In Peru close to 42% of the 268,000 ha in potato production has high or very high levels of late blight requiring more than six fungicide applications each growing season for an economically acceptable yield (Egúsquiza and Apaza, 2003). The department of Huánuco is a major potato producing area. During 2001–2004, monitoring and surveys during several growing seasons by the author, agricultural knowledge experts from AFDR (Asociación para el Fortalecimiento y Desarrollo Rural, a non-governmental organization in Huánuco), along with other collaborators revealed that growers use from eight to 30 fungicide applications to control late blight (AFDR, 2002). Many of these applications are homemade cocktails that are often ineffective due to problems of dosage, quality, spraying procedure and timeliness. Throughout the growing season, growers commonly use mixes of systemic fungicides from different manufacturers — but with the same active ingredient. An apparent loss of effectiveness of systemic fungicides observed in farmers fields’ during 2001–-2004 was first shown experimentally in 2001 (Villodas and Fernández-Northcote, 2001). Another problem is the wide use of tin-based fungicides throughout the growing period, which control blight effectively, but cause yield losses due to phytotoxicity. In addition, tin poses a threat of contaminating the aquatic environment.

In 2001 a collaborative effort began to adjust and validate in Huánuco the chemical control strategies developed by PROINPA (Foundation for the Promotion and Research of Andean Products) in Bolivia (Fernandez-Northcote and Navia, 2003). The participants included growers, agricultural experts and students from the local university UNHEVAL (Universidad Nacional Hermilio Valdizan), the university UNALM (Universidad Nacional Agraria La Molina), Papa Andina (a regional collaborative project between the International Potato Center and the Swiss Agency for Development and Cooperation ) and AFDR. Funding was provided by the Peruvian Ministry of Agriculture through INCAGRO, Papa Andina and agrochemical suppliers, who also provided logistical support.

One important control strategy for susceptible cultivars is prevention. The first application is at 80% emergence if emergence is uniform or at 50% and 100% emergence when not uniform. For resistant cultivars, the first application is made when the first symptoms are observed.

Another strategy is the alternation of a systemic fungicide with a contact fungicide until 50% flowering and then continuation with only a contact fungicide. The number of systemic fungicides used is another component of the strategy — each systemic should only be used three times during the growing season and care must be taken not to use another systemic with the same active ingredient. Usually in areas or growing seasons of high incidence of late blight, two systemics, each in alternation with a contact fungicide, are needed to protect the crop. In this case, systemics are used until the flowers start to fall or the foliage starts to change color. To reduce costs, one of these is a translaminar fungicide.

Generally, for susceptible cultivars the spraying interval is 5 to 7 days after a contact or translaminar fungicide, and 7 to 14 days after a systemic, the intervals depending upon whether or not the conditions are favorable for late blight development. For resistant cultivars, spraying takes place when the disease is seen to be progressing.

Using these strategies, it was possible to reduce the number of applications by 30–50% for susceptible cultivars and by 44–70% for resistant cultivars in comparison to local practice. Fewer applications of fungicides reduce the chances of contamination of the grower and of the environment. Yield increases were at least 50% higher in comparison to the growers who used their own “cocktails” and more numerous applications.

--------------------------------------------------------------------------------

Enrique Fernandez-Northcote, Coordinator of this collaborative effort

Universidad Nacional Agraia La Molina, Lima, Peru

Literature cited

AFDR. 2002. [Baseline study. INCAGRO Project on Competitive Potato Production in Huánuco. Responding to New Marketing Opportunities] Estudio de línea de base. Proyecto INCAGRO sobre Producción Competitiva de la Papa en Huánuco. Respondiendo a Nuevas Oportunidades de Mercado. Huánuco, Perú.

Egúsquiza R and Apaza W. 2003. Rancha of potato (Phytophthora infestans) in Peru. Country Profile. pp 27–37 In: Proceedings of the International Workshop Complementing Resistance to Late Blight (Phytophthora infestans) in the Andes, 13–16 February 2001, GILB Latin American Workshop 1, Fernandez-Northcote E, ed. International Potato Center, Lima, Peru. Online at http://gilb.cip.cgiar.org. First published in Spanish in 2002.

Fernandez-Northcote E N and Navia O. W. 2003. Decisions for the application of fungicides to control potato late blight. PROINPA's strategies. pp 133–137 In: Proceedings of the International Workshop Complementing Resistance to Late Blight (Phytophthora infestans) in the Andes, 13–16 February 2001, GILB Latin American Workshop 1, Fernandez-Northcote E, ed. International Potato Center, Lima, Peru. Online at http://gilb.cip.cgiar.org. First published in Spanish in 2002.

Villodas, L and Fernández-Northcote E N. 2001. [Schedules and chemical control strategies for controlling late blight in susceptible cultivars. Effect on the pathogen population] Programas y estrategias de control químico de la rancha para cultivares susceptibles. Efecto en la población del patógeno. pp 17–25 en: Validación y ajuste de las estrategias de PROINPA para el control químico de la rancha (Phytophthora infestans) de la papa en cultivares susceptibles y resistentes en zonas tizoneras (ranchosas) del departamento de Huánuco. Informe Campaña 2002-2001, Proyecto Papa Andina.