Organic Garden Pest Control

The number and diversity of bugs that want to eat what you grow is truly staggering, but we’ll tackle organic garden pest control together.

With new insects coming into our gardens every season (thanks climate change) it can seem like a losing battle.

But looking at each insect as part of a larger ecosystem can calm fears and get us into the right mindset when finding yet another new bug eating our plants.

Spending time in your garden with an insect identification book (like the Audubon Society Field Guide to North American Insects & Spiders) will give you quite an education. And if you find an infestation of insects, take a minute to learn more about them by asking some questions like:

Is this their larval or adult stage?
How long do they stay in certain stages?
What do they ultimately turn into?
Where do they go at night?
Where do they overwinter?
How do they reproduce?
What do they eat?

Asking these questions can really help you plan your attack. Because say there’s a caterpillar eating your dill, but you find out it’s a swallow tail butterfly and you love those. You might choose to plant more dill rather than remove the caterpillars, a practice based on the “Appropriate/Inappropriate Landing theory. For more info on that and other ways to balance your garden, read my Companion planting article for tips on pollen and nectar rich flowers to attract beneficial insects helps curb these infestations! I’ve also got a free 5 page Companion Planting Guide to download.

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Let’s dig in together, Michelle

Integrated Pest Management

This introduces the idea of Integrated Pest Management (IPM). IPM gives us a framework to asses and choose options that are less harmful to the overall ecosystem, yet effective at stopping the spread of insects and plant diseases. For a good overview of IPM and how to implement it check out the U of MN Extension Services page on Preventing pests in your yard and garden

When searching for information on a pest or disease in your garden, try adding “.edu or .extension” and look for information near your area to find researched information.
Pro Tip

The Usual Suspects

Imported Cabbage Worms:

Eggs are oval and start white but turn a tinted yellow and are found on both sides of leaves. These are the bright green, and velvety soft to the touch caterpillars. You’ll often have to look very closely as the tend to blend into the broccoli, cabbage and cauliflower leaves that they eat. The adults are the white butterflies with a black dot. The best way to manage these are hand picking or capturing the butterflies before they lay eggs as one butterfly can lay 300 or more eggs! Floating row cover helps deter. Planting early to get plants well established before they arrive en-masse helps too. You can confuse the butterfly egg laying by interplanting different herbs (like dill) that have very different leaf structure from typical brassicas. Parasitic wasps will lay eggs inside the caterpillars ending the lifecycle.

Cabbage Looper at the top and Imported Cabbage Moth at the bottom — Cabbage Looper larva at the top and Imported Cabbage Moth larva at the bottom

Cabbage Looper larva at the top and Imported Cabbage Moth larva at the bottom

Cabbage Loopers:

The eggs are tiny, white and laid on the underside of the plant leaves. The caterpillars move like inch worms. They look more segmented with more pronounced ‘legs’. The adults are gray-brown moths. Hand picking and floating row cover work to deter, as does early planting. You can confuse the moth egg laying by interplanting different herbs (like dill) that have very different leaf structure from typical brassicas. Parasitic wasps will lay eggs inside the caterpillars ending the lifecycle.

Cucumber Beetles:

Cucumber beetle on plant — Striped Cucumber Beetle

You can discourage egg laying (they lay by burrowing into the soil) by heavily mulching around newly planted cucurbits, or by add floating row cover early in the season- but remove in time to aid in pollination. Hand pick beetles early in the season, I’ve found having soapy water to drop them into helps- good luck, they’re fast! Plant a trap crop like a Blue Hubbard squash nearby as the beetles are drawn to the plant’s higher level of cucurbitacin. Larva cannot overwinter in Zone 4 or colder but migrate from the south each spring.

Colorado Potato Beetles:

Look for clusters of orange eggs on the underside of leaves and are easily squished. Larva are deep red and eat the most leaves compared to other stages, they are easy to hand pick. But these are seriously one of the grossest bugs for me- so I wear gloves). The adults can fly in from other gardens so stay watchful, especially as the tubers are bulking up which is right after flowering. There’s been some luck with capturing beetles in plastic lined trenches set in the midst of a potato bed. Check daily and remove. If infestations persist, consider taking a year off from growing potatoes. Or see if another gardener can grow those for you, while you grow something else for them.

