Angular leaf spot is a bacterial disease that can affect cucumber leaves and fruit, caused by the bacterium *Pseudomonas syringae pv. lachrymans*. It's also known as bacterial leaf spot of cucurbits. Resistant cucumber varieties are available. Limit the use of overhead irrigation. Pick fruit when the vines are dry to prevent spread in the field. Use pathogen-free seed and rotate out of cucurbits. Treat when symptoms first appear if the weather is predicted to be cool and rainy.

https://plantclinic.nmsu.edu/documents/bacterial-leaf-spot-of-cucurbits.pdf

Angular leaf spot is a bacterial disease that can affect cucumber leaves and fruit, caused by the bacterium *Pseudomonas syringae pv. lachrymans*. It's also known as bacterial leaf spot of cucurbits. Resistant cucumber varieties are available. Limit the use of overhead irrigation. Pick fruit when the vines are dry to prevent spread in the field. Use pathogen-free seed and rotate out of cucurbits. Treat when symptoms first appear if the weather is predicted to be cool and rainy.
https://plantclinic.nmsu.edu/documents/bacterial-leaf-spot-of-cucurbits.pdf