Phomopsis viticola: prohibited disease

Page last updated: Tuesday, 5 May 2020 - 4:31pm

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Phomopsis cane and leaf spot is caused by the fungus Phomopsis viticola which is a prohibited organism in Western Australia. The disease can cause significant yield loss in areas where weather conditions are favourable.

Characteristic symptoms include small dark leaf spots with yellow halos that appear during spring and black cane lesions on the lower internodes.

Background

Phomopsis cane and leaf spot caused by the fungus Phomopsis viticola is a disease of grapevines that can be highly destructive if weather conditions are favourable. It is not known to occur in Western Australia but is present in other grape growing regions of Australia and overseas.

The disease is favoured by extended periods of rainfall post budburst that can lead to yield losses of up to 30%. Yield loss can occur through reduction of viable canes, reduced budburst and bunch infection. This leads to reduced production of bunches, lower quality of fruit and reduced yields.

The introduction of DNA sequencing methods has resulted in extensive taxonomic revision of the Phomopsis group of fungi in recent times and name changes have occurred. This information has supported prior studies showing that P. viticola is absent from WA.

Hosts

Vitis vinifera is the primary host of this pathogen. Secondary hosts are other Vitis spp. including sand grape (Vitis rupestris), fox grape (Vitis labrusca) and Virginia creeper (Parthenocissus quinquefolia). This fungus is known to infect leaves, stems, inflorescences, canes, rachis and berries.

Distribution

Phomopsis cane and leaf spot has been recorded in Victoria, New South Wales and South Australia. Phomopsis viticola is present in the viticultural areas of Coonawarra, Mildura, Rutherglen, Mudgee, the Hunter Valley and the Barossa Valley.

Phomopsis viticola is present throughout other viticultural areas in Asia, Europe, Africa, North America, parts of South America and New Zealand. Countries where it is present include China, India, Japan, Turkey, Belgium, Serbia, Montenegro, France, Germany, Greece, Hungary, Italy, Netherlands, Portugal, Romania, Switzerland, Ukraine and the UK.

In North America, P. viticola is found in California, New York and Canada, and in South America it is found in Venezuela and Chile.

Symptoms

In spring, small dark spots (about 1mm in diameter) surrounded by yellow halos develop on the leaves (Figures 1).

Phomopsis leaf infection with yellow halos
Figure 1a Leaf infection of Phomopsis viticola in a New York state vineyard 
Severely infected leaf by Phomopsis viticola
Figure 1b Leaf severely infected by Phomopsis viticola
Grape leaf infected with Phomopsis viticola under a light box highlighting the characteristic yellow halos surrounding black spots
Figure 1c Grape leaf infected with Phomopsis viticola under a light box; the yellow halos are highlighted 

The older, lower leaves are the first to show symptoms. Severely infected leaves may experience premature leaf fall.

On canes and shoots the symptoms are often restricted to the lower internodes. Small dark spots develop on the cane or shoot and with the growth of the shoot these spots expand and elongate to form black lesions 3-6mm in length (Figures 3 and 4).

Grape stem infected with Phomopsis viticola showing small spots which develop in spring
Figure 3a Small spots develop on the grape stem or cane in spring
Young stem infection
Figure 3b Young stem infection of grapevine caused by Phomopsis viticola
Grape stem infected with Phomopsis viticola showing the small spots which enlarge as the shoot grows
Figure 4 Small spots enlarge as the shoot grows to form lesions

These lesions may coalesce to form large scabby areas (Figure 5). The lesions may girdle the shoots as they mature or cause the shoots to become stunted and die. If infection spreads into the rachis, the young bunches may dry out and fall off.

Grape stem infected with Phomopsis viticola showing lesions that may coalesce to form large scabby areas
Figure 5a Phomopsis viticola lesions may coalesce to form large scabby areas
Older stem infection of Phomopsis viticola
Figure 5b Older stem infection of Phomopsis viticola, note the lesions merging into a larger lesion. 

