Organic Insect Control for Every Garden

As a home gardener living here on planet Earth, I occasionally have insect infestations that must be solved. While I am an organic gardener, there are times when I need to act to save the plants I love to grow.

This is the first of three articles on insects where I share my organic solutions for navigating the insects we all love to hate! In a following article I will share information on deterring caterpillars specifically; with my final article featuring my favorite pollinator hosts plants.

Organic Insect Control Starts with Good Soil

The real solution to all garden problems is the soil. Healthy plants are less attractive to pests and can recover more quickly. This is why I rely on Soil³ compost and mixes to make my garden healthy from the ground up.

One of the standout benefits of using Soil³ compost and Veggie Mix is their ability to naturally support pest control. Healthy soil enriched with organic matter fosters strong plants with robust root systems and resilient growth.

Additionally, the beneficial microbes and fungi in these mixes help establish a thriving soil ecosystem, encouraging natural predators like beneficial nematodes and other beneficial microorganisms to keep harmful pests in check. Soil³ compost and mixes also provide valuable nutrients, reducing the need to add fertilizer, which leads me to my next important point.

Beneficial nematode - Microscope photo by Nestor Vela, Soil³ Senior Agronomist

How Fertilizer Affects Insect Control

Did you know that applying too much fertilizer leads to pest infestations? Excessive use of high-ratio fertilizers is indeed a major contributor to pest infestations, as it promotes rapid, nutrient-dense growth that is highly attractive to insects.

Unfortunately, many fertilizers marketed in garden centers inadvertently set gardeners up for these challenges by encouraging over-fertilization with unbalanced N-P-K ratios. Opting for organic fertilizers with ratios below 10 is a far more sustainable and effective strategy. Lowering the fertility rate fosters steady, resilient plant growth that is less appealing to pests.

Specifically, reducing the use of nitrogen fertilizers can significantly decrease pest problems by promoting more balanced plant growth. Excessive nitrogen application often causes plants to grow rapidly, producing tender, sugar-rich foliage that attracts pests such as aphids, whiteflies, and caterpillars. These pests thrive on lush, overly vigorous growth.

By limiting nitrogen inputs, plants grow at a more natural pace, developing stronger cell walls and better defenses, which make them less appealing to insects. This balanced growth also encourages plants to allocate more energy toward producing natural pest-deterrent compounds, such as secondary metabolites.

Moreover, reducing nitrogen fertilizer helps maintain soil health and balance, which supports a thriving ecosystem of beneficial organisms like predatory insects and microbes that naturally keep pest populations in check. Excess nitrogen can disrupt this balance, leading to a buildup of harmful organisms while diminishing the diversity of beneficial soil life. By adopting practices like using Soil³ compost, organic fertilizers, and growing nitrogen-fixing cover crops like crimson clover and peanuts, gardeners can provide plants with steady, natural nutrients while avoiding the pest-attracting side effects of over-fertilization.

Crimson clover (the red flower) is a legume that adds nitrogen to the soil.

Organic Insect Control Methods

As gardeners, we know some insects simply do not fit into the “beneficial” category. For those species that cause considerable damage, we need practical, safe solutions. Organic pest management focuses on prevention, diversity, and targeted control measures to keep pest populations in check without harming beneficial organisms. Start by fostering a healthy garden through proper crop rotation and interplanting with diverse species.

Despite your best efforts, there may be occasions when a pest population becomes unmanageable. In such cases, consider these additional practical strategies for managing insects in your garden effectively, before resorting to insecticides.

Strategies to Deter or Remove Insects:

1. Physical Barriers: Row covers, fine mesh, and collars protect plants from beetles, moths, and aphids. Copper tape around pots repels slugs.
2. Handpicking: Regularly inspect plants and remove pests like squash bugs and Japanese beetles.
3. Companion Planting: Use garlic, chives, and nasturtiums to deter aphids and squash bugs.
4. Beneficial Insects: Attract ladybugs, lacewings, and predatory beetles by planting alyssum, cosmos, zinnias, and sunflowers. I recommend attracting them to your garden, rather than ordering them.

Ladybug juveniles (larvae), as shown in this picture, prey on aphids, as do the adult ladybugs.

