Vine Crop Edition - by Elaine Roddy, Vegetable Crop Specialist, OMAFRA, Ridgetown (elaine.roddy@ontario.ca)

Downy Mildew - Current Status
Unsprayed Areas
Pumpkin, Squash and Melon Disease Control Recommendations
Looking for More Information on Cucurbit Crop Disease?

Downy Mildew - Current Status

Downy mildew has now been identified in three Kent County cucumber fields.  Infection levels at all three sites are low.  An outbreak has also been identified in Sandusky County, Ohio.

The long range forecast predicts a return to more favourable growing conditions.  Given the extended period of wetness we have experienced this week, combined with a fair amount of new growth on the cucumber plants; growers may choose to shorten the spray interval to ensure thorough protection of the plant.

Use only targeted downy mildew fungicides at this time.  Ranman and Tattoo C fungicides offer the most consistent protection available in Canada.  Growers are advised to ensure they have adequate spray supplies on hand for the entire season.  Products such as Ranman and Tattoo C are also registered on other (larger acreage) vegetable crops.  If the wet weather continues, there may be considerable demand for these products.

Unsprayed Areas

Ensure that all areas of the field are sprayed.  We commonly see downy mildew enter a field in the small areas that have been left unsprayed.  Typical problem areas include: the field edges where the boom was turned off too early or started too late; and entire rows at the edge of fields where the field size does not match the spray boom width.

Pumpkin, Squash and Melon Disease Control Recommendations

Downy mildew is less common in pumpkin, squash and melon crops than it is in cucumbers.  The disease generally appears later in the season (if at all) and does not cause the same level of devastation.  Growers of these crops are more likely to encounter other foliar diseases including powdery mildew, gummy stem blight, anthracnose and alternaria.

In general, factors that promote disease development include: high humidity and extended periods of leaf wetness.  Foliar infections often appear once the crop canopy has closed and air movement is restricted.  Consider applying a broad spectrum fungicide just prior to row closure.  This is an optimum time to achieve good spray coverage and to eliminate any low levels of disease present in the crop at this time.

Fungicide controls are most effective when they are applied prior to infection, or at a very early stage of infection.  There are a number of different broad spectrum fungicides registered for use in the cucurbit crops.  Rotating between several different products will help to extend the range of diseases controlled as well as prevent the development of resistance.

Looking for more information on Cucurbit Crop Diseases?

Visit the Ontario CropIPM website.  Simply type “Ontario CropIPM” in your web browser.  

CD versions of this new OMAFRA tool are available for $10.  Call Service Ontario Publications at 1-800-668-9938 or visit https://www.publications.serviceontario.ca/ecom/