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Root mealybugs

Also known as Ground mealybugs, Rhizoecus

PestHarmful

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In short

Root mealybugs are mealybugs that live below the soil surface on roots, so they are usually discovered only when a plant is unpotted. White, waxy deposits on the roots and around the root ball are the giveaway; cacti, succulents, African violets and palms are common hosts.

How it looks

Adults are about 1.5–3 mm (1/16–1/8 in) long, slightly flattened and rounded at each end, bluish-white under a thin, fluffy white bloom. Unlike above-ground mealybugs they have no obvious waxy filaments, and they have tiny or no eyes. They resemble large springtails but move slowly. Females lay eggs in fluffy white nests among the roots, and nymphs look like small females. Some species produce a net of slender wax threads over themselves.

Signs

Powdery or fluffy white deposits on the roots, seen when the plant is taken out of its pot; the white secretions can give the potting mix a bluish tint. Plants weaken because the insects suck sap from the roots, and damaged roots are more open to bacterial and fungal rots.

What favours it

They move between pots by crawling out of drainage holes, especially when plants are watered, and arrive in infested plants and potting media.

Prevention

  • Slide new plants, especially cacti, succulents and African violets, out of their pots and look at the root ball before buying or adding them to a collection.
  • Quarantine new plants and keep suspect pots apart, since root mealybugs can crawl out of drainage holes to neighbours.
  • Look at the roots whenever you repot.

Treatment

Start with the first step and move down only if the problem persists.

  1. If you find them when repotting, wash the mealybugs off the roots before replanting.
  2. A systemic insecticide drench (such as the neonicotinoid class) labelled for this use is the chemical option; follow the product label.

Pros and cons

Cons

  • Hidden below ground, so infestations are usually advanced when found.
  • Root damage can lead to rot.

Look-alikes

Springtails
Harmless; jump away quickly when disturbed and have no waxy coating.
Above-ground mealybugs
Live on stems and leaves and have obvious waxy filaments around the body.

Affected plants

Cacti and other succulents, African violets, palms (including queen, majesty, fishtail, triangle, kentia, lady, pygmy date and MacArthur palms), bamboo, chrysanthemum, ginger, gladiolus, hibiscus, iris and ornamental grasses.

Sources

  1. Root Mealybugs — NC State Extension
  2. Insect pests of cacti and succulents grown as house plants — Missouri Botanical Garden

Written in our own words from these sources. Check a product label before using any treatment.