Johannes Mellet P O Box 22, Ladismith WC, 6655
Abraham Vermeulen ARC Infruitec-Nietvoorbij, Private Bag X5026, Stellenbosch 7599
Fungi have the ability to develop resistance to chemical fungicides that are used regularly and indiscriminately. In the viticultural industry the demand for new fungicides is therefore ongoing, either to replace products that have become ineffective or to extend the useful lifetime of existing products. New fungicides have to control the target fungus effectively without harming the vineyard, grapes, vinification process, wine or the consumer.
The law and registration
In terms of the Fertilisers, Farm Feeds, Agricultural Remedies and Stock Remedies Act (No 36 of 1947), all new products must be thoroughly tested and comply with high standards before they may be marketed. The Disease Management Division of ARC Infruitec-Nietvoorbij evaluates fungicides on a contract basis for companies who want to register new products for use on deciduous fruit and grapes in South Africa. Researchers also supply the Registrar with technical advice regarding applications for registration. In this way ARC Infruitec-Nietvoorbij remains up to date with the latest products, while producers can rest assured that new fungicides are thoroughly tested by independent researchers and that only effective products are recommended for registration.
Evaluation of fungicides’ effectiveness
To determine the effectiveness of fungicides, at least three trials are conducted over a period of two seasons, in two areas at least, and on two cultivars at least. In the trials the new fungicide must be applied at its recommended concentration, as well as half and double this concentration. The fungicide’s effectiveness is then compared to that of a registered fungicide and an untreated control. However, it is not possible to determine the effectiveness of a fungicide accurately if the target fungus is not present in large quantities. For this reason a disease garden (Fig. 1) has been established at Nietvoorbij. In this vineyard cultivars that are generally susceptible have been planted and conditions that are conducive to the development and distribution of fungal diseases are created.
Wynboer – August 2000 – Evaluation of new fungicides for use on vines by Nietvoorbij
Wynboer - August 2000 - Evaluation of new fungicides for use on vines by NietvoorbijSample text
Apart from the fact that a fungicide should control the target fungus effectively, it should not cause any damage to the foliage or cause crop losses. The vineyard should therefore be monitored on a regular basis for any phytotoxic reactions (Fig. 2). The new product is also sprayed in tank mixtures to ensure that the substance can be mixed with other chemicals already registered.
Residues and vinification
Grape samples of the treated vines are taken to determine the kind and quantity of residues remaining on the grapes. When residue samples are taken over a period of time, a curve may be drawn to indicate how fast the fungicide decomposes. By using the decomposition curves, the ideal withholding period for the fungicide may be determined. At the end of the withholding period, residues should be at an acceptable safety level for human consumption according to international standards.
The end product of wine grapes is wine. Fungicides can influence the fermentation process as well as the eventual character of the wine. To ensure that new fungicides do not harm the wine quality, experimental wine (using two different, neutral white grape cultivars) is made from treated grapes. Treatments include the new product at the recommended and one and a half times the recommended dosage. Fermentation and wine quality of the treatments are then compared to that of an untreated control and of a product that has already been registered.
Fungicides that have passed all these tests will control the target fungus effectively and not harm the vineyard, grapes, vinification process, wine or the consumer. Nietvoorbij strives to provide an essential and professional service to chemical companies and producers with regard to the registration of new fungicides.
For more information do not hesitate to contact the following persons:
Dr Ilse Trautmann (021) 809 3142
Mr Abraham Vermeulen (021) 809 3161
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