Shield bugs and stink bugs, not so welcome in the garden!

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It nests in homes and leaves a nauseating smell behind, but in the vegetable patch the stink bug does worse: it stabs its mouthpiece through leaves, fruits and flower buds and sucks out the sap. Plants are weakened and sometimes killed, and a net over the bed is the only way to keep it out.

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Different species of bugs

You’ve certainly come across the stink bug that sometimes nests in homes, leaving a nauseating smell behind. Indeed, the Latin source for its botanical name is putinasius, which means “to smell bad”…

In the garden, several species of shield bugs also do their best to annoy gardeners.

• The green stink bug: it’s the most feared because it particularly likes nightshades (tomato, eggplant, potato), as well as bean and cucumber. As its name suggests, it is recognizable by its characteristic green color.
• Cabbage shield bugs: Eurydema ventralis, Eurydema ornata and Eurydema oleracea which puncture leaves and feed on sap. This group of insects has red and black patterns.
• Brown marmorated stink bug: its dreadful name describes this brown-gray insect, native to Asia. Marmorated means “marble-like”, meaning it looks like polished marble stone. It’s spreading in Europe because of global warming. It wreaks havoc in orchards, and also on squash and cabbage. It has two white marks on its antennas, unlike the European bug which has three.
• Lygus pratensis: light brown color, it affects both flowers and vegetables such as cucumbers, strawberries, peppers, etc.

Description

No matter the species, every shield bug consists of a head, thorax, and abdomen. It also has two antennae and two pairs of wings. Three pairs of legs (it’s an insect) let it move on plants and it measures between 0.4 inch and 0.6 inch (between 1cm and 1.5cm).

• In shield bugs, the broad triangular scutellum in the middle of the back is a useful identification feature, though their common name comes from the shield-like outline of the whole body.
• In true bugs (Hemiptera), the piercing rostrum is typically held folded back beneath the head and thorax when not feeding, lying against the underside between the bases of the legs.

Lifecycle

Shield bugs reproduce by laying small, translucent eggs on the underside of leaves of their favorite plants. Several weeks later, small larvae hatch. They already resemble the adult insect, but morph through five stages to reach their final development.

These sap-sucking insects feed on garden plants, orchard trees, or flowers depending on the species. They stab their mouthpiece through leaves, fruits, and flower buds, and then suck their sap. They weaken the plant and sometimes even cause its death.

Rather than crushing shield bugs on a fruit, knock them into a jar of soapy water, since the bugs release a pungent defensive secretion from their scent glands when disturbed or squashed.

Which shield bug is in your garden?

Four shield bugs turn up again and again on vegetables, orchard trees and flowers. Their colour and markings tell you which one you are dealing with, and what it is likely to attack.

Whichever species it is, the feeding damage is the same: punctured tissue and sap drained from leaves, fruits and buds.

How to avoid shield bugs

The only preventive technique is setting up a bug net that will keep all pests out of a plot or growing bed in the garden.

• Peg or bury the edges of the net because any gap can admit shield bugs: adults usually fly in and land on plants, while flightless nymphs can crawl under a loose skirt.
• Put the net in place at planting, before the bugs arrive: covering a crop that already carries eggs on the leaf undersides simply shuts the pests in with the plants.
• Turn a few leaves over each week to check their undersides, and identify any egg clusters you find before removing them, since some belong to beneficial insects such as ladybirds and lacewings.

Natural treatments against shield bugs

Garlic and Chili Decoction

This decoction reportedly has a repelling effect on stink bugs.

1. Boil about 1 quart of rainwater or filtered water (1 liter).
2. Add 3.5 ounces of crushed garlic and 1 finely chopped chili (100g garlic).
3. Maintain the boil for 15min.
4. Cover and steep for 12h.
5. Pour the preparation into a sprayer using a kitchen strainer to filter it.

You can store this decoction cool for 10 days. To use it, simply spray it on the affected plants.

Wormwood slurry (or weedy tea)

Some gardeners recommend wormwood fermented tea. To make it yourself, nothing could be easier!

1. Fill a non-metal container with about 2.5 gallons of rainwater or filtered water (10 liters).
2. Insert 2.2 pounds of chopped fresh wormwood or 3.5 ounces of dried wormwood (1kg fresh or 100g dried) into a fabric bag.
3. Put the bag in the water.
4. Mix daily with a stick, prodding the sack of plant material to stir it up.
5. As long as bubbles rise to the surface, fermentation is ongoing. When it’s over, your weedy tea is ready!
6. Pour it into bottles or cans.

To use it, you’ll need to dilute it to 10% in water. For instance, use about 3.5 fluid ounces of wormwood concoction per quart of water), or 100 ml of preparation for 1 liter water.

Mint Spray

Mint, like wormwood, reportedly repels bugs. This means you can make another mixture, this time based on mint essential oil.

Simply add 5 drops of mint essential oil in around 1 cup of boiling water (250ml). Let it cool and spray this solution on your bug-infested plants. You can try plant mint near your crops as a companion plant, but this technique might be less concentrated, less targeted, and therefore less effective.

Diatomaceous earth

Experienced gardeners often mention it as an excellent bug repellent.

• Learn all about diatomaceous earth