Identifying Garden Pests: How to figure out who's eating your plants.

Identifying garden pests: How to figure out who’s eating your plants

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Most gardeners face pest issues from time to time, and though we have a wonderful Guide to Vegetable Garden Pests here on our site, many gardeners often find themselves needing to be able to properly identify a pest before turning to such a guide for solutions to their problem. Garden pest ID is a task that can be very difficult, especially if the pest isn’t physically present on the plant when the damage is discovered. Today, we’re sharing an excerpt from the book Gardening Complete by the authors of Cool Springs Press (including several chapters by Savvy Gardening contributors Jessica Walliser and Tara Nolan!). We’re excited to be able to share it with you because the excerpt offers some very practical advice on identifying garden pests using methods you may not have considered before.  

Excerpted from Gardening Complete by the authors of Cool Springs Press (February, 2018)Excerpt from Gardening Complete on how to identify garden pests.

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.

Though some insects are garden pests, many more are not.

Gardens are complex ecosystems with many layers of organisms living in them. It’s important to remember that while some of these organisms are harmful to our plants, the vast majority of them are not.

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.

Identifying garden pests by the damage they cause.

Aesthetic damage is often not harmful to the health of your plants; it just detracts from their appearance. In most cases, some amount of aesthetic damage should be tolerated by the gardener.

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.

Garden pest ID is made easier with these tips.

Determining whether or not a pest is worth controlling, involves considering your personal tolerance, the extent of the damage, and the number of pests present on the plant.

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

1. 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.

Pest identification guides are useful tools.

Identifying insects, such as this blister beetle, by their physical traits is one way to determine who is nibbling on your plants. Use a good insect ID book or website to help with the sleuthing.

2. 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.

3. 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.

Pest identification can take place by using signs of their damage.

Some pests have very distinctive damage that makes identifying them easy. Hibiscus sawfly larvae are responsible for this hole-filled leaf.

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.

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
Gardening Complete book

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13 Responses to Identifying garden pests: How to figure out who’s eating your plants

  1. Sally says:

    A slug like thing small eats leaves on are Lille’s from the top of the leaves to the bottom and work it way though the hole stem and on to the next what is it

  2. Shirley Lucas says:

    1/4″ green caterpillars on underside of Columbine leaves. They devour every leaf within 24-48 hours. Also found some on rosebush, damage not as bad. They barely seem to grow despite all the eating. Did drop off leaves when sprayed with insecticidal soap. Thanks

    • These are sawfly larvae. Columbine sawflies are a separate species from rose sawflies, but both can be managed with insecticidal soap or horticultural oil. Be sure to make direct contact with the insect.

  3. Virginia Franco says:

    A large ladybug looking beetle is eating my butterfly bush only. They eat it completely. What is it and how do I manage to get rid of it without hurting my other plants.

    • Do you mean butterfly bush or butterfly weed? There aren’t many pests that eat butterfly bushes, but your description sounds like a milkweed beetle, which does feed on butterfly weed.

  4. Patricia says:

    Small, black winged bugs, about the size of a small ant are in the soil of my container plants. I don’t see these bugs on the plants but they are thriving in the soil and the plants are turning an ash coloring and dying. What can I do?

  5. Reaz says:

    I identified – its called ‘ CUCUMBER BEETLES’ . What exactly I need to use for quick remedy?

  6. Kathy Stein Simeral says:

    I need help! In all my years of flower gardening, I finally decided to add a Midnight Marvel Hibiscus plant to my yard. Absolutely beautiful! I have gone out in the early part of the day, midday, and at dusk and cannot find any bugs, beetles, flies are larvae present on the leaves. There is damage to leaves at all different levels (not just top or bottom). There are holes that are fairly large and odd shaped. There is a rusty or brownish color (maybe larvae?) before the holes develop.

    • Sounds like hibiscus sawfly larvae which are extremely small and hide out on the undersides of the leaves. They are very difficult to see because they are the same color green as the leaves and are very miniscule. The damage you describe is pretty classic of this pest.

  7. Andy says:

    Thank you SO MUCH for your information! I was chasing a ghost. As it turns out from your picture and site, my oregano was NOT being eaten by pests! It was just a degree of aesthetic damage! Thanks again, Andy

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