A trial participant from southern Vancouver Island contacted us about yellowing on the leaves of her potatoes:
“Some of my plants are not looking so good. I wonder if you can tell by looking at the photos what the problem might be. I wonder if I have not been watering them deeply enough and therefore there is a drought problem around the roots.”
I think I see some flea beetle damage (little shot holes in the leaves). Also very typical and much to be done, I think they do not have a huge impact on yield.
The touch of brown on the leaf spots may indicate blight, not surprising because it has been so wet lately. I have some German yellow potatoes that show this much more severely. You can cut off the blight bits, but avoid having leaves wet (hard to do with this rain). I think I will harvest my German Yellows to avoid having the blight spread. You can probably still give deep watering and bulk up the tubers, However water below the leaf crown.

Russet potato showing yellowing on leaves
Richard replies:
There is not much unusual about your potatoes. Yellowing is widespread in mine I think because of early drought and potatoes basically moving in to the late maturity stage because of some warm temperatures a few weeks ago.
Cariboo potato showing yellowing on leaves.