Ruud Kleinpaste: Mealybugs and Scale Insects - tricky pests for the summer

One of the rottenest pests gardeners get on their plants are Pseudococcus longispinus, or any of its close relatives.

Longispinus derived from the word meaning “with a long spine or tail”, so we’re talking about the Long-Tailed Mealybug. Mind you, there are other rotters that don’t look anything like these mealybugs – a variety of scale insects do the same kind of damage, which you really don’t want to see in the garden.

All these insects feed by plumbing their mouthparts into the veins of the plants where they extract honeydew, a sweet sap that contains Nitrogen, which makes the young bugs grow.

Ah! Yes, the group of sap-sucking bugs is the only invertebrate cohort that can be called “bugs” in the naming game of Entomology!

They ingest the sap and poop out honeydew. But their numbers (huge groups) and activities are debilitating for your plants, causing yellowing and ill-thrift, plus black sooty mould all over the place.

The sooty mould is a fungal cover that feasts on the sweet honeydew – you can always tell the suckers because of the sooty mould!

To identify these mealy-insects you’ll need to have a good eyesight. The way to start your identification is to look for dense, white patches of silk all over your plants, especially over the leaves and on the stems.

If you scrape off the fluffy white deposits, you’ll get to the insects hiding underneath that fluff. Big ones and smaller ones all living together out of the rain and out of the sun. 1-4 mm in size.

They eat a massive range of plants, both edibles and ornamentals.

The spines and tails give the game away – there are also droplets of honeydew in amongst the mix.

Scale insects are a different-looking critter. These pests are characterised by looking like randomly shaped and coloured pustules on the stems and leaves of the host plant.

Often the “caps” of the scale insects are pretty hard; the actual insects live under the caps, often in perfect protection.

Control of mealy bugs and scale insects is difficult. The white fluffy silky stuff makes the bugs waterproof – water-based sprays cannot penetrate through their skin, unless you use some systemic insecticide that is taken up by the plants. Groventive is such a systemic spray but read the label and you find it cannot be used on edible crops!

Conquerer Oil and Neem Oil are non-systemic treatments that will give the immature Mealybugs a run for their money (suffocation and inhabit their feeding from the plant). But it will require regular spraying (once a week) until all bugs have starved to death or suffocated. Thoroughly cover the infested plant – and don’t forget the underside of the leaves too!

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