Cucurbit Downy Mildew ipmPIPE: A Next Generation Web-based Interactive Tool for Disease Management and Extension Outreach

Abstract

Cucurbit downy mildew (CDM), caused by Pseudoperonospora cubensis, is one of the most important diseases affecting cucurbits worldwide. In the USA, host resistance in cucumber had adequately controlled the disease with very minimal application of fungicides from the late 1960s to 2004. In 2004, there was a resurgence of the disease that devastated the cucumber crop in several states in the eastern USA. Since then, host plant resistance alone has not been sufficient to adequately control the disease and now control relies heavily on application of fungicides. To effectively apply fungicides in a timely manner, cucurbit growers, extension personnel, and crop consultants and advisors can now utilize information on disease occurrence and predicted spread disseminated through the United States Department of Agriculture's CDM ipmPIPE decision support system developed by scientists at North Carolina State University. Based on a survey conducted in Georgia, North Carolina, and Michigan, the CDM ipmPIPE resulted in an average reduction of 2 to 3 fungicide applications in 2009 compared to calendar-based fungicide sprays. With approximately 122,000 acres of cucurbits in these three states, this translates to more than $6 million in savings to the producers in these three states. Economic savings and positive environmental implications of reduced fungicide applications demonstrate the value of a coordinated national monitoring network for management of a plant disease that is disseminated aerially over long distances. Accepted for publication 31 January 2011. Published 11 April 2011.

Epidemiology and Population Biology of Pseudoperonospora cubensis: A Model System for Management of Downy Mildews

“…In North America, P. cubensis is not known to overwinter in the field in areas approximately north of the 30 • latitude, where hard frost occurs annually, killing the cucurbit host plants. Thus, CDM outbreaks in northern latitudes rely on the annual dispersion of P. cubensis sporangia from overwintering sources in the south (72,74) or from protected cultivation due to the presumed absence of overwintering oosporic inoculum. The absence of local initial inoculum, herein defined as inoculum that originates at the mesoscale (farm or county level), accentuates the role of long-distance dispersal in the seasonal dynamics of CDM.…”

“…Although CDM occurs annually in the eastern United States (74), the timing of its spread from overwintering sources in the south to fields in northern latitudes is the most uncertain feature within the prediction framework (73,74). This uncertainty is expected because regional spread of disease tends to be curtailed by limited opportunities for pathogen establishment (i.e., susceptible host tissue) rather than by atmospheric transport of inoculum (7).…”

“…Oospores have been considered to be of limited importance, and most attention in disease prediction and management is given to long-distance dispersal of inoculum from overwintering sources. Indeed, the basic premise of the CDM forecast system rests on this assumption (74). The role of oospores in CDM epidemiology needs to be determined because of their potential to significantly complicate disease management efforts.…”

“…The CDM ipmPIPE has been instrumental in predicting disease onset (74). The structure and information content of disease hazard warnings issued by the CDM ipmPIPE are characteristic of predictive systems that typically have sustained use in disease management (32).…”

“…Growers must continuously weigh the threat of sporangia influx into their region, assess weather conditions suitable for disease development, and estimate the cost of fungicide sprays. To support their decision-making process, the CDM ipmPIPE system allows growers to track in near real time where CDM has developed and, indirectly, the movement of P. cubensis in the eastern United States (74). Linking disease hazard warnings from the CDM ipmPIPE system with current and forecasted disease risks and sporangia measurements within individual fields would be desirable.…”