Recipient Organization
NORTH CAROLINA STATE UNIV
(N/A)
RALEIGH,NC 27695
Performing Department
Plant Pathology
Non Technical Summary
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 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.
Animal Health Component
60%
Research Effort Categories
Basic
(N/A)
Applied
60%
Developmental
40%
Goals / Objectives
Beginning January 2010, current funding for the Cucurbit forecasting system will expire for the sentinel monitoring network for reporting disease outbreaks via the website and as of October 2010, current funding will expire for the entire project. Currently, collaborators in the sentinel network depend on the cucurbit downy mildew forecasting system to serve their clientele efficiently. Given the importance of the already established network in delivering service to cucumber growers in the eastern U.S., California and Ontario, Canada, the 25 collaborating institutions on the Cucurbit ipmPIPE have agreed to continue with sentinel monitoring and reporting of disease outbreaks as part of their regular extension activities, at their own expense at an estimated cost of $100,000 per year. Likewise, our programs and those of our collaborators will continue to screen fungicides and other control practices to improve control recommendations. However, the backbone of effective development of recommendations, dissemination of information and timely disease forecasts relies on an effective website and program coordination. There is no other institution or organization that currently provides growers with downy mildew forecasts on the scale of the Cucurbit ipmPIPE project. Integrated management of cucurbit downy mildew is based on the use of sound IPM principles, including host plant resistance, disease forecasting and the preventive use of effective fungicides. Project cooperators are investigating these inter-connected disease management strategies, and have chosen to focus this proposal on filling critical and timely research needs. Specifically, we propose to conduct the research necessary to enable growers to improve cucurbit downy mildew control, reduce ineffective fungicide applications, and implement improved resistance management programs. Our objectives will be: i) refine the cucurbit downy mildew disease forecasting system, and ii) establish the population structure of P. cubensis population in the sentinel network in eastern United States.
Project Methods
The enhancement of the downy mildew forecasting system will be accomplished through two sub-objectives: i) Quantitative relationship between disease severity and source strength. Experiments will be conducted in two locations, Clayton and Clinton, North Carolina during the summer. The susceptible cucumber variety will be used at both locations in 22 rows, 100 m long plots. Sites will be selected carefully to ensure that the area surrounding plots will be fairly flat and no obstacles to wind movement are present in the surrounding area. Cucumber leaves from plants inoculated will be used to inoculate plots 4 weeks after planting. Inoculation will be accomplished by scattering the infected leaves in a 5-m diameter circular area of cucumber plants. To protect plants within the source area from infection outside the source area, Presidio will be applied to the un-inoculated area before inoculation. Disease severity will be monitored periodically and the following variables will be determined: a) standing crop of sporangia in the source, and b) airborne sporangia concentration. Each morning, before the dew dries from the plant surfaces, four sites within a 5-m diameter circle will be sampled to obtain the number of sporangia per unit of ground area within the canopy. The total number of lesions within a 0.25-m2 grid will be counted at each of the four sites in the canopy. At each of the four sites, three to five lesions will be destructively sampled to assess sporulation per unit area. Aerial concentrations of P. cubensis sporangia will be measured above the spore sources using Rotorod spore samplers with retracting-type sampling heads. The Rotorods will be operated for 15-20 min every hour for each sampling period. At the end of each sampling period, the sampling rods will be replaced and a new sampling period begun. Eight 1-h periods (8 h of sampling) will be carried out on each day. Counts of sporangia on the Rotorods will be 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. ii) Effectiveness of FLEXPART model. Currently, spore transport in the atmosphere is calculated using the HYSPLIT trajectory model from the National Oceanic and Atmospheric Association's (NOAA) Air Resources Laboratory (ARL). The data of primary interest are the forecast wind fields in the atmospheric boundary layer. HYSPLIT trajectories are provided by ARL via a restricted-access website. The trajectory is a plot of the future atmospheric pathway of a "parcel" of air likely to contain spores; in other words, the prediction of the spatial and temporal positions of a spore cloud center for the next two days following release from a source site. Here, outputs from the HYSPLIT will be compared to the FLEXPART model to determine the similarity in the predictions. The FLEXPART model is particularly attractive since it has a finer resolution and effects of environmental conditions and source strength can easily be incorporated in the model.