Fruit infection can occur, the berries developing brown spots which enlarge and darken as the disease progresses. The berries may become mummified and fall from the bunch. Fruit infection is rare in Australia.

The disease overwinters as small fruiting bodies on canes and other woody tissue (spurs and prunings), that can often appear bleached with small dark spots. Phomopsis viticola has also been associated with vine decline and grapevine cankers overseas.

When am I likely to see it?

Phomopsis cane and leaf spot is most visible early in the season after budburst but prior to full canopy development obscuring leaf and lower cane tissue. Leaf lesions are the most obvious initial symptom.

Infection can occur at a range of temperatures but is optimal at 23°C with infection favoured by successive periods of wet weather and high humidity in spring. It can take three to four weeks from the infection event until symptoms are visible in the vineyard.

Can be confused with

Symptoms of Phomopsis cane and leaf spot may be confused with other fungal diseases and damage caused by other agents, such as frost, which cause stems to bleach. A related fungus, Diaporthe australafricana, that is present in WA can produce bleached canes with black fruiting bodies (Figure 6).

Bleached grape vine cane which could have been caused by several factors in the vineyard including Phomopsis viticola
Figure 6 Bleached canes can be caused by several factors in the vineyard including Diaporthe australafricana

Grapevine black spot (anthracnose) infections caused by Elsinoë ampelina can also produce leaf and stem symptoms. Grapevine black spot produces black leaf spots but these are not associated with yellow halos and enlarge with age with the centres falling out (Figure 7).

Cane infection of black spot differs to that of P. viticola in that they are usually more circular in appearance with a whitish centre surrounded by a black margin (Figure 8) as detailed in Black spot of grapevines in Western Australia.

Grape leaf infected with black spot where the small black spots enlarge and the centre falls out of the infected area
Figure 7 With black spot leaf infection the small black spots enlarge and the centre falls out of the infected area

Cane infections of black spot differ from P. viticola in that they are usually more circular in appearance with a whitish centre surrounded by a black margin (Figure 8).

Grape stem showing black spot cane infection which is characterised by circular white lesions with a dark margin
Figure 8 Black spot cane infection showing circular white lesions with a dark margin

Berry rot may be confused with infection caused by Botryosphaeria species. See Know your grapevine bunch rots.

Applications of contact herbicides can cause small spots on leaves where the contact has occurred. The spot will initially appear yellow but progress to black as the herbicide kills the leaf tissue (Figure 9).

The spots are often larger than those caused by P. viticola. Spray damage is likely to occur over a larger area of the vineyard rather than localised infection caused by P. viticola and will include all leaf material on the vine.

Grape leaf showing characteristic symptoms of contact herbicide spray damage of yellow spots which develop into dead tissue as the herbicide kills the leaf tissue
Figure 9 Contact herbicide spray damage initially appears as yellow spots but develops into dead tissue as the herbicide kills the leaf area contacted

These spots are larger than those caused by P. viticola. Spray damage is likely to occur over a larger area of the vineyard than a localised P. viticola infection and will include all leaf material on the vine as the herbicide kills the leaf tissue.

Spread

Spores of P. viticola are dispersed within the vineyard by rain splash and spread is generally localised. Infection comes from spores located within the fruiting bodies on canes or spurs that were diseased in the previous season.

Long distance dispersal of the disease occurs through the movement of infected or contaminated propagation materials such as budwood, cane cuttings and nursery stock. Phomopsis viticola has also been reported to be spread by pruning equipment and agricultural machinery.

What to do if infection suspected

Phomopsis viticola is a prohibited organism for WA. It is important that suspect infestations are reported. Please contact the Pest and Disease Information Service (PaDIS) using the contact details at the bottom of this page. You can also send photos of suspect symptoms using MyPestGuide.

Contact information

Pest and Disease Information Service (PaDIS)
+61 (0)8 9368 3080