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How to Control Garden Insect Pests

Updated on January 13, 2019
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Common Garden Insect Pests and How to Control Them

Aphids are related to cicadas. They can kill garden plants by sucking out essential juices and sap.
Aphids are related to cicadas. They can kill garden plants by sucking out essential juices and sap.

Every Garden Has an Insect Pest Problem

According to the Journal of Experimental Biology, "Ecological interactions between insects and plants are complicated and dynamic. What occurs in one system at one snapshot in time may not occur again at another snapshot at a different time and each insect." What this means for our gardens is simple: every garden has its own, unique set of challenges from insect pests. This article will help you understand which insects are attacking your garden, and what your options are for fighting back.

Tomato Hornworm Control

Tomato hornworms are a major pest of cultivated tomatoes
Tomato hornworms are a major pest of cultivated tomatoes

Diatomaceous Earth to Control Hornworms and Other Caterpillars

Hornworms are the larvae of a large brown moth called a hawk moth. These caterpillars can decimate your tomatoes, eating fruit, leaves, and even stems. They are also very hard to see on the plant, since they are perfectly camouflaged among the leaves. The most natural way to control tomato caterpillars is to find them and pick them off, but finding them all can be very difficult.

The next best solution is diatomaceous earth. This is simply dirt from an area that was once a pond where diatoms lived. Diatoms are single-cell organisms with a shell made of silica -- basically glass. The millions of broken diatom shells make a jagged, sharp surface when dusted on your plants, and caterpillars crawling over it get sliced and diced and soon die. The diatomaceous earth washes off with the next rain and goes back to being dirt.

Using diatomaceous earth means you are controlling caterpillars and other garden pest insects without any chemicals, toxins, or man-made materials.

Common Garden Insect Pests

When we're out working in our garden and we come across an insect, the first question in, "good or bad?" This guide will help you know the difference.

Aphids, Grubs, Japanese Beetles, and Hornworms

Don't let these insects eat up all of your hard work this year! When you know what to look for, you can help save yourself from some of the most destructive garden insects. There are many different insect pests that attack your garden during the growing season. This article will focus on a few of the most common, and the most destructive.

Garden Insect Control: Aphids


Aphids are small insects in the order Hemiptera, otherwise known as the "true bugs" -- so calling these little critters "bugs" is scientifically accurate. There are several families of aphids within the superfamily Aphidoidea, including Mindaridae, Pemphigidae, Phloeomyzidae, and Thelaxidae. Aphids typically occur in large numbers, clustered near the top of plants. They use their piercing mouthparts to suck tiny amounts of juices from plants they attack -- but since there are so many of them, the cumulative effect on your plants can be devastating.

How Ants Protect Aphids

One reason your aphids can be tough to get rid of is the symbiotic relationship they have evolved with ants. Ants are aggressive protectors of aphids because aphids release a substance, called "honeydew," that the ants feed on. As a result, ants tend to aphids in much the same way farmers tend to cows -- they harvest the honeydew, and in return protect the aphids by chasing away or killing predators. Ants are in the same order as wasps (Hymenoptera), and will sting and bite to protect their aphid "herd."

Aphids versus Ladybugs

One good option for controlling aphids in your garden is to introduce ladybugs. Ladybugs are actually beetles -- another name is "ladybird beetle" -- of the family Coccinellidae. Despite their quaint name, they are ferocious predators of many aphid species. Both the highly visible black and red beetle and the larvae, which look a little like tiny lizards, will attack aphid colonies and can be effective natural control methods.

Garden Insect Pest Control: Grubs

Beetle Grubs: Pests That Live Under Your Grass

Grubs are the immature form of beetles (Order Coleoptera). The kind that does damage to your lawn and plants are often members of the Scarabaeidae family, a very large group that includes some of the world's largest and most attractive insects. Unlike these, lawn grubs grow up to be plain brown beetles known in some parts of the country as May beetles or Junebugs. The adults are generally harmless and eat relatively little, but the grub stage can do damage by feeding on roots just below the surface. You probably won't even see them unless you 're doing yard work, but you can tell if you have grubs by unexplained die-off in grassy areas or among garden plants.

