that we don't like. The pesticides we buy to kill the insects we don't want very often wind up killing other insects that we may not even know about, some of which could help us in our fight against the pests. For example there are a number of insects that prey upon aphids, those destroyers of flowers and vegetables alike, such as green lacewings, bigeyed bugs, parasitic wasps, damsel bugs and ladybugs (or ladybird beetles to be more precise) and hoverflies.
Getting these insects on your property is sometimes a matter of ordering them from supply companies and releasing them, while other times, you can lure them in from neighboring places with the right cover, food and/or habitat. In this example from the ARS, they found that planting Sweet Alyssum flowers in amongst their rows of lettuce attracted the hoverflies, which then laid eggs. The eggs hatched releasing larvae that devoured the aphids on the lettuce. A link to that article is here.
Now, if someone had come along, seen the tiny flies around the lettuce and sprayed for them, they would have prevented them from laying eggs which would have prevented there being eggs to hatch into the larvae that could have eaten the aphids. Even if they had tried to spray something to kill the aphids, they would have never gotten them all since they hide so well.
Not the beneficial insects nor anything else gets rid of pest insects or weeds completely, not even the expensive, and potentially hazardous chemical pesticides. The best we can do is to keep the populations of pests under a threshold, or number of them that does so little damage that we can still achieve the garden goals we set. The best way to deal with any kind of pest is to plant enough of the desired plants so that if a few are lost to pests, there will still be enough left over for the harvest or for the landscape design to look good to us.
What other pests are you most concerned about on your property? Have you wondered if there was a way to control them that didn't involve using chemicals?
Getting these insects on your property is sometimes a matter of ordering them from supply companies and releasing them, while other times, you can lure them in from neighboring places with the right cover, food and/or habitat. In this example from the ARS, they found that planting Sweet Alyssum flowers in amongst their rows of lettuce attracted the hoverflies, which then laid eggs. The eggs hatched releasing larvae that devoured the aphids on the lettuce. A link to that article is here.
Now, if someone had come along, seen the tiny flies around the lettuce and sprayed for them, they would have prevented them from laying eggs which would have prevented there being eggs to hatch into the larvae that could have eaten the aphids. Even if they had tried to spray something to kill the aphids, they would have never gotten them all since they hide so well.
Not the beneficial insects nor anything else gets rid of pest insects or weeds completely, not even the expensive, and potentially hazardous chemical pesticides. The best we can do is to keep the populations of pests under a threshold, or number of them that does so little damage that we can still achieve the garden goals we set. The best way to deal with any kind of pest is to plant enough of the desired plants so that if a few are lost to pests, there will still be enough left over for the harvest or for the landscape design to look good to us.
What other pests are you most concerned about on your property? Have you wondered if there was a way to control them that didn't involve using chemicals?