Numerous factors impact cucumber health and fruiting, and some leaf symptoms across different ailments look very similar. Leaf spot diseases can be prevalent by midsummer, particularly in periods of warm, rainy or high-humidity weather. Leaf spotting and tissue damage can also occur due to poor air quality (high-ozone days) or malnutrition. Fortunately, this degree of spotting looks very minor, especially compared to other cucumber questions we've received recently.

Our Cucumbers page provides an overview of the ideal growing conditions as well as several of the common ailments they contract. It can be difficult to distinguish between anthracnose and angular leaf spot, for instance; the leaf symptoms in the photo appear to be a fungal leaf spot, but we can't determine exactly which one. Overlapping symptoms of environmental stress are also possible in this case, such as reflected heat from the nearby wall and the reduced air circulation it causes, which can increase temperatures as well as slow leaf drying time. (Prolonged leaf surface wetness, either from rain, irrigation, or heavy dew, create conditions more conducive to infection from fungal and bacterial spores.)

There are no fungicides useful in this situation, but if the leaf worsens, you can clip it off. When the plant has finished producing a crop, be sure to remove all plant debris and dispose of it so it doesn't harbor spores for next year.

Miri