Damage From Grubs

Controlling Grubs

Unfortunately, one of the most popular ways to control grubs is to use chemicals. Many of the products out there don't even work because they don't get down into the soil where the grubs are. For example, products containing lambda-cyhalothrin, gamma-cyhalothrin, bifenthrin, deltamethrin, cyfluthrin and permethrin are generally going to be a disappointment when it comes to grub control because they don't get down into the soil where the insects are.

This excellent article describes the best way to control beetle grubs. You need to dig up a patch of your dying lawn and see if you have grubs there. From that point, it's going to be a matter of applying a pretty serious pesticide.

Garden Insect Control: Japanese Beetles


Japanese beetles, otherwise known as Popillia japonica, are one of the most significant pests in North America. They are native to Japan, where a number of natural predators keep the species in check. Since being introduced by accident in 1916 in a New Jersey nursery, the Japanese beetle has spread nearly everywhere in North America, attacking upwards of 200 species of plants, including rose bushes, grapes, hops, canna, crepe myrtles, and others.

Lacking natural predators here, the beetle has been able to grow without challenge. Finding efficient natural, or even chemical control methods has proven to be nearly impossible.

Leaf Damage Typical of Japanese Beetles


These beetles tend to eat leaves and flowers, leaving the parts too tough for their jaws. In this case, they eat the soft leaf parts but leave the fibrous veins, producing a characteristic "web" look.

Options for Control of Japanese Beetles

There is a pathogen called "milky spore disease" that is deadly to Japanese beetles. Milky spore is a naturally occurring host-specific bacterium (Bacillus popillae-Dutky), that acts as a natural control vector for P. japonica. Since the immature grub of the beetle feeds in the ground, applying this substance to the ground reaches and kills the grub.

Garden Insect Control: Kill Japanese Beetles Without Spraying!

Japanese beetles are a serious pest that can really chew up your rose bushes, not to mention just a out any other plant. They are an invasive species that has few natural predators here and pose a serious threat to our ecosystem. There are passive attractant traps draw Japanese Beetles into a container using pheromone bait. You never have to handle or even see the dead beetles -- just dispose of the container and set out a new one.

This method is used by professional biologists and entomologists to attract and assess pest insect populations.

Garden Insect Control: Tomato Hornworms


As we have already discussed, these large caterpillars are the larval stage of a large hawk moth, Manduca quinquimaculata, or the tomato horn worm moth, which is a member of the Sphingidae family in the order Lepidoptera. They commonly show up in mid to late summer, when tomato vines are just starting to bear fruit. They are quite large and heavy, but can still be hard to find among tomato plants thanks to their excellent camouflage. It is unusual to find just one of these garden pests, since the female moth typically lays dozens of eggs on the plant -- in other words, if you find one, don't stop looking, since more are almost certainly nearby.

Control of Tomato Hornworms

Chemicals and pesticides are notoriously ineffective against hornworms, but there are other measures that do work well. One of these is the application of talcum powder. The dust clogs up the insects' spiracles, the holes along the side of the body through which they breathe. You may also want to enlist your family and friends to go on a seek and destroy mission, since it often takes more than one pair of eyes to find every caterpillar. Another option is to soap your plants with an anti-insect soap -- but be sure to get a quality product, since there many "anti-insect soaps" out there that are really nothing more than a little diluted dish soap in an expensive spray bottle...

Natural Control of Caterpillars and Other Insects

With hornworms and other insects that crawl over leaves are susceptible to the jagged broken shells of diatoms contained in diatomaceous earth. This natural compound is one of the best, and least toxic, options for garden pest insect control.

Here's to a Healthy Garden!


The following sources were accessed for this article:



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