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A Guide to Mealybugs: What Are They and How To Get Rid of Them

ukhouseplants
Published on January 20th 2021
9
A birds eye view of a plant potting station with gloves and a spray bottle

What are Mealybugs?

Mealybugs are a common pest found on plants both indoors and out, affecting all parts above the soil line. Most infestations will arise from a recently-purchased specimen, taking several weeks to become easily visible to the naked eye. The mature females can lay up to twenty eggs a day in their adult life (two months), with a total of three hundred before her death. The difference between the females and the rarely-seen males is stark, with the latter loosely resembling a Fungus Gnat instead of a white oval.
A close up of a mealybug from the family Pseudococcidae

Mealybug

Pseudococcidae

What do Mealybugs look like?

A mature Mealybug can measure up to 0.5cm (one-fifth of an inch), with the majority reaching this size within six weeks of their eight-week life. They will be accompanied by a white cottony-web that’ll house the large quantities of singular eggs which will hatch within a few days.
white mealybug pests on a leaf
Mealybug insects on a pink orchid flower

How to spot a Mealybug infestation

  • Most critters are ovular and ivory-white, wiggling across the foliage searching for plant sap and hatching grounds. The spring and summer months are the most active period for this pest, in terms of reproduction and activity.
  • All plant portions above the soil line are susceptible to Mealybugs, including both sides of the leaf, any flowers & cubbyholes across its stems or petioles.
  • Smaller Mealybugs that are found soil are called Root Mealybugs and should be addressed differently.
  • Newly-purchased plants are most likely to be attacked first, but the infestation may lie in older plants that have taken a while to support a large colony.
  • The female Mealybug will initially stay close to her web before the offspring moves on to new, uncolonised areas of the same plant or nearby specimens.
A dried out yellow leaf
Mealybugs suck the sap from leaves causing them to turn yellow

Plants most susceptible to an infestation

Most indoor plants are susceptible to Mealybugs, ranging from Cacti to Chinese Evergreens. If your specimen is in bloom, be sure to prune the flowers off via the stalk’s base to eliminate any risk of a further infestation.

How to treat plants with a Mealybug infestation: a step-by-step guide

Addressing any infestation (regardless of pest species) requires both patience and consistency. The following section will discuss how you can eliminate an infestation using six simple steps, along with either an organic or chemical-based pesticide.
1. Crush as many bugs and their cottony webs as possible using either your bare fingers or a damp cloth with lukewarm water. Be sure to both sides of the leaves, its stems and the petioles that join the two together. Smaller instars (the stage between the egg and a mature adult), may bury itself in tight nooks within the plant, so it’s important to scan the WHOLE plant from the soil line upwards.
2. Gently rinse the stem, leaves and each cubbyhole using an outdoor hose in at least three different angles to ensure thorough administration. This is a critical part of addressing an infestation, so be sure to put aside several minutes for this step.
3. While the plant is drying-off from the hose, remove the top quarter of the soil in favour of a fresh batch of the appropriate product - ‘Cactus & Succulent’ compost for arid-dwelling species, tropical plants for ‘Houseplant’ labelled potting mixes, etc. It's vital to replace the soil’s top portion, as once summer arrives, any burrowed instars may hatch and continue to wreak havoc on the hosting plant.
4. Situate the plant in a warm, bright room away from other specimens to dry-off. If the temperature is above 15℃ (59℉) at night, keep it outside so that natural predators, (like Ladybirds and Green Lacewings) can have a go at the critters, too.
5. Once the specimen is bone-dry, which may take a few hours, it’s time to administer a pesticide. Although there is a choice between two options (organic or chemical-based sprays), we would recommend using the former option first to avoid using synthetic chemicals.
6. Keep the affected plant away from others in a quarantined room until the symptoms have subsided for at least six weeks. In some cases, dormant eggs may hatch several months after deeming the specimen pest-free, so it’s always important to keep an eye out for a potential relapse. Keep other, non-affected specimens safe by distancing the pest ridden plant at least a metre away from each other.
N. B. - Although you should perform the wiping and hosing-down process BEFORE each pesticide application, you can wipe/wash the foliage at any given time to keep the infestation under control. Remember to respect the pesticide’s recommendations though, as frequent applications could result in burnt foliage.
Mealybug pests on a ficus plant
Frequently check your plants and squash or wipe away insects when they are spotted
Organic Pesticides
Neem Oil is used across the world, and for a good reason. Not only is it accessible in many stores, but it'll also get to work after the first application. Dilute the liquid, (to the manufacturer's recommended strength) with water and/or dish soap and spray thoroughly onto the foliage and its cubbyholes. Any flowers must be removed instead of mist, due to the heightened chance of another infestation lurking in the background.
Diatomaceous Earth (D.E. or DE) is grounded diatom mantels (skeletons) that can be highly abrasive to many arthropods, including Mealybugs. Although the white powder may be soft to the human touch, the sharp tooth-like edges off each grain will begin to cut its way into the pests' eco-skeleton, causing significant discomfort and weakened health. After a period of several days, the infestation will decrease as the mature mothers won't be able sufficiently to lay her eggs. Usually, DE is applied as a thin layer across the foliage of outdoor plants, which will work until there is a rainstorm; however, you'll have to change the method of application to eradicate indoor pests. Instead of using powder to combat your infestation, mix the DE with water to create a more efficient solution to access the plant's cubbyholes and hard-to-reach areas. Add one tablespoon of DE to 500ml of water (0.11 imperial pints) and mix well. Finely mist both sides of the leaves and its stems so that the plant is covered in a thin film, which will begin its work within twenty-four hours once dry. Its eggs may be immune to the pesticide, so it's important to perform another fine spray seven days later to attack the recently-hatched instar. As you have followed the first four steps mentioned in the previous section, you shouldn't see any signs of an infestation for several weeks. We'd recommend waiting six weeks before deeming the specimen pest-free, as relapses of later-hatching critters could occur. If pests do return, follow the four steps mentioned above, along with the misting of its foliage with this solution. If the infestation is large, you may wish instead to opt for a chemical-based pesticide to destroy the infestation more effectively. DE is considered safe to both pets and humans and has no links to the development of illness or cancers.
Natural Predators (unrecommended) - The last non-organic method is acquiring adult ladybirds or green lacewings. This method can take several days, if not weeks, to work and could even be unsuccessful, which is why other products are favoured.
Chemical Pesticides
We'd recommend using 'Bayer Garden Provado Ultimate Fruit and Vegetable Bug Killer Concentrate', as it worked IMMEDIATELY after one application. It's a concentrated product, meaning you'll have to dilute it with the appropriate amount of water. Spray both sides of the leaves, along with any cubbyholes that could house the infestation. Keep the plant away from other specimens once there are no signs of an outbreak for over a month.
If you're looking for something with even more strength, try an Isopropyl Rubbing Alcohol, which can be bought from many online stores. This pesticide will work immediately, killing the bugs within a few hours of contact. Follow the manufacturer's recommendations and repeat hosing the plant down and pesticide application steps fortnightly until the infestation has elapsed. Keep it well away from others until the plant is deemed safe.

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