Phomopsis Cane and Leaf Spot on Grapevines

Note Number: AG0992
Published: April 2002
Updated: April 2006

 

Phomopsis cane and leaf spot of grapevines is caused by the fungus Phomopsis viticola. For many years this disease has been known as ‘dead arm’. However, it has been shown that dead arms and pruning wound cankers may also be caused by the fungus Eutypa lata and other fungi and not necessarily by Phomopsis viticola. For this reason the name ‘dead arm’ is now considered misleading, and the disease is referred to as ‘phomopsis cane and leaf spot’.

The disease is favoured by wet spring weather, and is widespread in many of Victoria’s wetter, cooler regions. It can often be confused with the grapevine disease black spot. With phomopsis the small, black, dead spots are surrounded by a yellow halo, but with black spot, the dead spots are larger and not surrounded by a yellow halo.

It also occurs in grape growing areas along the Murray River from north-east Victoria (Rutherglen-Wahgunyah) to Mildura. The incidence of phomopsis in the Mildura and Robinvale districts has been low compared to other areas such as Swan Hill and Rutherglen. Affected vines commonly lack vigour and do not crop to their potential.

Most Vitis vinifera varieties can be infected by phomopsis but not all are affected sufficiently to cause economic loss. Some table grape varieties are quite susceptible to damage, particularly Waltham Cross, Purple Cornichon, Thompson Seedless (Sultana) and Cardinal. Among the wine grape varieties, Grenache and Tokay are particularly susceptible.

Two types of phomopsis have been described in the past – named taxon 1 and taxon 2. Taxon 1 has now been identified as the sexual stage Diaporthe perjuncta, and the symptoms and potential damage have yet to be defined. Taxon 2 is Phomopsis viticola and is the one described in this note.

Symptoms

Infections occur on leaves, shoots and bunches.

Leaf symptoms

Tiny dark brown to black spots rarely greater than 2 mm diameter with a 2-3mm wide yellow halo around the dead spot. The spots appear three to four weeks after rain and mainly on the lower leaves on a shoot. With heavy infection, basal leaves become quite distorted and may not develop to full size. Petioles may yellow off and abscise, causing leaf drop. Later developing uninfected leaves often cover the infected basal leaves and the problem is not so noticeable.

Shoot symptoms

Small spots with black centres also appear on shoots in spring, usually at the base of the shoot. These can expand and join up into thin black cracks about 5-6mm long. When infections are severe, the thin cracks join together to produce elongated brown to black legions up to 20 mm long. These may open up and become scabby looking. Heavily infected shoots usually lack vigour and may not develop fully; some are completely girdled and die.

Bunch symptoms

Occasionally, spots similar to those on shoots and leaves also develop on the flower cluster or bunch stem. Severely infected bunches shrivel and die.

Cane symptoms

Canes become discoloured, with dark brown or black patches surrounded by white bleached areas. The infected patches may become speckled with the tiny black fruiting structures (pycnidia) of the phomopsis fungus. The latter mostly develop around original lesions or at nodes.

Crop losses caused by phomopsis are mainly associated with the breakage and loss of heavily scarred shoots. This weakening may also lead to loss of infected canes or spurs, all of which reduce potential bunch number and yield. Also, if canes weakened by infection are retained at pruning time, they are more susceptible to frost damage.

Life cycle of phomopsis

The disease overwinters in the woody parts of the vine and infection initially occurs in the spring. Spores released from the over-wintering pycnidia on canes and wood infected in previous seasons are splashed by rain onto newly developing shoots. At least 10 hours of rain is required for spores to be released and subsequent periods of high humidity favour the disease. Growth occurs over a wide range of temperatures but hot temperatures in summer stop it developing.

Infection requires prolonged periods of free moisture to be present on the unprotected green tissue. Heavy rains for extended periods in September, October and November are particularly favourable for disease development. The disease tends to spread slowly from localised sources within a vineyard.

Disease Management

Monitoring for the disease should start about 3 weeks after budburst, and then 1-2 weeks thereafter if wet conditions persist. For the protection of developing shoots and foliage in spring, apply chemicals according to label directions through a properly calibrated and adjusted spray machine. Spray initially at bud break, again when shoots are 100-150 mm long, and then at fortnightly intervals while conditions favouring the disease persist. Up to five sprays may be required.

Note the sections of the vineyard where phomopsis occurs and inspect those areas in winter for signs of the disease. Where practicable, prune out badly infected canes and spurs which provide inoculum for new infections.

Chemicals registered for the control of phomopsis are available in the booklet “Agrochemicals registered for use in Australian Viticulture”, published each year by the Australian Wine Research Institute. A copy is also available at the Australian Wine Research Institute website.

When establishing new vineyards, care should be taken to select cuttings for propagation from vines free of phomopsis, as the disease is readily introduced to a vineyard, with infected planting material.

Acknowledgement

This Agnote was developed by John Whiting,  April 2002.

It was reviewed by John Whiting, April 2006.