As organic gardeners, we have a duty to protect our health, our plants’ health, and the environment – but this is no easy task. Plenty of unwanted bugs and microorganisms come to feast on our vegetables. While a few of them are acceptable, we need to take serious measures when we’re dealing with infestations.
Organic pest control methods can be divided into a few categories: pest barriers, physical removal of pests, biological methods, and home-made sprays or dusts. Organic pesticides allowed by current regulations must be natural, environmentally safe, and should not lead to soil accumulation.
There’s no such thing as a universal pest control method. This is why we should focus on prevention rather than treatment. Strong, healthy plants are scientifically proven to suffer less from pests and disease than weak, fragile seedlings.
Rules for using these methods in the garden
Regularly inspect your garden. Spend time in your garden every day, if possible, inspect the leaves and check your plants for any kind of damage. The sooner you spot an issue, the easier it will be to fix it.
Diagnose the problem. Different problems have different solutions. As gardeners, we’re continually learning about different kinds of symptoms of disease and pest issues. We learn about the cycle of pest infestations – flea beetles are active in late spring, blight, and mildew strike in the summer heat. Sometimes, simply knowing when to expect a problem is enough for preventing it.
Decide how serious the problem is. Most of us can live with a few holes in our plants due to slugs, snails, or birds. However, when the damage starts to get out of hand, it’s time to intervene. We need to learn to share part of our crops with other organisms – it’s a small price to pay for getting clean, organic vegetables.
Take the least harmful action. Whatever we decide to use as a pest control method, it needs to be as safe as possible – for us, the plants, the soil, and our garden’s ecosystem. Few of the pest prevention methods work in a completely safe way, that’s why it’s important to choose the least harmful ones first and leave the others as a last resort.
Crawling pests barriers
Abrasive strips or materials that are placed on the soil, surrounding the plants, can be an effective method against soft-bodied crawling pests such as slugs, snails, or caterpillars.
You can use whatever you have at hand and creates a rough, unattractive surface for these pests to cross – spread sawdust, wood ashes, crushed seashells, coffee grounds, or eggshells. They will break down and feed the plant in the process.
This method is simple to use but isn’t always effective, especially in wet, rainy conditions, and when slug populations are high.
Electric slug & snail repeller fence
Slugs are extremely persistent little creatures, and they will try to cross whatever terrain to get to the plants they deem delicious. Some gardeners resort to a clever method that delivers mild electric shocks to the slugs’ soft bodies.
Mount copper or steel wires all around your raised beds – use two wires that are close together, so that the snails touch both wires when attempting to cross over. Connect the wires to a 9V battery and regularly check its power throughout the season.
Many gardeners swear by this method, but the slugs and snails that were already inside the soil will continue to damage the plants, so it would be a good idea to set some beer traps or handpick them at night.
Floating row covers
Floating row covers are a very efficient way of preventing any flying insect or bird from accessing the plants underneath. These covers don’t “float” per se, but are light enough to allow the vegetables to grow and push the covers as they become taller.
During early spring, gardeners use fleece row covers as season extenders, as they supposedly increase the temperature slightly underneath, and shelter the plants from the elements.
You can water your seedlings through the fleece covers, as they’re permeable to water.
Later in the season, fleece covers make way for mesh covers, which are completely transparent, super light, and allow air to move freely. These mesh covers are particularly useful for protecting brassicas from cabbage white butterflies, cabbage whiteflies, and similar pests.
Bird nets and other similar structures are used to prevent animals and birds from eating certain vegetables or fruits, especially strawberries.
Many organic gardeners choose to use these physical barriers as a prevention method so that they don’t have to deal with an infestation later in the season.
Cabbage root fly or cabbage maggot fly is an insect that lays eggs at the base of cabbage plants. As the eggs hatch, the maggots that emerge don’t have to travel far to get to the cabbage stem.
By placing 8-inch circles of cardboard or other rigid, similar materials at the base of each cabbage seedling so that they will fit snugly around their stem, you’ll discourage cabbage root flies from laying eggs below the plants.
Cabbage collars aren’t a foolproof method, they will rot eventually, but they can also be covered by soil or blown away by the wind. It’s best to combine this method with using row covers and mesh, as there are many other predators out there throughout the season.
Cutworms are moth larvae that feed at night and hide under a layer of soil, at the plant’s base during day time. They like to feed on tender seedlings, destroying the base stems of vegetables like tomatoes, potatoes, peas, beans, or brassicas among many others.
