Biosecurity Operation mealybug

Operation mealybug

They might be tiny and slow-moving, but mealybugs have caused a swift mid-to-late season infestation in table grape vineyards in Sunraysia.

Mealybug populations are generally controlled naturally by a range of beneficial predatory and parasitic insects. But when natural biological control is inadequate, favourable breeding conditions occur, and spray program applications become out of sync, populations build up in the midto-late season in the vineyard, enabling a perfect storm.

A perfect storm

Mealybugs prefer mild warm weather with temperatures about 25°C and high relative humidity. Hot dry conditions in summer can kill juveniles and reduce mealybug infestations, but this year’s summer in Sunraysia – lacking its usual weeks’ long heatwaves of 40°C or greater – presented an opportunity ripe for mealybugs to strike.

Growers expecting mealybugs to build up in November or December did not recognise the shift in the season, or realise that their spray treatments would be thrown off their spray schedule and couldn’t be enacted by date.

Growers who waited for the first sign of mealybugs in the crown, or among fruit, applied their initial spray too late to achieve control.

Numbers would have already been building to significant levels by the time growers became aware of the rapidly developing issue, which meant that eradication programs were reactive, rather than proactive. Replacing some of the previously used chemistry with new and unfamiliar chemicals has also impacted treatment programs.

Timing is everything! Proactive treatment begins while mealybugs are still in debris and under bark on trunks. Using summer oil or systemic insecticides to control the population in the early season has minimum impact on the beneficial insects that help control mealybug outbreaks.

Pest identification and damage

Infested table grape bunches are unmarketable. The mealybugs are unsightly and sooty moulds grow on the honeydew that mealybugs produce.

Mealybugs have also been identified as vectors that transmit grapevine viruses, especially leafroll-associated viruses. Some of these viruses can reduce vine growth, yield and fruit quality, and may cause graft incompatibilities.

Long-tailed and other mealybugs

Adult mealybugs are soft-bodied, flattened, oval shaped insects covered in secreted white powdery wax. They have characteristic filaments around the edges of their bodies and are around 5mm long. They live in colonies predominantly composed of adult wingless females, eggs and nymphs (juveniles).

Various species of pest mealybugs can be found in Australian vineyards. Body filaments and the colour of body contents of mealybugs can be used for their identification:

- the long-tailed mealybug (Pseudococcus longispinus) has pale yellow body contents and long tail filaments - the citrophilus mealybug (Pseudococcus calceolariae) has dark-red body contents, and short, thick tail filaments.

- the obscure mealybug (Pseudococcus viburni) has orange body contents and short, thin tail filaments.

Vigilance is key

Australia has continuing pressure from mealybug. It’s not a matter of if but when, so growers must remain vigilant and proactive, not just reactive.

Even young vines and new plantings play host. Growers must inspect and be prepared to treat young vines early in the season.

Waiting until there is evidence of adults on the crown is too late, growers should monitor vine trunks by removing bark to check for dormant insects early in the season, and continue monitoring throughout the season, noting first appearance of crawlers to establish an effective early eradication program.

Some agronomists recommend treating earlier with oils and systemic applications before mealybugs are visible. This is key to prevent the first generation of crawlers from surviving.

Frequent or poorly timed use of contact chemicals in the vineyard will reduce beneficial insect populations. An integrated pest management program will increase the effectiveness of natural predators.

It is important to ensure vineyard hygiene programs are kept in place. Canopy and trunk hygiene management will reduce hiding places and allow eradication programs to be of more use.

Vineyard workers should also be made aware of transference risks through equipment, and machinery should be cleaned between patches.

MEALYBUG LIFECYCLE

Egg

100-350 eggs/ Instar I Instar I

Instar II Instar II

Instar III

Instar III Pre pupae

Post-harvest treatment program

For early varieties, straight after harvest, while the vine is still active, some agronomists recommend applying a systemic treatment.

Later varieties may not be actively growing after harvest, so systemic treatments wouldn't be very effective: wait until after leaf fall to gain better access to the vine. Prune and remove trunk bark to expose overwintering mealybug and apply a contact treatment.

From budburst, be vigilant, looking under bark and on shoots for the first signs of crawlers, and then apply a contact spray to keep numbers low.

Before making any chemical choices, read the product labels carefully, be aware of any risks to foraging bees, and check MRLs of your export markets. v

Pupae