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Dealing with Powdery Mildew on Cucumbers & Squashes

August 08, 2011
Cucumbers Forming

Cucumbers Coming on Strong in Overcrowded Greenhouse Space

Seeing white powdery mildew on cucumbers, squash, melon or other curcurbit plants?

It’s cucumbers galore for us right now. The plants are over-crowded and the vines are intermingling all over the greenhouse, which is dripping with cucumber-y goodness. Unfortunately, the powdery mildew has arrived as well.

I’m not surprised about the mildew. I’ve never made it through a growing season when cucumbers and squash didn’t get hit with this disease of decimation. And, given how crowded these plants are, it was just a matter of time. Even with close monitoring, good air-flow and disease-resistant varieties, I expected a hardy mildew crop at some point.

Today’s that day.

Fortunately, I check the greenhouse crops several times a day. I check for and complete needed watering in the morning. This gets the plants through any overly hot stresses on a summer day. It also gives the plants time to dry out; water resting on leaves is a great way to encourage disease. When I see mildew, I cut out the leaves and dispose of them. This thins the foliage and encourages better airflow & light to the inner portions of the plant while also reducing the speed disease spreads throughout the plants. It also removes disease from the plants themselves and usually keeps it at bay.

Powdery Mildew on Cucumber Leaf

Seeing Spots? Cut out Infected Leaves Like this at the First Sign of Mildew

In past years, I have tried home-grown mixtures of baking soda sprays to keep the mildew away. But, I find it tedious to spray all over the leaves multiple times a day, and frankly, it didn’t work very well. Instead, I cut the plants to take out the infections. And, these plants are resilient. They just add on more foliage to feed themselves. It is just critical that the leaves be checked and cleaned of infected foliage at least once or twice a day — every day.

But guess what? When you cut back foliage, you’ll probably also be harvesting. This morning, when I was trimming out the powdery nasties, I revealed a large, ripe cucumber that I hadn’t even seen forming. And, this tasty morsel had to have been maturing over the last week or so. A big leaf hid it from view!

So, with that, I cut out about 10 diseased leaves from a total of about 9 plants. And, I harvested three big cukes to add to our drawerful in the fridge. And, there are many more coming on fast.

Harvesting the cukes before they get really big is also important. Left on the vine too long, cucumbers can become tough and bitter. And, if a cucumber fruit gets to a point where the seeds begin to mature inside the fruit, the plant will really divert a lot of energy to those fruits. The reason the plant forms the fruit, filled with seed, is to spread its genetics by way of new babies from those seeds. So, at a certain point, the plant will begin to give up its own short life to get those seeds good and ripe and read to form new babies. But, if you cut out a maturing fruit, the plant will start over, refocusing its efforts on newer, younger fruit.

So, harvest early and harvest often. And, if you harvest more than you can eat, share it with a friend or donate it to a local food distribution center. Guaranteed somebody out there will really appreciate getting some of your homegrown goodness!


  1. […] this link: Crops & Disease: Harvest Early & Harvest Often « GardenHelp.org AKPC_IDS += "15199,";Popularity: unranked […]

  2. Jami says:

    Thanks for this post. It’s validating to know that a professional gardener still has to contend with powdery mildew on her plants. It always seems like despite my best efforts, my squash and melons always succumb to it.

  3. It’s one of those things just about everyone battles. Reseeding for succession cropping can sometimes keep the harvest coming even if the earliest plants poop out early.

  4. […] Learn how to identify early infestations of this common squash problem and learn how we manage powdery mildew on all sorts of plants in this related post. […]

  5. Nick Sanderson says:

    Hi ,my name is nick I have a problem with my cucumbers, I only seem to get male flowers occasionly a female flower .
    What am I doing wrong? I live in Western Australia with very hot summers.

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