Cutworms can do a lot of damage in no time at all, but they don’t attack plants that are already established. If you’ve had a cutworm soil infestation in the past, using cutworm collars is a good way to protect your precious seedlings.
Cutworm collars can be as simple as toilet paper rolls, paper cups, small plastic containers, or even commercially manufactured collars. The collar protects the seedling’s stem and root system from damage and doesn’t allow cutworms to access them at this stage.
Mulching has many purposes in a vegetable garden. It protects the soil from erosion, keeps moisture in, and acts as a weed suppressant. Organic mulches decompose and improve the structure of topsoil, while commercial mulches act as a barrier both against weeds and pests.
Mulch protects against pests in two ways: it provides protection against soil pathogens, as rain no longer splashes them on top of plants’ leaves, and it discourages certain pests from laying eggs on the soil’s surface or finding shelter for wintertime.
Physical methods of removing pests
It might seem like a nasty job, but regularly hand-picking pests is a good way of controlling bug populations before they get out of hand. The best candidates for picking are large, slow-moving pests such as caterpillars, snails, and slugs, Colorado potato beetles, or squash bugs.
Most insects are safe to pick with bare hands and they don’t bite through human skin, but for comfort and hygiene, wear rubber gloves and carry a container with soapy water, or a medium from which your “victims” can’t escape. Check your garden regularly – at least a couple of times each week – so that pest populations don’t have time to multiply.
Slugs and snails only get out at night, so it’s best to look for them after sundown, using a flashlight. Remove egg buildup if you find any identifiable clusters. Check for hiding places for squash bugs and Colorado potato beetles – either on the backside of leaves or lower towards the ground.
Lastly, make sure you kill the insects or dispose of them in a medium from which they can’t escape – like a plastic bag or a lidded container. Insects make a great feed for chickens and can even be hot composted after you’ve ensured they’ve died.
Water sprays or high-pressure watering are a safe, efficient way of getting rid of small, soft-bodied insects such as aphids, spider mites, or thrips.
A simple water hose with a nozzle set on the flat setting is enough to mechanically wash away even the most stubborn pests. The water will act like a blade, which might temporarily bruise tender leaves, but they will recover. Flowers, however, are too tender to withstand water pressure, so work your way around them.
Washing aphids away is a great way to get rid of them for good, although it’s a grueling process to go through every single affected leave. Aphids cause leaves to curl and will seriously affect a crop if left unchecked, so watering them down is well worth it.
With large aphid infestations, you must also take the extra measure of getting rid of the ants that placed them on your plants in the first place – pour boiling water on top of their colonies or place borax mixed with sugar where you see them the most.
At some point, when all else fails and pests, their eggs, and their products are too heavily concentrated on certain areas of a plant, it’s best to remove that part.
Pruning is an important component of maintaining the health of your vegetables. Remove old, wilted leaves that are close to the ground to discourage slugs from hiding underneath them. Prune leaves that have been curled by aphids or show any sign of disease.
Immediately remove leaves that have been affected by blight, so that it doesn’t spread, or if the plant has too many sick leaves, pull it out of the ground and discard it away from your garden.
Always use clean, sharp instruments and sanitized hands when dealing with disease and moving from one plant to another. It might seem like an insignificant detail, but you could be spreading plant disease without even knowing it.
Biological methods of organic pest control
When we hear nematodes, we think of the harmful type that sometimes leads to plant infestation. But there is such a thing as beneficial nematodes – beneficial to us, and harmful to other susceptible pests. The most widely used beneficial nematodes are Steinernema carpocapsae and Heterorhabditis bacteriophora.
When released into the soil, beneficial nematodes immediately search for hosts. They enter insects’ bodies through their natural openings – mouth, shedding tissue.
Nematodes carry a specific bacteria, and they kill their hosts by releasing this bacteria inside their intestines, which leads to paralysis and death within 24 to 48 hours. You’ll know the treatment has been effective when the harmful pests appear chalky white or gray.
The nematodes will continue to feed on the remains of the insects, and their larvae will survive inside the soil for many months, provided that the darkness and humidity levels are right.
Nematodes are effective against insects that live inside the soil or at the soil surface: cutworms, armyworms, earwigs, onion maggots, sowbugs, white grubs, and many more.
