One of the biggest obstacles that gardeners face is what to do when pests overtake your garden and you can’t reach for the pesticides? Will you be left on the sidelines, staring helplessly as insects devour all your hard work?
Never fear. In this ultimate guide, you’ll find out what garden pests are, the most common garden pests you’ll face, easy prevention methods, and how to naturally and organically get an infestation under control.
Garden pests are any insect or animal that negatively affects or even kills your garden plants and vegetables. Mostly by eating them.
The good news about garden pests is that they’re a hundred times easier to identify than diseases or nutrient deficiencies. The insects are pretty distinct and easy to remember – once you’ve seen them, you’ll remember them forever.
Identify and control common garden pests by their leaf signatures in this useful gardening video:
Aphids are tiny green insects that blend in pretty well with green leaves, although different species come in different colours.
They suck the sap out of the leaves, stems, or flowers, which results in curling, stunted or yellowing leaves. You might also see a sticky substance on the leaves, which is a sugary liquid called “honeydew”.
They prefer to hide on the underside of leaves. And they can spread diseases from plant to plant. Some species prefer one plant species, while others will eat anything.
Ants are actually beneficial insects, either by eating actual garden pests or by fertilising your plants. However, they get troublesome for the gardener by making tunnels under roots that need to keep moist.
This is because ants farm aphids as they produce a sugary liquid, which ants love. So if you want ants to leave, just get rid of the aphids.
Getting rid of aphids once they occur is pretty easy. Spraying soapy water on the affected plant usually does the trick.
Flea beetles are small black beetles that particularly love brassicas like kale, and other plants like radish, beets, and potatoes. You may or may not see the actual beetles, but their damage is pretty unique.
They leave pinprick holes on leaves. Their underground larvae may eat plant roots and tubers.
The produce is fine to eat. The damage is only cosmetic. They may however spread disease from plant to plant, but if the rest of the leaf looks healthy, it probably is.
Applying row cover helps prevent flea beetles from coming to a garden plot in the first place, but once you have them, row cover will just trap emerging flea beetles with your plants.
Basil and catnip repel flea beetles or you can use nasturtium and radishes as decoys.
If you have an infestation, you can use beneficial nematodes to kill larvae. For adult flea beetles, you’ll want to apply organic products like a diluted neem oil spray or spinosad.
Colorado Potato Beetles are small and compact ⅓” beetles with brown bodies and black spots. Their larvae are chubby with reddish-purple colouring and rows of black dots and measure around ½”. Eggs are bright orange spheres in groups.
They go after the nightshade family, including potatoes, tomatoes, eggplants, and peppers. Both the adult and the larvae are troublesome as they both strip leaves down to the veins. They’re more often found at the top of the plant.
To prevent Colorado Potato Beetles, cover plants with row cover until harvest. As adult beetles will overwinter in garden debris, clean up garden debris in the autumn (you can leave roots in place) and rotate your crops (if you have a big enough garden).
- Squish eggs
- Knock the adult beetles off the plant (like by shaking it) into a bucket of water
- Apply neem or spinosad
Cucumber beetles are extremely easy to identify as they’re bright yellow with either black stripes or dots.
They eat the leaves and flowers of the cucumber family, including cucumbers, pumpkins, squash, gourds, and melons. A healthy plant will survive and even thrive despite the holes, although they can sometimes transmit bacterial wilt.
But if a horde descends, they’ll wipe out all your squashes. If they eat the flowers, then your plants will have a hard time producing fruit.
Floating row cover will prevent them from accessing the plants.
If it’s too late for that, then in the early morning when it’s cool (the beetles will be slow and sleepy), dip the tip of your finger (or garden glove finger) with vaseline to catch the cucumber beetles and either squish or put in water to drown.
Hornworms are green caterpillars with white stripes on the side of their body and they blend in super well with tomato vines and leaves. They’re nocturnal, eating during the night and hiding among the foliage during the day.
If you suspect hornworm damage, the most effective control is to inspect your tomatoes for green worms and kill them. However, if they have white cocoons that look like rice sticking out of them, leave them.
Parasitic wasps have laid their eggs on the hornworm, and they’ll destroy it for you – and then lay eggs on other hornworms. Disgusting, yes. But very useful.
To encourage parasitic wasps to hang out in your garden, plant flowering herbs with tiny flowers (like carrots, celery, parsley, caraway, or flowers of the Umbelliferae family) by your tomatoes.
Adult leafminers are actually flies that don’t hurt plants at all. The problem is that they lay their eggs on plants like spinach, chard, and beets, and when their eggs hatch, the larvae tunnel in the inside of the leaves, eating everything but the skin.
You can identify leafminers by their tunnels through leaves and by the sets of 4 to 6 small, oblong, straight white eggs laid in patches.
The leaves are still fine to eat, larvae, eggs and all. But if that’s a little too gross for you, then destroy leaves with tunnels in them and scrub off the eggs.