Potato bug beelte and larvae — Potato Bug Beetle

Japanese Beetle with three white Winsome Fly eggs

Japanese Beetles:

Eggs are laid underground and become white grubs which feed on the roots under the soil. They emerge as flying beetles to eat all the things, they eat well over 300 types of plants! Thankfully they don’t usually spread much disease, just devour leaves. The plants usually survive, but repeated stripping of leaves can eventually stunt or kill plants, shrubs and trees. Start picking off bugs as soon as possible, the more damage, the more beetles will come. Netting can be added as a physical barrier but needs to be removed if pollination is required.

GOOD JAPANESE BEETLE NEWS!

A parasitic tachinid fly, the Winsome Fly, has finally followed the Japanese beetle north! This unassuming looking fly lays white eggs on the thorax of the Japanese beetles. So if you see Japanese beetles with the tell tale white dots on them- do not kill them, let nature take its course. The beetles will burrow underground within a few days where the eggs will hatch and bore into the beetle and kill them from the inside out. Making more Winsome flies and less Japanese beetles!

Winsome Fly are attracted to marigolds, calendula and nasturtium
nature is neat

Squash Vine Borers:

The adult squash vine borer moth is bright orange and black with two long antennae. They’re also very fast and can fly in from neighboring yards so be aware through the end of July. They lay eggs at the base of your squash and cucumber plants and the larvae bore into the base of the vine and feed from inside. Careful inspection of plants is the best defense.

Wilted plants, especially in the morning, is a sign of squash vine borer. Look for the entry wound at the base of the vine. Slice the vine open where you see the entry point until you find the grub. Then remove and then cover the wound with the soil. If caught soon enough many plants survive. Plant a trap crop like a Blue Hubbard squash nearby as the beetles are drawn to the plant’s higher level of cucurbitacin. Also, planting resistant alternatives like butternut, ‘Cocozella Di Napoli’ and ‘Costata Romanesco’ helps.

PS- All Hand Picked Pests = Chicken Approved Treats 😉

We haven’t covered slugs, pill bugs, cut worms, jumping worms or tomato horn worms… A great place to start digging deeper into the world of garden pests is Jessica Walliser’s book, “Good Bug, Bad Bug”.

Recipe for Organic Garden Pest Control Spray

Sometimes the bugs become too much, and you need a solution. This simple, organic garden pest control spray works great on any soft bodied larvae like cabbage worms and potato bugs, as well as aphids, leafhoppers, thrips, and mealy bugs. This spray will not hurt pollinators like the bumblebee!

Use a 1 quart bottle
Add ¼ Cup Olive Oil (or another organic vegetable oil)
Add 1 tablespoon of castile soap
Fill the rest of the way with water.
Swirl the contents to mix (shaking creates too many bubbles) before each use.

Spray directly onto pests in the morning or evening, avoiding spraying in full sun. As with all natural remedies, this will have to be reapplied more often. But this spray is quite effective in quickly suffocating the larvae by coating their skin. It lasts an entire season.

Quick Tips:

TP/Paper Towel collars placed into the soil around newly emerged seedlings will fend off cutworms.
Place short pieces of 2×4 lumber or corrugated cardboard in the garden to lure in earwigs and Roly-polies/Pill bugs over night and remove in the mornings.
Adding sound ‘scare’ tactics can work, if used infrequently, so save for right before a harvest for racoons, even a talk radio station can work!
Place copper strips in the soil to fend off slugs, it makes their slime sizzle!
Apple Maggots are lured in by red balls hung in trees, so coat with a non-drying glue and you’ve got a non-toxic trap.
Molasses and water mixed together lures in flies, ants and grasshoppers, which will often drown in the mixture.

**One trap I avoid are the pheromone traps to lure in Japanese beetles etc. I find they just bring in more trouble than they kill.**