Control of powdery mildew and downy mildew during the post-harvest period

Project Number
WW 06-18

Project title
Control of powdery mildew and downy mildew during the post-harvest period

Project leader
Vermeulen, A K

Project description
Control of grapevine diseases is terminated prior to harvest due to the fact that fungicides have a with holding period. When no post-harvest disease control is applied, the inoculum pressure increases during the post-harvest period. The aim of this project is to investigate the effect of post-harvest disease control on the disease pressure and the influence that it has on the plants nutritional status. Cost-effectiveness of these sprays will also be investigated.

No significant differences between any of the treatments were recorded during the past two seasons with respect to carbohydrate content and shoot mass. A significant difference in total bunch mass was recorded between treatment A (no preventative programme, only post-harvest) and the rest of the treatments.

Four different spray programmes were applied during the season. The untreated control (no pre-harvest sprays, only post-harvest sprays applied) resulted in a high disease incidence of powdery mildew, whilst a low disease incidence of downy mildew was recorded. No differences were recorded between the other treatments. During the withholding period of the fungicides during the past season, the disease incidence of powdery and downy mildew increased sharply. Shortly after the post-harvest treatments were applied, infection levels decreased.

Due to the high disease pressure in treatment A, the leaves could not stay functional as long as the leaves of other treatments. Once again an earlier drop of leaves was noted in this treatment.

No statistical differences were recorded between the different treatments up to now. Some tendencies were noted after the past two seasons. Shoot mass has risen by more than 1,5 kg per six plants in both the post-harvest treatments. An increase in yield mass has also been noted in both post-harvest treatments. A decrease in disease incidence has also occurred in both seasons after the application of post-harvest sprays.

Producers are advised to spray at least two post-harvest sprays when disease incidences were high during the season. Although no statistical differences were recorded up to date, these applications could slow down or prevent the possible forming of over-wintering structures of the fungi.

Poster(s)
Vermeulen, A K. 2001. Preliminary results on post-harvest control of powdery and downy mildew. Poster presented at the 25th National Congress of the South African Society for Enology and Viticulture. 15-18 November, Somerset West, South Africa.

Fourie, P H. 2003. Metalaxyl resistance of grapevine downy mildew, Plasmopara viticola, in South African vineyards. Poster presented at the 8th International Congress of Plant Pathology. 2-7 February, Christchurch, New Zealand.

Fourie, P H and Vermeulen, A K. 2003. Fungicide resistance in downy mildew populations in Western Cape vineyards. Poster presented at the 27th National Congress of the South African Society for Enology and Viticulture. 5-7 November, Somerset West, South Africa.

Presentation(s)
Fourie, P H. 2000. Beheer van swamsiektes. Eksteenskuil Subsistence Farmers’ Day, 6 April, Eksteenskuil.

Fourie, P H. 2000. Epidemiology and control of downy mildew on grapevines. South African Society for Enology and Viticulture Table and Raisin Grape Short Course. 1 August, Upington, South Africa.

Vermeulen, A K. 2002. Vordering met die Winetech projek oor na-oes swambeheer. Presentation at the Winetech and VinPro Vineyard Virus and Post-harvest Information Day. 8 May, Worcester, South Africa.

Vermeulen, A K. 2003. Identifisering en bestryding van wingerdsiektes. Presentation at the Eksteenskuil Subsistence Farmers’ Day. 13 November, Eksteenskuil, South Africa.

Fourie, P H. 2003. Survey for metalaxyl resistance in Plasmopara viticola populations in Western Cape vineyards. Paper presentation at the 41st Congress of the Southern African Society for Plant Pathology. 19-22 January, Bloemfontein, South Africa.

FinalReport.pdf

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