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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)?

Data for 2002²

Blight was first observed 25 May in early potatoes grown under cover and in one potato field without cover. These very early infections originate from oospores. Many fields in this area were infected seven to ten days later. Dry weather from July saved the situation for most of Sweden and kept the infection pressure comparatively low. However, in some locations the disease level was surprisingly high despite the dry weather. As usual, the biggest problem with late blight occurred in the Southwest where the rainfall was higher. Many fields had late blight in late June in this area.

Despite the dry weather, blight was a problem in organic crops. Some fields were heavily attacked early in the growing season. As a whole the situation was better compared to 2001. In many organic fields, late blight can develop freely for long periods. Surveys in 2001 and 2002 showed that in the majority of fields where potatoes are grown organically, oospores are formed.

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

Data for 2002²

Dry weather in the later part of the growing season and excellent harvesting conditions resulted in a high quality harvest. No problems with tuber blight were reported except in home gardens.

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

Data for 2002²

In the southern region, the first spray against blight was again earlier than last year. However, due to the dry weather during the season, the number of sprays in Sweden as a whole is probably lower compared to last year. It is estimated that blight is controlled with 6-8 sprayings in the South, 4-6 in Mid Sweden and 2-4 in the North. The standard fungicide is Shirlan. There is a lot of discussion whether Acrobat or Tattoo should be used as an alternating fungicide. Epok is used for the second and/or third spray in the program, but is also used curatively. As usual, there were reports of failing effects of metalaxyl.

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

The NegFry forecasting system was introduced in the late 1990s. Recently, a Dutch system, Plant Plus, has been introduced commercially.

The project Studies on the new Nordic populations of Phytophthora infestans to improve potato late blight forecasting and control, with the participation of Denmark, Finland, Norway and Sweden, is underway. The results will be integrated into existing and new forecasting and DDSs (Decision Support Systems). Core Internet based late blight decision support systems will be developed within a common framework.

Since February 21, 2003, Web-blight, an international web-based information and decision support system for potato late blight is bringing day-to-day information on the first occurrences and the development of late blight in Denmark, Norway, Sweden, Finland, Estonia, Latvia, Lithuania and Poland (http://www.web-blight.net)

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

As in other years, in 2002 there were reports of failing effects of metalaxyl.

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

The A2 mating type was first detected in Sweden in 1987 (Kadir and Umaerus, 1987) and in 1989 reduced sensitivity to metalaxyl was reported (Olofsson, 1989). Both mating types were found throughout the country in 1997 and 1998 (Sandström and Andersson, 1999) and oospores have been observed in blighted crops in several locations (Andersson and Sandström, unpublished). Indications of sexual reproduction resulting in soil borne inoculum (oospores) were first reported in 1998 (Anderson et al, 1998a).

7. Disease risks and/or major needs?

8. Any publications on late blight in the country?  

Andersson B, Sandström M and Strömberg A. 1998a. Indications of soil borne inoculum of Phytophthora infestans. Potato Research 41:305–310.

Andersson B, Sandström M and Strömberg A. 1998b. Sexual reproduction of Phytophthora infestans on potato in Sweden. pp 92–96 in: Schepers H and Bouma E (eds), Proceedings of the Workshop on the European network for development of an Integrated Control Strategy of potato late blight, 24–27 September 1997, Carlow Ireland, PAV-Special Report no. 3. Applied Research for Arable Farming and Field Production of Vegetables, Lelystad, Netherlands.

Hansen J G, Lassen P and Röhrig. 2001. Monitoring of potato late blight based on collaborative PC-and Internet applications. pp 39–54 in: Westerdijk K and Schepers H T A M (eds), Proceedings of the Workshop on the European network for development of an Integrated Control Strategy of potato late blight, 6–10 September 2000, Munich, Germany, PAV-Special Report no. 7. Applied Research for Arable Farming and Field Production of Vegetables, Lellystad, Netherlands.

Kadir S and Umaeus V. 1987. Phytophthora infestans A2 compatibilty type recorded in Sweden. pp 223 in: 10^th Triennial Conference of the European Association for Potato Research, Ålborg, Denmark.

Olofsson B. 1989. Metalaxyl sensitifity of Swedish strains of potato late blight (Phytophthora infestans). Växtskyddsnotiser 53:139–143.

Nilsson B A and Umaerus V. 1977. Recent research in Svalov in the mechanism of field resistanct to Phytophthora infestans. Potato Research 20: 272–273.

Sandström M and Andersson B. 1999. Distribution of mating types of Phytophthora infestans in Sweden. pp 281–282 in: Schepers H and Bouma E (eds), Proceedings of the Workshop on the European network for development of an Integrated Control Strategy of potato late blight, 9–13 September 1998, Uppsala, Sweden, PAV-Special Report no. 5. Applied Research for Arable Farming and Field Production of Vegetables, Lelystad, Netherlands.

Stromberg A, Persson L and Wikstrom M. 1999. Infection of potatoes by oospores of Phytophthora infestans in soil. Plant Disease 83:876

Strömberg A. 1999. Experiences of oospore germination and formation in potato cultivars with different levels of resistance to leaf late blight. pp 205–209 in Schepers H and Bouma E (eds), Proceedings of the Workshop on the European network for development of an Integrated Control Strategy of potato late blight, 9–13 September 1998, Uppsala, Sweden, PAV-Special Report no. 5. Applied Research for Arable Farming and Field Production of Vegetables, Lelystad, Netherlands.SPAN>

Wiik L and Olofsson B. 1996. Control of potato late blight (Phytophthora infestans) in Sweden. Potato Research 39:119–120.

9. Is tuber blight an increasing problem?

Occassionally. 

Comments, additions and corrections are very welcome. Please contact us at GILB(at)cgiar.org

[2] Schepers, H T A M. 2003. The development and control of Phytophthora infestans in Europe in 2002. pp 9–22 in: Westerdijk C E and Schepers H T A M (eds), Proceedings of the Seventh Workshop of an European Network for development of an Integrated Control Strategy of potato late blight, 2–6, October 2002 , Pozan, Poland, PPO-Special Report no. 9. Applied Plant Research BV, Wageningen, Netherlands. Information regarding the late blight epidemic in 2002 in Sweden provided by B. Andersson.