Cucumber mosaic primary symptom is mosaic pattern of leaves. But the symptoms can vary depending a variety of other factors including host varietal, viral isolate and environmental factors.
Necrotic sections can be seen on leaves of affected plants. The affected leaves may be small, and the plants stunted. The disease tends to be spotty in the field, but can affect yield of affected plants.
Another symptom characteristic of cucumber mosaic in the field is strapping of leaves which is a similar symptom caused by the virus on tomatoes also.
Nuclear inclusion of the virus can be seen as hexagonal shaped structures in plant cell. This is a diagnostic tool but needs molecular assessments of plant samples for pathogen confirmation.