Cucurbit Disease Update – July 7th, 2015

By Elaine Roddy, Vegetable Crops Specialist, OMAFRA

Do you ever just get completely overwhelmed by choices? I do.  Especially when it comes to cucurbit fungicides.  In a few short years, we have gone from having a very limited fungicide tool kit, to having over 20 distinctly different fungicides to choose from. In many ways, it is a nice problem to have; but it doesn’t make building a fungicide program any easier.

Fungicide product selection is extremely important, and the best choices will vary depending on the type of cucurbit crop grown. Each of the cucurbit crops is impacted by the various cucurbit diseases to a different degree.

Each product has its own strengths and weaknesses; product rotation helps to spread out the risks while building on the strengths. Publication 838, Ontario Vegetable Crop Protection Guide, outlines each of the registered fungicides and which diseases they control. Click here to see Table 3-48, Activity of Fungicides on Cucurbit Diseases. Specific fungicide program suggestions are outlined for each type of cucurbit crop, below.

All fungicides are most effective when applied preventatively, or at a very early stage of infection. Whenever possible, apply fungicides before a predicted rainfall.

Cucumbers

Most common foliar disease: downy mildew.

Product Selection: disease pressure is very high this year, and resistance is a big concern. Growers are encouraged to rotate using at least three of the four available downy mildew targeted fungicides. Maintain a 5-7 day spray interval, especially if downy mildew is present in the crop. If wet fields are preventing growers from spraying with a ground sprayer, aerial applications are permitted on the Torrent 400SC and Zampro labels.

For more detailed information on downy mildew management in cucumbers, see:

• Downy Mildew Control in a Challenging Season – ONvegetables, June 30, 2015
• 2015 Downy Mildew Control Strategy for Cucumber Crops

Melons

Most common foliar diseases: alternaria, anthracnose, scab and downy mildew (more common in cantaloupe).

Product selection: use broad spectrum products, such as Bravo 500, Echo 90DF, Quadris Top, Pristine WG and Cabrio EG as the basic program. Due to the heavy downy mildew pressure in 2015, consider tank-mixing a downy mildew targeted product (see the cucumber section, below) with a broadspectrum fungicide like Bravo 500 to improve downy mildew control.  Note: Tattoo C does contain chlorothalonil, however it is not present at the full rate required to control other foliar diseases.

The mancozeb products (Dithane Rainshield, Manzate Pro-stick and Penncozeb 80WP) are also an option; however, take note of the 14 day pre-harvest interval.

Pumpkins and squash

Most common foliar disease: powdery mildew.

Sporadic foliar diseases: scab, septoria, alternaria, anthracnose and gummy stem blight.

Product Selection: powdery mildew targeted fungicides include: Inspire, Nova, Fontelis and Quintec. Powdery mildew has already been identified in Ontario in 2015. This is an unusually early arrival; which is not surprising, given the weather we had in June. Leaves are most susceptible to infection while they are still growing. Good control requires keeping the new growth (upper and lower leaf surfaces) protected.

For control of additional foliar and fruit diseases, consider rotating with broad spectrum products, including: Quadris Top, Pristine WG, Cabrio, Bravo 500 and Echo 90DF. All of these products control powdery mildew and a variety of other diseases.  The fruit are most susceptible to disease infections like black rot, scab and septoria while they are enlarging. Good control requires contact with the fruit surface.

The mancozeb products (Dithane Rainshield, Manzate Pro-stick and Penncozeb 80WP) are also a good broad spectrum option; however, take note of the 14 day pre-harvest interval.

Visit Ontario CropIPM – Cucurbit Diseases and Disorders, for a gallery of cucurbit disease photos and information sheets.