Yucky, yucky, yucky. Powdery mildew.
What is it you ask? Its a fungal disease, that no plant is immune to. So bearing that in mind, its useful to know how to treat it! As even the best gardener may have a powdery mildew attack.
How do you know if you have powdery mildew? Well your plants will basically look like the above photos. The surface of the leaves, or underneath, or steams even, will be covered in a silvery, grey powder. It is quite matte, and makes it look like your plants have died when you look from afar which often causes gardeners to have panic attacks until they get closer and notice that it is powdery mildew.
Its important to stop powdery mildew from spreading as quickly as possible, as it can potentially stop a plant from fruiting.
As you can see in the above photos, the powdery mildew spread between my courgette plant to my squash plant while I was away for the weekend. Powdery mildew is very common when there is hot humid weather, but watering the leaves of plants actually helps to spread this disease. So in humid weather especially, make sure you are just watering the base of the plants. Dry plants, crowded planting, or poor air circulation also helps to spread this nasty, so ensure that your plants have enough room when you are planting them and that you are watering them well in the hot summer months, as this acts as a preventative measure!
So now you know the important things about powdery mildew, what exactly are you supposed to do??
If just a few of the leaves are affected, pull those out quickly and dispose of them. This helps to remove the fungus, but can also improve air circulation as the plant is getting slightly pruned. If the powdery mildew has spread to most of the plant (as what happened to my babies), using a baking soda spray (an inexpensive, and not dangerous fungicide) is something that really helps. It can also be made organically!
The basic "recipe" for this is
1 Tbsp baking soda
1/2 tsp liquid soap (not detergent)
3.8 litres of water (1 gallon)
Spray this onto leaves of the affected plant when the plant is in shade (in the evening is ideal). Also ensure that the plant has been watered the day before as well, so that the plant isn't too thirsty. This can be repeated every one or two weeks, depending on how your plant is going. Make sure that you don't store the unused mixture though as it is more effective when used straight away!
And hey presto! Your powdery mildew should start to disappear and your beautiful plants will become happy once more!