If you have chickens, feed the affected leaves to them. They’ll eat and destroy the larvae and eggs.
The only thing you can do to control them is prevention. Since the larvae are on the inside of the leaf, organic products will have minimal effect.
Use a floating row cover over spinach, chard, and beets. You can plant nasturtiums as decoys.
You’re not likely to see cutworms as they come out at night, but you can easily identify them from their damage: rows of seedlings dying on the ground as if someone came with scissors and snipped them all off. (If the seedling itself is missing, then it’s probably a mammal or a bird.)
Cutworm will attack any seedling, but they particularly like tomatoes and brassicas like kale and broccoli.
Adding collars around seedlings from toilet paper rolls or aluminum foil will prevent them from being able to attack the seedling. You can also use cornmeal or wheat bran in sunken holes as a natural pesticide.
One of the biggest challenges to growing carrots is managing carrot rust flies. Adult rust flies are small and black with an orange head and legs. Their larvae are tiny, beige-coloured maggots.
Like with leafminers, the larvae are the problem as they eat the roots, leaving tunnels and scarring. They don’t just go for carrots. They’ll lay their eggs near other plants and root crops such as celeriac, celery, parsley, and parsnips.
The best preventive measures are to:
- Rotate crops so that you’re not planting vulnerable plants in the same garden beds. This works best if you have a large vegetable garden where you can move plants at least several feet away.
- Wait to plant carrots and vulnerable crops until after the carrot rust fly’s mating season. This can depend on where you live, so it’s best to ask your local extension office, but, in general, you can plant in late May or early June.
- Use floating row covers to prevent flies from laying eggs.
- Interplant with onions, garlic and chives to discourage the adults from laying eggs.
If carrot rust fly has already hit your garden, then beneficial nematodes (especially genus Steinernema) released into the soil will eat the larvae.
Such cute creatures can absolutely destroy your garden as they eat plants down to the stem, destroying any chance that the plant will come back. They generally strike during the night.
Prevention is easy. Build a fence around your garden plot that is at least 2 feet high (so rabbits can’t jump over) and with chicken wire buried 1 foot under the soil to keep them from digging under.
Having a dog running around your yard will also discourage them from coming in.
Deer is another animal that will ravage your garden and even kill saplings, although you’re unlikely to deal with them unless you’re on the outskirts of a city or out in the country.
A fence that’s 8 feet high will help keep deer out. Better yet, build the fence at an angle. Deer have trouble judging depth, so they won’t even try jumping a tilted fence.
You can also hang aluminum cans in your garden so that they clang when the wind moves them. The sound will startle any deer, rabbits, or other wildlife and keep them well away.
With organic gardening (or any gardening), you’ll have a much better time if you focus on designing your garden to prevent garden pests. These are a lot easier than dealing with a swarm that’s already taken root.
Garden pests prey on your vegetables, other insects prey on them. You don’t need to get rid of insect pests 100%.
Your vegetable garden can survive low numbers. A healthy population of predator insects will keep those numbers low.
How to Identify
How to Attract
Braconids, Chalcids, and Ichneumon Wasps (Parasitic Wasps)
Depends on the species, but if you find eggs laid in pests, you’ve got parasitic wasps
Depending on the species, leaf-eating caterpillars like hornworm, beetles, ticks, aphids, and more
Plant carrots, celery, parsley, caraway, and/or Umbelliferae family and allow them to flower. The flowers attract the wasps to pollinate them.
Red or orange compact beetles with black heads and white spots
Aphids, mites, whiteflies, scale
Plant Compositae family (daisy family), tansy, or yarrow.
You can also buy them from online catalogues, but this is more suited for farmers and market gardeners.
A long body supported by four legs and two longer front legs that tilt down.
A wide variety of garden pests
You can buy eggs through online catalogues and place them in your garden to hatch.
Lacewings and hover-flies
Lacewings are green with their signature lacy wings, while eggs are small and white, attached to the plant by a filament. Hover flies look like a cross between a wasp and a fly.
Both adult and larvae eat aphids
Plant composite flowers like yarrow, goldenrod, Black-Eyed Susans and asters.
Nematode eggs are microscopic and they live under the soil.
Depends on the species, but can be useful against cutworms, flea beetle larvae, and Carrot rust fly larvae
You can buy specific nematodes through garden centres and online catalogues.
Covering vulnerable crops with floating row covers is one of the simplest solutions that will discourage a wide variety of insects. They are pretty much your only defense against flea beetles and leafminers.
Invest in insect barriers, rather than floating row covers. The insect barriers are designed to be used throughout the heat of the summer and to keep even tiny insects like flea beetles out.
Use hoops to raise the insect barrier above the plant. If a leaf presses up against the barrier, then the pest can lay eggs through it.
