Pest & Disease Factsheet - Mealybugs

Heavy infestations of these sap-sucking pests can kill plants but preventive measures can be taken.

Image: Flickr / Martin Lagerwey
Image: Flickr / Martin Lagerwey

There are four common mealybug species found in the UK, the most common being citrus mealybug (Planococcus citri) [pictured]. The others are vine mealybug (Pseudococcus viburni syn. affinis) , which can be found on cactus, passiflora and tomato, long-tailed mealybug (Pseudococcus longispinus) found on tropical plants, and the New Zealand flax mealybug (Trionymus diminutus) found on phormiums and Cordyline.

Non-native mealybugs found on imported plant material include
the bougainvillea mealybug (Phenacoccus peruvianus), coffee mealybug (Planococcus lilacinus)
and golden root mealybug (Chryseococcus arecae). Notifiable pests include the lantana mealybug (Phenococcus parvus) and root mealybug (Rhizoecus hibisci). Check imported stock carefully. Some root mealybugs are not notifiable — such as Rhizoecus falsifer.

How to distinguish them

Female mealybugs are wingless, immobile, up to 5mm long and covered with waxy threads that can be white, brown or pink. Males are winged, about 1mm long and shorter-lived than the females.

Biology

Female mealybugs, when mature, can lay up to 500 eggs in a white, woolly egg mass. The long-tailed mealybug produces live young. On hatching, the young disperse and find suitable feeding sites. On average, from egg to adult takes four weeks at 26°C and eight weeks at 20°C.

Symptoms

Many pests are host-specific. Nymphs and adult females suck plant sap, causing distortion, yellowing, defoliation and honeydew that supports sooty moulds. Heavy infestations can kill a plant.

Treatment: biological control

The Australian predatory ladybird Cryptolaemus montrouzieri feeds almost exclusively on mealybugs and is effective in large pest colonies. Adults are about 4mm long, mostly brown or black with a distinctive orange head.

The white larval stage grows up to 1cm in length and looks like an oversized mealybug. Adults and larvae feed on pests. After mating, females can lay up to 500 eggs in the mealybug masses.

The life cycle from egg to adult takes 25 days at 30°C and 72 days at 18°C. Cryptolaemus work best between 21°C and 30°C in bright, sunny conditions.

Parasitic wasps are also available. Leptomastix dactylopii is effective against Planococcus citri. It lays its eggs into the third larval and adult stages. From egg to adult takes 16 days at 26°C and 13 days at 30°C.

Leptomastix epona is effective against Pseudococcus viburni (syn. affinis). Both wasps are yellow/brown and about 3mm long. Leptomastix are more effective against lower infestations than those that are more widespread.

Female Anagyrus pseudococci are brown and about 2mm long. They will mainly control Planococcus citri but will also attack Pseudococcus viburni (syn. affinis).

In all efforts to control mealybugs, parasitic wasps are best used in conjunction with Cryptolaemus.

Treatment: cultural control

• Avoid encouraging lush growth. Pests can multiply quicker on plants with higher nitrogen levels.

• Install yellow sticky traps to capture winged males.

• Check for honeydew deposits, sooty mould growth and ants.

• A pheromone trap is available for the winged males of Planococcus citri.

• Quarantine and check all imported stock.

Treatment: chemical control

Active ingredient Deltamethrin
IRAC code 3
Formulation Various including Decis (Bayer)
Action(s) Contact pyrethroid insecticide with residual activity. Incompatible with biological controls.

Active ingredient Fatty acids
Formulation Savona (Koppert)
Action(s) Contact-acting insecticide. Compatible with some biological controls.

Active ingredient: Nutrient-based plus additional natural products
Formulation SB Plant Invigorator (Fargro)
Action(s) Contact insecticide with physical action. Compatible with some biological controls.

Active ingredient Pyrethrins
IRAC code 3
Formulations Pyrethrum 5EC (Agropharm), Spruzit (Certis)
Action(s) Short-term knockdown product. Reintroduce predators after seven days.

Active ingredient Spirotetramat
IRAC code 23
Formulation Movento* (Bayer)
Action(s) Contact and ingested insecticide. Compatible with some biological controls.

Fully updated by Dove Associates.

Use plant protection products safely. Always read the label and product information before use.

* Extension of authorisation required for use in ornamental plant production outdoors and/or under protection.

Dove Associates shall in no event be liable for the loss or damage to any crops or biological control agents caused by the use of products mentioned.

For pest and disease alerts, fact sheets and management, see
www.HorticultureWeek.co.uk/pests.


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