Mealybug

Mealybugs are small, sap-sucking insects that cover themselves in a white, mealy, fluffy, wax coating – hence the name mealy-bug. This partially disguises the actual insect below and gives them some protection from predators and from being affected by some chemical, contact, insecticides. The actual adult mealybug is oval, flattish and around 4mm (less than ¼in) and are white or pink.

Mealybugs suck sap from leaves, stems, fruit and any other relatively soft part of the plant.

Female mealybugs lay numerous tiny orange to pink eggs under the white coating and the resulting nymphs are fully developed in about a month in summer. In greenhouses and houses, activity and breeding continue throughout the year, although it is slower in winter. As they prefer warmer conditions, on outdoor plants there is less activity in autumn/winter and breeding stops.

The mealy covering means they are often confused with woolly aphids or even fungal plant diseases.

• Widespread on greenhouse, conservatory and indoor plants
• Ceanothus
• Citrus
• Fuchsia
• Grape vines
• Peach and nectarine
• Phormium
• Ribes

Being sap suckers, mealybugs extract sap from the plant by using their piercing mouthparts. Even quite small infestations can cause reduced or stunted growth. Large well-established plants are rarely severely damaged, but can be weakened.

As they tend to cluster together, they can seriously damage areas where they congregate and, if on leaves or fruit, cause premature leaf or fruit fall.

As they feed, mealybugs excrete a sugary, sticky substance, known as honeydew, which drops on to the stems and leaves below where they’re feeding. This not only makes the plant sticky, but the sugar attracts sooty mould, which can cover the whole leaf with a black deposit that reduces or prevents light reaching the leaf and so reducing the plant’s overall vigour.

Mealybugs breed very quickly in summer, and just a few can quickly get out of hand. Once numbers build up, control becomes more difficult. When large numbers are present, more damage is done to the plants, and this will affect your plants more severely. So, it is important to check plants regularly, and dealing with any you see – as soon as you see them.

You can easily control a small numbers of mealybugs by either squashing them, scraping them off with damp kitchen tissue or a sponge or removing and destroying the plant parts where they are congregating and feeding. Just be aware of the nymphs and eggs, which are easy to miss.

In the greenhouse or conservatory, mealybugs can be controlled using the biological control, based on a specific species of ladybird.

You could try blasting colonies of mealybugs with a strong jet of water from a pump-up sprayer or hosepipe. However, those mealybugs not killed by this method could be dislodged and end up on other parts of the plant, or other plants, so spreading the problem.

There are numerous chemical insecticides available that will kill soft-bodied insect pests, such as mealybugs. The majority of these are what are known as “contact” insecticides. That is, you have to spray the actual insect (make contact with it) to kill it. If you miss some, or others land on the plant after spraying, these will not be affected and will carry on feeding, breeding and building up the mealybug numbers. Also, most are based on “organic” or “naturally-occurring” materials and have very little persistence once sprayed on to the plant. This means you have to spray regularly – which could be as often as every couple of days in a warm summer – to stand any chance of controlling them.

Contact insecticides may not penetrate the mealy coating on mealybugs, and so may not be very effective. A systemic insecticide (BugClear Ultra) – which also kills on contact – is absorbed by the leaves and moves all around inside the plant, so will control future attacks from insect pests, for up to two months.

Spraying affected deciduous plants with a winter tree wash may also help to kill mealybug.

Use plant protection products safely. Always read the label and product information before use. Plants in flower should not be sprayed due to the danger to pollinating insects. Either spray early in the morning or late in the evening when pollinating insects are less likely to be active.

Not all insecticides have approval for use on all edible crops. Check the label before spraying.

Adult mealybugs cannot fly nor crawl far, so infestations are usually started from recently bought plants. So thoroughly check these before placing in their permanent growing position.

• Contact insecticides
• BugClear Ultra