Powdery Mildew

[chuckp]

Is this Powdery Mildew?
I am noticing more on my roses in the greenhouse this year on roses that never showed signs of susceptibility before. What is the recommended treatment?
chuckp

[roseseek]

Looks like it to me. Can you increase the air circulation to move out the dampness? And, you might try increasing the water. Even highly resistant plants in conditions which do not favor mildew can be forced to mildew when water stressed. The same holds true for rusting. Water stress inhibits the plant's immune system. If neither of those help, you get to decide whether you want to actually spray with anything or let Darwin decide. Potassium bicarbonate (acid reduction powder used in wine making) is a suitable mildew treatment. https://www.growingagreenerworld.com/co ... ry-mildew/ I found mine on line for about $8 a pound.

[chuckp]

Kim,
Thanks for your input.
The air circulation is very good. The problem is low overnight temperature, even holding the overnight temperatures
at 25 deg. Celsius doesn't seem to help. I'll normally used powdered Sulphur to treat PM, but I was told that it shortened the live or the greenhouse plastic skin.
I'll look into Potassium bicarbonate.
chuckp

[roseseek]

That's a pretty high temp for mildew, Charles. My daily highs often don't hit that high and mildew is not an issue here, even with the nightly dew and fog baths. Have you checked the irrigation to insure they aren't water stressed? I know my air circulation is good with these $#$(#U#)&!!! winds and they are COLD, right off the Pacific. In the mean time, there are the other "organic" methods mentioned in that article I linked (baking soda, milk, etc.). The milk idea likely has some merit as long as you're using whole milk and not non fat as it would seem to me the milk fat would be the active ingredient. Good luck!