Mealybug

Two closely related piercing-sucking pests commonly attack roses:

• Mealybugs (Pseudococcidae): soft-bodied insects covered with a powdery white waxy coat resembling cotton wool, typically clustering in leaf axils, bud eyes, the underside of leaves, and around the crown.
• Scale insects (Coccidae / Diaspididae): armoured or soft scales with a hard or waxy shield that clings tightly to stems, canes, and leaves, often camouflaged against the bark.

Both groups feed on phloem sap, progressively weakening the plant, and excrete copious honeydew that supports the growth of sooty mould. Outbreaks intensify under hot, humid, still-air conditions, particularly on plants stressed by poor nutrition. They are spread by ants (which tend the colonies for honeydew), wind, irrigation splash, contaminated tools, and infested planting stock.

While feeding, mealybugs and aphids often inject saliva containing enzymes or toxins that disrupt the plant's hormonal balance (e.g., auxins and cytokinins). This causes cells on the upper leaf surface to divide and expand excessively while growth on the underside is inhibited, forcing the leaf to curl downward or cup.

Note: armored scale (family Diaspididae) does not excrete honeydew, so sooty mould and ants may be absent — unlike mealybugs and soft scale.

A layered approach combining sanitation, biological agents, and selective insecticides delivers the most durable control:

• Isolation: Move the infested plant away from other roses in the garden.
• Manual removal: Dab individual mealybug colonies with a cotton bud soaked in 70 % alcohol, or gently scrape scale insects off stems with a soft brush.
• Hydro-blasting: Hose the canopy with a strong jet of water — focus on leaf axils and the underside of leaves — to dislodge colonies mechanically.
• Pruning: Prune out and destroy heavily infested canes and leaves.
• Ant control: Bait or treat ant trails around the base — without ant protection, parasitoids and predators rapidly suppress mealybug and scale populations.
• Biological (recommended): Spray neem oil (azadirachtin) at 1–2 % every 7–10 days, drenching the canopy, leaf undersides, and crown. Neem is effective against both mealybugs and scales.
• Organic contact options: Insecticidal soap (potassium salts of fatty acids) or horticultural mineral oil smother the insects by blocking their spiracles. Particularly effective against immature scales (crawlers) before the protective shield hardens.
• Natural enemies: Release the mealybug destroyer ladybug Cryptolaemus montrouzieri against mealybugs; release the parasitoid wasp Metaphycus helvolus and predatory assassin bugs against scales.
• Sooty mould clean-up: After the pests are controlled, wipe foliage clean or spray a dilute copper solution to remove residual sooty mould.

Recommended products

The 2 most widely used and effective products are:

1. Movento 150OD

A highly systemic insecticide with two-way translocation, ideal for cryptic sap feeders.

• Description: Two-way systemic activity (xylem and phloem) that targets the digestive system of sap-feeding pests.
• Application: Dilute with water and spray to thorough coverage of the canopy. Long residual activity and very low odour.
• Frequency: Apply on a programme to catch successive emerging generations; follow label rates.
• Where to buy: Refer to the product label.

2. Radiant 60SC

A next-generation, biologically derived insecticide that knocks down piercing-sucking pests quickly.

• Description: A spinosyn-class product with rapid contact and ingestion activity against mealybugs, scales, and thrips.
• Application: Dilute with water and spray in the early morning or late afternoon.
• Frequency: Reapply as needed per label instructions.
• Where to buy: Refer to the product label.

For particularly stubborn armoured scale outbreaks, Chlorpyrifos may be added as a clean-up treatment where locally permitted.

• Inspect new planting stock carefully before purchase — check stems and canes for abnormal scaly bumps (scales) or white cottony tufts (mealybugs).
• Routinely scout leaf undersides, axils, and canes to catch both pests early.
• Maintain an open, well-ventilated canopy and avoid overcrowded plantings.
• Manage ants in the garden with baits or barriers to break the mutualism that protects the colonies.
• Fertilise in balance — avoid excess nitrogen, which produces soft, sappy growth that is preferentially attacked.
• Apply preventive neem oil or horticultural oil sprays every 2–4 weeks, particularly during hot, dry weather.