Thanks for contacting "Ask Extension" with your question about your cucumber plant. There are several fungi and bacteria that could cause the damage shown in the picture. Possibilities include angular leaf spot, alternaria leaf spot and anthracnose.

Below are recommended management options.

• Rotate crops. Do not plant cucumber or related crops in the same location for at least two years. 
• Plant resistant varieties. (Link to disease resistant cucurbit varieties)
• Avoid overhead watering.
• Avoid crowding plants too closely.
• Clean up and dispose of symptomatic leaves and stems.
• Wash with soap and water after handling plants. Do not handle healthy plants after working with infected plants. Do not handle wet plants.

Copper fungicide spray or dust has been shown to reduce the spread if caught early. I don't think it will be effective at this point. 

For a fee,  you can submit a sample to the OSU Plant-clinic for fungal or bacterial ID. https://bpp.oregonstate.edu/plant-clinic 
   Hope this helps!

Hi Deb,

According to WSU, Alternaria Leaf Spot doesn't usually spread to fruit in the PNW. It sounds like that may be what you have. In that case it's ok to leave the leaves on the plant until harvest.

Thanks for the info- I’ll look into Alternaria Lead Spot.