Time for citrus lovers to kick up a stink
Stinkbugs love citrus

Every year it's the same story. Just as the sweet scent of orange blossom drifts through the spring air, it's overwhelmed by the stench of stinkbugs.

For anyone who owns and loves citrus trees, spring and summer ere spent in constant war (weapons of choice: tweezers, tongs or size 10 boots) against the evil blighters.

Stinkbugs are well-camouflaged and devious, lying low under leaves, dropping to the ground when they sense danger, and squirting out a caustic and evil-smelling liquid. (I developed conjunctivitis after being zapped last year, so wear safety goggles or wraparound glasses.)

The stench lingers for hours and, when you resume the fight, the bugs' numbers seem unaffected and they go on to develop from little pale green nymphs to big, brown monsters.

By winter, you sadly collect a crop of a dozen oranges from a tree that, in the absence of stinkbugs, would have given you hundreds. Then it's spring and the whole cycle starts again.

Stinkbugs are a native pest prevalent on Australia's east coast, according to gardening expert Jennifer Stackhouse, who blogs on the GardenDrum website.

There are two main varieties - the more common bronze orange bug (the one most likely to infest your orange tree), and the spined citrus bug (smaller, with distinctive "shoulders" and a taste for lemons). Both are bad news.

"They suck the sap out of the stems of the plant - that's why they do damage to your crop," Stackhouse says.

"They are actually feeding away on the stem and that means that the fruit withers or drops when it starts to form - or, if the fruit does develop, you find when you cut it open there's a brown ring inside."

Stinkbugs start off as green nymphs, half a centimetre long and well camouflaged as they set about their evil business in spring. This is the best time of year to take action, Stackhouse says, "but a lot of people do not notice them because that green is exactly the same as the new leaf".

As they mature, stinkbugs turn grey-green, yellow, pinky-orange and dark brown, reaching up to 2.5cm in length.

Organic gardeners recommend waging war with tongs, tweezers, gloves, safety goggles and a bucket. You can even hoover them up - so long as your vacuum-cleaner is earthed and has a paper-bag liner in which you can throw out both the bugs and their indelible smell.

Lyn Bagnall, author of Easy Organic Gardening And Moon Planting, blogs on aussieorganicgardening.com. She says a tree that is infested with stinkbugs is likely to have an underlying health problem such as the wrong soil pH or being "hungry or thirsty".

Her advice: "Check your patient, find out the base of the problem ... Stressed plants get attacked by pests."

Generous watering, a good feed with an organic fertiliser and mulching is likely to make your tree much happier, she says. So is making sure the soil's pH is between 6 and 7.2.

But if stinkbugs already have a grip, set to work manually. Bagnall recommends wearing gloves to knock them into a bucket containing methylated spirits.

Maintain the battle through summer and autumn - to cut down on immediate damage and stop the adults laying eggs.

Stackhouse says gardeners can use pest oil with a relatively clear conscience, even when bees are busy doing their work among the blossoms.

"Pest oil is a good thing to use because it's benign to the pollinators," Stackhouse says.

Pest oil was developed by NSW Agriculture a couple of decades ago as a lower-impact way of combating scale on citrus trees.

Grant Herron, who is a senior research scientist specialising in insecticides and chemical management for the NSW Department of Primary Industries at its Elizabeth Macarthur Agricultural Institute, was instrumental in pest oil's development.

He says you should choose a pest oil specifically recommended for citrus. These are "high paraffinic petroleum sprays with a narrow carbon range" whose residues tend to be much less toxic than other insecticides.

Even so, any insect that happens to "get hit at the specific time is likely to cop some damage".

Pest oil, Herron explains, works at biochemical levels but the main reason it kills is because stinkbugs, like other insects, breath through holes in their bodies. When these are covered with oil, the bugs suffocate.

Herron recommends spraying at cooler times of day because pest oil is heat-sensitive and "phytotoxic".

Stackhouse says that, even by using pest oil, "you'll never get rid of them all".

A manual approach is a good back-up - and surprisingly satisfying.

Stackhouse and Bagnall say that, on very hot days, stinkbugs cluster in the shade at the base of the trunk, where it is easy to spray or wallop them.

Hunt down stinkbug eggs from the height of summer into autumn. "The eggs are like little balls ... and they're in rows," Bagnall says.

"Remove the leaves that have got eggs on them, put them in a sealed bag and dispose of them that way. Don't put them in the compost."

Spring gardens are under assault from myriad pests, including caterpillars, lawn beetles, lawn grubs, millipedes and bindii. But for me, stinkbugs are the arch enemy. What else destroys your hard-grown food AND gives you red-eye?

The West Australian

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