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Monitoring and Reporting of Cucurbit Downy Mildew in Mississippi

Monitoring and Reporting of Cucurbit Downy Mildew in Mississippi


Photo: Chlorotic lesions on the upper surface of leaves, as seen giving the leaves of the squash plants in this photo a yellow appearance, are symptoms of downy mildew in cucurbits. Credit: R. A. Melanson, MSU Extension,


Project Summary: Downy mildew is an important disease that can cause significant losses in cucurbit crops, such as cantaloupe, cucumber, pumpkin, squash, and watermelon. In order for downy mildew to develop, the pathogen must be present along with a susceptible host and favorable environmental conditions. Downy mildew development is favored by high humidity and moderate temperatures. The downy mildew pathogen, Pseudoperonospora cubensis, requires a living host to survive and does not survive in areas where freezing temperatures prevent the survival of cucurbit hosts through the winter. Each year, the pathogen spreads on air currents from areas where it is able to survive through the winter. In an effort to help growers manage downy mildew in cucurbits, a disease forecasting system for downy mildew was developed (CDM ipmPIPE: This forecasting system is a decision support tool that provides disease forecasts and risk prediction maps to help growers determine the best time for application of fungicides to protect against downy mildew. The disease forecasting system is based on weather forecasts and reports of downy mildew outbreaks. These reports are submitted by university personnel and plant pathologists who confirm the disease on cucurbit samples obtained from farms, gardens, and other plantings. The accuracy of the forecasting system depends on the timely reports of downy mildew outbreaks. In an effort to detect when these outbreaks first occur and when the pathogen reaches an area, sentinel plots are planted and used to monitor for the occurrence of cucurbit downy mildew. These sentinel plots include varieties of various cucurbit hosts that are susceptible to downy mildew and are monitored weekly for downy mildew development. They are maintained to keep plants as healthy as possible, but fungicides that are effective against downy mildew are not applied. Cucurbit downy mildew sentinel plots have been planted and monitored in two locations in Mississippi each year since 2016. Since 2018, their use in monitoring for the occurrence of downy mildew in cucurbits in Mississippi has been supported by funding from the USDA. This funding has also supported the development of educational programs and resources to increase stakeholder knowledge and awareness of this disease and its management. More information about cucurbit downy mildew and the CDM ipmPIPE forecasting system is available below.

2021 Report: Downy mildew was confirmed in nine counties in Mississippi in 2021. The first confirmed report was in mid-June on cantaloupe in Kemper County. Downy mildew was confirmed on butternut squash and cucumber in the spring sentinel plot at the Truck Crops Branch Experiment Station. Downy mildew was also confirmed on butternut squash, cantaloupe, and cucumber in the fall sentinel plots at the Truck Crops Branch Experiment Station and the North Mississippi Research and Extension Center. Downy mildew was also confirmed on various cucurbit crops in research plantings, home gardens, or commercial fields between June and November in the counties of Attala (pumpkin), Covington (pumpkin), George (cucumber, squash), Perry (cucumber), Pontotoc (pumpkin, unknown cucurbit), and Winston (pumpkin). In 2022, sentinel plots for cucurbit downy mildew are planned for spring and fall at the Beaumont Horticulture Unit (Perry County) and fall at the North Mississippi Research and Extension Center.

Factsheet: Cucurbit Downy Mildew

Photo Guide: A Photo Guide to Cucurbit Downy Mildew (Note: Images alone should not be used to obtain an accurate diagnosis.)

Cucurbit Downy Mildew Forecasting & Reporting Website (CDM ipmPIPE website): Check out the latest reports and downy mildew forecasts and sign up to receive downy mildew alerts in your area here.

Article of Interest: Citizen Scientists Wanted: Cucurbit Downy Mildew 

Trainings: Trainings on cucurbit downy mildew for county agents, commercial cucurbit producers, and Master Gardeners were offered in September 2019 at the Truck Crops Branch Experiment Station in Crystal Springs, MS (Southwest District) and at the North MS Research and Extension Center in Verona, MS (Northeast District).  Online trainings (webinars) were offered for county agents, commercial cucurbit producers, and Master Gardeners in 2020.  



Mississippi Project Collaborators:

  • Dr. Rebecca A. Melanson (State Project Leader)

Central MS Research & Extension Center; Raymond, MS

(601) 857-2284

  • Dr. Shaun Broderick (Collaborator)

Truck Crops Branch Experiment Station; Crystal Springs, MS

  • Dr. T. C. Barickman (Collaborator)

North Mississippi Research & Extension Center; Verona, MS

  • Thomas Horgan

North Mississippi Research & Extension Center; Verona, MS

  • Brenton Breland

Truck Crops Branch Experiment Station; Crystal Springs, MS


Acknowledgement:  This project is supported by a United States Department of Agriculture Agricultural Marketing Service Specialty Crop Multi-State Program grant administered by the Pennsylvania Department of Agriculture, PDA No. 44187029, Subaward No. 6060-MSU-PDA-7029. Any opinions or recommendations expressed in this publication do not necessarily reflect the views of any of these organizations.


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Portrait of Dr. Rebecca A. Melanson
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