Pests use smell to find their favourite plants, so to discourage them, you can use that sense of smell against them either through companion planting or interplanting.
If your garden is big enough to have rows, then plant other crops in between like crops. Like if you have 2 rows of brassicas, plant another family in between.
That will break up the scent and give enough distance that even if one row is hit, they probably won’t find your other row.
You can discourage some pests by planting things they hate around the plants that they love.
Carrot rust fly hates onions, garlic and chives, so if you interplant your carrots with any of those, then the carrot rust fly will avoid it. Likewise, plant basil and catnip to repel flea beetles.
Some pests have a wide range of plants they enjoy or inhabit. Leafminers are as happy to lay their eggs on nasturtium as they are on spinach. However, you might then have populations that get way out of control and spread to your vulnerable plants.
If you have a big enough garden, then rotate your crops every year by plant species (brassicas, nightshades, etc). That will keep overwintering larvae from getting a toehold on your garden again.
Crop rotation is less effective if you have a garden that’s under 20 sq feet. You just can’t rotate the crop very far from its original place.
Healthy soil has ~5% organic matter and a thriving ecosystem of beneficial microbes. The organic matter will feed the beneficial microbes and worms, which turn the organic matter into nutrients that your plants can absorb. The beneficial microbes also help your plants.
Meanwhile, tilling and using synthetic fertilizers destroy the microbiology and should be avoided when possible.
Healthy soil means healthy plants, and healthy plants can defend themselves against pests.
Ok, so how do you build healthy soil? With compost! Don’t worry, we’ve got you covered. Check out our ultimate guide to composting.
Strong plants can defend themselves against disease and pests, but weak and dying plants don’t have those defenses. They’re more likely to get infected by disease and will attract predators. So pull the plant and dispose of it.
If you’ve had wireworms before, place potato slices under the affected soil’s surface. The wireworms will attack the potato slices and, before planting, remove the potato slices. You’ll have removed the wireworms too.
The earlier you catch problems, the more effective these methods will be! Once a plant is towards the brink of death, no pest control method is going to save it.
Try to use manual methods before using pest sprays. Even natural pesticides shouldn’t be applied unless necessary.
Before you do anything, figure out what exactly you’re dealing with. That way, you can find the most effective way to deal with the pest.
Organic insecticides are still insecticides and can be detrimental to your garden and beneficial insects. Only use if it’s the best way to handle your garden pest.
When you’re dealing with beetles and caterpillars, often the most effective thing to do is to simply pick the pests out of your plants and either squish or put them in a bucket with water on them.
If you’re dealing with soft-bodied insects like mites, aphids, and mealybugs, then mix a bit of glycerin soap with water and spray the affected plant from the top down, making sure to spray underneath the leaves.
The soap will disrupt the insects’ cell membranes, dissolving their exoskeletons and killing them from dehydration.
Neem oil is derived from the seeds of the Indian neem tree and is a naturally occurring insecticide.
Diluted neem oil can work as a general organic bug spray as it repels insects and also interferes with the insect hormone system so they don’t grow or reproduce and works best on soft bugs.
If applied correctly (and not directly on), neem oil won’t affect beneficial insects. Spraying in the evening when beneficial insects are resting will help you avoid spraying them.
You can also use neem oil as a proactive measure if you know from experience that a particular plant will become infested. Neem oil is best used on plants like tomatoes and squashes where you’re not eating the leaves, as it can leave a residue that’s hard to wash off.
You can either buy it premade in an insecticide (which comes with other less savoury chemicals) or DIY your own spray.
Spinosad is a mixture of soil bacterium that are toxic to insects and can even help control mosquitoes. When insects eat or touch it, spinosad messes up their nervous system, leading to paralysis and death in 1 or 2 days.
It has a low toxicity to humans and mammals, although direct contact with skin can cause irritation and redness.
Spinosad is highly toxic to bees! If you are going to use spinosad, spray in the evenings when bees aren’t active. Once dried (between 3 hours and 1 day), it’ll be safer (although not entirely safe) for bees.
Don’t spray on or near plants that are habitats for endangered butterflies, as you will kill them off.
To get rid of earwigs, slugs, and other soft-bodied insect pests, sprinkle a bit of diatomaceous earth over the plants.
The diatoms are small and sharp, harming the small exoskeletons of insects, slugs and snails. It generally won’t affect humans, but wash produce well before eating. You don’t want to be ingesting it.
Sticky insect traps, where insects land on the sticky strip and get trapped, seem like an effective organic method of pest control, but organic gardeners who try it end up swearing it off.
Yes, they kill garden pests, but they also kill beneficial insects who would have otherwise eaten a lot more pests than the strips remove.
Garden pests are no match for a bit of knowledge and foreplanning!
By identifying what you’re dealing with, putting in place common preventative methods, and using manual and natural pesticides to get infestations under control, you (and not the pests) will enjoy your organic vegetables this summer.