Organic Pest Control Products:

1. Diatomaceous Earth: Sprinkle around plant bases to deter soft-bodied pests. This is especially effective for controlling squash vine borers.
2. Neem Oil: Spray to combat aphids, spider mites, scale, and many other pests.
3. Bt (Bacillus thuringiensis): This bacteria targets caterpillars such as cabbage loopers, hornworms, and mosquito larvae without harming non-target species.

Diatomaceous earth, neem oil, and Bt products can be found at local garden centers or ordered online. Physical barriers are usually ordered, rather than found locally, unless you have a really good garden center!

Examples of Bt insecticide

Organic Pest Control by Insect Type

To make your life a bit easier, here is a useful resource for identifying and managing the worst insects in our southeastern region.

Aphids:

• Plants Attacked: Tomatoes, peppers, beans, lettuce, and many ornamental plants such as milkweed, roses, and hydrangeas
• Impact: Suck sap, causing stunted growth and sooty mold
• Management: Introduce ladybugs and lacewings, or wash them off with water, use insecticidal soap

Aphids (there are many colors of aphids) are surprisingly easy to wash off - it may take repeat attempts.

Cabbage Loopers & Cabbage Moths:

• Plants Attacked: Cabbage, broccoli, kale, and other brassicas
• Impact: Chew large holes in the leaves of cabbage, broccoli, kale, and other brassicas
• Management: Handpick caterpillars, use floating row covers, and apply Bt sprays to the caterpillar phase

Cabbage moth: charming as a moth, yet so destructive as a caterpillar.

Cutworms:

• Plants Attacked: Seedlings of vegetables and flowers
• Impact: Chew through seedlings at the base, killing young plants overnight
• Management: Place collars around plants, handpick at night, and apply Bt sprays or powder

Fire Ants:

• Plants Attacked: Roots of seedlings and low-growing plants like turf
• Impact: Build mounds in gardens, damaging roots, and posing a stinging hazard to gardeners
• Management: Use bait traps, pour boiling water on mounds (though that will kill garden plants and turf), or apply diatomaceous earth. To be fair, I have yet to find a full proof strategy for eliminating fire ants - they just seem to move a few feet away. I try to keep my distance as I am becoming highly allergic to their bites.

Fire ants form mounds like these all over lawns and gardens, sometimes even around the base of plants, like this panicle hydrangea shrub. Photo by Hillary Thompson.

Fungus Gnats:

• Plants Attacked: Houseplants, greenhouse plants, and young seedlings are typically at risk for severe damage. They are particularly drawn to plants in moist, organic-rich soils such as those used for indoor plants, herbs, and seedlings.
• Impact: Fungus gnat larvae feed on the roots and organic matter in the soil, which can weaken plants and stunt growth. In seedlings and young plants, significant root damage can lead to wilting or death. Adults, while less harmful, can become a nuisance as they swarm around plants indoors.
• Management: Reduce water! Overwatering is the main reason fungus gnats become a problem. Allow the top layer of soil to dry out to discourage larvae from establishing. Top-dress with coarse sand, gravel, or tumbled glass to deter adults from laying eggs.

Grasshoppers:

• Plants Attacked: Highly opportunistic feeders that attack a wide variety of plants, including grasses, vegetables like lettuce, beans, and corn, flowers, shrubs, and tree foliage. They are the only creatures I have ever seen eating castor bean foliage with no consequences!
• Impact: Cause significant damage by chewing leaves, stems, and flowers, leading to defoliation, stunted growth, and reduced yields in crops. In severe infestations, they can strip entire plants, leaving them unable to photosynthesize effectively.
• Management: Attract birds and frogs who feast on them, plant sacrificial crops like sunflowers to lure them away from other plants, apply neem oil to disrupt their life cycle.

There are many types of grasshoppers.

Japanese Beetles:

• Plants Attacked: Many ornamental and edible plants like hydrangeas, roses, hibiscus, okra
• Impact: Skeletonize foliage and damage flowers
• Management: Handpick beetles and apply milky spore powder to lawns to eliminate grubs. Traps may attract more to your property, so use with caution. 

Japanese beetles have a distinctive metallic green sheen, as you can see in this purchased image.

