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How to identify, prevent, and fight off mildew

White spots on the leaves of your vegetables? It's probably mildew.

Is that bad, how do you identify it, and what's the solution?
Meeldauw op blad van pompoen
Mildew on my pumpkin leaves

What is mildew?

Mildew is a common fungal disease. It's easy to spot: you'll see white, powdery spots on the top of your vegetable leaves.

A little mildew is no problem, your plants can handle it.  

But if mildew covers over the whole leaf, then the leaf dies. If it spreads to the whole plant, well, that's not great. 

Mildew prefers summer vegetables: zucchini, cucumber, pumpkin, and sometimes tomato plants. But it can also strike other vegetables and flowers, like peas, chard and marigolds.
Meeldauw op sugarsnaps en erwten
Mildew on my sugar snaps

How do you identify mildew?

The first signs of powdery mildew are mostly spotted on warm, dry days.

You can recognize it by the white spots. If you look closely, you'll see that a sticky, flour-like substance on the top of leaves and stems.

After a while, the mildewed spots will darken and the leaves will curl.
17-sept-courgette-meeldauw.jpg
The first signs of mildew on the zucchini leaves

Powdery mildew vs. downy mildew

There's a similar plant disease called downy mildew. It looks a lot like powdery mildew. 

But there are a few differences: downy mildew creates a fungal fluff on the underside of the leaves. The tops of the leaves become covered with yellow spots that can turn brown.

Which vegetables are most affected?

So, like I mentioned, mostly the big summer vegetables.

But it also can be found on peas, chard, marigolds and some herbs. 
Meeldauw of witziekte op snijbiet
Affected chard

When does it occur?

Mildew mainly appears in dry and warm weather.

But for zucchinis and cucumbers, it's normal to see mildew at the end of the summer the when the weather gets wet and cold.

Summer plants just can't cope un-summery weather: they become weaker and more vulnerable to mildew.
17-sept-courgette-meeldauw-2.jpg
Zucchini at the end of the season

Can you prevent mildew?

You can take some preventative steps to limit mildew:
  • Put your plants in the right place, so they get enough sunlight.
  • Provide sufficient nutrients. When planting summer vegetables, give them some extra MM-Plantfood and every 5 weeks thereafter.
  • Water your plants sufficiently during dry weather, so that they don't droop and get weak.
  • Don't plant your plants too close together. Stick to our planting rules and cut away any leaves that get in the way.
  • Use varieties that are less susceptible to mildew as much as possible.

What do you do if you have mildew?

Again, a little mildew isn't bad, but you need to stop it from getting worse. As soon as you notice the first signs, take action:
  1. Cut off badly affected leaves.
  2. Spray the rest of the plant with a mixture of 40% milk and 60% water. Do this on a sunny day.
(The combination of the proteins in the milk and the sunlight is lethal for the fungus: skim milk or whole milk doesn't matter.)
17-sept-courgette-meeldauw-1.jpg
The bottom leaves the this zucchini have got to go
Usually, just these two steps are enough to prevent the whole plant from being covered in mildew. But sometimes there is no stopping it. Especially in the fall.

In that case, prune all the affected parts of the plant as much as possible - especially the leaves - and remove them from your garden. 

You got this 🙂

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