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Cucurbit downy mildew update

Posted: July 28, 2011

Additional reports on cucumber and now confirmed on muskmelon in New Jersey!
Cucurbit downy mildew risk map for Monday 25 July 2011. Areas of the map shaded by red, orange and yellow are at high, moderate and low risk of downy mildew development and spread.

Cucurbit downy mildew risk map for Monday 25 July 2011. Areas of the map shaded by red, orange and yellow are at high, moderate and low risk of downy mildew development and spread.

During the past week there have been several reports of downy mildew on muskmelon in New Jersey, North Carolina and Wisconsin. It is not uncommon for outbreaks in NC and NJ to be a source of inoculum (pathogen) for cucurbit fields in PA. Although there have no additional reports in PA this past week, the unsettled weather over the past few days has created conditions that have been favorable for the movement of downy mildew from both the southeast and around the Great Lakes region. Symptoms resulting from these infections could be seen in as few as 3 to 12 days depending on temperature, relative humidity and number of spores (inoculum concentration).

Keep in mind that risk is determined in part by the forecasted weather and that local microclimates can play a considerable role in disease development. The environmental factors that favor downy mildew infection are temperatures of 41 to 82°F along with 2 to 6 hrs of dew. The more downy mildew spores around, the shorter the dew period required. Spores are typically produced at night and released into air between 8am and 1pm.

At this time it is recommended that all cucumber and muskmelon crops be protected with at a protectant fungicide and incorporation of downy mildew specific fungicides should be strongly considered. Link on the following link to view the 2011 downy mildew fungicide recommendations (http://extension.psu.edu/vegetable-fruit/production-guides/2011-fungicide-resistance-management-guidelines-for-cucurbit-downy-mildew-and-powdery-mildew-in-the-northeast/view).

Please visit the Cucurbit Downy Mildew Forecasting website (http://cdm.ipmpipe.org/index.php) for the latest list of disease outbreak locations and forecasts. This information is updated by the end of the day on Monday, Wednesday and Fridays. Also contact me or your local Penn State Cooperative Extension office if you suspect downy mildew.