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Increasing reports of cucurbit downy mildew in the Southeastern U.S.


Pennsylvania, USA
June 26, 2014


Angular chlorotic lesions characteristic of downy mildew on cucumber. Lesions will eventually become necrotic and the centers will fall out.

In Pennsylvania, the first reports of downy mildew on cucumber typically occur in late June into early July. Now is the time to be scouting. Downy mildew is most easily managed before symptoms are observed in the crop.

Currently there are no confirmed reports of cucurbit downy mildew in Pennsylvania or in the mid-Atlantic and northeastern region. However, downy mildew is starting to advance up the east coast with several reports this past week on cucumber, acorn and summer squash in South Carolina and on cucumber in North Carolina.

The forecasts from the CDM ipmPIPE indicate that pathogen spread over the next few days is most likely right along the eastern seaboard with parts of New Jersey and Long Island being a low risk. Low risk indicates that the majority of factors (potential for long-range transport of the pathogen, forecasted weather conditions, potential for spores to rain out onto the field) are unfavorable. Similarly, when there is forecasted high risk, this indicated that nearly all the factors are favorable for the pathogen to infect and cause disease. Below is the breakdown of the risk assessments and the weather forecast that is typically associated with that assessment. Keep in mind that sky conditions will often supersede the chance of rain in a forecast.

  • Low: Sunny to partly cloudy and dry through the forecast
  • Weakly moderate: Partly cloudy with a slight (20%) chance of rain
  • Moderate: Partly sunny/partly cloudy with a chance of scattered showers
  • Strongly moderate: Partly cloudy with afternoon/evening showers likely or mostly cloudy with a 30 to 40% chance of rain
  • High: Cloudy with rain likely

The forecasted risk maps are also based on knowing where there are downy mildew infected fields (sources of the pathogen) so it is important if you suspect downy mildew on your farm to let me know or contact your local Penn State Cooperative Extension Office. For the latest information on outbreaks and to receive email or text alerts please visit the Cucurbit Downy Mildew Forecasting website. Updates will also be made to the 1-800-PENN-IPM hotline weekly or more frequently if needed to provide growers with information that can be used to help make timely management decisions.

Remember that the pathogen that causes cucurbit downy mildew does not survive overwinter unless on living plant tissue so for Pennsylvania growers, the pathogen is typically moving in via long-distance transport from other infected fields sometimes over 100 miles away. Awareness of where potential sources of the pathogen and forecasted weather conditions can help guide in-season management decisions.



More news from: Penn State University


Website: http://www.psu.edu

Published: June 26, 2014

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