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Funded Project

Funding Program: Regional IPM Grants (S-RIPM)

Project Title: Enhancing The Cucurbit Downy Mildew Forecasting System

Project Director (PD): Peter Ojiambo [1]

Lead State: NC Lead Organization: North Carolina State University

Cooperating State(s): New York

Undesignated Funding: $198,714

Start Date: May-01-2010 End Date: Apr-30-2012

Summary: This Joint Research ($108,714)-Extension ($90,000) project will focus on cucurbit downy mildew caused by Pseudoperonospora cubensis. The U.S. grows about 466,250 acres of cucurbits valued at $1.7 billion. In 2004, severe outbreak of the disease occurred in the eastern U.S., devastating cucurbit crops. Many fields were abandoned without harvesting and suffered 100% loss. Fungicide programs initially failed either because applications were made after disease was established, and/or ineffective products were used. Resistance of Pseudoperonospora cubensis to specific fungicides was suspected as a contributor to the ineffectiveness of fungicide programs. A forecasting system was developed to help growers to make decisions on if and when to spray based on disease outbreaks in sentinel plots located in 25 states and Ontario, Canada. The ultimate goal is to automate the current forecasting system and minimize the input of human element. However, a series of research projects to develop pathogen biology models is needed before the forecasting system can be fully automated. We propose to conduct the research necessary to enable growers to improve cucurbit downy mildew control, reduce occurrence of ineffective fungicide applications, and implement improved resistance management programs. This Joint Research- Extension project will focus on enhancement of the disease forecasting system, documentation of the presence/absence of differential fungicide resistance in the eastern U.S. and establish the population structure of P. cubensis within the sentinel network. We will continue to work with stakeholders to enable growers to reduce costly and unnecessary fungicide sprays, reduce risk of resistance development to fungicides and improve chemical control of cucurbit downy mildew. Objectives: 1. Enhance the cucurbit downy mildew forecasting system 2. Characterize the genetic variation in the Pseudoperonospora cubensis population in the eastern U.S. utilizing the cucurbit downy mildew sentinel network 3. Determine the differential fungicide sensitivity of P. cubensis isolates derived from Cucumis sativus, Cucumis melo and Cucurbita species.

Final Report:

Results From report submitted by the PI to USDA CRIS report system PROGRESS: 2010/07 TO 2011/06 OUTPUTS: Field experiments were conducted at two sites in North Carolina namely; Clayton (Johnston County) and Clinton (Sampson County) to determine the relationship between the severity of cucurbit downy mildew and the amount of P. cubensis sporangia produced and proportion of sporangia that escaped the canopy. The experiments were performed using the cucumber cultivar Poinsette 76 and plants relied on natural infection. Disease severity was monitored during the summer and assessed visually based leaf area infected. At disease levels of 1, 5, 15, 20, 30 and 40%, total standing sporangia was estimated based on lesions with a 0.25 by 0.25 m grid and sporulation per unit area. Aerial concentration of sporangia was quantified using Rotorod spore samplers mounted at 0.5, 1.0 and 1.5 m above the canopy. Concentrations were monitored from 7 to 3 pm on each level of disease severity. Counts of sporangia on the Rotorods were then converted to spore concentrations by accounting for the proportion of the sample surface that was counted, the sampling rate, and the duration of the sampling period. The relationship between standing crop of sporangia in the source and airborne sporangia concentration at different heights above the canopy and disease severity was analyzed using PROC REG in SAS. PARTICIPANTS: 1. Katie Neufeld, Graduate Student working on the epidemiology and management of cucurbit downy mildew. 2. Mike Adams, lab manager who worked and coordinated activities of the graduate student in the lab including field layout and data collection. 3. Rob Kautz, undergraduate summer student that assisted with field experiments, 4. Wendy Britton, project coordinator, and 5. Thomas Keever, forecaster who both worked to compile data to compare the effectiveness of the HYSPLIT versus the FLEXPART models in predicting trajectories of sporangia transport. TARGET AUDIENCES: 1. Cucurbit growers, 2. Extension country agents, 3. Industry specialists PROJECT MODIFICATIONS: Nothing significant to report during this reporting period. IMPACT: 2010/07 TO 2011/06 Results of sporangia concentrations indicate that across all levels of disease severity, peak sporangia production occurred between 8 to 10 am and then decreased thereafter. The concentration of sporangia also decreased linearly with increasing height above the canopy with the concentration being highest at 0.5 m above the canopy and lowest at 1.5 m above the canopy. Sporangia concentration at 1.0 m above the canopy was intermediate. These results were similar for both experiments conducted at Clayton and Clinton. Graphical results of the relationship between disease severity and sporangia concentration indicate that the relationship is best described by a gamma function with concentration increasing with increasing severity up to 20% and then tailing off as disease severity increases.

Outcomes N/A

Impacts From report submitted by the PI to USDA CRIS report system Results of sporangia concentrations indicate that across all levels of disease severity, peak sporangia production occurred between 8 to 10 am and then decreased thereafter. The concentration of sporangia also decreased linearly with increasing height above the canopy with the concentration being highest at 0.5 m above the canopy and lowest at 1.5 m above the canopy. Sporangia concentration at 1.0 m above the canopy was intermediate. These results were similar for both experiments conducted at Clayton and Clinton. Graphical results of the relationship between disease severity and sporangia concentration indicate that the relationship is best described by a gamma function with concentration increasing with increasing severity up to 20% and then tailing off as disease severity increases.

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