Scale:

• Plants Attacked: Broadleaf evergreens like citrus, camellias, magnolia and deciduous shrubs and trees such as hydrangea and roses
• Impact: Feed on plant sap by attaching themselves to stems, leaves, or branches. This weakens the plant, leading to yellowing, leaf drop, stunted growth, and in severe cases, plant death. They also excrete honeydew, which attracts sooty mold and ants, further damaging the plant's health
• Management: Horticultural oils can be applied to suffocate scale. This is particularly effective for armored and soft scales. Beneficial insects like ladybugs and parasitic wasps will feed on scale insects. Neem oil disrupts the life cycle of scale insects and works well on young, active crawlers in spring.

Scale is often thick on the undersides of leaves, as shown here on Camellia.

Spider Mites:

• Plants Attacked: Veggies like tomatoes, beans, and eggplant and many ornamental flowers and shrubs
• Impact: Suck sap, causing yellowing and webbing
• Management: Increase humidity, use insecticidal soap, or introduce predatory mites

Spongy Moth Caterpillars (Formerly Gypsy Moth):

• Plants Attacked: Native trees such as birch, maple, and oak
• Impact: Invasive species that defoliate deciduous trees
• Management: Manage by adding sticky traps, encourage natural predators, and apply Bt, when possible, to limit their impact

Spongy moth caterpillar photo from the USDA website.

Squash Vine Borers:

• Plants Attacked: Squash, zucchini, and pumpkins
• Impact: Bore into squash, zucchini, and pumpkin stems
• Management: Use row covers, apply diatomaceous earth, and inspect stems for entry holes

Squash Beetles:

• Plants Attacked: Squash, zucchini, pumpkins, cucumbers
• Impact: Skeletonize leaves
• Management: Use row covers, manually remove egg clusters, apply diatomaceous earth, neem oil, or insecticidal soap, rotate crops, remove old debris to eliminate overwintering sites

Squash beetle juvenile (larvae) and adult beetle.

Squash Bugs (a type of leaf-footed bug):

• Plants Attacked: Tomatoes, peppers, melons, and squash
• Impact: Pierce fruits and seeds, causing discoloration and rot
• Management: Remove by hand, use insecticidal soap, and maintain clean garden beds

Stink Bugs (they look similar to leaf-footed bugs):

• Plants Attacked: Tomatoes, peppers, beans, and squash
• Impact: Pierce fruits, causing blemishes and discoloration
• Management: Handpick, use trap crops, and apply neem oil

Stink bugs overwinter in homes, then move outside to our crops. Shown here is a purchased pic of a brown marmorated stink bug.

Tomato/Tobacco Hornworms:

• Plants Attacked: Anything in the Solanaceae plant family 
• Impact: Feed on tomatoes, peppers, and eggplants
• Management: Handpick caterpillars, encourage parasitic wasps, and apply Bacillus thuringiensis (Bt)

Parasitic braconid wasp eggs laid on a hornworm caterpillar. Also shown at the top in the picture with my cat.

Whiteflies:

• Plants Attacked: Vegetables like tomatoes, peppers, and cucumbers, ornamental plants such as hibiscus, poinsettias, and fuchsias, and fruit trees. They are particularly common in greenhouse and indoor garden settings.
• Impact: Feed by sucking sap from the underside of leaves, causing yellowing, wilting, and stunted growth. They excrete a sticky substance called honeydew, which can lead to sooty mold growth and further weaken plants. Severe infestations can result in plant decline or death, particularly in younger or stressed plants.
• Management: Spray neem oil to target nymphs and adult whiteflies. Spray thoroughly on the undersides of leaves where whiteflies congregate.

Whiteflies congregate on the undersides of leaves.

I hope these organic methods to manage garden pests will serve you well this growing season.

Remember, plant health starts from the ground up, and using Soil³ compost not only protects your plants but allows them to grow strong and naturally resist pests.

Focus on soil health, reduce your fertilizer applications, plant with diverse species to attract beneficial insects, and watch for pests before their population explodes. Embrace these organic practices, and watch your garden flourish with healthy, resilient plants and fewer pests!

Brie the Plant Lady

All photos by Brie Arthur, unless noted.