Green shield bugs are small green beetles about the size of a fingernail. Adults have a shield-shaped green back – some with a darker blackish-brown patch at their base - and are often seen basking in the sun on the leaves of a wide variety of plants in summer. When disturbed or crushed, shield bugs emit a foul smelling odour that is meant to deter predators from attacking them. This also sends an alarm signal to other bugs that a threat is in the area.
Green shield bugs appear in the garden from early spring through summer to autumn. They have strong mouthparts with which they pierce leaves, stems and fruit of plants so that they can suck sap and juices. This causes plants to wilt and produce becomes impaired with holes that can cause fruits to rot. Tomatoes, beans, melons, squashes, grapes and capsicums are popular targets as well as a range of other plants. Shield bugs can establish whole communities in a stand of plants and they are tricky to catch.
Adults lay eggs in clusters on the underside of leaves. Eggs look like tiny barrels and are arranged in rows. The eggs hatch into nymphs that are rounded in shape and often black or dark brown with small red and yellow markings on them. Within 4 to 5 weeks the nymphs mature into adult beetles.
At the end of summer, any remaining adult beetles will find shelter beneath bits of wood, in leaf debris and old pots where they’ll wait out the winter before emerging to start new communities of shield bugs as soon as weather warms in the spring.
Adults and nymphs: Adult shield bugs can be picked off leaves by hand and should be the number one target as a female can lay hundreds of eggs over summer. Best time to do this is in the early morning when they are still sluggish. Once the sun warms them up they move fast and can even fly to escape capture. Often they’ll simply fall off plants and then scurry away, if you hold a jam jar underneath them before they leap off a leaf they’ll fall in and can then be disposed of. If you do catch one, squeeze it and throw at the base of a plant. Any shield bugs in the vicinity will act on this warning sign and jump of plants to play dead on the ground. If you put a sheet underneath plants it makes it even easier to spot and collect the fallen bugs. Dispose of them permanently, chucking them out of the garden will only see them returning in next to no time.
Eggs: If you have the time to check the underside of outer leaves on your plants eggs are fairly easy to spot and can be rubbed off. Due to numbers though, this is only going to have an effect if you remove adults too.
Catch crops: A catch crop is a plant or group of plants that are introduced into the garden to lure pests away from cherished plants. Plant blocks of ‘catch crops’ away from plants like tomatoes, capsicums and beans – this provides place for shield bugs to congregate in numbers making it easy for you to then remove shield bugs in large quantities.
Sunflowers – check the back of flower heads
Mustard – sow every four weeks from early spring to keep up a flowering stock that will match the flowering phases of your food plants.
Cleome – these grow quite large so only one or two might be needed. Bugs will hide out in flowers and foliage