Phomopsis cane and leaf spot

Phomopsis cane and leaf spot is a fungal disease of grapevines caused by Phomopsis viticola. It occurs in most Australian grape-growing regions, although it has not been reported in Western Australia.

Why Phomopsis matters

Phomopsis can significantly reduce vineyard productivity when wet spring conditions favour disease development. While often considered a sporadic disease, Phomopsis can persist in vineyards for several seasons and become an ongoing management issue if not identified and controlled early.

For growers and viticulturalists, effective Phomopsis management relies on understanding seasonal risk, monitoring vineyards at critical growth stages, reduce carry-over inoculum by removing infected canes, spurs and prunings, and applying preventative fungicides before infection occurs.

Phomopsis primarily affects young shoots, leaves, canes and occasionally bunches. Severe infections can:

Girdle and weaken shoots
Reduce vine vigour and productivity
Cause shoots to break under crop load or during windy conditions
Lead to cane cracking and poor wood maturity
Reduce yield through bunch stem infections and berry rot
Create a long-term source of infection that carries over into future seasons

Because infections occur early in the season, damage is often done before symptoms become obvious. By the time leaf spots and shoot lesions appear, infection has already occurred and management options are more limited.

Understanding the disease cycle

The fungus survives over winter in infected buds, bark, canes and spurs. During spring, spores are released from infected wood and spread by rain splash onto newly emerging shoots.

Wet conditions are critical for disease development. The highest risk occurs when:

Spring is cool and wet
Rainfall events are prolonged
Shoots remain wet for extended periods
Vine canopies stay damp due to poor airflow

The fungus becomes relatively inactive during hot, dry summer conditions, but infected vineyards can continue to harbour inoculum for several years if sources of infection are not removed.

Identifying vineyard risk

Some vineyards are more vulnerable than others. Higher-risk situations include:

Low-lying or sheltered blocks where moisture remains for longer
Vineyards with poor air movement
Dense canopies with prolonged leaf wetness
Blocks with a history of Phomopsis infection
Vineyards where infected canes or spurs are retained from previous seasons
Mechanically hedge-pruned vineyards where infected canes remain in the canopy

Understanding these risk factors can help growers prioritise monitoring and management activities throughout the season.

Symptoms to look for

During winter inspect canes and spurs for:

Bleached white areas on dormant wood
Small black fruiting bodies (pycnidia)
Longitudinal black cracks on canes

Bleached canes alone are not sufficient for diagnosis, as weather damage and other fungi can produce similar symptoms.

During spring and early summer watch for:

Small dark brown leaf spots surrounded by yellow halos
Black lesions or elongated cracks on lower shoot internodes
Distorted, stunted or weakened shoots
Shoots that snap easily in wind or under crop load

In severe cases:

Flower clusters may wither
Bunch stems can become infected
Berries may develop rot in cool, wet conditions

Monitoring and early detection

Monitoring is the foundation of effective Phomopsis management.

Most infections occur during or shortly after budburst, making early-season surveillance essential. Growers should not rely solely on visible symptoms later in the season.

Practical monitoring tips

Before budburst

Inspect canes and spurs approximately four weeks before budburst
Look for bleaching, cracking and black fruiting bodies
Pay particular attention to blocks that showed symptoms previously

From budburst onwards

Monitor susceptible blocks every one to two weeks
Inspect around 200 shoots across representative vineyard areas
Focus on lower leaves and lower shoot internodes where symptoms often appear first

High-priority areas

Low-lying sections of vineyards
Blocks with dense canopies
Sheltered areas with poor airflow
Sites with previous disease history

If long wet periods occur during flowering, inspect bunches and rachises for symptoms as the season progresses.

Management strategies

An effective Phomopsis program combines monitoring, cultural practices and, where necessary, targeted fungicide applications.

Only spray when risk exists

Preventative treatment is generally unnecessary where the disease is absent and risk is low.

However, where vineyards have a recent history of infection and conditions favour disease development, early season protective fungicide applications are often required from around 50% budburst to protect emerging shoots. Importantly, fungicides registered for Phomopsis are protectants rather than curatives and are most effective before infection occurs. Good spray timing and coverage are critical to ensure newly emerged shoots remain protected. Once symptoms are visible, infection has already taken place.

Improve vineyard hygiene

Reducing sources of inoculum can significantly lower future disease pressure.

Consider:

Removing infected canes and spurs during pruning
Avoiding retention of diseased wood as fruiting canes
Removing or destroying infected prunings where practical
Using clean propagation and planting material

Good sanitation reduces the amount of fungal inoculum available to infect new shoots the following season.

Manage canopy density

Canopy management plays an important role in reducing infection risk.

Practical approaches include:

Reducing excessive vine vigour
Maintaining open canopies
Positioning shoots effectively
Removing excess shoots or foliage where appropriate
Improving spray penetration
Encouraging airflow and faster drying after rain

These practices help shorten leaf wetness periods and create conditions that are less favourable for disease development.

Practical decision-making throughout the season

Timing	Key actions
Winter	Inspect canes for bleaching and black fruiting bodies. Remove infected wood where practical.
Pre-budburst	Review disease history and assess block risk. Prioritise monitoring of high-risk areas.
Budburst to early shoot growth	Intensify monitoring, particularly after rainfall events.
Wet spring periods	Consider protective management strategies where disease history and risk justify intervention.
Growing season	Maintain an open canopy and continue monitoring for symptoms.
Pruning	Remove infected canes and avoid retaining diseased wood for next season's crop.

Key takeaway

Phomopsis is primarily a disease of wet springs and vineyards with persistent sources of inoculum. The most effective management strategy is to understand risk early, monitor regularly from budburst onwards, reduce carry-over inoculum by removing infected canes, spurs and prunings, and use preventative fungicides before infection occurs. Early action is critical because infections occur before symptoms become obvious, and preventative measures are far more effective than responding after disease development.