Pests / Plant Thoughts

Downy Mildew – Pseudoperonospora cubensis!

cucumber-downy-mildew-4L_Lindsey du Toit - Washington State University

Photo Source: Lindsey du Toit, Washington State University

Pseudoperonospora cubensis,  is that a word for everyday conversation? Yes! Especially if you are growing summer squash, cucumbers, pumpkins and the like. Maybe I need a dictionary! Anyway, as fall nears, then it’s good-bye to the all-important summer sun and heat. Then to make the situation worse vine plants are crowded, need air circulation, improperly watered, rain fall, high humidity, whatever, the leaves do not dry. Water on the leaf is the problem. Soon little brown spots begin to appear on the underside of the leaf.  Then yellow – brown spots begin to appear on top of the leaf. Good-bye leaf!

cubensis is the species or water mold that is a cause of downy mildew. The mildew does not attack the fruit. When the leaf dies because of growing colonies of downy mildew, the plant produces less fruit, often-misshaped fruit and fruit with sun scald. Downy mildew is the cause of the plant’s early demise and a major problem in the northwest. Not much a Gardener can do if downy mildew is on a plant.

The pathogen lives only on the plant leaf’s green tissue. Downy mildew cannot over winter in cold weather – Hurray! Bad news – winters are warmer. Also, there is more than one variety of downy mildew that lives happily on weeds and any size pile of plant debris all winter. So, clean your yard!

Next year before planting or holding up a help sign, you might look for cultivars that are tolerant to mildew or have some genetic resistance to mildew. Give plants a lot of space and water correctly. For this year’s home garden vines, remove infected plants immediately. As for sprays, I did use them one year. For me it was a waste of money and time, but that is something you might want to learn about. Call your local Ag center for information.

By:  Garden Chatter with Nancy Lee Benthin

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