whitish slightly blue "dust" on swiss chard

Asked July 28, 2016, 4:29 AM EDT

I'm enjoying the giant swiss chard I planted on my roof top. Some of the leaves have a slight whitish-blue discoloration which can be scrubbed off. It's hot and dry here in Israel and the plants are watered with drip irrigation. The chard isn't so far from the cress, the cherry tomatoes and the kale. Any idea what this coating can be?

Outside United States horticulture vegetable gardening

5 Responses

Could you please include a picture with your question, especially since I am in the US, not in Israel.

You'll see that it is really whitish, not whitish/light blue. It is on some of the leaves not all. I was able to scrub it off but it really mingled the leaf. I'm very interested in your opinion. Is it from the leaf or could it be being blown on but something external? Thanks for taking the time to help.

Yep, that looks like powdery mildew to me. It is a fungal disease. I have no idea what you could get in Israel to treat fungal diseases on vegetable plants, but that is what you would need.

In addition, you may want to get rid of the diseased leaves. When you are watering your plants, make sure to just water the soil and keep the leaves dry. In other words. don't put a hose on the entire plant. Hope this helps.

Thank you!
Is it dangerous to scrub clean a leaf with a mild fungal infection and eat it?

New question,
Last year my kale grown in pots on a roof got aphrids. Should I have any concern that the soil could have eggs. Perhaps I just gave away that I know nothing about these pests, how that got to my roof in the first place or how they regenerate. I'd really appreciate any information to know more than "nothing".

Hello Michael,

I am not a microbiologist or a nutritional expert, so I have no idea whether it would be dangerous. At the very least, It may not be very tasty!

The soil in your pots could have eggs. More likely, the aphids found a crevice somewhere to overwinter. Most of the time aphids are wingless. But at some point in their life cycle, they can develop wings and that is how they disperse: they simply came drifting on the wind. Aphids like succulent growth. So, if your potting soil already contains fertilizer, do not add any more. You can get rid of the aphids by simply blasting the plant with a stream of water (only if the plant is sturdy enough). Insecticidal soap or horticultural oil will take care of them as well.