Grapevine scale and sooty mould

Scale Insect Management 

Why scale matters  

Scale insects are an increasingly important pest in Australian vineyards. While they are often present at low levels, populations can build rapidly and lead to honeydew, sooty mould, reduced fruit quality and potentially spread virus.

Key points 

• Scale insects are commonly present in vineyards and can build to damaging levels if not managed early. They shelter under bark, making them difficult to control once established.
• Scale insects can excrete honeydew which can lead to sooty mould and may result in downgraded or rejected fruit.
• Risk factors for damaging scale levels include:
  • spur pruning systems, which retain more permanent wood
  • high amounts of old wood and rough, craggy bark that provide shelter
  • mild seasonal conditions, allowing populations to build
  • susceptible varieties
  • vineyard edges, particularly near shelter belts or neighbouring vegetation.
• Promoting beneficial insects and removing or mulching pruning material can support control but are unlikely to be sufficient on their own where populations are high.
• Regular monitoring (particularly in winter and early spring) is critical to detect population increases and determine whether chemical control is required.
• The most effective timing for control is at crawler emergence, when scale insects are most vulnerable. Later life stages are harder to control.

Understanding scale and sooty mould

Scale insects feed on vine sap and excrete honeydew, a sticky substance that attracts ants and promotes the growth of sooty mould. Sooty mould can coat leaves and bunches, reducing fruit quality and increasing the risk of downgraded or rejected fruit, particularly where contamination is visible on bunches.

Even low levels of sooty mould can create issues for wineries due to its effects on processing, fermentation and visual quality.

In addition to causing sooty mould, scale insects have also been associated with the following impacts:

• reduced vine vigour
• delayed budburst
• increased susceptibility to bunch rots
• spread of viruses within vineyards

Life cycle and timing

Image: Ag Communicators

Field studies across multiple regions in South Australia has improved our understanding of the scale insect lifecycle, helping identify key windows for effective chemical control (SARDI, 2026, unpublished).

Scale insects overwinter as juveniles (second and third instars) under bark on spurs, canes and cordons. In early spring (September in warmer regions, October in cooler regions) they become active and rapidly develop into mature females over 3-4 weeks. As females mature, they harden and become more convex before laying eggs beneath their protective covering.

These eggs hatch into crawlers — the small, mobile stage — that move to leaves, shoots and bunches to feed. Crawlers emerge over several weeks with approximately half emerging around EL25 (flowering). 

After settling, crawlers develop into ‘first’ and then ‘second instars’, with about half the population reaching second instar within four weeks of hatching. Scale insects remain on vines through summer, feeding and increasing in size. In late summer to autumn, they migrate back under bark to overwinter, completing the cycle. A second generation may occur, but it is typically small and contributes little to overall population levels.

Recent research shows that two scale species are commonly found in Australian vineyards. In northern NSW and Queensland, the dominant species is Parthenolecanium persicae, while in southern NSW and South Australia it is Parthenolecanium corni (SARDI, 2026, unpublished).

Risk factors

Field observations indicate that the following factors are commonly linked to increased risk:

• Some evidence suggests scale insect numbers are often higher in spur pruned vineyards than in cane pruned vineyards, likely due to the greater amount of permanent wood providing more shelter.
• Seasons with mild winter and spring conditions can increase risk by improving over winter insect survival and accelerating population build-up.
• Older vineyards can harbour higher numbers of scale insects, increasing the risk of scale damage, likely due to greater amounts of old wood and rough, craggy bark providing more shelter.
• Infestations are often observed to be higher along vineyard edges near shelter belts, perennial crops, gardens and buildings, possibly due to increased shelter, alternative hosts or reduced spray coverage.
• Some differences between grape vine varieties have been observed. Pinot Noir, Sauvignon Blanc, Merlot and Cabernet Sauvignon tend to show lower scale incidence, while Riesling, Chardonnay, Tempranillo, Sangiovese and Shiraz may be more susceptible. However, varietal susceptibility is likely less important than vineyard management and site conditions.

Impacts of sooty mould

Beyond the risk of downgraded or rejected fruit, heavy sooty mould can affect vine performance by:

• reducing photosynthesis by blocking light interception on leaves
• contributing to heat build-up on exposed bunches and foliage during hot conditions.

While some research has shown limited impact of sooty mould on wine sensory characteristics, the presence of sooty mould remains a significant commercial risk. Fruit affected by sooty mould can show visible colour differences at crushing and may affect processing efficiency.

Even low levels of sooty mould can result in downgraded or rejected fruit and should be avoided.

Monitoring for scale and sooty mould

Winter is a good time to monitor scale levels. Growers should check for scale underneath bark on spurs, canes and cordons during pruning. Hot spots where high numbers of scale are found should be tagged for further monitoring and control.

In early spring, the first indications of scale activity include ants appearing and sticky honeydew being visible.

Sooty mould may become visible later in the season once populations are well established. However, by the time the mould is visible, scale will already be hard to control, so action should be taken based on early indicators rather than waiting for visible mould.

When scale insects are concentrated in a particular area, it is best to only treat that spot where possible. This helps minimise costs, reduce impacts on beneficial insects and decrease the risk of insecticide resistance.

Managing scale insects 

Scale control strategy

Scale insects are often present at low levels, but populations can increase rapidly, making early decision-making important.

Beneficial insects help control scale by feeding on them, lowering their numbers. Removing or mulching pruning materials can also limit scale insect damage as this reduces the places where these pests can survive during winter.

It is recommended to:

• Maintain an environment that supports beneficial insects — mulch pruning materials regardless of scale insect populations. 
• Act early before sooty mould develops, especially when monitoring shows scale insect numbers are increasing. Consider whether a winter oil spray or in-season insecticide is warranted.
• Be proactive with winter or early-season sprays, especially if sooty mould was observed in the previous season.

Recommendations for spraying scale insects

When spraying is required during the season:

• Check the ‘Dog Book’ for current insecticide options.
• When time is less pressured, winter mineral oil sprays can help reduce scale populations, but are unlikely to eliminate scale completely as many scale insects are protected under bark.
• Systemic insecticides are typically more effective than contact sprays because they canr each insects that ares heltering underbark from spray coverage.
• For maximum impact, target sprays at crawler emergence in early spring (before EL18).
• Spot-spraying affected areas is strongly recommended where infestations are localised to minimise harm to beneficial insects.

Promoting beneficial insects

Beneficial insects, including wasps, beetles, moths and lacewings, can contribute to controlling scale insect populations, particularly by targeting eggs and crawlers. However, field observations suggest that natural parasitism levels are often low and may not be sufficient to prevent outbreaks on their own.

One way to support these insects is to plant native species that host them. See ‘AWRI factsheet: Scale - factors influencing their prevalence and control’ for a list of beneficial insects and native plants that can help encourage them.

Limiting the use of broad-spectrum insecticides and keeping sulphur application rates as low as possible can help support beneficial insect numbers.

For more information and resources on vineyard biodiversity.