Excerpted from Gardening Complete by the authors of Cool Springs Press (February, 2018)
What is a Garden Pest?
In order for an insect to be deemed a pest, it has to cause a significant amount of economic or aesthetic damage to a plant. Yes, a lot of insects eat plants, but most of them do not cause significant damage. And, in most cases, the harm these insects cause is not life-threatening; it just makes the plant look not so hot for a short time. It’s surprisingly rare for a pest insect to outright kill its host plant; after all, it’s not in an insect’s best interest to eliminate its food source and the food source of future generations.
Exactly what amount of economic or aesthetic damage is deemed “significant” depends on the tolerance of each particular gardener. Once you come to realize that most leaf-munching insects are not out to kill your plants, your tolerance for their damage should naturally go up. Obviously, if you’re a farmer who needs to grow near-perfect crops for your livelihood, your tolerance of pest damage that cuts into your bottom line will be far less than Joe Homeowner who’s just growing a garden to help beautify his outdoor living space.
Pest numbers also matter. One teeny tiny aphid is not a pest because the damage it causes is minimal, but hundreds of aphids can cause a far more significant amount of damage, and the gardener may need to step in with a management strategy. On the other hand, one tomato hornworm can nibble an entire tomato plant to the nub, so implementing a few management tactics is certainly called for, even when there’s just one hornworm present.
All this means is that deciding whether or not a particular pest is worth the time, money, and effort to control is best determined by careful consideration of your personal tolerance, the type of damage caused, and the number of pests present. Every gardener’s opinion on when it’s time to step in will vary, but I encourage you to not step in too soon, because not only are properly cared for plants very forgiving, but also, as you’ll come to learn later in the chapter, many pest issues are naturally managed by beneficial predatory insects.
Why You Need to Identify Pests in Your Garden
Another essential step in determining whether anti-pest action is required is to make sure you’re properly identifying garden pests and that you understand their life cycles and the extent of damage they can cause. For example, some pests have life cycles that only last a few weeks, while others only feed on plants for a short period of their lives, so taking action against a pest in one of these two groups isn’t worth the time and effort because the pest will be gone before they can cause much damage. On the opposite end of the spectrum are the insects that are capable of producing multiple, overlapping generations within a single growing season. Their populations can explode in short order, causing a great amount of damage in a relatively short period of time. The only way to know how much a pest’s life cycle influences the amount of damage it can potentially cause is by properly identifying garden pests and learning about them before you decide to take any action. There are several different ways to do this.
Methods of Identifying Garden Pests
Identify garden pests by physical description. This identification method considers the insect’s size, shape, coloration, leg count, wing count, and other physical attributes. It’s a useful method if you have access to a good insect ID book (see list below) or website where you can compare photos to the live insect in your garden.
Identify garden pests by type of damage. Often the insect itself isn’t actually present on the plant; instead we just come across the damage. Identifying insects by the damage they cause is easier than it might seem. Many insects have very distinctive feeding patterns and the damage they leave behind is unmistakable. This method of identification often goes hand in hand with the next method, because when you find a particular type of damage on a particular host plant, it helps narrow down the possibilities even further.
Identify garden pests by host plant. In many instances, a leaf-munching insect pest only dines on a select few species or families of plants. Some insect pests are even so specialized that they can only consume one species of host plant (think asparagus beetles, holly leaf miners, and rose sawflies, to name just a few). Matching up the plant species with the insects that commonly feed on it is just another key to unlocking the identity of a pest.
Sometimes just one of these three methods is all you’ll need for properly identifying garden pests. Other times, it may require using a combination of two or three of them.
Our online course Organic Pest Control for the Vegetable Garden, provides even more information about identifying and managing pests using natural techniques in a series of videos that total 2 hours and 30 minutes of learning time.
Great Books for Identifying Garden Pests
To confirm the identity of the pest, you should then consult a good pest insect identification book or website. Here are some of my favorites for identifying garden pests.
Garden Insects of North America: The Ultimate Guide to Backyard Bugs by Dr. Whitney Cranshaw Good Bug Bad Bug: Who’s Who, What They Do, and How to Manage Them Organically by Jessica Walliser National Audubon Society Field Guide to Insects and Spiders: North America by the National Audubon Society Kaufman Field Guide to Insects of North America by Eric R. Eaton and Kenn Kaufman
Identifying Non-Insect Garden Pests
For non-insect garden pests, you can use the same three methods you use for identifying garden pests that are insects. If you can’t see the animal eating your garden long enough to get a physical description (perhaps they dine at night?), look at how they feed on the plants and what plants they’re consuming. You can also look for footprints in and around the garden. Or, if you don’t see any footprints, sprinkle a coating of all-purpose flour around the nibbled plants and see whose footprints are in the dust the following morning.
Once you’ve properly identified the culprit and read up on its feeding habits and life cycle, it’s time to look into ways to prevent and control it. For that task, we recommend visiting our Guide to Garden Pests.
Related posts to help with pest management: 12 Organic weed control tips Managing disease in the garden Identifying and managing tomato plant diseases Guide to vegetable garden pests Deer-proof gardens: 4 sure-fire ways to keep deer out of your garden Cabbage worm control methods
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