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1. Late blight occurrence and LB severity by major production area in the country. What crops were affected (tomato, potato, others)? Disease sources (seed, cull piles, volunteer plants, soil)?

Epidemics are usually sporadic in most of the northern production regions. However, in the coastal regions, namely the southwestern Cape, southern Cape and Kwazulu-Natal, late blight poses a constant threat to production. In 1995 and 1996 weather conditions in all the potato production areas were very conducive to late blight development and epidemics soon became explosive and difficult to control. There are fourteen potato production areas in South Africa (map on following page).

Tomato is a host.

2. LB impact (foliar damage, yield losses, tuber rot occurrences)?

Yield losses caused by late blight epidemics are substantial. Tuber rot is a serious problem

3. Fungicide use (amounts, types, etc.)?

4. Other LB control measures (resistant cultivars, forecast systems, none)?  

Cultivars grown in South Africa

5. LB control effectiveness (fungicide or host resistance failures)

6. Pathogen strains (mating type, fungicide resistance, virulence factors, etc)?

A country-wide survey of potato (656 isolates/101 fields) and tomato (57 isolates/16 fields) was made during 1996–1998. All isolates tested had the characteristics of the “old” pre-1980 P. infestans population (A1 mating type, the US-1 RG-57 DNA fingerprint, 86/100 Glucose-6 phosphate haplotype and mitochondrial DNA haplotype 1b.

In 1997 both the southern coastal regions and the western Free State had a high (51%) frequency of metalaxyl resistant isolates. Even though phenylamides were withdrawn in the southern coastal regions in December 1996, in 1998 resistance levels were found to high (more than 83%). However, sensitive isolates predominated in the other potato production areas. No resistant strains were isolated from tomatoes.

7. Disease risks and/or major needs?

8. Any publications on late blight in the country?

Thompson A H, McLeod A, Denner F D, Zondo P T. 2002. Characterization of Phytophthora infestans populations in South Africa (abs). pp 141 in: Lizárraga C (ed), Late blight: Managing the global threat. Proceedings of the Global Initiative on Late Blight Conference, Hamburg, Germany, 11–13 July 2002. International Potato Center, Lima, Peru.

McLeod, A. Denman, S. Sadie, A. Denner, F.D.N. 2001. Characterization of South African isolates of Phytophthora infestans. Plant Disease 85:287–291.

Glass, J.R. Johnson, K.B. Powelson, M.L. 2001. Assessment of barriers to prevent the development of potato tuber blight caused by Phytophthora infestans. Plant Disease 85:521–528

9. Is tuber blight an increasing problem?

Yes

10. Other comments

Potato production and utilization

Potatoes (Solanum tuberosum L.) are the third most important food crop grown in South Africa. South Africa had an output of between 160,000–170,000 tons in the 1996–1997 production season. The total area planted to seed and table potatoes in 1996 and 1997 was 58 703 ha and 55 147 ha, respectively. Sixty seven percent of all potatoes produced were sold locally on fresh markets, 13 % were processed and 6% were exported. The majority of potatoes (± 70%) are grown under irrigation in both summer and winter rainfall regions.

Information provided by Freddie Denner, ARC-Roodeplaat Vegetable and Ornamental Plant Institute, Pretoria, South Africa. Email: freddie(at)vopi.agric.za