Identification of diseases for the grapevine farmer

A Technical Guide
for Wine Producers

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Michelle Groenewald

Identification of diseases for the grapevine farmer

Michelle Groenewald
As far as vineyard management is concerned, producers and consultants are confronted daily by a variety of challenges. These challenges involve decisions regarding irrigation, fertilisation, disease and pest management as well as other viticultural practices. Sometimes a decrease in production or poor growth is observed and in drastic cases vineyards may suddenly die.

Figure 1. The flow chart of photos represents the process undergone by a grapevine sample submitted to the diagnostic laboratory at Nietvoorbij.

1. Grapevine samples are received by staff of the Plant Protection Division at Nietvoorbij.

2. Symptoms are photographed and the sample prepared for isolations in laboratory.

3. Fungi grow from the infected tissue.

4. Symptomatic parts of the sample are placed on the growth medium.

5. Fungi are identified by the senior plant pathologist.

6. A report is compiled and sent to the producer or consultant.

Strange or unknown symptoms are often noticed. In such instances it is difficult to determine the cause of the problem; therefore the Plant Protection Division of ARC Infruitec-Nietvoorbij offers a diagnostic service for grapevine producers and consultants to determine whether these occurrences are caused by diseases (Fig. 1.).
Samples submitted for diagnosis (root, trunk and unknown diseases) must comply with the following requirements:

Where possible the entire vine with its roots must be submitted, together with a soil sample.
If the former is not practical, large vines may be divided into sections (keep graft joint and crown intact, and include roots).
Supply a vine that is representative of the problem in the vineyard.
Dead plant material must not be submitted, rather send a vine that shows symptoms and is still alive.
To prevent desiccation, samples should be delivered to the diagnostic laboratory (Nietvoorbij, Stellenbosch) as soon as possible after being removed from the soil.
Soil samples should be taken in the area where most of the root growth occurs, approximately 30 cm deep.
Soil samples (approximately 1 to 2 kg) must be placed in a plastic bag to prevent desiccation.
Samples submitted for the diagnosis of leaf diseases (including symptoms on shoots and bunches):

This include leaf diseases like oidium, downy mildew, dead arm disease, Botrytis, anthracnose etc.
Wrap leaves, shoots or bunches in newspaper. Place in plastic or paper bag so that sample does not desiccate and is not exposed to unnecessary moisture either.
Deliver as soon as possible to the diagnostic laboratory (Nietvoorbij, Stellenbosch).
Upon arrival at the diagnostic laboratory the sample is examined visually to determine the process of analysis. A form is completed to obtain relevant information regarding the age, cultivar, rootstock, nursery and symptoms of the vine, as well as distribution of symptoms in the vineyard block. The above information, together with any characteristic symptoms that may be observed, will make a more comprehensive diagnosis possible.
After the visual inspection, entire vines are sawn up to expose the symptomatic areas. Photos are taken of the various symptoms. Small pieces of wood are cut from the symptomatic parts and placed on suitable growth media for fungi. The causative organism will grow out of this wood in 2 to 4 weeks, whereafter it may be identified. Following diagnosis of the sample, a report will be sent to the client with an explanation of the diagnosis. An addendum about the causative disease, comprising the latest research and control thereof, is included in the report.
Over and above being an essential service that is offered to the grapevine industry, the information may be used to good effect by researchers. The information thus gathered may point towards certain trends associated with fungal diseases as well as research priorities. Analyses are conducted mostly on grapevine samples with unknown symptoms, and young vines that do not establish successfully.
At the Plant Protection Division of ARC Infruitec-Nietvoorbij we aim to provide the grapevine industry with a value for money service. The cost involved in submitting one grapevine and soil sample to the diagnostic laboratory is R490 (including VAT). The cost includes isolations and the identification of fungi from the grapevine and soil sample. In some instances a visual examination only is required to diagnose the problem, in which case a fee of R114 (including VAT) is charged. In the case of grapevine trunk diseases a visual examination is insufficient and comprehensive analyses are recommended.
Grapevine and soil samples may be submitted to Michelle Groenewald at ARC Infruitec-Nietvoorbij, Stellenbosch. She may be contacted on (021) 809-3104 or groenewaldm@arc.agric.za for more information.
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