Always diagnose the problem and consult a specialist before releasing beneficial nematodes into the soil. Commercial suppliers manufacture many strains and they may not all work the same. Mix the formulation thoroughly with water, according to instructions, and water the soil around the plants with a watering can.
BT (Bacillus thuringiensis)
BT is a microbial method of organic pest control that is now widely used in organic gardening, with dozens of varieties directed at various pests. The most recommended types of BT are:
- BT israelensis (BTI) – this bacillus targets mosquitoes, fungus gnats, and black fly larvae;
- BT kurstaki (BTK) – this variety of BT is best used for caterpillars such as cabbage worms, tomato hornworms, cabbage loopers, or gypsy moth larvae among many others;
- BT san diego (BTSD) – this bacillus eliminates pests that feed on plant leaves, like Colorado potato beetles. However, this product is not approved by NOP (National Organic Program), because its manufacturing process involves genetic engineering.
You can find BT in many forms: dusts, liquids, or granules. It’s best to mix it with dish soap for better adherence and apply it multiple times for optimal effects, preferably in the evenings. Repeat applications if it rains.
Studies on BT have shown that this substance is non-toxic for humans and safe for the environment, although certain species of wasps can be affected with high doses. Although it’s generally effective, repeated applications can lead to resistance in the case of certain pests, which can potentially create future problems.
Organic sprays and dusts
For decades, gardeners have been using home-made sprays and potions to treat their plants, and what has withstood the test of time is the simple, humble dish soap. Diluted dish soap can be used on its own or as part of more complex homemade pest sprays.
The compounds in soap penetrate the delicate cuticles of soft-bodied pests such as aphids, whiteflies, or mealybugs. They can also be effective against earwigs, flea mites, thrips, and ticks. More robust pests such as beetles aren’t deterred by soap sprays, so choose a different method for getting rid of them.
Dish soap sprays used for insecticidal purposes have their drawbacks. Aside from killing soft-bodied pests, they can also harm beneficial insects that come in their way. Soaps have a drying effect on leaves as well and used in excess, they strip the leaves of their natural oils and protection.
If you decide to mix soap with your sprays, make sure that it’s true, organic soap, and not any generic detergent from your household. For an optimal effect mix a tablespoon with a gallon of water. You can use it as a stand-alone product or mix it with BT, baking soda, essential oils, and many other organic substances used in pest control.
Using bicarbonate (baking soda) on plants’ leaves changes their PH and makes them less susceptible to fungal disease. This method works particularly well in preventing powdery mildew, blight, rust, and scab.
When mixing baking soda with water, be careful not to overdo it – high concentrations can burn the foliage, especially in the heat of summer. Mix one teaspoon of baking soda with one quart (one liter) of warm water, add a drop of liquid soap to the mix for better adherence, and spray weekly.
It’s best to use baking soda spray as a preventative measure against disease, a couple of weeks before plants become susceptible to mildew or blight. Baking soda will act as a coating, although it can also affect pests that were already present on your plants.
As with any organic method of pest control, it’s best not to overdo it. Your plants may survive, but this doesn’t mean that baking soda won’t affect them at all.
Diatomaceous Earth (DE)
Diatomaceous Earth, or DE, is a naturally occurring sedimentary rock that has been grounded into a very fine powder. This non-selective dust damages insects through a process called adsorption, which wicks moisture out of their bodies.
DE works well against slugs on the soil or aphids, caterpillars, and thrips on plant foliage, but DE doesn’t discriminate and can harm beneficial insects as well, that’s why it’s best to use it sparingly. Apply on the soil around cabbage seedlings, onions, and other susceptible seedlings. For leaf infestations, powder the underside of leaves and the soil beneath the plant.
Diatomaceous earth isn’t toxic to humans – in fact, it’s even used as an additive in toothpaste and facial scrubs, where it acts as a very gentle abrasive.
Neem is a popular choice among gardeners because it’s safe to use repeatedly and has proven to be very effective. It deters pests by making leaves unpalatable, and by interfering with the pests’ reproductive mechanisms. In addition to this, neem also has a system effect within the plants, as they carry the neem compounds through their roots and leaves, protecting them from pests both above and below ground.
Neem is effective against many insects that aren’t normally destroyed by other dusts and sprays – such as leaf miners and all kinds of beetles. By altering the plants’ biochemistry, it can prevent fungal diseases like powdery mildew.
There really isn’t much that neem products can’t do, while also remaining safe for humans and the environment. The only drawback is the strong smell during application. Mix the oil according to the manufacturer’s instructions and spray immediately.
Neem oil works best in hot weather, and its effects last about a week. Repeated applications are needed, and for best results, alternate neem oil treatments with soap sprays. Rain may wash away the neem coating, so spray again as soon as the weather clears up.
Bleach / Vinegar
Chlorine bleach is a powerful disinfectant, and it shouldn’t be used on plants or in its undiluted form. Bleach and vinegar are both used for sanitizing garden tools and surfaces inside the greenhouse.
When pruning, digging, or even using plant containers, we can spread various microorganisms to other plants and other parts of the garden. You can skip this step if your plants and soil are generally healthy, but in case of serious disease, never use the same pruning shears, hand trowels, and other instruments on healthy plants without disinfecting them first.
Use a 10% bleach solution to wash instruments and containers, and rinse them with water. Make sure to prepare a fresh solution in small quantities, as the bleach evaporates, and the concentration can drop even from one day to the next.
If you prefer a more natural solution, mix water and vinegar in a ratio of 4 to 1, and this will work just as well. Wear gloves and protect your eyes when applying any kind of disinfectant or pest spray.
All-purpose insect spray (garlic & hot pepper)
This spray leverages the insecticidal properties of garlic as well as the deterring effects of hot peppers to keep bad bugs away. Mixed together with soap, it creates a powerful organic weapon against a wide range of pests.
Garlic is known for its fungicidal effects and works well on aphids, squash bugs, and whiteflies, but it has little effect on larger insects like beetles. As a drawback, garlic kills pests indiscriminately – good and bad.
Hot peppers owe their fieriness to a substance called capsaicin which attacks aphids and other soft-bodied pests, with no harm to beneficial insects.
You can make your own all-purpose spray at home using only a few ingredients: blend one garlic head, add a teaspoon of hot pepper powder and one quart of water, and let it steep for a couple of hours. Strain the mixture and add one tablespoon of dish soap to the liquid. Spray your plants and store the spray in the refrigerator for up to a week.
Aromatic herbs aren’t generally affected by pests, and gardeners have used them for centuries as pest repellants by interplanting them with their most precious crops. By using essential oil extracts, we’re going one step further and selecting the exact substances that make these plants so effective.
- Sage, thyme, rosemary, and white clove extracts can be used to discourage many types of pests from laying their eggs;
- Mosquitoes hate citronella, cinnamon, geranium, and lemon eucalyptus oils;
- Repel gnats with citronella, geranium, and lemongrass;
- Nasturtium tea repels aphids from fruit trees;
- Marigold, chives, and catnip extract discourage leaf-eating insects;
- Ticks avoid lemon eucalyptus and geranium.
You can find a variety of recipes for essential oils, herbal extracts and herbal teas to use as organic pest control sprays. Be sure to experiment until you find combinations that work for you. These substances are gentle and have little to no side effects.
Tomato and potato leaves contain considerable amounts of alkaloids. This substance doesn’t act as a pest killer, but it attracts predatory insects that will come searching for their prey. It’s a way to signal beneficial insects to come feast on those unwanted bugs.
Achieving a fine balance between pests and their natural enemies is what keeps those pest populations under control, and using the tomato-leaf spray, along with planting a variety of flowers, is one way to do that.
Finely chop one to two cups of tomato leaves, mix them with two cups of water and let them sit overnight. Strain the slurry and dilute it with two more cups of water. Spray as you would with any organic pest spray.
Before using this method, make sure that you and your close ones aren’t allergic to plants from the nightshade family, and only choose healthy tomato leaves to avoid spreading disease.
Industrial agriculture is widely responsible for soil erosion, water pollution, and the concentration of harmful chemicals inside the soil that sometimes take decades to break down. As small-scale gardeners, we have a moral responsibility to our environment and to our own health to only use organic methods of crop protection – and to use them sparingly.
Pests will always be a part of our garden, and we should allow them to coexist in the ecosystem that we’ve unintentionally created, as long as they don’t take over entire crops.
Keep your soil healthy – first and foremost, keep your seedlings and plants healthy and regularly inspect your garden. Focus on prevention rather than treatment and continually educate yourself on types of pests and diseases.
“The Organic Gardener’s Handbook of Natural Pest and Disease Control ” by Fern Marshall Bradley